wetland values and the importance of wetlands to man

Chapter 3

Wetland Values and the Importanceof Wetlands to Man

Contents

Page

Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Attitudes Toward Wetlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Intrinsic Values of Wetlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Wetlands as Natural Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Wetlands for Recreation and Education . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Other Intrinsic Values.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Ecological Services or Resource Values of Wetlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Floodpeak Reduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Shoreline Erosion Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46Ground Water Recharge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Water Quality Improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Fish and Wildlife Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Climatic and Atmospheric Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Chapter preferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

TABLES

Table No. Page

4. Summary of Input-Output Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515. Selected Commercial or Sport Fish and Shellfish Utilizing

Coastal Marshes as Nurseries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566. Endangered Wetland Species on the Federal

Endangered and Threatened Species List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577. Game and Fur Animals Identified by State Game Managers as Found in Wetlands . . 588. The 10 Most Recreationally Important Marine Fish in the United States

in 1979 Ranked by Number of Fish Landed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589. The 15 Most Important Fish and Shellfish Harvested by U.S. Fisheries in 1980 . . . . . 59

10. Wetland Plant Productivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

FIGURES

Figure No. Page

4. Relationship Between Wetland Processes and Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445. General Pattern of Duck Distribution in North America . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Chapter 3

Wetland Values and the Importanceof Wetlands to Man

CHAPTER SUMMARY

Some people value wetlands for their intrinsicqualities. They may wish to protect wetlands simplyout of a desire to preserve natural areas for futuregenerations or because they are often the last areasto be developed. Others value the varied and abun-dant flora and fauna that may be found in wetlands,and the opportunities for hunting, fishing, andboating and other recreational activities. Whilethese recreational benefits can be quantified to someextent, the other intrinsic values of wetlands are,for the most part, intangible. For this reason, thejustification for protecting wetlands has often fo-cused on the importance of the ecologicalservicesor resource values that wetlands provide, which aremore scientifically and economically demonstrablethan intrinsic qualities. These ecological servicesinclude floodpeak reduction, ground water re-charge, water quality improvement, food and hab-itat, food-chain support, and shoreline stabilization.

The intrinsic values and ecological services pro-vided by wetlands can vary significantly from one

wetland to another and from one region of the coun-try to another. Some wetlands provide benefits thatprimarily are local or regional in nature; other ben-efits may be national or even international in scope.Because of the wide variation among individualwetlands, the significance of their ecological serv-ices and intrinsic values must be determined on anindividual or regional basis.

The dollar value of the ecological services thatwetlands provide sometimes can be quantified. TheU.S. Army Corps of Engineers, for instance, esti-mated that the loss of the entire 8,422 acres of wet-lands within the Charles River Basin, Mass., wouldproduce average annual flood damage of over$17million. However, because the many intrinsic qual-ities of wetlands cannot be quantified, it is difficultto place generally accepted dollar values on wet-lands.

ATTITUDES TOWARD WETLANDS

The use of wetlands has become a public policyissue because of conflicts between those who wishto develop them and those who wish to preservethem. Developers, for instance, regard wetlands asprime locations for development because of theirtypical proximity to open water. Farmers drain orclear wetlands to plant crops in their rich organicsoil. While there also are private gains involved,the creation of new jobs or the production of foodthat results from the development of wetlands di-rectly benefits society.

On the other hand, undeveloped wetlands haveimportant intrinsic qualities that are estheticallypleasing and provide numerous ecological services,

such as flood control, that benefit society. The con-flict between developers and conservationists overwetlands often is viewed as an issue that ‘‘involvesquestions of public good as opposed to private gain’(21). However, the issue is not simply a matter ofpublic versus private interests but of conflictingpublic interests.

The values associated with wetlands were notalways widely recognized. For example, in the 19thcentury when a national priority was placed on set-tling the country, wetlands were considered a men-ace, the cause of malaria, and a hindrance to landdevelopment. Through the Swamp Land Acts of1849, 1850, and 1860, Congress granted to States

37

—

38 • Wetlands: Their Use and Regulation

all swamps and overflow lands for reclamation toreduce the destruction caused by flooding and elim-inate mosquito-breeding swamps. A total of 65 mil-lion acres of wetlands were granted to 15 States forreclamation (81).

With increasing concerns about preserving dif-ferent ecosystems, the public’s perception of andattitude toward wetlands has changed graduallyover the last half century. An inventory of wetlandsconducted by the U.S. Fish and Wildlife Service(FWS) in the mid-1950’s perhaps did the most tochange attitudes about wetlands over the past threedecades (81). The introduction to the inventorystated: “So long as this belief prevails (that wetlandsare wastelands), wetlands will continue to bedrained, filled, diked, impounded, or otherwisealtered, and thus will lose their identity as wetlandsand their value as wildlife habitat. The inventorycreated the lasting perception that wetlands rapid-ly were disappearing-a perception that galvanizedcertain groups to preserve wetlands.

