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N E W C O L L E G E . S A R A S O T A , f L O R I D A

A REPORT

ON

THE HYDROGRAPHY AND BIOLOGY OF TWO MAN-MADE

CANAL SYSTEMS - HERON LAGOON AND

GRAND CANAL - OM SIESTA KEY

SARASOTA COUNTY, FLORIDA1

John B. M o r r i l l

Cynthia deNarvaez

Robert Foster

Freder ic 0. Ayer I1

and

Edward Connor

D i v i s i on o f Natural Sciences , New Co l l ege

Sarasota, F lo r ida

1. Supported by a grant from the New College Environmental Studies Fund, a grant from Bayside Club, Inc., a special g i f t t o the New College Biology Program from Paul and Stanley Paver, and the D iv i s ion o f Natural Sciences.

Common Law Copyright 1974 No p a r t o f t h i s r epo r t may be reproduced o r t ransmit ted i n any form wi thout permission i n w r i t i n g from the authors.

ACKNOWLEDGEMENTS

We wish t o thank-the fo l low ing persons f o r the informat ion and suggestions they provided during the course o f t h i s study:

Mrs. Doris Davis, Sarasota H i s to r i ca l Society

M r . Jim Slader , Sarasota County Engineering Department

Derr Real Estate Company, Sarasota, F lo r ida

M r . John Z i l l a s , Sarasota County So i l Conservation D i s t r i c t

M r . Wi l l iam Murphy, Siesta Key U t i l i t i e s Associat ion

M r . Ralph Davis, Sarasota County Engineering Department

M r . M i l l a r Brainard, Siesta Key, F lo r ida

We thank M r . J . J. Steinmetz f o r copies o f photographs o f the two canal systems. Ke i th W i l l iams , Karen Siedenburg , Nancy Wiedirhol d, Sandra M o r r i l l and Becky I re land helped i n the f i e l d and lab. W i l l i e M i tche l l and h i s crew a t Siesta Key Marina kept our power boat running. Bernie Vossler o f the D iv i s ion o f Natural Sciences helped t o maintain our c o l l e c t i n g gear i n operating condi t ion. Furman Arthur o f the New College Publ ic Relat ions O f f i ce helped t o pub l i c i ze our p ro j ec t and inform the pub l i c o f our strange behavior i n the canals a t odd hours o f the day.

F i na l l y , we are indebted t o Ms. Madeline McDermott f o r preparing the diagrams, t o Mrs. Mary Gal l f o r typ ing the repor t and t o Ms. Pat Bryant f o r obtain ing mater ia ls on i n t e r l i b r a r y loan. Without these three persons the repo r t may never have been completed.

TABLE OF CONTENTS

INTRODlJCTION ....................................................... 1

PROPOSAL ........................................................... 3

CONCLUSIONS ....................................................... 5

............. RECOMMENDATIONS ........................ .. .......... ... 6

HISTORY OF HERON LAGOON AND THE GRAND CANAL ON SIESTA KEY ..................................... 8

PHYSIOGRAPHY AND BATHYMETRY I N HERON LAGOON AND THE GRAND CANAL .................................................... 11

POTENTIAL SOURCES "POLLUTION"

HYDROGROGRAPHY ..................................................... 18

Sal i n i t y

................................................ Tida l Currents 21

Dissolved Oxygen ............................................... 24

Tu rb id i t y ..................................................... 28

................................ Chlorophyl l - a and Phytoplankton 31

........................................ Nitrogen and Phosphorus 34

Water Q u a l i t y . a Synthesis ............................... 35

BENTHIC AND EPIBENTHIC ..................................................... ORGANISMS 37

REFERENCES ......................................................... 42

APPENDIX . A . METHODS

INTRODUCTION

Today "we a l l know tha t dead end finger canals and upland canals adversely affect the ecology of the aquatic environment as well as periodically and then chronically cause considerable displeasure to those who have come to Florida seeking a pleasant l i f e . " This general impression i s supported i n a report by Barada and Partington (1972) t o Governor Askew. This report w i t h i t s eighty-six references i s a powerful document on the adverse e f fec ts of man-made canals.

The authors of t h i s report point out tha t a review of the ex is t - ing l i t e ra tu re revealed tha t a complete ecological study of private canal systems had never been made and recommended such studies be in i t i a t ed in order to develop adequate guidelines fo r any future can- a l construction. Their own recommendations and guidel ines incl uded:

1 ) Periodic tes t ing of canal waters fo r coliform bacteria and gas gangrene bacteria.

2) Elimination of box cut excavations.

3 ) L i m i t i n g canal depths to a1 low maximum sun1 i g h t penetration to bottom sediments ( i .e., 6 f ee t or less ) .

4 ) Require sides of canals t o have an adequately wide berm and sloping bottom similar t o natural waterways. The sides of the canals should be planted w i t h appropriate native s o i l - holding shore1 ine vegetation.

5) Canal w i d t h s should be i n relation t o depth and length of canal s .

6) Canals should have adequate circulation and flushing charact- e r i s t i c s (i .e., guidel ines of Bruun & De Grove, 1959).

7) Standardized methods fo r measuring water qua1 i t y and sediment quality should be established.

These recommendations supplement and echo those of Woodburn (1 963).

Subsequent to the Barada-Partington report the Department of Pol- l ution Control and the Department of Natural Resources of the State of Florida as well as a variety of Federal agencies, particularly the U. S. Army Corps of Engineers and the Federal Environmental Protection Agency, began t o develop stringent guidel ines and permit c r i t e r i a fo r dredge and f i l l operations of a l l kinds t o slow down the rates of deterioration of the "quality" of natural waters.

I n the l a s t fou r years the guidel ines, recommendations and r e - quirements have increased a t an exponential ra te . A t the same time, ecological studies have been made, and others i n i t i a t e d on the short term and long range e f f ec t s o f man made canal and marina systems. One o f the e a r l i e s t o f these was t h a t o f Taylor and Saloman (1968) on the e f fec ts of hydrau l ic dredging i n Boca Ciega Bay, F lor ida. A more recent study on the f ishes, macroinvertebrates and hydrological condi t ions i n a newly created upland canal system i n Tampa Bay i s reported by Linda11 e t a1 (1973). Other studies inc lude a comparison of phytoplankton i n a t m a r s h channels and man-made canal systems, West Bay, Texas (Corl i s s & Trent, 1971), a survey o f water qual i t y i n waterways and canals i n the F lo r ida Keys, w i t h proposed guidel ines for developmental a c t i v i t i e s i n F lo r ida 's coastal zone (Dept. Pol 1. Control , 1973), a p r e l iminary study o f a F lo r ida dead end canal (Mook, 1974) and a repo r t on the ecology o f small boat marinas i n Rhode Is land (Nixon -- e t a1 . 1973).

I n addi t ion, unpublished repor ts on p a r t i c u l a r canal systems have been made ( i .e., Marco Is land Canal Study Report, Cape Coral Canal ~ystem~hydrographic study). Such repor ts are becoming rou t i ne i n the development o f environmental impact statements. Their avai l a b i 1 i ty varies; they are being generated by both p r i va te and pub l i c sectors o f the community as we l l as by county, s ta te and federal agencies concerned w i t h water qual i t y and f i she r i es resources. As the pressure mounts fo r more people wanting t o l i v e along the coast as close t o water as possib le we may expect increasing numbers o f ecological studies of ex i s t i ng and proposed canal systems i n F lo r i da and the southeast. For example , D r . Oscar L . Paul son, Univers i ty o f Southern M i ss i ss i pp i recen t l y i n i t i a t e d a reconaissance of f l ush ing i n coastal canals and i t s e f f ec t s on water qua l i t y .

The present study was undertaken t o compare the water q u a l i t y and marine l i f e i n two dead end canal systems on Siesta Key, F lo r ida and the bays w i t h which they connect. As described i n our o r i g i n a l proposal we chose the Heron Lagoon waterway system as a canal system which appeared t o meet several o f the c r i t e r i a desired by governmental agen- c ies and the Grand Canal system which exemplif ied some o f the concerns o f the governmental agencies. Other complex dead end canals i n Sara- sota County l i k e those i n Whitaker Bayou, Hudson Bayou, P h i l l i p i Creek, Curry Creek, Hachett Creek, Godfrey Creek, Lyons Bay, Sackett Creek, Forked Creek and Bishops Bayou remain t o be studied as do dead end f i n g e r canals. The l a t t e r are numerous and o f d i f f e r e n t ages thereby prov id ing the po ten t ia l f o r studies on ecological succession and a1 t e r - a t ions o f water q u a l i t y over long periods o f time.

PROPOSAL

A t the present period of development of the South Florida area, conservationists are concerned w i t h the question of whather or not i t i s ecologically healthy for developers to create canals in order t o provide the public with waterfront housing. Only within the past decade have we begun to realize the extent of the deterioration that takes place in aging canals. To date very few studies have been done on these man-made ecosystems. In the Canal Evaluation Re or t which +--3 was sent to the governor, the E c o l o g i c ~ f o r m a t i o n Serv ce escribes the effects sf closed-end canals on their surrounding environments and includes recommendations for the development of canal systems that would not cause marked changes in neighboring marine and terrestr ial environments. Unfortunately, the report was mere a coll ection of "con- census of opinion" rather than a complete ecological study. Along the Florida coasts, man-made finger canals are an integral part of housing developments which advertise waterfront access. These canals vary in width and depth according to the amount of f i l l the developer needed to raise the elevation of the development above the mean high water line.

The new canal typically begins as an ecologically s te r i le environment surrounded on three sides by a concrete seawall. As the canal ages, organic sediment accumulates from various sources. Since the canal i s a semi -dead end system, tidal flow may not Plush i t clean, and the organic rich sediment accumulates, providing a nutrient medium i n which offensive and/or harmful bacteria may thrive.

Some few developers do not use sea-walls, b u t instead plant natural shoreline vegetation. Mangrove i s the logical choice as i t i s adapted to this role and thrives i n such an environment. The eventual effect natural vegetation may have on the condition of the canal bottom has not been extensively studied.

In an attempt to add to the ecological data on canal systems we propose to establish a survey of seawalled finger canals and "natural" canals to discover what changes occur with age. Data taken will i ncl ude :

1 ) Hvdroara~hv: consisting of dissolved oxygen content, salinity, temperature, currents, and water exbkange. These figures wi 11 give us some idea of the water quality.

2 ) Benthos: This will give us comparative data as to the amount mt and animal material that 'is present in the natural and ar t i f ic ia l canal systems.

3) Sedimentation vs. original depth: this study can give in- ?omation about the age, location, use, and water flow in the comparative systems.

4) Phytoplankton: these investigations can give us the density and composition of the phytoplankton i n the different canal systems, and may possibly reveal an indicator species o f plankton tha t would demonstrate the water quality i n each canal.

When the study has been completed and the data compiled, we may bet ter understand what happens in an a r t i f i c i a l canal as i t ages. We hope t o be able t o suggest modifications i n the design and execution of canal building which will prevent fur ther damage t o the waterways of the Sarasota Bay area.

The canals we plan t o investigate are:

1) The Grand Canal on Siesta Key. This i s a long, in t r i ca t e system, bounded by sea walls, which winds l i ke a maze throughout the northern end of Siesta Key. I t i s heavily bu i l t up w i t h single family houses and receives the eff luent from the Siesta Key Ut i l i t i e s Sewage treatment plant. I t s only out le t is into Roberts' Bay a t the north end of L i t t l e Sarasota Bay.

Heron Lagoon. This i s a long "natural" canal system, sea walled along few of the many properties l ining i t s shores. The houses are relat ively f a r apart and s e t well back from the water's edge. Nearly a l l are connected t o the SKUA Sewage system; there a re no known sewage out fa l l s i n to the 1 agoon. I t is heavi 1 y planted w i t h mangrove, a1 ternat i ng w i t h some areas of sloped grassy lawn or ground cover and various sor t s of t rees and shrubs. I t s only out le t i s a t i t s extreme northern end, where i t receives t ida l flow through a pipe leading under Midnight Pass Road t o North Basin, which opens into L i t t l e Sarasota Bay. Heron Lagoon runs down the southern extension of Siesta Key.

Some of the questions we will t r y t o answer are as follows:

1 . blhat happens t o a canal w i t h age?

2. Are there any "good" canal systems?

3 . Do canals present a public health hazard?

4. If there are any "good" ones, why are they good?

5. I s there any way t o design the new or restructure the old so tha t they can also become "good"?

CONCLUSIONS

In our original proposal we l i s t ed f ive questions concerning the water quality and marine l i f e i n canal systems. In retrospect this study does not provide d i rec t answers to these questions. Rather i t revealed the ,complex nature of two canal systems thereby providing a preliminary analytical model with overt cautionary undertones regarding premature "obvious" conclusions from superficial observations and data collected a t only one season of the year.

Of the two canal systems the overall water qual i t y and diversi ty of marine l i f e i s greater i n the Heron Lagoon system than i n the Grand Canal system. In the l a t t e r system sluggish t idal circulation and nutrient enrichment appear t o be the primary causes of "undesirable" water qual 4 t y conditions and the development of organical l y rich ,sof t bottom sediments and the i r communities of macro and m i cro-organi sms . Neither canal system appears to constitute a health hazard a t the present time. However, unless corrective measures are taken, waters in sections of the Grand Canal system will continue to deter iorate and ultimately influence the water quality and marine l i f e i n the adjoining areas of Roberts Bay.

The Heron Lagoon system i s a potential model for designing new canal systems and i l l u s t r a t e s the guide1 ine principles fo r upland canals and waterways described by s t a t e and federal agencies. Yet even here our study shows improvements i n water circulation and shore- l ine management a re desirable. The three mile long dead-end lagoon i s a c r i t i c a l part i n the maintenance of water quality i n this sytem and i l l u s t r a t e s a possible way for the construction of upland canal systems i n certain areas.

Some of the ways of maintaining and improving the water qual i t y i n these two systems and other canal systems are outlined under RECOMMENDATIONS.

RECOMMENDATIONS

The water qua1 i t y management and improvement i n both the Heron Lagoon and Grand Canal systems include several measures t h a t are feasib le, s imple , re la t ive ly cheap and appl icable t o other canals and others t h a t are possib le bu t probably no t feas ib le u n t i l some sector o f the pub1 i c becomes s u f f i c i e n t l y aroused. Improvement o f maintenance o f water q u a l i t y and marine l i f e i n the Grand Canal system i s complicated by the o u t f a l l o f the major sewage treatment p l a n t on Siesta Key. Given these reservat ions we p ro f f e r the fo l lowing recommendations (not necessar i ly i n order o f p r i o r i t y ) .

1) The degree and r a t e o f t i d a l f lushing i n the two canal systems could be increased. I n the case of the Heron Lagoon waterways, box cu lve r ts instead o f the present c i r c u l a r 30-inch concrete pipes beneath the roads, espec ia l ly a t the Midnight pass Road cu l ve r t would increase c i r c u l a t i o n and reduce eddy currents and debris and organic sediment accumulation i n the v i c i n i t i e s o f the culverts. A f low-through t i d a l cur rent c i r c u l a t o r y system would f u r t he r increase t i d a l f lushing. One possib le s i t e f o r a second opening t o the Bay o r Gulf i s Sanderling Beach a t the west s ide o f Heron Bay. Indeed dur ing Hurricane Agnes, June 1972, such a breakthrough near ly occurred. Had t h i s "Act o f God" succeeded L i ttl e Sarasota Pass would e x i s t again.

Increasing the t i d a l f l ush ing i n the upper reaches o f the Grand Canal system would be more d i f f i c u l t . The natura l drainage area lead- i ng t o the pond i n Sands Cove i s the most obvious place t o consider f o r a second opening. A t one t ime t h i s pond and i t s upland drainage area d i d discharge i n t o the Gul f o f Mexico. I n the Siesta I s l e s area a c ~ n n e c t i n g waterway t o Roberts Bay v i a the Royal Palm Harbor Canal would be one way o f increasing t i d a l f low i n t h i s sect ion o f the Grand Canal system. The Palm Is land loop could be connected t o e i t h e r ( o r both) the Siesta I s l e s o r the Sarasands Canal sections. Whether such connections would a c t u a l l y funct ion as planned would requ i re hydrau l ic engineering studies and models. Furthermore, such proposals would meet strenuous objections from a l l sides. A t the very l e a s t the q u a l i t y o f the waters of the Palm Island, Siesta I s l e s and Sarasands-Harmony Shores sections might f i r s t have t o be improved before various agencies would permit i t t o enter the Bay o r Gulf.

2) The shorel ine vegetat ion needs t o be pruned and managed t o r e - duce the amount o f l e a f fa1 1 enter ing the waterways and canals . Sub- merged branches t ha t impede waterf low should be removed. Debris t h a t co l l ec t s a t the upper ends o f the dead end canals should be removed w i t h d i p nets. I n the case o f developed l o t s , the residents should be en- couraged v i a construct ive education t o maintain t h e i r water f ronts as they

do the r e s t o f t h e i r property. I n the case o f undeveloped l o t s and pub l i c owned lands along the canals e i t h e r the l oca l government, the l oca l development associat ion such as the Siesta Key Club o f Heron Lagoon o r the Siesta Key Associat ion could assume t h i s r espons ib i l i t y .

3) Consideration should be given t o an overa l l removal o f n ine ty percent t o t a l n i t rogen and carbonaceous matter i n the discharge water o f the SKUA f a c i l i t y .

4) Appl ica t ion o f biocides and f e r t i l i z e r s t o the uplands border- i n g the canal systems should be confined t o periods o f low r a i n f a l l i n March-May and October-December t o reduce the amount o f surface runoff of these mater ia ls i n t o the canal systems.

5) Ways o f increasing the l eve l s o f dissolved oxygen economi- c a l l y i n the bottom waters o f canal sections w i t h l i t t l e c i r c u l a t i o n should be explored. I f the dissolved oxygen i n these waters were kept above 2.0 ppm, the n i t rogen and phosphate compounds i n the bottom sediments would enter the over ly ing water s lowly and tend t o remain trapped i n the sediments ( F i l l o s and Molof, 1972). Devices such as submerged perforated a i r l i n e s and ag i ta to rs are cu r ren t l y employed throughout the country t o improve the water q u a l i t y i n ponds, s e t t l i n g basins, etc. This remedial measure, i f appl ied t o the dead end canals, would n o t on ly aerate the water bu t improve the c i r c u l a t i o n i n these canals as wel l as r e ta rd the accumulation o f organic matter i n the sediments and main- t a i n an aerobic microbial f l o r a i n the surface layers o f the sediments.

6 ) The water q u a l i t y and marine l i f e should be monitored a t i n - t e r va l s throughout the year f o r several years t o determine the changes i n ecological condi t ions i n these canal systems. I n addi t ion, shor t term perturbat ions such as those associated w i t h Hurricane Agnes should be studied.

7) Surface runo f f water discharges i n t o the canal systems fo l lowing heavy r a i n f a l l s v i a storm sewer p o i n t source o u t f a l l s should be minimized wherever possible. Discharges from storm sewers n o t on ly invo lve large amounts o f freshwater bu t contain such t o x i c po l lu tan ts as lead, mercury, automobile f ue l wastes and a lso d i r t , animal feces, p l a n t mater ia ls and other BOD and COD substances. Consideration should be given t o d i v e r t i n g storm sewer discharges, construct ion o f proper drainage swales along ex- i s t i n g roads neighboring the canals and the use o f porous asphal t as paving mater ia l fop roads and driveways so t h a t surface water i n these areas may percol a te i n t o the ground d i r e c t l y.

THE HISTORY OF HERON LAGOON

AND THE GRAND CANAL ON SIESTA KEY

U n t i l 1907 Siesta Key was undeveloped and l a r g e l y unoccupied because no br idge connected i t t o the mainland. I n t h a t year Harry L. Higel , I the Mayor o f Sarasota, showed h i s awareness o f the i s l and ' s po ten t ia l by organizing the Siesta Land Company w i t h Captain Louis Roberts and E. M. Arbogast. They p l a t t e d the town o f Siesta, bu t found they had picked the wrong moment i n time. The depression o f 1907 ruined t h e i r plans, bu t on ly temporari ly. Between 191 1 and 191 3 Bayou Hansen, Bayou Nett ie, and Bayou Louise were dredged and canals opened. I n 1912 they rep la t t ed the f i r s t subdiv is ion "Siesta Sub- d iv i s ion" . Thereafter the Key was known as Siesta Key. The Board o f Geographic Names, however, o f f i c i a l l y t i t l e d i t "Sarasota Key" on February 1, 1922, bu t s ince no one seemed t o know where "Sarasota Key" was and everyone was f a m i l i a r w i t h "Siesta Key", the name was o f f i - c i a l l y changed on Ju l y 3, 1952. 1917 saw the opening of the f i r s t Siesta Bridge and p a r t i a l development o f the town was begun. The development rush began l a t e r w i t h the const ruct ion o f Stickney Po in t Road and Bridge i n 1926-27. The o r i g i n a l Siesta Bridge, b u i l t o f wood, was considered unsafe by then, and a new Siesta Bridge was erected i n 1927.

Heron Lagoon. Before 1921 the southern end o f the key had a very - d i f f e r e n t appearance from the present (Figure 1). What i s now Heron Lagoon was the northern h a l f o f L i t t l e Sarasota Pass. The Pass opened i n t o L i t t l e Sarasota Bay i n the v i c i n i t y o f B i r d Keys. There was no Midnight Pass then. L i t t l e Sarasota pass c u t nor th between the southern t a i l o f Siesta Key on the east and the northernmost s t r e t ch of Casey Key, an area then known as Treasure Is land, on the west, and opened i n t o the Gul f o f Mexico through what i s now known as Sanderling Beach. The Pass was 8 t o 10 f e e t deep, inc lud ing i t s opening i n t o the Gulf. When the 1921 hurr icane struck, the Gu l f broke through Casey Key a t the southern end o f L i t t l e Sarasata Pass and formed "Musketeer's Pass", now known as Midnight Pass. I n 1926 another hurr icane dumped masses o f sand and she l l i n t o the center o f L i t t l e Sarasota Pass where there were once two small mangrove is lands, and the Pass was c u t i n ha l f . However, according t o Bruun, e t a l . (1962), t h i s pass was closed and the present day Midnight Pass formed dur ing the 1947 hurr icane. The Gulf opening of the Pass had been p r a c t i c a l l y f i l l e d w i t h sand by the f i r s t storm; the second succeeded i n c los ing i t completely. The r e s u l t was a landlocked Heron Lagoon near ly two mi les long (Figures 2, 3, 4) . The southern end o f L i t t l e Sarasota Pass i s known today as B l i nd Pass and opens ra ther to r tuous ly i n t o Midnight Pass.

1 . "The Story o f Sarasota," Karl H. Grismer, M. E. Russel 1 , 1946.

2. Informat ion received from Mrs. Dot ty Davis o f the Sarasota County H i s t o r i c a l Society.

%/' Figure 2.

Figure 1 .

The f i r s t l o t s p l a t t e d on Heron Lagoon were p a r t o f a Government subdivision. Miramar was p l a t t e d on A p r i l 17, 1925. This development i s on the east side o f the Lagoon and runs southward from the middle o f the length o f the Lagoon . 3 I t meets w i t h land once owned by M r . and Mrs. G. W . Cr is t , Jr., who so ld the land t o the Government. This piece i s ca l l ed Ocean View and was p l a t t e d on September 5, 1925. Ocean View adjoins Heron Lagoon Lodges, owned by M r . and Mrs. G. A. Fu l le r . This land was surveyed i n A p r i l and p l a t t e d i n May o f 1954 as a p r i va te club. Just no r th o f Miramar are The Cedars o f Siesta Key, o r i g i n a l l y owned by Mr . and Mrs. R. M. Lock, who had the small property surveyed and p l a t t ed i n March o f 1946.

The r e s t o f the Heron Lagoon area was bought i n 1940 by M r . El dr idge S . Boyd, a land co l lec to r , who owned and developed Hidden Harbor, Coconut Bayou, and other areas on the Key. He incorporated h i s holdings on Heron Lagoon i n 1945 and ca l l ed them "Siesta Propert ies, Inc." They were developed i n four un i t s . U n i t #l , p l a t t e d on Ju l y 27, 1946, comprised a1 1 o f h i s holdings on Heron Lagoon proper, i nc lud ing the land nor th of The Cedars, around the northern end o f the Lagoon and the e n t i r e west bank between the Lagoon and the Gulf. The p l a t shows a proposed s i x t y f o o t canal running nor th through the marshy area ad jo in ing the Lagoon.

Boyd began s e l l i n g l o t s as ea r l y as 1941 .'+ By 1950 a " s i x t y foot wide canal" became the completed East Waterway, over a quarter o f a m i l e long. The West Waterway was we1 1 begun, w i t h plans t o continue i t up t o an ex i s t i ng curved sect ion t h a t connected w i t h the East Waterway through a t h i r t y inch cu lve r t . A l l o f t h a t area was p l a t t e d as U n i t #2 i n J u l y o f 1950. Un i t #3 was p l a t t e d a t the same t ime and included the land around the Boat Basin, a dead end docking canal j u s t east o f Midnight Pass Road ( former ly Siesta Boulevard). A double cu l ve r t l e d under the road t o connect the East Waterway w i t h the Boat Basin. Heron Lagoon was no longer landlocked; t i d a l f low passed throughout the new system o f canals i n t o Heron Lagoon.

The l a s t area t o be p l a t t e d was U n i t #4, the man made i s l and west o f Mid Waterway. This completed Siesta Propert ies, Inc. i n March o f 1959. A l l the waterways and a l l road construct ion were complete and i n t e r - connected. East, Mid and West Waterways were connected t o each other and Heron Lagoon through cu l ver ts under Sander1 i ng Road. Me1 a1 euca Way, Pine Needle Road, Turnstone Road, and Plover 's Way (Fig. 5) l e d t o the new residences spr inging up along the banks o f the waterways.

3. Information, County Engineering. Ctsy M r . Slade . 4. Information c t sy ner r Real Estate.

F i g u r e L Out1 ine o f Heron Lagoon '.b Ls and waterways as o f 1960.

' *. * 'b,

Grand Canal. The history of the growah of the Grand Canal system of canalsissummarized i n Figs. 6 & 7 and Table 1 . The main portion of the Grand Canal, including Palm Island, was dredged i n 1925. The Canal followed a natural drainage ditch tha t wound through saw grass f l a t s from the Bay. Palm Island was created w i t h the f i l l from the dredging. Archibald's Canal was the Canal's f i r s t name, since it was the then mayor of Sarasota, Frank Archibald, who had the work done. A few houses were b u i l t on and around Palm Island. This seemed t o sa t i s fy the needs of the time fo r there was no fur ther development fo r twenty- seven years except fo r a single dead end canal north of Avenida del Mayo tha t joined the Grand Canal eas t of Palm Island.

The boom began i n 1952. Ocean Beach, a small area growing out of the f i r s t curve of the Canal, was platted i n t ha t year and was followed by Harmony i n 1954-55. Sarasands mushroomed in 1957. I t joined Harmony via Siesta Manor and Paradise Island i n 1958. Today this whole complex, from Ocean Beach through Sarasands, is a maze of long, narrow, dead end canal s .

In 1960 Siesta Key Ut i l i t i e s Authority (SKUA) was bu i l t t o provide water and sewage treatment t o the growing numbers of people crowding onto the Key. A t the same time, the neck of what would become Siesta I s les was dug. 1962 saw the f i r s t area of Siesta I s les designed somewhat different ly from the r e s t of the Canal. The f inger canals were short and wide, not dead water traps (Fig. 7 ) . As the r e s t of this area was dredged someone apparently became aware of water quality a t l a s t . The three main canals of Siesta I s les interconnect and provide f ree t ida l flow from the Grand Canal (Fig. 7) . Siesta I s les was complete and platted by 1964.

Unfortunately the Siesta I s les design was not continued in l a t e r developments along the Grand Canal . Waterside Nood and Waterside West, 1966, are both dead end canals (Figs. 7 & 8). Bay Point, 1968, has i n - novations including a circular flow of water w i t h i n i t s e l f . I t a l so has a culvert leading t o the Bay, providing a f ree flow of water. Waterside East, 1970, the most recent addition on the Grand Canal, consists of two dead end canals forking off an entrance from the Grand Canal (Fig. 8 ) . They are wider than the older canals.

Table 1.

AGE AND AVERA.GE DEPTH O F WATERWAYS AND CANALS

OF GR4ND CmAL SYSTEM, SIESTA KEY,

Canal Y e a r ' I Age i n I 4verage nepth Constructed Years in Feet.

Grand Canal - 1925-26 I 47 I 6 - 1 0 Palm Island loop

Ocean Beach 1952 I 2o I 5

Harmony 1954-55 Sara.sands 1957 Paradise Island 1958

Siesta Manor 1958 Siesta Isles, North 1960 S i e s t a Isles, West 1962 S i e s t a Is les , Kast 1964

Waterside W a y 1966 I 6 I 8

Waterside Wood 1966

Ray Point 1968

Waterside East 1970 I 2 I 8

' From " In t records , Engineert s Office, Sarasota County.

t h e Grand Canal system, Siesta Key, SCALE I N MILE Florida.

Figure 7. Dates o f construction and names o f sections and subdivisions o f the Grand Canal system.

PHYSIOGRAPHY AND BATHYMETRY

IN HERON LAGOON AND THE GRAND CANAL

Siesta Key is 1 i t t l e more than two large sandspits coalesced near Point of Rocks. In some areas there are outcroppings of limestone and sandstone. The water table i s normally w i t h i n 3 t o 5 f ee t of the surface, although i t descends i n droughts of any duration. The so i l s in the vicini ty of Heron Lagoon and the Grand Canal a re primarily coastal beach ridge and Arzell f ine sand, shell phase (Wildermuth and Powell, 1959).

According t o Wi ldermuth and Powell coastal beach ridge soi 1 s con- s i s t of thick beds of sand mixed with shell fragments tha t run i n paral le l , low uneven ridges 3 t o 4 f e e t h i g h . This is best seen i n the 1948 aer ial photo of Sarasota County. T h i s so i l has a low moisture holding capacity and rapid internal drainage. Typical native vegetation i n - cl udes: cabbage palmetto, saw palmetto, wiregrass, myrtle, cedar, bracken fern and Spanish Bayonet.

Between the coastal beach ridges, Arzell f ine sand, shell phase so i l occurs naturally. (This a1 kal ine, poorly draining soi l i s found beneath the f i l l e d areas a t the north end of Heron Lagoon and i n Sarasands as well as i s the low lying sections around the Grand Canal where there were once broad swales such as Harmony Is les and Siesta I s l e s ) . This so i l i s part icular ly low i n organic matter and deficient i n plant nutrients. I t s ' water table is high and the root zone of plants relat ively shallow.

The dis t r ibut ion of both so i l types on Siesta Key is clear ly shown i n the 1948 aer ia l photos i n the Sarasota County Soil Survey of Wildermuth and Powell (1959).