Since the intrinsic values-recreation and a senseof the need to preserve the unique flora and faunaof scenic, natural areas—that motivated wetlandprotection at the outset were not appreciated uni-versally, proponents began to investigate more tan-gible, ecological services provided by wetlands. Ini-tially, these other services were suggested in theFWS wetland inventory report:

. . . the storage of ground water, the retention ofsurface water for farm uses, the stabilization of run-off, the reduction or prevention of erosion, the pro-duction of timber, the creation of firebreaks, theprovision of an outdoor laboratory for students andscientists, and the production of cash crops, suchas minnows (for bait), marsh hay, wild rice, black-berries, cranberries and peat moss (81).

In his 1977 environmental message, PresidentCarter conveyed an attitude about wetlands thatstood in sharp contrast to the attitude of the early1900’s:

The Nation’s coastal and inland wetlands are vi-tal natural resources of critical importance to thepeople of this country. Wetlands are areas of greatnatural productivity, hydrological utility, and en-vironmental diversity, providing natural flood con-trol, improved water quality, recharge of aquifers,flow stabilization of streams and rivers, and habitatfor fish and wildlife resources. Wetlands contributeto the production of agricultural products and tim-ber and provide recreational, scientific, and estheticresources of national interest.1

Knowledge of the importance of the ecologicalservices provided by wetlands has increased steadi-ly, especially over the past two decades. As wetlandsresearch continues, knowledge about the values ofindividual and different types of wetlands will, inall likelihood, improve. For example, some wetlandservices, such as ground water recharge, have beenfound to be less significant than once thought. Onthe other hand, the ecological services of inlandfreshwater wetlands with the exception of wildlifehabitat are not widely recognized by the generalpublic. It is quite possible that some wetlands mayprovide ecological services that are as yet unknownor poorly documented. In addition, the overall sig-nificance of continuing, incremental losses of wet-lands is well known only in a few cases. Waterfowlmanagers, for example, use the number of prairiepotholes in the Midwest to predict fall duck popula-tions; without these wetlands, North Americanduck populations would decrease by about half. Onthe other hand, the importance of wetland-deriveddetritus for estuarine fish and shellfish populationsrelative to other sources of food, such as algae anddetritus from upland areas, is not well known. Fu-ture research may resolve many of these uncertain-ties.

1Statement by the President accompanying Executive Order 11990;42 FR 26961 (1977).

Ch. 3—Wetland Values and the Importance of Wetlands to Man ● 3 9

INTRINSIC VALUES OF WETLANDS

In recent years, the case for preserving wetlandshas been based more and more on the ecologicalservices provided by wetlands2 and on the avail-ability of scientific evidence documenting these ser-vices. For example, in a recent paper, William Reil-ly stated:

Every bit of evidence that does exist suggests thatour interior wetlands are vital elements of nationalestate. But there are many challenging voices—questioning voices. These will become stronger infuture years. They will demand to be shown thescientific evidence behind wetland conservationdecisions (81).

This situation perhaps has obscured one funda-mental motivation of some for preserving wet-lands—the desire to preserve, intact and unspoiled,unique natural ecosystems. For many personal rea-sons, whether ethical, religious, esthetic, or recrea-tional in nature, people value wetlands for their in-trinsic qualities. Because these intrinsic values areintangible and thus difficult to express in quanti-tative and economic terms, they are often over-looked in a society where decisions are based onnumerical cost-benefit analyses. Although therehave been attempts to quantify these values, thisdiscussion simply identifies those characteristics ofwetlands that people value.

Wetlands as Natural AreasSome people are attracted to an environment that

essentially is untouched by man’s presence,3 whichis an attraction akin to the lure of wilderness. Onescientist, for instance, writes in the preface to a wet-land study:

The river swamps are, for many of us in theSoutheast, the last wilderness. True, they are nar-row, even the mighty Altamaha swamp scarcely ex-

‘Massachusetts, for instance, the first State to enact a wetland law,recognizes seven wetland values: flood control, prevention of pollu-tion, prevention of storm damage, protection of the public and privatedrinking water supply, protection of ground water supply, protectionof fisheries 1978-79; Act of Mar. 25, 1965; ch. 220, 1965;Massachusetts Acts 116; Act of May 22, 1963; ch. 426, 1963;Massachusetts Acts 240.

3In the following discussion, examples illustrating these character-istics of wetlands are presented. Unless otherwise noted, these exam-ples are taken from J, Perry and J. G. Perry, Guide to Natural Areasof the Eastern United Stares (New York: Random House Publishers).

ceeds 5 miles in width; yet in length they are largeindeed, often stretching more than half the lengthof the state. Narrow as they are, many provide atrue wilderness experience. Where else in thismechanized, modern world can we so quickly loseourselves in wildness without evidence of the mas-sive civilization that surrounds us? (97).