What may prove of in t e res t is tha t the Canal systems and upland development to the north and south of Palm Island are located i n Arzell f ine sand so i l areas. What does t h i s mean? Fi rs t , the canals have been dug through so i l s t ha t were a t the surface of a ground water aquifer; second, the present uplands bordering the canals are composed of this same so i l type removed i n the course of canal construction. Thus surface water and waterbsrn materials probably readily percolate through the soi 1 s into the canals proper. That t h i s may be the case is reflected by anomalous sa l in i ty and temperature changes we observed during th i s study i n the waters of these canals.

Physi oqraphy

The several physiographic features of the two canal systems are summarized in Table 2. The data in the table were obtained by measurements from maps of known scale and from field observations in counting residences, building lots and powerboats.

Heron La oon. There are 41 acres of open water in Heron Lagoon ne p r o p e r acres in i t s man made canals. With the exception of approximately 1,000 feet of sea wall, concrete bag or r ip rap on the east shore of Heron Lagoon, the shore 1 ine i s vegetated. In many of the shore properties grass, vines or other ground cover extend down the low banks t o the mean h i g h t ide line. Palm trees, gold trees, Jacaranda, palmetto and "weedy" Brazilian pepper trees grow along the water's edge. In several waterways Brazilian pepper trees and other shore vegetation have extended over the water and affect the tidal flow, Australian pines are prevalent. Much of the shoreline, however, i s vegetated w i t h red, white and black mangrove. Some property owners trim the mangroves to hedge height or lower (Fig. 10) ; others prune the trees to more natural looking bush-1 i ke growths (Fig. 13). The original mangrove forest fring- ing the west shore of Heron Lagoon (Fig. 4) has been largely preserved. In one instance (Fig. 11 ) the red and white mangroves have been pruned to hedge height while the lower branches of the black mangroves have been pruned, resulting in an ecologically desirable and esthetically pleasing managed natural shore line. Where people have removed the natural mangrove vegetation along the shore erosion has and i s occurring. In one yard the shore has been stabilized by the owners leaving one relatively large black mangrove whose pneuma tophore-root system extends nearly 50 feet along the shore (Fig. 12). A t the same time, the tree i t se l f pro- vides an attractive area of shade.

We have then in the Heron Lagoon area many examples of how water front properties may be landscaped with native species of plants t o stabil ize shore1 ines and to provide esthetical ly pleasing "greenery". While a l l three species of mangroves - red, white, black - can be transplanted and pruned, i t appears that each has i t s own se t of optimal values. The unsung white mangrove i s by fa r the best for the development of quick growing hedges, The black mangrove i s best as a shade tree. The red mangrove will tolerate more submersion in s a l t water b u t i s slow to become established in an area. For further information see Savage (1972a,b). We are currently studying various parameters of mangrove ecology in the Sarasota Bay area and are in the preliminary phases of mangrove horticulture.

Grand Canal. The Grand Canal system of some 9 miles of waterways has / 89 a c r e s f w a t e r surface. Over 13 miles of canal banks are sea walled (Figs. 14, 15 & 18) while 5 miles are vegetated with native or cultivated plants. Here again weedy species of ornamentals have grown into the canals (Figs. 16 & 17).

T > I ~ ~ - E 2 . P h y s i o g r a p h i c d a t a f o r t h e Heron Lagoon and Grand Cana l sys t ems , 1972-1973.

-.----. - --.-.-. . - -

H e r o ~ . 1 , a ~ o o r 3)-s t nrlr

T 3 e r o r J - s -c~n

H. L . Tip?!and C a n ~ l s

- -... -.- - *... - ----- - G r a n d C a . n a l

-----. ---.* - Slrrface A r e a Acres

---. - -. - -- --

H e r o n L a g o o n S y s t e m

H e r o n Lagoon

G r a n d C a n a l

----- --..a -.- -..̂ -- -r-A--Lr--n-- - - nr

TTpland Rat 4 - n

Q r a i n a y e Canal. 2 r e a / ~ a s i n , / , l c r e s D r a i n P a s i . ~ ~

---. - -- - -. '-. - - - . - - . -

N u m b e r o f Number o f X m p t y L o t s Pnve rboa t s P o w e r b o a t s

4/73 D o c k s i d e 8/72 - Of I I D o c k s i c l e 4/73 -----*.-- .-.- - - . - - - - *-- - - . . , - . .,--*..---- ,-- , .- -.-- - . - - - - . * . ,- .-- ,

Figure 14_ Seawalled canals, Siesta I s les , Grand Canal. Note the narrow barnacle-oyster zone on the seawall i n the lower l e f t foreground.

Figure Sea wal led canal , Siesta Is les .

Figure - 16 Palm Island section of canal w i t h overgrowths s f shore vegetation south of Calle Florida bridge .

Figure - 17 Palm Island / c b n ~ l r non sea walled sect i on, looking north from Calle Florida bridge. The overgrowth of shore vegetation is primarily Brazilian pepper bushes.

SCALE IR MILES w i t h o u t c o n c r e t e s e a w a ' l l s o r

Bathymetry - Descriptions of Heron Lagoon and the Grand Canal

Heron La oon . Heron Lagoon proper varies between 7.5 and 11 .5 f ee t seep. -h itt e dredging is evidenced here except i n Heron Bay by Sanderl ing Beach where f i l l fo r Sanderl ing Road has been removed. The deepest areas are i n the central and northern ends of the Lagoon. The east shore of the Lagoon is steeper than the west shore and drop-offs of 5 t o 10 fee t w i t h i n 6 f ee t of the shore prevail.

Heron Bay is shallow w i t h depths between 1.5 and 3.5 f ee t except along i ts northern perimeter where a 10-20 foot wide channel 6.5 f ee t deep was dredged, probably for land f i l l .

The depths of the 50 to 100 foot wide waterways a t the north end of Heron Lagoon vary from 2 to 7 f ee t except for shallow sand- bars i n the vicini ty of road culverts. The deepest areas are i n the northern ends of West and Mid Waterway; the shallowest around the small island a t the northern end of the East Waterway. One may speculate tha t the depths of these man made waterways are pro ortional t o the f i l l re- g quirements in the adjoining uplands. The Nort Boat Basin eas t of Mid- n i g h t Pass Road i s 5 t o 6 f ee t deep by the boat docks and 7 t o 8 fee t deep i n the basin and waterway proper leading t o L i t t l e Sarasota Bay.

Periodically the areas i n the vicini ty of the culverts are dredged t o maintain t ida l flow. However, the two long 30 inch diameter culverts under Midnight Pass Road do not appear t o be maintained t o prevent the build-up of oysters tha t fur ther r e s t r i c t the t ida l flow a t t h i s point.

Grand Canal. The general distribution of depths i n the Grand Canal -- system i s summarized i n F i g . 19 and Table 1. The depths of the Grand Canal proper range from 8 t o 10 fee t w i t h holes such as a t Hydrographic Station 2 near the entrance and Station 15 near SKUA as deep as 12 fee t . In the Palm Island loop depths range from 5 to 10 fee t . The finger- l ike dead end canals north and west of the Grand Canal range from 7 t o 9 fee t . However, i n the Ocean Beach and Sarasands most of the canals are less than 5.5 f ee t and i n some places less than 3 f ee t a t MLW, especially the oldest canal along Avenida del Mayo. The v ic in i t ies of road box culverts and bridges where the canals narrow are shallower than other areas.

l/4 1 12 314 SCALE I D MILES

& - ~ p M e a n L o w "z;. - Q & s i'n Grand fs

& J e s s <, L' t h a n 5 f e e t -

POTENTIAL SOURCES OF "POLLUTION"

IN HERON LAGOON AND THE GRAND CANAL

"The Obvious And The Unknown"

The most obvious sources of "pollution" i n these canal systems include: 1 ) surface sheet water run off from the adjoining developed up1 ands ; 2) ground water seepage bearing bi oci des , f e r t i 1 i zers , and sept ic tank leachates; 3) storm sewer out fa l l s whose waters carry urban pollutants from roads and developed uplands; 4) sewage t r ea t - ment plant out fa l l s such as SKUA.

Less obvious sources include: 1) powerboat eff luents ; 2) plant l i t t e r such as grass clippings, dead leaves, and pollen tha t are thrown or f a l l into the canals; 3) ra infal l which t ransfers atmospheric pollutants t o the open water direct ly; and 4) waters of the adjoining bays tha t enter the canal systems on r is ing t ides and may a t times re- s u l t i n the accumulation of masses of algae, waterweeds l ike water hyacinth and human garbage.

In the paragraphs tha t follow we will review some of these sources i n regard t o the two canal systems.

Heron Lagoon. The upland drainage basin of Heron Lagoon and i t s u p l a n d e r w a y s i s approximately 132 acres (Tab1 e 2 ) . The drainage basin i s delineated by several roads tha t surround the area. The amount of pollutants from the uplands appear minimal except i n times of heavy rainfal l when surface sheet r u n off can carry f e r t i l i z e r s and biocides over the vegetated banks into the waterways. No storm sewers empty into the Lagoon or waterways. Nearly every house i s on SKUA sewage l ines . The few sept ic tanks s t i l l i n use along the west shore of Heron Lagoon are located so t h e i r drainage f ie lds are toward the Gulf of Mexico. While sept ic tanks along the eas t shore of Heron Lagoon do drain in to the Lagoon, they a re associated w i t h single family residences.

Pollution from human effluents seems minimal. T h i s is fur ther evidenced by examination a t low t ide during the winter months of the inter- t ida l areas along the shores. A t this time of the year sources of ground water seepage from sept ic tanks and washing machines can be pinpointed by patches of the green alga Enteromor ha i n the in te r t ida l zone. We observed only ten patches i n the Heron ---- agoon system during t h i s study. Fecal nutrient enrichment of these waters then i s primarily from fecal wastes of marine 1 i f e , birds and other w i ldl i f e . Biological Oxygen Demand (B.O. D. ) t e s t s of water samples collected May 17, 1972 showed tha t the B.0.D.s of water from hydrographic Stations 1 through 7 and Station 8, L i t t l e Sara- sota Bay ranged from 1.5 to 1.7 ppm. (Tests, courtesy of SKUA) .

A h a l f dozen small outboard motor boats are docked along the east shore o f Heron Lagoon. Four t o s i x power boats w i t h 60-100 H.P. motors are docked i n the North Boat Basin. Motor boat p o l l u t i o n appears minimal i n the Heron Lagoon system.

From time t o time fo l low ing major storms and f resh water discharges water hyacinths may be dr iven by wind and t i des i n t o the boat basin and accumulate i n decayins masses along the shore by the Midnight Pass Road cu l ve r t and around the oysters on the boat dock p i l i n g s . One such occur- rence took place August, 1973 fo l low ing heavy ra ins , abnormally h igh t ides , and southeasterly winds f o r two days. I n one four f o o t square area beneath the Boat Basin dock some 80 water hyacinth p lants were removed and l a t e r d r ied a t 1 0 0 ~ ~ f o r 24 hours. Their combined dry weight was 5.5 k i 1 ograms .

The po ten t ia l s ign i f icance o f t h i s chance observation i s t h a t s t ruc - tures 1 i ke p i e r p i 1 i ngs , docks, and overhanging , submerged shore vegetat - i on provide po ten t ia l t raps f o r mater ia ls ca r r i ed by the t ides. This i s a nuisance fac to r , but equal ly important i s the f a c t t ha t when these mater- i a l s are water hyacinths, the f i l t e r feeding organisms dwel l ing on p i l i n g s and submerged branches o f shore p lants are subjected t o abnormally low oxygen tensions as the water hyacinths decompose. Furthermore, d r i f t i n g water hyacinths have the po ten t ia l o f catching on the oyster growths w i th - i n road cu lve r ts and thereby a f f e c t the normal t i d a l f low. F i na l l y , the massing and subsequent decay o f these p lants i n r e s t r i c t e d areas 1 i ke canals provide an addi t iona l source of nu t r i en t s f o r the support of l oca l plankton blooms. Another po ten t ia l source o f "pol 1 u t ion" i n both canal systems, bu t p a r t i c u l a r l y i n the Heron Lagoon system, i s the annual r a i n of 1 eaf , f r u i t and tw ig 11 t t e r as we1 1 as ae r i a l pol 1 en o f pines and other p lants i n t o the waterways. Not a1 1 o f the shore1 i n e of the Heron Lagoon system i s vegetated w i t h mangroves. The waterways are overgrown w i t h B raz i l i an peppers (Figs. 34,35,36) and bordered by Austral i an pines i n sev- e ra l areas. One can r e a d i l y see the accumulation of leaves and p ine needles i n slack water areas o f waterways and eddies near cu lve r ts (Fig. 37) . I n these spots the bottom i s covered w i t h s o f t organic deposits.

While the s ign i f icance o f these accumulations i s no t known, t h e i r po ten t ia l f o r lowering o r a1 t e r i n g "water qua1 i ty" i s present. On the one hand, the decaying 1 i t t e r may provide both organic and inorganic nut - r i e n t s f o r marine food chains. The ac t i ve microbial a c t i v i t y involved i n decomposing t h i s 1 i t t e r can lower oxygen tensions i n the water. Organic substances present i n the l i t t e r of upland species o f na t i ve p lan ts as wel l as ornamentals may ac tua l l y be as poisonous t o marine l i f e as the more ob- v i ous man made b i oc i des .

We do no t know how much p lan t l i t t e r enters the Heron Lagoon waterways annually nor the e f f ec t s o f t h i s l i t t e r on marine l i f e . One p i l o t exper i - ment, however, showed t h a t over a three day per iod i n November, 1973 some

19.3 gm (dry wt . ) o f Aust ra l ian pine needles and f r u i t f e l l on a 3 square meter dock surface. Few p lants grow beneath Aust ra l ian pines. I s t h i s because t h e i r 1 i t t e r releases p l an t growth i n h i b i t o r s ? We do no t know the answer, but i f t h i s were the case we might expect s im i l a r i n h i b i t o r y effects on the phytoplankton and macro-algae i n the water. A t the very l e a s t the l i t t e r from the shore and upland p lants i s p a r t i a l l y responsible f o r the brownish co lo r of the water i n the Lagoon and waterways. A t the same time, the seasonal r a i n o f pol l en forms the yel low green "scum" on the water 's surface as we l l as provid ing a r i c h source s f organic nu t r i en t s for the microbial f l o r a i n the water.

Grand Canal. The upland drainage basin del ineated by roads around the per ip-sOfthe canal system i s approximately 531 acres. As o f March 1973 some 739 residences f ronted on the canal and 98 l o t s remained undeveloped. The number o f dockside powerboats was 346 i n July, 1972 and 291 i n March, 1973. It i s unknown how many others were i n use a t the times of counting. These boats ranged i n s ize from 12 f o o t outboard runabouts t o cabin cru isers . The p o l l u t i o n po ten t ia l from motor boat a c t i v i t y i s thew1 but ye t t o be studied.

Because a1 1 the houses on the canal system are on SKUA 1 ines there i s 1 i t t l e pol 1 u t i on from domestic wastes. Abandoned sept ic tank systems do occur i n the o lder subdivisions. The major human waste discharged i n - t o the Grand Canal, Roberts Bay and Big Sarasota Bay are sumnarized i n Table 3. Next t o the City of Sarasota's discharge i n t o Whitaker Bayou, SKUA's d a i l t reated discharge i n t o the Grand Canal i s the l a rges t s ing le sewage d isc if, arge enter ing the Sarasota Bay system (McNulty e t a l . , 1972). While the SKUA o u t f a l l water i s t rea ted and monitored t o meet State of F lo r ida standards, "adverse" condi t ions have prevai 1 ed , especial l y during and fo l lowing major storms l i k e the one o f June, 1972 when about 5.6 inches of r a i n f e l l i n 36 hours.

I n add i t i on t o the SKUA discharges the water q u a l i t y i n the canal may be a f fec ted by discharges from P h i l l i p p i Creek which dra ins both urban and ag r i cu l t u ra l lands. While the actual d i s t r i b u t i o n o f Ph i l 1 i p p i Creek d i s - charges i s no t known, fragmentary hydrographic data i nd i ca te t h a t a t l e a s t pa r t o f the discharge enters Roberts Bay and thus could enter the Grand Canal sys tem.

In te res t inq ly , va r ia t ions i n discharges from Phi 11 i p p i Creek para1 l e l monthly r a i n f a l l (Figs. 20 & 21 thus confusing the general impression t h a t freshwater r uno f f i n t o the cana 1 s i s a major con t r ibu t ion t o a l te red water qua1 i t y i n the canals. No one knows how much freshwater runof f ac tua l l y enters the canals. Most houses along the canal are b u i l t on "ra ised pads" o f s o i l and the yards slope toward the seawalled canals. Since the sea wal ls are capped and extend a few inches above the ground they form a dam for sheet water run off i n a l l but the heaviest ra ins . Furthermore, the s o i l i s porous, we1 1 drained and has 1 i t t l e water hol ding capacity . Thus u n t i l proven otherwise we propose t h a t the major routes o f surface water run off i n t o the canals are through pub l l c storm sewers, cracks and subsurface t i l e drains i n the sea wal ls , and ground water i n t r us i on through the canal beds proper which a c t as chemical f i l t e r s .

Table 3

MAJOR WP-STE WATER DISCHARGES ENTERING RORERT1'S RAY DIRECTLY OR

INDIRECTLY V I A GRAND CANAL OR PHILLIPPI CREEK. (4daptad from

McNulty et al., 1972. )

--- Source of Waste cceiving Waters Average D a i l y Discharge Discharge or

Capacity in

--

SKUA Grand Canal

Casa Mar Apts. Grand Canal.

Nine Outfalls Phil lippi Creek

Field C l u b Robert's Bay ----

Sarasota (city) W h i taker Bayou 6,200,000 ---

I As of June, 1972, discharp water contazned 7-10 ppm phosphate; (3.7, 0.9 ppm chi-orj-ne after 6 hours of contact, Nitrate-nitrite not measured. (!,d.Murphy, yrsonal commtmication, June, 1972), Estimated average 5-day R e 0.1). in discharge of 16 ppm ( ~ c ~ u l t y et ale, 1972).

PUal t - m a k rfraau 8;harharg~s, .tto Ralmrbrr B a y arWf LJtQlr, Suwm@$ta Bq. Me- wmr?l$ d i a ~ e l ~ ~ g e fn @ W a b+sf prr sas~nd f w 1963 - 1966, U,S.Q.ole( l icrl S u r w y Station 24997.5* (M-W et a%., 1 9 ~ ) .

As i n Heron Lagoon, ornamental and native plant l i t t e r i s a hidden pollution fac tor in the Grand Canal System. In parts of the Palm Island C i rcl e Canal the Brazi 1 fan pepper t rees have overgrown the canal margins. (Fig. 16).

A f inal source of "pollution" in the canals as well as bays is rain- f a l l . While outside the pervue of the present study, i t is an environmental parameter the New College Environmental Studies Program is emin- en t ly qualified t o pursue. The nutrient potential i n ra infa l l resul t ing in eutrophic conditions (algal blooms) i n canal systems is i l l u s t r a t ed i n two recent studtes. Reimold and Daiber (1967) report t ha t to ta l phosphorus concentrattons in rainwater col lected a t Lewis , Delaware varied

4.9 ug A per l i t e r i n winter-spring t o 150 ug A per l i t e r i n the summer. The authors conclude tha t "atmospheric eutrophication" may be the cause of unusual phosphorous cycles On the marshes and coastal waters along the eastern coast of the United States. In another study ( ~ l len e t a l . , 1968) tn Great Britatn, to ta l quantit ies of major plant nutrients in ra infa l l were (Kg/ha/annum) nitrogen 8.7-19.0, phosphorus 0.2-1 .O, potassium 2.8-5.4, calcfum 6.5-24.0, magnesium 2.9-6.1 and sodium 1.4.0- 51 .O. In a recent study t i t l e d Eutro hication Factors i n North Central Florida Lakes (Environmental Protect * ve gency , w ' o T 1 * Contrvil R e s e a r c h m e s 16010 BON02/72) Putnam - e t a1 . found tha t the nutr ient content of ra infa l l varied as follows : t o m nitrogen , 0.01 -0.67 mg/l ; NH3-N 0.01-0.86 mg/l ; ~03-N, 0.04-0.94 mg/l; organic P04, 2.2-230.0 ug/l; to ta l P04, 20-70 ug/l .

Vitale and Sperry in t h e i r 1973 report t o the Federal EPA t i t l e d Total Urban War P o l l u t i ~ : The Im a c t of Storm Water show tha t 7

par t i a l ly t reated sewage is only o n e 7 -I?-- t e s o u r c e s u F b a n w a t e r pol- lut ion, Between 40% and 80% of the total annual BOD and COD (chemical oxygen demand) entering receiving waters from the c i t y i s caused by sources other than treatment plants. Dog feces, papers, 1 i t t e r and plant materials a re major factors. Natural processes of weathering of man made structures contribute large amounts of water borne inorganic materials incl uding heavy metal s .

I t i s in te res t in tha t the Grand Canal system 4s "peppered" w i t h storm sewer ou t fa l l s 9 Figure 21a) draining surface waters from roads, non-guttered and curbed road margins, driveways, e tc . Many of these out- f a l l s are located a t the upper ends of deadend canals. The Palm Island Loop of the Grand Canal alone has a t l e a s t 13 storm sewer out fa l l s and concrete aprons draining d i rec t ly from the perimeter roads in to the Canal. Interest ingly, the Palm Island Loop was one of the lowest water qua1 i t y areas w i t h the 1 eas t number and kinds of benthic invertebrates we encountered i n our study. I t a l so has a very sluggish t ida l circu-

lation. T h i s section of the canal functions then as an oversized cess- pool, WhSle i t is yet t o be demonstrated, one may expect, accumulations of organic matter and toxic substances such as heavy metals i n the vicin- i t y of these out fa l l s .

HYDROGRAPHY

Two major hydrographic surveys were conducted on the Grand Canal (July 8-9, August 7-8) and Heron Lagoon (July 2-3, August 14) i n 1972. Additional hydrographic data were obtained a t irregular intervals before and a f t e r these studies. The f i e ld and analytical procedures a re summarized i n Appendix A .

The selection of hydrographic sampling s tat ions was eventually limited by the access ib i l i ty of a s ta t ion and the number of s ta t ions tha t could be sampled within a 2-hour interval . The collection of samples fo r chemical assays was limited to dawn and dusk surface water samples a t 6 s ta t ions i n each of the two canal systems because of 1 imi ted manpower and laboratory fac i l i t i e s .

Sam l i n Stations. Fiqure 22 shows the locations of the eighteen hydrograp 9hP c s tat ions for 'the Grand Canal system. Table 4 describes the location of the s tat ions. Dawn and dusk sampling for chemical analysis were limited t o Stations 1 , 4, 15, 10, 9 , and 14 which were located along the Grand Canal between the entrance (Sta. 1 ) , SKUA (Sta. 15) , Palm Island (10, 9) and Siesta I s les (14) .Figures 23-28 show views of t h e Canal a t these hydrographic s ta t ions. The hydrographic s ta t ions i n the Heron Lagoon system (Fig. 29, Table 5) were selected mainly on t h e i r access ib i l i ty from nearby roads. Again dawn and dusk samples for chemical analysis were taken a t a l l s ta t ions except Stations 2 and 5. Figures 30-35 show views of the Heron Lagoon Water- ways a t several hydrographic s ta t ions.

Rainfall and Tides. During the course of t h i s study the monthly cumulative raixl-orted i n the Sarasota Herald Tribune was as follows: June, 6.96 inches of which some 6.5 inches occurred during Hurricane Agnes; June 12, ; July, 3.82 inches; August, 7.07 inches. No rain f e l l during or on the day pr ior t o each of the hydrographic surveys. Thus we conclude tha t the hydrographic conditions i n the canals and bays during t h i s study were not direct ly affected by r a in fa l l .

Since the water i n the canals and bays i s affected by the ebb and flood of t ides as well as day-night l i gh t cycles the times and heights of Sarasota Bay t ides fo r the sampling dates a re summarized i n Table 6. We t r i ed to choose sampling dates i n July and August where the times of high and low water were similar. However, t h i s was not operationally possible. As we l a t e r learned (Langdon Ross, Florida Pol 1 ution Control Board, personal communication), water sampling programs of canals should s t r i v e to sample the canal waters a t dawn on ebbing t ides since t h i s i s when the canal waters are expected to have the lowest "quality" w i t h respect t o pH, D. O., and nutrients. In our study dawn samples were collected on r is ing t ides and d u s k samples on ebbing t ides ,

TABLE 4

S t a t - ' o?. N o . --- --- -- l o c n t i - ~ n -...- - - ( 1 R o b e r t s R a y 200 yards s o u t h e a s t o f o n t r a n c e

tc Grand C a r l z l and ~011 th o f I : j r y e c.poi.1 i s l - a n d ,

1 Bond j.n Canal 5 0 y a r d s w e s t o f Caual entrance.

2 W e s t a r m o f B a y P ~ i n t Canal .

3 TTpper end o f Wate r s ide Wood Canal .

4 Grand Canal. at j u n c t i o n w j t11 Ocenn 9car.h C a n s 1 e ? s t of H i y e 1 Avenue.

5 J u n c t i o n o f Harmony C a n a l and Paradisc T F ~ and C a n a l s ~ r s t ~ r n r , .

6 nead enc? o f one P a r a d i s e I s l a n d Canal .

Jumot ion of Sarasand and S i e s t a M a n ~ r Canal s .

Oearl End of one S a r a s a n d C a n a l .

9 West side o f Pa1.m I s l a n d n o r t h of Calle Florida R r i d g e .

10 .Timcti.on o f Palm 7-sland Canal loo? .

1 5 G r a n d Canal 2 0 f e e t off o f SI'llF outfall.

16 Thad end Watrrsicle West Canal.

17 Yest branch, W3tersi.de F a s t ?anal.

Figure - 29 Location of hydrographic stat ions 2 through 8 I n the Heron Lagoon system. Stat ion 1 was the foot bridge a t the southern end o f Heron Lagoon proper. The stat ions are des- cr ibed i n Table 5.

TABLE 5 FY I)IIOG'$A TIC: $T,ALrI?7-( t 5 F TJN FI3RON L AGnr)l\l

S ta t ion N o . - -- -. ----- I pcati-on .- - ---- 1 Cen ker o f f o o t bridge south end o f H e r o n Li-~goon.

2 Heron B a y bv Sander! i n g Road.

' 3 Midwaterway cu lver t , Sander3 ing Road.

It East Waterway cu lver t , Sander1 j ng Road.

5 D o c k , north end East Waterway.

6 Pine Needle Road cu lver t , North Waterway.

Boat Basin, S i e s t a Club.

L i t t 3 e Sarasota Pay, 100 yards eas t o f entrance t o S i e s t a CI-ub Boat Basin.

Table 6 Sarasota Bay t i d e s f o r dates of hydrographic surveys, July, August 1972. Times o f h igh and low water and he ight i n f e e t above mean sea l e v e l are from the "Sarasota Herald Tribune".

High Low High Low High Low High Low

Grand Canal

Ju ly 8 1011 2.6 1930 -0.2 - - - - J u l y 9 1107 2.7 2021 -0.3 - - - - August 7 0240 1.5 0604 1.2 1301 2.5 2111 0.2

August 8 0249 1.5 0704 1.1 1348 2.4 2135 0.4

Heron Lagoon

J u l y 2 0534 1.7 1147 1.0 1655 1.8

J u l y 3 - - 001 5 0.5 0615 1.8 1317 0.8

August 14 0354 2 .O 1116 0.6 1652 1.7 2249 1 .l

S a l i n i t y

Da i l y and seasonal f l uc tua t ions i n the s a l i n i t y o f surface and subsurface waters i n the two canal systems and t h e i r ad jo in ing bays are summarized be1 ow.

Solar and Wind Evaporation

/

Sewage . P lant

Gul f o f Mexico /

Water, Flooding T i des

Increase -1 I I

Decrease It-

Out fa l l s I Ra in fa l l

Stream Discharges

Among the questions we examined were: 1) d i f ferences i n s a l i n i t i e s of surface, mid depth and bottom waters i n the canals and bays over day- &

n igh t and t i d a l cycles, 2) s a l i n i t y f l uc tua t ions w i t h i n each canal system, 3) f luc tuat ions i n surface water s a l i n i t y fo l l ow ing heavy r a i n f a l l , and 4) the distances which water from the bays may extend i n t o the canal sys terns.

Grand Canal . During July and August, 1972 the sal i n l ly i n the bay , y a r i e d m x t o 28%0. Our measurements represent then sal i n i ty-GGF d i c t i o n a n these months when there i s l i t t l e or no r a in fa l l . Figure 36 i l l u s t r a t e s the variations i n s a l i n i t i e s of surface waters on flood t ide a t dawn and ebb t ide a t dusk i n different regions of the Grand Canal system. Our data from two hydrographic surveys indicate the sa l in i ty / profiles i n the canal system are affected by freshwater discharges ground water seepage and s t r a t i f i ca t ion of water layers.

On flood t ide the sa l in i ty of the surface water decreases from the Roberts Bay t o Station 15. Above Station 15 there is a measurable drop in sa l in i ty i n the Palm Island, Siesta m e s and Sarasands - Paradise -k I s l e areas. The surface wateFG-mGn-7-%p%rticularly low w - ( y S G . N ~

suggesting a local source of freshwater intrusion in th i s area of the &iic4 canal system or e l se water from the SKUA outfal l being transported in to 4" this and other areas of the upper canal system. In the dead end canals .w%

off the Grand Canal bayward of Station 15 the surface s a l i n i t i e s are . relat ively h igh .

The surface water s a l i n i t i e z on ebb t ide ( ~ i g . 36) d i f f e r from those on flood t ide . One could expect increases i n s a l i n i t i e s resulting from solar evaporation during the day. Contrarily, freshwater discharges o r seepage would cause decreases i n s a l i n i t i e s a t the canal s ta t ions. In the Grand Canal proper there i s a general increase i n s a l in i ty from Palm Island t o the Bay. However, there i s a marked decrease i n s a l in i ty a t Station 15 ref lect ing the freshwater discharge of the SKUA ou t fa l l . The influence of t h i s fresh water discharge resu l t s i n a measurably lower sa l in i ty a t Stations 1 and 4 i n the canal proper and possibly the waters i n the dead end canals of Stations 16 and 17, b u t not Stations 2 and 3. On the other hand, lowered s a l i n i t i e s a t Stations 16 and 17 on ebb t i d e a t dusk may re f l ec t local sources of ground water intrusion i n these canals .

In the Siesta I s l e s area (Stations 11 , 13 and 14) the s l ight ly lower - sa l in i ty on ebb t i d e a t the end of a b r i g h t sunny day could be caused by ,,!$ 7ai'd," 50.c~ intrusion of outfal l waters from SKUA and Qcal ground water seepage. The l a t t e r possi b i 1 + m i s t i n the Sarasands - Paradise I s les area g " 9 e - ~ ~ ~ ~ / (Stations 5, 6, g. 36). RemeiiibeF3hat--t3ie canals i n this area were cut through poorly drained Arzell f ine sand. That ground water i n - trusion i s occurring a t different places i n the canal system i s suggested by the bottom water s a l i n i t i e s summarized i n Table 7 . The data indicate ground water intrusion is occurring a t Stations 5, 6 , 7 , 8, 9, 13 and 14. While under normal conditions i t i s probably not suf f ic ien t t o create brackish water conditions re la t ive to the Bay, such ground water may carry nutrients and other materials into the canal i n these areas.

Table 7 Heron Lagoon, minimal salinities (%$ i n surface water on ebb tides

Hydrogra hic Stations 2 J 4 5

Date - May 18-19, 1972

July 3 , 1972

Aug. 14, 1972

- - **Sept. 1 1 , 1973

Sept. 12, 1972 . -

Sept. 16, 1973 " *** Dec. 16, 1973

* - * 2 hours after rains of Hurricane Agnes ceased

r - ** 1 hour after afternoon showers

L - *** 1 hour after rain storm

H y d r o g r a p h i c S t a t i o n s - G r a n d C a n a l

Figure 36 Surface water s a l i n i t y (%)hydrographic s t a t i o n s i n Roberts Bay (S ta . 0 ) and t h e Grand Canal system J u l y 8-9, 1972. S o l i d c i r c l e s , dawn, f lood t i d e ; open c i r c l e s , dusk, ebb t i d e , .

Heron Lagoon. Table 7 shows t h a t the minimal s a l i n i t i e s a t the sampljng s ta t ions i n Heron Lagoon proper and i t s waterways are s i m i l a r t o those i n L i t t l e Sarasota Bay (Sta t ion 8) i n May, Ju ly and August. The high s a l i n i t y i n the Bay on May 18-19 cor re la tes w i t h the low r a i n - fa1 1 and so la r evaporation t y p i c a l f o r t h i s month. While the s a l i n i t i e s i n the Heron Lagoon system are s i m i l a r t o those i n L i t t l e Sarasota Bay there i s evidence t h a t the water from the Bay i s being d i l u t e d by sources o f f resh water seepage o r discharge i n the Lagoon system. Typ ica l l y the s a l i n i t y a t S ta t ion 1 a t the southern end o f Heron Lagoon i s one t o two par ts per thousand lower than a t S ta t ion 7 i n the Boat Basin near the entrance t o the Bay. This i s a l so re f l ec ted i n the d i s t r i b u t i o n of several species o f macro invertebrates i n Heron Lagoon.

S a l i n i t y readings taken a t S ta t ion 5 fo l l ow ing heavy r a i n f a l l (Table 7 ) show t h a t the surface s a l i n i t y i n the waterways may f l u c t u a t e temporar i ly

from 35.4% t o a t l e a s t 9.6%. I n te res t i ng l y enough, t h i s l a t t e r - s a l i n i t y value was obtained 1 hour a f t e r a 3 hour thunderstorm. With in 12 hours l a t e r the s a l i n i t y a t t h i s s t a t i o n had r i s e n t o 20%.

From these sketchy data we conclude t h a t the surface water s a l i n i t y i n the Heron Lagoon system may f l uc tua te widely throughout the year. Because o f the r e l a t i v e l y h igh perimeter t o surface area r a t i o o f t h i s canal system ground water and surface water run o f f from the upland proper t ies are the major causes o f sudden decreases i n s a l i n i t y dur ing and fo l low ing ra ins .

T ida l Currents

A common b e l i e f i s t h a t there i s l i t t l e , i f any, t i d a l c i r c u l a t i o n i n dead end canal systems and t h a t there i s r e l a t i v e l y l i t t l e exchange o f water i n dead end canals w i t h ad jo in ing open waters o f bays. However, the water l eve l i n canals r i ses and f a l l s w i t h the normal t i des i n d i c a t i n g a ce r t a i n degree of exchange. Furthermore, our observations on surface and subsurface s a l i n i t i e s throughout the Grand Canal and Heron Lagoon systems ind icated there were t i d a l exchanges and f lush ing a c t i v i t y between these canals and ad jo in ing bays. I n order t o determine the qua1 i t a t i v e character o f these exchanges we performed several p r e l iminary t i d a l cur rent studies using one ga l lon p l a s t i c bo t t l es t o fo l low t i d a l f low i n the surface and subsurface waters of the canals during t i d a l cycles. While our r esu l t s are o f the most pre l iminary nature we include them here i f on ly t o r a i se questions t h a t lead t o future studies .

Grand Canal .On Au us t 24, 1972 f l o a t s a t the surface and 4 f e e t below the surface-d-depth 3 were released a t S ta t ion 1 a t the beginning of a 6 hour f l ood ing t i d e (Fig. 37). N i t h i n 5.5 hours both f l o a t s reached S ta t ion 15. The mid-depth f l o a t continued as f a r as Palm Is land. Then Ls

when the t i d e turned t o ebb both surface and mid-depth f l o a t s descended the Grand Canal proper reaching the entrance t o the Bay i n 4.5 hours, near- l y 3 hours before low water. Nei ther sets o f f l o a t s tended t o d r i f t i n t o the dead end canals alonq the main canal.

mcluded tha t the main t ida l exchange of water ,he canal system occurred within the Grand Canal

1 exchange occurred between Station 10 and the Bay c les . Tidal exchange may be expected t o be more .ing t ides and longer t idal cycles.

~ n d 29, 1972 surface and mid-depth f loa t s were re- s in the Palm Island loop (Fig. 38) and near Station

,Fig. 39) . In both instances the f loa t s traveled P 2d fee t over a 4 t o 5 hour period before the t ide to flood. T h i s suggests rather sluggish t ida l c i r - ; and l i t t l e flushing ac t iv i ty i n these two segments tern. While we know nothing about t idal circulation Harmony Is les - Sarasands section of the Grand Canal

d expect t ida l exchanges similar t o tha t i n the Siesta

& I . ,n t o our own current studies, the only other current study on the Grand Canal i s t ha t of Benson and Brainard (unpublished) who determined t ida l current veloci t ies a t the Midnight Pass bridge over 14 days i n July, 1972. Once t h e i r data were "digested" i t would be possible t o determine the volume of water i n the canal system tha t enters Roberts Bay on an average t ida l cycle as well as t idal flushing exchanges.

Heron La oon. Preliminary t ida l current studies i n the Heron Lagoon -+ waterways revea ed complex patterns of circulation i n the waterways. These patterns are d i f f i c u l t t o interpret and would require an analysis beyond the scope of our investigation. In general there i s t ida l exchange between the northern end of Heron Lagoon, the waterways, and L i t t l e Sarasota Bay through the several road culverts. We do not know the ra te of exchange of bay water with the waters of Heron Lagoon proper. From f i e ld observations we hypothesize tha t there i s l i t t l e t ida l exchange i n the southern half of Heron Lagoon.

Our t idal f l o a t study i n the East Waterway i s summarized in Fig. 40. Surface and mid-depth f loa t s released a t the Pine Needle Road culvert took 2 hours t o reach the Midnight Pass Road culvert on an ebb t ide . The surface f loa t s tended t o d r i f t southward toward the Sanderling Road culvert . Floats released a t t h i s l a t t e r culvert tended t o "waltz" i n the area i n eddy currents. Floats released on flood t i d e a t the Midnight Pass Road culvert dr i f ted down the East Waterway rather than toward the Pine Needle culvert . A t the junction of the waterways (Fig. 40) surface f loa ts tended t o move i n a large c i rc le .

From these data we tentat ively conclude tha t bay water enters the waterways and flows through the East Waterway on flood t ide . On ebb t i d e Mid-Waterway via Pine Needle culvert i s the main route of water movement. I t appears tha t t ida l circulation here involves a c i rcu lar movement through the waterways thereby creating an open ended flow through t ida l water movement i n the equivalent of a dead end canal system. The ro le the water in

Figure 38. F l o a t S t u d y , P a l m I s l a n d G r a n d Canal S i e s t a Key A u g u s t 2 8 , 1 9 1 2

H igh T i d e L o w T ide

Figure 39. F l o a t S t u d y S i e s t a I s l e s E b b t i d e , August 29,1972

High t i d e 1722( 1.5') low t i d e 2 i s d 1.1)

Her nof wo i n 07

odynamics of t ida l circulation here is j vantage point this system is a model i t could provide clues as to how t o

sections of the Grand Canal system and

i t i e s were measured w i t h current meters a t .st Waterways, Station 4; Mid-Waterway, iulvert , Station 5 - d u r i n g a t idal cycle. that the veloci t ies increased du r ing flood ,he velocity highest a t Station 4. Inter- ind ebbed f i r s t a t Station 5. After the and 4 the current velocity decreased and then

increaseu ,, g again. Whether this rebound ef fec t as well as the actual velocitie3 dre due to the culverts themselves are not known. However, the general picture shown by these t ida l current velo- c i t y data are not inconsistent w i t h our t ida l f l o a t data.

In summary, our sketchy t ida l flow data of the two canal systems demonstrate tha t t ida l circulation and t ida l exchange i s complex. More detailed studies are required before one draws concl usions regarding circulation patterns and part icular ly the amount of water i n these canal systemsthat actually enteras the adjoining bays. I t is quite pos- s ib l e t h a t du r ing ordinary t idal 'cycles the b u l k of the water tha t enters the bay on ebb t ide i s the same water mass tha t entered the canal J system on flood t ide . Water masses i n the upper segments of both canal systems may only exhibit a slow exchange and mixi'ng w i t h bay water over long periods of time. If this were the case, then the pollution of the bays by canal waters may need t o be reassessed.

H e r o n L a g o o n E a s t W a t e r w a y C u r r e n t F loa t S t u d y

H i g h T i d e 1 2 4 8 Lo-w T i d e 2 0 5 9

Fi g r e 40. -

H i g h T i d e 1 3 3 2 . B i g Pass. S a r a s o t a 4 , ~ i r n e w h e n t i d e t u r n e d

1 1 0 0 1 2 0 0 1 3 0 0 1 4 0 0 1 5 0 0 1 6 0 0 Time

Figure41,Current - v e l o c i t y during f lood and ebb t i d e a t hydrographic s t a t i o n s 3, 4 and 5, Heron Lagoon, June 13, 1972. Current readings taken a t openings of 38 inch diameter road c u l v e r t s

DISSOLVED OXYGEN

The amount of oxygen i n the water and the daily fluctuations of oxygen concentrations a t different depths during t idal regimes are the most frequently used measurement of assessing water qual i ty . Throughout the 1 i terature on water qual i t y there are statements indicating dissolved ox gen (D.O.) levels below 4.0 ppm are deleterious to marine l i f e , par t i - T cu a r ly fishes. However, the dissolved oxygen requirements and to1 erance 1 i m i ts of a l l but a few marine organisms are unknown. Of those organisms whose respiration and survival a t different levels of dissolved oxygen i s known, many are able to survive D. 0. 1 eve1 s of 1.0 ppm f o r a few hours and D.O. levels of 2.0 ppm for several days ( i .e., Federal Water Pol 1 ution Control Adm. , 1968; Vernbetl , 1971 ; Doudoroff & Shumway, 1967). Pamatant (1 971 ) found tha t benthic community respiration was relat ively constant w i t h decreasing oxygen tension t o a c r i t i c a l level of 1 ml/ l i ter .Fi l los and Malof (1972) found tha t there was no appreciable release of nutrients, phosphate and ammonia from benthic deposits until the D.O. f e l l below 1.5 ml / l i te r . The l i t e ra tu re on the comparative physiology of marine organisms shows tha t benthic organisms readi l y adapt t o sudden changes i n D . O m ( i .e., Mangum, 1972) . Nevertheless, the general impression is tha t chronically low D.0.s as well as occasional lowering of the D.O. i n surface and bottom waters i s biologically damaging ( i .e., Dept. Poll. Control, 1973). In a r t i f i c a l l y created bodies of water 1 i ke canals water movement i s frequently minimal and the minimal D.O. levels lower and diurnal fluctuations greater than in adjoining waters of the bays. Whether one is dealing w i t h the open waters of the bays or the waters of canals variations i n D.O. a re a function of the interaction of several factors outlined below. Briefly th i s function involves discharge of soluble organic material, nutr ients , oxygen demand and ra t e of uptake of benthic deposits, photosynthesis and respiration by plankton and benthic plants, water temperature, freshwater input and t ida l exchange.

In the present study we were interested i n the following:

1 ) The maximal and minimal dissolved oxygen levels i n various sections of the canal systems and the adjoining bays.

2 ) The maximal and minimal dissolved oxygen levels i n the surface, mid-depth and bottom waters of the canals.

Although we measured dissolved oxygen a t 6-hour intervals over 24- hour periods and complete t ida l cycles, we limit our presentation here t o measurements taken a t dawn when D.O. values were minimal and dusk when D .O. values were maximal .

Phytoplankton 1 ower sa l in i ty

lower respiration of 1 ower marine organi sms

Nonstratification s f water masses

Increase i n organic nutrients

1 DISSOLVED OXYGEN 1

Respiration (B.O.D .)

f ishes

~ e n t h i c organisms

r \ 7 macro? bacterla plants fauna

meiofauna

Decrease S t ra t i f ica t ion

r t ' T of water - temperature & sal in1 t y

H i aher I ~ e i ~ e r a ture \ Increased Turbi d i t.y

Chemical Higher oxidation sa l in i ty (C.O.D.) T

C.O.D. B.O,D.

During the per iod o f our study the 100% saturat ion l eve l o f dissolved oxygen i n the waters o f the canals and bays was approximately 4.5 ppm. Thus values above t h i s l eve l represent supersaturation. I n the w in te r months higher saturat ion leve ls are t o be expected.

Grand Canal . Figure 42 shows the maximal (dusk) and minimal (dawn) D.O. ~ s ~ o b e r t s Bay and a t s i x s ta t ions i n the Grand Canal f o r Ju l y and August. The Bay shows the l e a s t dawn-dusk f luc tua t ions i n D.O. ; Stat ions 15,14,10 and 9 the greatest f luc tuat ions. Dawn surface D.0.s were lowest a t Sta t ion 9. The highest D.O. readings were a t Stat ion 14 and cor re la te w i t h high chlorophyl l measurements a t t h i s s ta t ion.

The di f ferences i n D.O. i n surface and bottom waters a t the 18 s ta t ions are i l l u s t r a t e d i n Table 8 . This t ab le shows t h a t the lowest surface (dawn) D.O. readings were i n the Sarasands-Harmony Shores sect ion o f the canal system and Stat ion 9, Palm Is land as were the bottom water D.0.s. Low D.0.s occurred i n the bottom waters a t Stat ions 2, 16 and 17 a t the upper ends o f dead end canals (Figure 43 1. I n mid-afternoon on the same date there was a marked s t r a t i f i c a t i o n o f dissolved oxygen i n the upper sections o f the canal system i l l u s t r a t e d as fo l lows:

Stat ion

14 5 and 6

D.O. ppm Surface Bottom

This D.O. s t r a t i f i c a t i o n cor re la ted w i t h a s a l i n i t y and temperature s t r a t i f i c a t i o n . In te res t ing ly , Stat ions 2 and 17 exh ib i ted the lowest bottom water D.O,s a t a l l times even though no marked s t r a t i f i c a t i o n o f s a l i n i t y o r temperature occurred a t these stat ions.

Figure 43 shows t h a t i n the Grand Canal proper there was a progres- s i ve decrease i n dissolved oxygen i n the bottom waters between the canal entrance and Palm Island. However, a t dusk on ebb t i d e the D.O. a t Stat ions 0, I , 4 and 15 was above the 100% saturat ion l eve l . The D.O. i n the bottom water above Stat ion 15 had increased a t Stat ion 10, decreased a t Stat ion 9 and remained approximately the same a t Stat ions 11, 13 and 14 i n the Siesta I s l e s sect ion compared t o the dawn readings.

Heron La osn. The maximal (dusk) and minimal (dawn) D.O. values ob- t a i n e d s- sur ace water a t the e igh t hydrographic s ta t ions i n the Heron Lagoon system are shown i n Figure 44 . The minimal D.O. values a t dawn were as low o r lower than those f o r the Grand Canal . The maximal D.O. values were comparable t o those from the Grand Canal system. The d:iurnal f l uc tua t ions were l e a s t a t Sta t ion 8, L i t t l e Sarasota Bay and greatest a t Sta t ion 2, Heron Bay.

' PPM u -

H y d r o g r a p h i c S t a t i o n s - - G r a n d Cana l

Figure - 42 Maximum (dusk) and minimum (dawn) dissolved oxygen

(Pr m) 1 foot below surface i n the Grand Canal system, Ju y (J) 8, 9 and August (A) 7, 1972.

Table - 8 Dissolved Oxygen, Temperature and S a l i n i t y i n Surface and Bottom Water Grand Canal System, July 9, 0700 - 0900, Rising Tide

Stat ion Depth Dissolved 02(ppm) Temp°C S a l i n i t y .-

Surface Bottom Surface Bottom Surface Bottom

0 5 4.8 5 .O 28.5 28 .O 35.5 35.1

H y d r o g r a p h i c S t a t i o n s -- G r a n d Cana l S y s t e m

Figure 5 MaxlMum (dusk) and minimum (dawn) dissol ved oxygen (ppm) 1 f o o t below surface i n the Heron Lagoon system July (J) 3 and August (A) 14, 1972.

In conclusion, the larger diurnal D.O. fluctuations i n the surface waters in the canal systems compared t o the adjoining bays are probably due to the relat ively large phytoplankton populations i n the canal waters (Barda and Pantington, 1972). The photosynthetic ac t iv i ty of the phytoplankton during the day resul ts in elevated D.O. values; a t night phytoplankton and microbial respiration markedly lower the oxygen i n the surface waters. The percent difference between dawn and dusk D.O. values may be used as a measure of eutrophication and basic productivity of waters i n different sections of the canal systems. The low D.O. values i n the bottom waters i n the canal systems, par t icular ly the upper sections and dead end canals of the Grand Canal system, are associated w i t h chemical oxidation and microbial respiration a t the surface of the bottom sediments and the relat ively weak t ida l circulation i n these areas.

Studies on the oxygen uptake (respirat ion) by subtidal natural benthic marine communities show tha t up t o 70% of the respiration can be due t o bacteria (Kanwisher, 1962). In a recent study Smith (1973) found i n a subtidal community off Sapelo Island, Georgia tha t macro- faunal respiration comprised 5 to 20%; bacteria 30 t o 60%; and meiofauna 25 t o 58% of the to ta l community respiration. Sediment chemical oxidation i n July accounted fo r about 8% of the to ta l oxygen uptake.

TURBIDITY

Although there i s a general lack of information on the effects turbidity has on marine organisms over long periods of time, turbidity i s frequently measured in water quality studies. According to the Florida State water quality standards the turbidity of Class IV waters - a ricultural and industrial water supply - "shall not exceed f i f t y (503 Jackson Units as related to standard candle turbidimeter above background." However, the use of Jackson Turbidity Units to measure turbidity has been criticized by May (1973) who points out that turbid- i t y meter readings are unreliable and a questionable measure of the suspended solids in water. In the present study we used both a Secchi disk and a mi 11 i pwe f i 1 t e r technique for suspended matter [See Manheim e t a l . (1970) for a critique of the millipore method and open ocean values. I The degree of turbidity i s a measure of the number of particles i n suspension. An increase in the number of suspended particles i n - creases the absorption of l ight in the water. In the shallow bays of the west coast of Florida nearly a l l the l ight i s absorbed i n the top 6 feet. This means that the euphotic zone o f phytoplankton and benthic plants i s limited to depths less than 6 feet. Periodic and seasonal variations i n turbidity occur natural 1 y . Dredging , spoi 1 i ng and urban- agricultural runoff increase the turbidity thereby reducing the euphotic zone to less than 1 foot a t times. In general, increases in turbidity result i n lower oxygen concentrations i n the water particularly a t n i g h t ; b u t the qua1 i tative character of turbidity varies. The potenti a1 nature of the suspended particles causing turbidity i s out1 ined below.

Pollen j Atmospheric +- oust '=T=' Benthic Animals

pel l e t s , Excretia

hyto-Zoopl ankton ac te r i a i Marine Construction,

TURBIDITY Dredging, F i 11 ing

/ Water \ Column \

~ t . ,. Boa twa kes \

wind generated turbulence Fish a c t i v i t y

1 Surface Bottom Sediments - Organic I l and Inorganic I

Increases i n turbidi ty then can r e su l t i n the following adverse conditions : 1 ) 1 ower 1 ight 1 eve1 s and narrower euphoti c zones, shorter submarine days, increased surfaces fo r bacterial adsorption and growth, competition w i t h marine plants for minerals and other plant nutrients , and increases i n the B.O.D. and C.O.D. levels i n the water. A t the same time resuspension of bottom sediments do provide a major source of nutr ients for the production of organic matter by phytoplankton, bacteria and benthic plants. The complexities of increases i n turbidi ty on water quality are i l l u s t r a t ed i n various reports and reviews ( i .e., Gustafson, 1972; Oschwald, 1972; Manheim - e t -a a1 3 1970; Pionke and Chesters, 1973; Berg, 1970; Buchan e t a1 . , 1967; Trevallian, 1967; and Marshall and Orr, 1964).

--

In the present study we f i r s t attempted to measure turbidi ty or transparency of the water in the bays and canal systems using a Secchi disc. In general, the depth below the surface a t which an 8-inch white disc i s no longer vis ible approximates the depth of the euphotic zone a t the time of measurement. In the Heron Lagoon system on July 3, 1972 Secchi disc reading> ranged from 3.5 fee t a t Station 8, L i t t l e Sarasota Bay t o 3.0 f ee t a t Station 4 , East Waterway t o 2.5 fee t a t Station 1 , south end of Heron Lagoon. Secchi disc readings on other dates were similar. All indicated a general increase i n turbidi ty between the Bay and Heron Lagoon. In the Grand Canal system Secchi disc readings on July 8 ranged from 3.0 f ee t , Roberts Bay t o 2.0 fee t a t Stations 15 and 9 t o 1.5 f ee t a t Station 16, a dead end canal.

To fur ther study the nature of the turbidi ty and i t s variations i n the canal systems we measured both the amount of par t iculate matter (suspended sol ids ) and chlorophyll 2 i n water samples from the several hydrographic s ta t ions on flood and ebb t ides . The data f o r the two canal systems a re summarized i n Table 11 and Fig. 45. In general , the par t iculate matter and chlorophyll a i n the bays and canals were lower on flood than ebb t ides . The amount of chlorophyll g (measure of the amount of phytoplankton) was highest i n the upper reaches of the Grand Canal system a t dusk on ebb t ides (Fig. 45). Our data indicate tha t much of the suspended part iculate matter and resul tant turbidi ty in both canal systems i s associated w i t h large populations of phytoplankton. However, organic-inorganic resuspended sediments, bacteria and dead phytoplankton i n dead end canals l i ke Waterside Wood, Station 16, Grand Canal may be the major cause of turbidi ty i n those areas w i t h sluggish t ida l flow.

In Fig. 45 we have circled three se t s of chlorophyll 2 part iculate matter points to i l l u s t r a t e the comparison between Gulf of Mexico water, open bay water and water a t the entrance t o the Grand Canal.

Figure 45- Relat ion of Chlorophyll a and p a r t i c u l a t e matter i n sur face water samples Ju ly 8-9 and August 7, 8 and 10, 1972. Flood t i d e a t dawn; ebb t i d e a t dusk.

6 0

F l o o d E b b G u l f M e x i c o

5 0 R o b e r t s Bay Sta. 0 @

4 0

0 /

30

2 0

10

4 8 12 16 20 24 28 32 36

C h l o r o p h y l l A (mg / l i t e r )

CHLOROPHYLL-A AND PHYTOPLANKTON

The amount o f ch lorophy l l g per u n i t volume o f water i s f requent ly used as one measure of the amount o f phytoplankton present and i s i n d i - ca t i ve o f the amount o f basic p roduc t i v i t y and degree o f eutrophicat ion and water qual i ty .

I n the present study ch lorophy l l p values i n the Grand Canal system were an order o f magnitude higher than those i n the Heron Lagoon system (Table 10). The highest values obtained were i n the Siesta I s l e s sect ion of the Grand Canal a t dusk on ebb t ides.

While plankton samples were co l lec ted i n both canal systems, t ime permit ted only the analysis o f the phytoplankton from one se t of samples from Heron Lagoon. As seen i n Table 9 the phytoplankton community o f L i t t l e Sarasota Bay and Heron Lagoon i s dominated by the diatom Skele- tonema costatum. Prel i m i nary examinations o f the Grand Canal s a m m m t e d s t a t u m was a l so the dominant phytoplankton i n the Grand Canal. However, our sampling and preservation procedures may have re - su l ted i n a great reduct ion i n numbers o f d ino f lage l la tes i n the samples.

Quan t i t a t i ve data on ch lorophy l l g and phytoplankton f luc tuat ions are so sketchy f o r the west coast o f F lo r ida (see Saunders e t a1 . , 1965) i t i s d i f f i c u l t t o assess the s ign i f icance o f our data. ~ i $ m o r o p h y l l p val ues , high phytoplankton counts coupled w i t h the phytoplankton community dominated by a s ing le s ecies are f requent signs o f plankton blooms, eutrophicat ion and resu ! t a n t adverse water qua1 i ty condi t ions. However, Saunders e t a1 . , (1965) found S. cos ta tm the dominant diatom i n most of t h e i r inshore samples f o r m o s t - m o n t h s t h e year. Diatom communities dominated by large numbers of t h i s species may ac tua l l y be we l l balanced. For a b r i e f synopsis on the b io logy of t h i s diatom see Steid inger (1964). The phytoplankton numbers i n samples from natura l waters along the west coast o f F lo r ida are so high r e l a t i v e t o studies i n other areas t h a t eutrophicat ion l eve l s o f chlorophyl l a - a and phytopl anton values from other areas may no t apply l o c a l l y .

One can expect qual i t a t i v e and quan t i ta t i ve seasonal f l uc tua t ions i n the phytoplankton populat ions ( i .e., Carpenter, 1971, Hul bert , 1970) i n the bays and canals t o be re l a ted i n p a r t t o seasonal va r i a t i on and d i s t r i b u t i o n o f dissolved nu t r ien ts , p a r t i c u l a r l y n i t rogen ( i .e., Thayer, 1971, 1974; Fournier, 1966). A t the same time, r ap id l y growing and photo- synthesizing 1 i v e phytoplankton and dead phytoplankton re1 ease ext ra- c e l l u l a r products ( i .e., Samuel e t a1 . , 1971 ) t h a t s t imula te microbial growth and resp i r a t i on ( i .e. ,Bell & M i t che l l ,1973)or t h a t i n h i b i t the growth o f natura l heterotrophic aquatic ~ a c t e r i a as we1 1 as co l i f o r m and patho- genic bacter ia (i.e., Sieburth & P ra t t , 1962; Sieburth, 1965; Duff, e t al. , 1966) .Thus wi thoutaddi t i o n a l studies on the phytoplankton populat ions i n these canal systems i t i s d i f f i c u l t t o determine t h e i r ove ra l l con t r ibu t ion t o the water qua l i t y .

A few o f the many fac to rs associated w i t h chlorophyl l a concentrat ion - and phytoplankton densi ty are summarized below.

Rainfa l l Streams Out fa l l s 4 Resusprsion

P04 Nitrogen

High 1 i g h t i n tens i t y 1 1 OrTnic Trace minerals low t u r b i d i t y Dissolved Nutrients /

Water ag i ta t ion shallow areas Increase water temp.

Increase

High death Low 1 i g h t Low water temp. ra te i n tens i t y

High Predation day length Zooplankton F i 1 t e r Feeding Benthic organisms

High competition by bacteria on suspended matter for nut r ients

Table -9- Percent composition o f the ten most abundant phytoplankton i n plankton co l lec t ions from the Heron Lagoon System, June 27, 1972

Flooding Tide (0700) - Dawn

Phytoplankton Species Stat ion Number 1 3 4 5 6 8

Skeletonema costaturn 51.3% Chaetoceros sp. 28.3 Rhizosolenia set igera 4 .O Thal assionema n i tzchiodes 5.0 N i t z ch i a c l osterum 2.7 N i t zch ia 1 ongissima 1.2 Ni tzch ia pangens * Para l ia sul cata 4.4 Gonyaul ax pol yramna 2.3 Per i d in t um conicum 0.8

tbbing Tide - (1800) - Dusk

Skel etonema costatum 83.2 Chaetoceros sp. 12.2 Rhi zosolenia set igera 1 .O Thalassionema nitzchiodes * Ni tzch ia c l osterum 2.6 Ni t zch i a long i ssima 0.7 N i tzch ia pangens - Para1 i a sulcata * Gonyaul ax pol yranna * Per i d i n i urn coni cum *

Table 10 Maximum concentrat ions o f cholorophyl l a , t o t a l hosphate, t o t a l n i t r a t e - ! n i t r i t e and dissolved oxygen observed a t Dusk ( 700-188~) ~ u l y & August 1972.

S ta t ion Chloro h y l l a Total PO4 Tota l N03-NO2 Dissolved 02 (mglm3Y (ug/ l ) (ug/ l ) ( P P ~ )

Number Ju l y Aug. J u l y Aug. Ju l y Aug . J u l y Aug . 0 10.5 20.0 4.3 6.8 0.2 0.3 - -

Grand 4 29.8 27.1 10.6 8.3 0.4 0.4 7.1 7.4

Cana 1 15 15.0 25.4 25.1 22.5 13.3 7.0 9.2 -- - 9.4 - System 10 31.6 26.1 12.6 9.7 0.2 0.3 9 .O 8.8

14 - 35.7 20.5 12.3 10.3 0.2 0.3 8.0 9.2

8 7,s 15.0 5.0 3.7 1.0 0.5 7 -4 5.6

Heron 7 7.0 14.1 4.8 3.3 0.7 0.6 6.5 5.9

Lagoon 6 15,6 19.8 5.5 3.6 1.2 0.7 5.6 4.2

Sys tern 4 18.4 13.4 5.8 4.1 0.9 0.6 5.6 5.1

3 21.0 10.8 4.3 4.3 0.8 0.7 5.8 5.2

1 11.7 18.2 4.2 3.4 - 3.1 0.6 5.8 6.5

NITROGEN AND PHOSPHORUS

Measurements of surface water n i t r a t e -n i t r i t e and inorganic-organic phosphate i n the two canal systems i n July and August, 1972 were signi- f icant i n furthering our understanding of the water quality i n the two canal systems. In the Grand Canal system the P-N data show there i s a major source of P-N rich water i n the Canal a t Station 15 (Table 10 & 11). During an ebb t ide , July 9 and August 7, both the n i t r a t e and inorganic phosphate values decreased markedly bayward of Station 15 as well as i n the Siesta I s les , Palm Island sections of the Canal. The most l ike ly explanation for t h i s is that these dissolved nutrients were assimilated i n rapidly growing phytoplankton populations.

These data coupled w i t h the chlorophyll a data (Table 11) and t ida l current movements indicate tha t the inorgani? nutrients released a t the SKUA outfal l are rapidly incorporated by phytoplankton and bacterial populations i n the canal system proper. Thus i n the upper reaches of the canal system where t ida l flow is sluggish plankton blooms tend t o occur. In the canal system bayward of Station 15 the assimilated n u t - r ien ts enter Roberts Bay i n planktonic organisms. Thus the d i rec t inorganic nutrient enrichment of Roberts Bay by the Grand Canal may be minimal.

The nitrogen and phosphorus values i n the Heron Lagoon system were on the whole measurably lower than those from the Grand Canal system (Tables 10 & 11) as might be expected. Samples from July 3, however, had relat ively h i g h n i t r i t e values indicating ground water seepage in to the system.

The general picture tha t emerges from Table 11 i s tha t during July and August of 1972 the nutrient enrichment of the waters of the Grand Canal primarily by the SKUA outfal l resul-ted i n elevated levels of par t i - culate matter (phytoplankton), chlorophyll g and supersaturation of d i s- solved oxygen in the surface waters of the canal system as compared w i t h Roberts Bay, L i t t l e Sarasota Bay and the Heron Lagoon Waterway system. How deleterious this i s t o Roberts Bay is subject t o argument and opinion.

A comparison of water quality parameters - chlorophyll 2, total hosphate and n i t r a t e -n i t r i t e - i n Roberts Bay, the Grand Canal, Station

!5 and other estuar ies and bays along the west coast of Florida i s given in Table 12. We leave i t t o the reader t o draw h i s own conclusions. The complexities associated w i t h any evaluation of levels and fluctuations in these water qua1 i t y parameters are amply i l l u s t r a t ed i n the l i t e ra tu re i . , Likens, 1972 ; Wil kinson, 1964; Johannes, 1968; Jones and Stewart, 1969; Ryther and Dunstan, 1971 ; Sutcl i f f e , 1972; Kerr e t a1 . , 1973).

Table 11 Summary o f physical and chemical data o f surface waters a t dusk f o r hydrographic stat ions, Grand Canal and Heron Lagoon systems, July and August 1972.

Table 12-Comparison of C h l o r o ~ h y l l A , t o t a l d i s so lved phosphate and n i t r a t e - n i t r a t e measurements i n Rober ts Bay a11d s t a t i o n 1 5 on t h e Grand Canal a i t h o t h e r s u r f a c e water sample s t u d i e s a long t h e w e s t c o a s t of F l o r i d a .

3 T o t a l P ospha te U ~ A R N i t r a t g - f f i t r a t e Reference Area Chlorophyl l A mum IC uq /

J u l y Auq. Annual J u l y Auq Annual J u l y Auq Annual Roberts Bay S t a . o . Dusk Ebb 10 .5 20 4.3 6.8 0.2 0 .3 Roberts Bay S ta . o . Dawn Flood 15.2 10.2 5 . 1 3.2 0 .5 0.3

Grand Canal Sta. l5,Dusk,Ebb 22.7 25.4 25.1 23.5 13.2 9.3 Grand Canal Sta.l5,Dawn,Flood 15.0 17 .5 10.3 14.0 1.1 0.5

Gulf Mexico o f f C h a r l o t t e Harbor Lower C h a r l o t t e Harbor Myakka River

Tampa Bay en t r ance Boca Ciega Bay Tampa Bay Old Tampa Bay

Upper Tampa Bay J 2 . 4 5 . . .

Hil lshorougl i Bay 35 2 Annual Range

Wacassa Es tuary , F l a . 1 5 5 82* 34 Prf %Y' A l l i g a t o r Harbor, F l a . Max. 14.6 4 .3 /mc. South A l l i g a t o r Harbor 3.4

Marsha l l 1956

Fenholloway Es tuary Waccassa Es tuary

Max 23.8 7.6 2.8-5.2 L2.5 30.6 21.3 13.3 20-100

0.1-2.4 S a v i l l e 10 ) 1966

- - - -- - - -

* 73% of t o t a l po4 w a s o r g a n i c po 4

WATER QUALITY - A SYNTHESIS

I n order t o provide a comparative p i c t u r e o f t h e water q u a l i t y i n t h e two canal systems and t h e i r a d j o i n i n g bays t h e data f o r e i g h t hydrographic parameters are d isplayed i n polygraphs. As seen i n Figure 46 which i s a key t o t h e graphs t h a t f o l l ow , each o f t h e e i g h t parameters - d isso lved oxygen, d isso lved carbon d iox ide, pH, i no rgan ic (or tho) phosphate, organic phosphate, n i t r a t e - n i t r i t e , ch lo rophy l l g and p a r t i c u l a t e mat ter - i s p l o t t e d a long a rad ius . When the i n d i v i d - ual po in ts are connected t h e shape o f t h e polygon f o r a p a r t i c u l a r sampling s t a t i o n may be q u i c k l y compared w i t h those o f o t h e r sampling s ta t i ons .

F igure 47 shows t h a t on a f l o o d t i d e , August 24, 1972, t h e chemical c h a r a c t e r i s t i c s o f t h e sur face water i n the Gu l f o f Mexico 2 m i les west o f Midnight Pass d i f f e r e d from those i n L i t t l e Sarasota Bay, e s p e c i a l l y i n the segment o f t h e Bay n o r t h o f P o i n t Cr isp. The major d i f ferences a t t he four sampling s t a t i o n s were ch lo rophy l l %, n i t r a t e - n i tri t e and d isso lved organic phosphate.

F igure 48 i l l u s t r a t e s t h e v a r i a t i o n i n water q u a l i t y a t f o u r hydrographic s t a t i o n s i n t h e tteron Lagoon system a t dawn and dusk, Ju l y 3, 1972- compared t o t h e water qua1 i t y p i c t u r e s o f t h e G u l f o f Mexico and t h e In t racoas ta l blaterway i n L i t t l e Sarasota Bay (Fig. 47), these graphs emphasize the increase i n n i t r a t e - n i t r i t e and ch lo rophy l l % i n t h e Heron Lagoon system. They a l so show a sharp a t tenua t ion o f n i t r a t e and n i t r i t e on f l o o d t i d e a t dawn between Sta t ions 8 and 6 and Sta t ions 3 and 1.

The water q u a l i t y p i c t u r e f o r S t a t i o n 0, Roberts Bay, fo r June and J u l y and S ta t i on 1 , Grand Canal f o r June, J u l y and August shown i n F ig . 49 i l l u s t r a t e s t h e v a r i a t i o n i n water q u a l i t y on d i f f e r e n t dates even when t h e samples a re taken a t t h e same t ime o f day and a t s i m i l a r phases o f a t i d a l cyc le . The June and J u l y graphs show t h a t t h e water en te r ing the Bay from t h e Grand Canal d i f f e r s from the water o f Roberts Bay. An a d d i t i o n a l ebb t i d e graph f o r S t a t i o n 1, J u l y 9, i s shown i n Fig. 50. This f i g u r e a l s o shows the marked d i f f e rences i n the water

u a l i t y o f f o u r s t a t i o n s (1, 4, 14 and 15) i n the Grand Canal system a t lawn and dusk. Furthermore, the water q u a l i t y p i c t u r e of these four s ta t i ons d i f f e r s from the f o u r I{eron Lagoon s t a t i o n s i n F ig . 48 as w e l l as from the s t a t i o n i n Roberts Bay (Fig. 47) and s t a t i o n s i n L i t t l e Sarasota Bay (Figs. 47 & 48).

I n the course o f t h i s study 71 water samples were assayed f o r t e n chemical and hydrographic parameters. The water samples inc luded those

D.O. p p m

P a r t i c u l a t e

O R G A N I C PO, ~ ( g ~1.p

Figure - 46 Key and scales fo r polygonal graphs o f e i gh t hydrographic parameters measured i n surface water samples from the Gulf o f Mexico, L i t t l e Sarasota Bay, the Heron Lagoon Canal system, Roberts Bay and the Grand Canal system.

2 m i l e s West of M i d n i g h t P a s s

M i d n i g h t Pass

A u g u s t 24, 1 9 7 2

1 3 0 0 - - 1 4 0 0

F l o o d i n g T i d e

L i t t l e S a r a s o t a Bay L i t t l e S a r a s o t a B a y I .C.W. M a r k e r 4 9 I.C.W. M a r k e r 57 S o u t h of P o i n t C r i s p N o r t h of P o i n t Cr isp

Figure 47 Polygonal graphs of surface water a t four hydrographic stations. See Figure 46 for Key.

Figure 48 Polygonal graphs o f surface water a t four hydrographic stations i n the Heron Lagoon system July 3, 1972. Shaded polygons, dawn, f lood t i d e ; open polygons, dusk, f lood t i d e . See Figure 46 for key.

Figure 4 9 Comparison of water quality polygonal graphs of Roberts Bay and Grand Canal, Station 1 on ebb tides at dusk, June, July and August 1972.

Sta .0 . R.B. June

Gm C. Sta . I July 7/2 4 2 0 0 0

S t a . 1 4 S i e s t a I s l e s

Figure 50 Polygonal graphs of surface water a t f ou rTd rog raph i c s ta t ions i n the Grand Canal system, Ju l y 9, 1972. Shaded ~ o l ~ g o n s s f lood t ide , dawn; o en polygons, ebb t i de , dusk . See Figure & for Key.

from the Heron Lagoon and Grand Canal systems as well as South Coconut Bayou and a relat ively natural mangrove pond system south of the Grand Canal. Multivariate analyses of principal components were performed on raw and l o transformed data and mapped on two-dimensional plots (Foster, 1974 3 summarized i n F ig . 51. T h i s f igure shows tha t w i t h respect t o the water quality parameters measured, the waters of the Heron Lagoon sys tem are "rawther" d i s t inc t from those of the Grand Canal system. However, t o paraphrase Foster "we leave i t t o the in te r - ested t o explore the significance of the plots , the polygonal graphs and the raw data". Our knowledge of the dynamics of the bio-geochemi- cal processes, the biota of the past, present and future i n the canal systems and the adjoining bays is too fragmentary t o warrant drawing firm conclusions and developing predictions.

BENTHIC AND EPIBENTHIC ORGAN ISMS

The distribution of macroscopic invertebrates and marine plants in the two canal s stems was surveyed via qual i ta t ive f i e ld observations !. and semi-quanti ativesamplin of the canal bottoms a t different locations w i t h a 1/64 m2 plug sampler a Taylor and Salomon (1969) and a bucket dredge (Taylor, 1965)). We were part icular ly interested in what animals and plants, i f any, occurred in the seemingly so f t , organically rich bottom sediments i n the canal systems as compared t o bottoms of s imilar depths i n the adjoining bays. We also were interested i n epibenthic o r fouling organisms such as oysters, barnacles and tunicates tha t grow on sea wall s , f loa t s , pier pi1 ings and submerged branches of shore vegetation. These l a t t e r organisms are primarily f i l t e r feeders which feed on phytoplankton and other par t iculate matter. Thus they can when present play a significant role i n controlling phytoplankton blooms in canals and waterways. Finally, we studied the distribution of benthic algae and sea grasses i n the canals and waterways.

Semi-quantitative benthic Sam le s . In the Heron Lagoon system benthic pl uq sarn~les were taken a t e ia 4- t stat ions. Julv 20-21 . 1972. The locat- , - ions of the s tat ions are in Table 13. ~i each i t a t ion four plug samples were taken a t A , M.L.W. in ter t idal zone; 1, L.L.W. (Low low water); and C , in the Center 07 the Waterway (4-5 f t . ) . The samples were screened throTgh 1/16 inch mesh screening; the numbers of individuals of each species of invertebrate recorded; and dry weights of the sea grass (Cuban shoal weed), a1 qae and de t r i tus determined. These data a re sumrnari zed in Table 14. 1n eneral , the so f t bottom sediments in the L i t t l e Sarasota Bay (Station 8 3 as well as in the waterways consisted of worms, de t r i tu s , and f i l t e r feeding bivalve molluscs, and b r i t t l e s t a r s . The total number of species an3 individuals decreased between the Bay and the southern end of Heron Lagoon (Station 1 ) . Table 15 shows the presence of the 10 most common benthic macroinvertebrates a t the eight sampling s tat ions. We can- not conclude whether the differences i n number of species and individuals per u n i t area of bottom ref lec t sampling errors , adverse water qual i ty , amount of food, recrui tment of juveniles, or physical -chemical differences i n the bottom sediments.

The f i e ld data from th i s study were further analyzed by Foster (1974). Ile found t h a t the amount of de t r i tus i n the bottom sediments decreased with increasing water depths and distance from the vegetated shore. The greatest amount of de t r i tus was obtained in samples from the center of the-& waterways a t Stations 3, 4, 5, and 7 where the shores were heavily vegetated. Most of the de t r i tus i n these samples consisted of par t ia l ly decomposed leaves, twigs and f r u i t s of neighboring t rees . Of the 50 species of macroinvertebrates i n 21 samples, 13 occurred i n a t l e a s t four samples. Eight of these were polychaete worms and f ive bivalve molluscs. The 13 species formed four faunis t ic associations. The f i r s t consisted of a l l b u t one

Table - 13

l3ER"TIIIC SAMVLTNG STATIONS

HERON TJ4GOON WATERW4Y SYSTEM, JWIY 2 1 , 1972

Sta.tion No. - .--..----

I

2

3

4

5

6

7

S

Location -....-- ---

Foot bridge, south end I-Iero~ J,aqnon,

Heron Bay .

Ji~nc ti.on Wes I- Waterway and Mi.dtrat e rmy .

East Waterway, south of Sanderling Hoad.

North erd of Ea.s.t Vaterway.

North Watertray.

Boat; Sasrin, Y i i n s t a C 1 1 1 h .

T,itt le 3 a r a s r ) t a Ea-y, outside of entrance to 3 ie s t a C l i i E Boat; Basin.

Table - 14 1Iumber of ind iv idua l s / s p e c i e s of mac ro in t e rve r t eb ra t e s and amount of Cuhan shoal weed, a l g a e , and d e t r i t u s i n 12 plug samples (3/16m2) a t R benth ic sampling s t a t i o n s i n t h e t!eron Laaoon system and L i t t l e Saraso ta Ray, Ju l y 20-21 , 1972.

Sample S t a t i o n s

1 2 3 4 5 6 7 8

Anne1 i d s 613 4316 2412 65/13 615 5117 135116 136113

1 USCS Snai 1 s 0 0 0 0 0 41 1 0 211 Bivalves 611 1214 48/5 712 1513 4915 2716 5819

Echi noderrns 0 0 513 0 0 3/2 1 /1 511

Crustacea Amphipods 0 0 0 0 0 0 0 0 Decapods 0 0 0 0 0 0 0 0

Tota l No. 4 10 10 15 8 15 2 3 24 Spec.

Tota l No. Individ,. 12 5 5 7 7 7 2 2 1 107 163 201

Gm dry w t / 3/16 m2

Cuban Shoal 10.9 25.3 2.8 0 0 9.2 0 5.1 weed

A1 gae 0 0 0 0 0 0 1.9 0.3

De t r i t us 20.3 4.0 47.4 73.3 56.1 23.8 43.8 19.5

Table - l5 Presence o f the 10 most common species i n benthic samples from Heron Lagoon -Li ttl e Sarasota Bay, Ju ly 1972.

Benthic Sample Stat ions

Species 1 2 3 4 5 6 7 8 Remarks

Annel i d s

Brackioacyhis americana + + + + + + + + Cuban shoal weed

Cerratul us sp. - - - + - + + - C i r r i f o rm ia

f i l opod ia + + - + - + + + Sandy, strong cur ren t

D i opatra cuprea + + - t + + + + Sandy mud

Me1 i n n i a maculata - - - + , - - + + So f t bottom

. Onuphis emerita - + - - + + + + Cuban shoal weed

Spiochaetopterus - - + + - - + + So f t sandy mud

Anamal ocardia cunemus + + + - - + + + Sandy mud

Semele pro f icna - + + + + + + - Sandy, i n t e r t i d a l

Crustacea

Tubiculous amphipod - + - + - + +++ + Sand, b u t most abundant on Tubes sof t , ofganic mud

o f the polychaetes; t h e second, suspension feeding b i v a l v e mol luscs; t he t h i r d , deoosi t feeding b i v a l v e mol luscs; t h e fou r th , a s i n g l e species o f polychaete, ~ r a c h ~ i o s ~ h c b u s americana . The f i r s t and t h i r d assoc ia t ions showed a preference f o r t h e upper t i d a l zones a long t h e margins o f t h e waterways. The second and f o u r t h associat ions were located i n t h e s o f t e r sediments i n deeper water. Foster (1974) con- cludes t h a t i n s p i t e o f t h e r e l a t i v e l y "poor" faunal d i v e r s i t y i n t h e Heron Lagoon system, t h e d i v e r s i t y has reached a h igh l e v e l f o r t h i s p a r t i c u l a r environment because o f t h e degree o f i n t e r r e l a t e d organi - z a t i o n and maximal p a r t i t i o n i n g o f n iche space. I n an academic sense the i nve r teb ra te co rnun i t i es i n t h i s system a re probably s t a b l e under normal environmental cond i t ions b u t a re unable t o main ta in t h e i r form under environmental s t ress . However, these benth ic samples were taken one month a f t e r Hurr icane Agnes, The data and t h e i r m u l t i v a r i a t e anal - y s i s may r e f l e c t t h e af termath o f t h e environmental s t resses caused by the hurr icane as w e l l as seasonal aspects o f t h e several communities.

Benthic samples were c o l l e c t e d i n the Grand Canal system a t n ine of t he hydrographic s ta t i ons . A sing1 e dredge bucket sample was c o l l e c t e d a t each s t a t i o n . Table 16 shows t h a t t he maximum number o f species and i n d i v i d u a l s were found i n Roberts Bay (S ta t i on 0) i n a f i r m sandy-mud bottom. The number o f i n d i v i d u a l s and species decreased measurably i n the Grand Canal up t o S t a t i o n 15. Table 17 shows t h e presence of t h e fourteen most common macroinvertebrates i n t h e benth ic samples .

Although n o t present i n t h e dredge bucket samples, t h e so f t canal bottoms a re populated by dense beds o f a tub icu lous amphipod. From a rev iew o f t he l i t e r a t u r e i t appears l i t t l e i s known about the b io logy - ecology o f t h i s animal. Our observat ions i n d i c a t e i t i s most f requent and abundant i n soft , o r g a n i c a l l y r i c h types o f bottom sediments whether i n dead end canals o r t u r t l e grass f l a t s o r o the r s o f t bottoms i n t h e open bays. Since they form small " lea thery" tubes and feed on bac te r ia and protozoa on t h e surfaces o f f i n e d e t r i t a l p a r t i c l e s , these amphipods may p lay important r o l e s i n s t a b i 1 i z i n g t h e s u p e r f i c i a l bottom sediments and metabo l iz ing the organic mat ter and microorganisms a t t h e sediment water i n t e r f a c e . I n add i t ion , they may be an impor tant l i n k i n c e r t a i n marine f i s h food chains.

Another i n v e r t e b r a t e c h a r a c t e r i s t i c o f s o f t bottoms 1 s t h e t u b i c u l ous polychaete worm Spiochaetopterus. Tubes o f t h i s worm occurred i n samples from Sta t ions 0, 1 , 4, 10, 14 and 16. Tubes of t he tub icu lous worm, Onu h i s emeri ta occurred i n samples from Sta t ions 0, 1, 4, 10, 11 and 15. & O m s e tubes occurred a t S ta t i on 15 w h i l e on ly one t o a few occurred i n the o the r samples. F i n a l l y , tubes o f t h e tub icu lous worm, Yaldane s a r s i occurred i n samples from Sta t ions 0, 1, 4 and 9. -

Tab1 e 16 Number o f ind iv idua l species of macroinvertebrates and amount o f de t r i t us co l lec ted w i t h a bucket dredge a t 10 samplin 9 stat ions i n the Grand Canal and Roberts Bay, Auq. 9 and 8, 1972.

- Macroi nvertebra tes Sample Stations

Anne1 i d s

Moll uscs Snai 1 s Bivalves

Echi noderms

Crustacea Amphi pods Decapods

Tunicata - ascidians

S i puncul i d s

Coelenterates 0 8/ 1 0 0 0 0 0 0 0

Tota l No. Speci es 34 24 16 9 0 1 0 0 1

Tota l No. Ind iv id . 139 108 58 11 0 1 0 0 2

Det r i tus gm dry w t / 2.6 2.6 37.4 28.4 17.0 11.4 14.9 28.1 11.8

bucket

~ a b l e x Presence of the 14 most common species in benthic samples from Grand Canal -Roberts Bay, August 1972.

Benthic Sample Station Number Species Remarks

0 1 4 15 10 9 111 14 16 I -

Annel ids

bran chi?^ nigro- + + + macu a a

Cirratulus sp. + Clymenel l a torquata +

D i opa t r a cuprea + tiyps'l comus el egans + + Loimia medusa + + Onuphis eremita t + + + Pista palmata + + +

Spiochaetopterus sp. + + + Si puncul ids

Phascal osoma sp. + + + ' Molluscs

Anamal ocardi a cunermus

Tell ina versi cular t

PI uroplaca gigantea

Crustacea

Tubiculous amphipod +

We conclude from these few samples tha t the macrobenthic invertebrate communities of the Grand Canal system are composed primarily of so f t sediment tubiculous annelids and crustacea tha t feed on de t r i tus and fine part iculate matter. They help t o s t ab i l i ze physically the bottom sediments and are involved i n the biogeochemical processes a t the bottom sediment water interface.

As might be expected i n a sea walled canal system, the amount of de t r i tus was considerably greater than i n the unvegetated bay bottom (Table 16). The macrodetritus i n the canal samples consisted of grass clippings, pine needles, leaves of shrubs, seeds and twigs. Such mater- i a l supplements the rain of dead phytoplankton and adds t o the B.O.D. and C.O.D. of the sur f ic ia l bottom sediments in those regions of the canal system w i t h sluggish t ida l circulation.

E ifaunal or foulin ( i e r i l i n ) cornmunit or anisms. A variety % +e7iep+€=----- of inverte rates mav ive on t e sur ace o t e o tom as well as on the surfaces of submer&d pi1 ings, f loating docks, boat hul l s , branches of t rees and shrubs along the shore, ropes, and other submerged sol id sub- s t r a t a . These invertebrates are primarily de t r i tus feeders o r scavengers ( i .e., the k ing crown snail (Melon ena corona), blue crabs, green crabs, spider crabs (Libinea sp.) an r-- young stone crabs) or f i l t e r feeders ( i .e., sponges, oysters, mussels , barnacles , tunicates or sea squir ts and tubiculous feather duster or plume worms).

In the Heron Lagoon system there was a considerable variety of these organisms attached to sol i d substrata especially pi 1 ings , f loa ts and s u b - merged'branches:of shore plants a1 ong the waterways. From the Boat Basin through the waterways to the northern half of Heron Lagoon suitable sol id substrata were colonized by f i l t e r feeding sol i t a ry tunicates (Stvela a r t i t a and Mol ula manhattenesis) colonial tunicates (Botryll us schlosse

h l r u ula sp.), oysCers (Crossostracea vir inica a n T E E E i f rons) , barnacles I-&- lanus sp . ) , sponges (Hal i condri a sp . colonies - of tube worms (Sabella sp., Spirobis sp. ,) and mussels < ~ y t i l u s sp.) . These animals occurred between M.S.L. and one foot below M.L .W. wherever there were sui table sol id surfaces. Floating submerged branches i n the narrow waterways were frequently festooned w i t h growths of these gregarious animals. Collectively these animals serve as important biological f i l t e r s for both plankton and f ine de t r i tus i n the flowing water. Their combined ac t iv i t i e s reduce the amount of 1 iving and dead organic matter in the water. A t the same time, they contribute to the rain of dead organic matter t h a t s e t t l e s t o the waterway bottoms via faecal pel le ts and pseudofaecal pe l le t s which are eaten by various benthic worms, b r i t t l e s ta r f i sh and clams.

Interestingly, the most we1 1 developed comrnuni t i e s of foul ing organisms occurred where the t idal currents were relat ively strong and where sol i d

substrata were floating beneath the water surface. In other words, f l oating submerged surfaces several f e e t from the waterway shores, especially along the heavily vegetated East and North Waterway shores had the best developed fouling communities. Wi th respect t o water quality the presence of these organisms from the Boat Basin t o Heron Lagoon i s probably an important factor along with t ida l flushing in maintaining the water qua1 i t y in the waterways. In sections of the waterways and Heron Lagoon proper lacking suitable sol id submerged surfaces or where the t idal currents were "sluggish" these organisms were absent.

Certain of these f i l t e r feeders a l so occurred on the bottoms of the waterways. These included 2 species of sponges and the tunicate Stye1 a parti t a .

In Hero~l Lagoon sui table submerged sol id surfaces were less abundant than i n the waterways and the fouling community less well developed except where there were pil ings a t the southern end of Heron La oon. Here i n the vicini ty of the foot bridge (Hydrographic Station 17 an interesting in ter t ida l mussel (Conrad's f a l se mussel, Con e r i a leucophaeta) + occurred in larqe numbers. This mussel i s limited to brac i s water where the sal hity fluctuates . This i s the only area we have found t h i s animal t o date.

In contrast t o the well developed f i l t e r feeding fouling organism communities i n the Heron Lagoon system such communities were poorly developed in the Grand Canal system. Here only barnacles, oysters and mussels were found on sea walls above the Midnight Pass Road bridge. From t h i s bridge to the upper reaches of the canal system the re la t ive abundance of these animals decreased becoming minimal in the Palm Island area. We can only guess tha t the absence of some species and reduction in numbers of other species i s primarily due to the sluggish t ida l c i r - culation i n the upper reaches of t h i s canal system. Sluggish t idal flow will impair both f i l t e r feeding ac t iv i ty and recruitment of the planktonic larvae of the majority of species of the fouling community.

In conclusion the diversity and abundance of fouling organisms in the Heron Lagoon system as compared t o the Grand Canal system could be used as a simple biological indicator of the differences in overall water qua1 i t y i n these two canal systems. Of course, one can argue tha t concrete sea walls are not optimal substrata fo r larval forms of fouling organisms t o s e t t l e on. The potential for the development of f i l t e r feeding, fouling communities in the Grand Canal system could be tested experimentally by suspending submerged plates , rope and f loa ts i n different areas of the canal system. Such a study could be extremely important t o discussions on improving the water quality and water circulation i n the Grand Canal sys tem .

Marine grasses and macrobenthic algae. We observed no marine arasses alona the canal margins, the berms or slopinq bottoms of the zanals anywh;re in the ~ r a n a canal system even though there were sub- s t r a t e s and depths sui table for the growth of marine grasses. The absence of grasses i s probably due t o impaired recruitment from grass beds i n Roberts Bay. However, other factors may be involved.

, patches of the marine grass Cuban shoal weed ( ~ i p l a n - occurred i n the Heron Lagoon system along the eastern

Lagoon, i n the shallows of Heron Bay and along t h e berms of the West and Middle Waterways. The patches of Cuban shoal weed i n the waterways were probably derived from grass beds i n Heron Bay.

I t i s possible tha t marine grasses may be transplanted successfully on the berms and bottom slopes i n the Grand Canal system (see Fuss and Kelly, 1969; Kelly e t a l e , 1971 ) . However, the successful establishment of these grasses may occur only where the t idal currents f a l l within certain velocity ranges (Conover, 1967) .

The most common macro-algae i n the two canal systems were the red algae Gracilaria sp. and Acanthophora sp. which d r i f t into the canal systems from the bays along the bottom on flooding t ides . Once i n the canal systems they may continue to grow, provide she l te r fo r various animals and then die thereby contributing t o the food chains and accumu- la t ion of organic matter. A t h i r d green alga, Caulerpa mexicana, was common i n the waterways of the Heron Lagoon system b u t a m y absent i n the Grand Canal System. In the Heron Lagoon waterways and boat basin i t grew on the so f t sediments of the bottoms as well as on sol id submerged substrates. The rather pro l i f ic growths of th i s algae a t certain seasons (July - November) may ref lec t the presence of nitrogen enriched waters. We have observed large growths of th i s alga i n other parts of the Sarasota Bay system where nutrient enrichment occurs. Similarly, extensive growths of the macro red algae occur seasonally and locally in association with high levels of dissol ved nitrogen compounds ( i .e., Hagan, 1969). During September-November 1973 the numbers of these dr i f t ing algal plants i n the grass f l a t s of Roberts Bay appeared t o shade the sea grasses and cause the death of the i r leafy shoots. Similarly, under certain t idal and wind regimes these algae may be expected t o accumulate i n sections of both canal systems and contribute to the B.O.D., especially in the water near the canal bottoms.

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References

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Appendix A

METHODS

Currents Direction and ra te of flow of t idal currents were measured -;ing the d r i f t of one gallon p las t ic bot t les weighted t o f l o a t jus t below the water surface. To follow the water movement 4 f e e t below the surface a weighted one gallon bot t le was suspended by a string from a baTlaon floating on the surface. Current velolcities a t the culverts t n the Heron Lagoon system were measured w i t h General Oceanics d tg i ta l flowmeters Model 2030.

H d m ra h . Depth, temperature, dissolved oxygen, pH and conductivity & d d & e d w l t h a Hydrolab Surveyor (Hydrolab COW.). Sal i n i t y was a1 so measured w i t h standardized hydrometers. In the 1 aboratory the f i e ld pH measurements were repeated w i t h a Corning Model 12 Research pH meter. Inorganic phosphate, n i t r a t e , n i t r i t e , chlorophyll a and suspended part iculate matter were determined according t o the-methods of Strickland and Parsons (1968). Dissolved C was cal cut ated from a1 kal in1 t y according t o Strickland and Parsons 1968). Dissolved organic phosphate was determined by difference a f t e r a l l phosphates i n the millipore f i l t e red sample were transformed t o the inorganic form by oxidation w i t h pensulfate according t o the method of Menzel and Corwin (1965). All optical measurements were made on a Gllford 240 spectrophotometer w i t h 1 cm l i g h t path cuvettes. Degree of l i g h t pene- t ra t ion sf water was determined w i t h a standard 8 inch secchi d i sk .

References :

Strickland, J.D.H. and Parsons, T.R. 1968. A practical Handbook of sea -water Analysis. rfsh. Res. ~ m d c O t t a w a

Menzel , D. W . and Corwtn , N. 1965. The measurement of total phosphorus i n sea water based on the l iberation of organi- ca l ly bound fractions by persulfate oxidation. Limnol. Oceanogr. 10, 280-282.

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