Part of the reason that marshes, swamps, bogs,and other wetlands are associated with natural, un-disturbed environments is that they are often thelast areas to be developed. The difficulty and ex-pense of draining wetlands for development haveencouraged people to develop other areas first.

Various studies have found that wetlands rankhigh in esthetic quality in comparison to other land-scape types (82). One particular value of wetlandsis the attraction of the land-water interface. Manypeople find the edge between land and sea, lake,or stream scenically appealing, and such areas ofteninclude wetlands as well as beaches and banks.Small wetlands are capable of being surveyed ina glance or traversed in a few minutes and offera contrast to the adjoining land or water. Seen froma passing car or hiking trail, wetland edges buffercommercially or agriculturally developed lands,providing scenic variety. Small wetlands also con-trast with other types of natural areas, such asupland forests or open water.

Large wetlands have a similar “variety” valuealong their edges but may have other esthetic at-tributes as well. Of all natural areas, the most mys-terious and haunting in appearance are the largecypress swamps draped with Spanish moss. Lessexotic are wooded swamps, which are full of dif-ferent shapes, textures, plants, and animals. Ac-cess and visibility are important factors; for exam-ple, pleasing wooded swamps should not be chokedwith underbrush that greatly impedes passage byfoot or canoe. A large, open, grassy marsh can pre-sent quite an esthetic contrast and a feeling of openspace.

In addition to the esthetic qualities of wetlandsthemselves, wetland flora and fauna lend a specialesthetic attraction to wetlands. Waterbirds are agood example: herons, egrets, storks, terns, peli-cans, and cranes all are found commonly or pri-

.


Photo credit: U.S. Fish and Wildlife Service, C. Kenneth Dodd, Jr,

Draped with Spanish moss, the haunting Santee-Cooper River Swamp in South Carolina providesan uncommon wilderness experience

marily in wetland habitats. Other species are moreunusual. Five genera of insectivorous plants canbe found in a North Carolina pocosin, includinground-leaved sundew, butterworts, Venus fly traps,bladderworts, and two species of pitcher plants. Inaddition, wetlands, particularly those whose originswere glacial, often provide habitat for ‘‘relict’plants and animals, that is, those that were once,but are no longer, endemic to an area. CranesvilleSwamp in West Virginia has a number of relict spe-cies, including Tamarack, Swainson’s, and hermitthrushes; Nashville and mourning warblers; andpurple finch, that typically are found much farthernorth.

Overall, wetlands are characterized by many dif-ferent kinds of flora and fauna relative to otherecosystems. For example, approximately 5,000 spe-

Ch. 3—Wetland Values and the Importance of Wetlands to Man • 41

cies of plants, 190 species of amphibians, and ap-proximately one-third of all bird species are thoughtto occur in wetlands across the United States (18,22,45). A single, freshwater tidal marsh may havefrom 20 to 50 plant species. Over 100 woody plantspecies may inhabit bottom lands. (19). This diver-sity of plant types creates, in turn, a diversity ofhabitats for animals. Living in the OkefenokeeSwamp in Georgia are over 200 species of birds,41 species of mammals, 54 species of amphibiansand reptiles, and all duck species found along theAtlantic flyway. In the Bombay Hook NationalWildlife Refuge in Delaware, an area of 12,000acres of brackish tidal marsh, over 300 bird specieshave been recorded. Tinicum Marsh, a nationalenvironmental education center outside of Phila-delphia, has more than 300 plant species and over250 bird species.

In addition to the many different kinds of floraand fauna, abundant populations of wildlife, espe-cially waterfowl and waterbirds, make wetlands

even more attractive as natural areas, The MerritIsland National Wildlife Refuge in Florida, an areawith over 34,000 acres of freshwater and saltwatermarshes and swamps, has a wintering waterfowlpopulation of nearly 70,000 ducks and 120,000coots. Hundreds of thousands of robins arrive atthe Okefenokee Swamp each year. Mass nestingsof wood storks—as many as 6,000 pairs—occur atthe Corkscrew Swamp Sanctuary in Florida.

Wetlands for Recreation andEducation

Wetlands provide direct enjoyment to inhabi-tants, visitors, and passers-by in many ways. Rec-reational activities in or around wetlands, includinghiking, boating, fishing, hunting, and the obser-vation of wildlife are pursued by millions of peo-ple and amount to billions of dollars in expendi-tures each year. For example, 19 of the 25 mostvisited National Wildlife Refuges (out of 309 refuge

Photo credit: U.S. Fish and Wildlife service, Lawrence S. Smith

A Youth Conservation Corps group is instructed in marsh ecology at a National Wildlife Refuge. Environmental educationis a major theme in many parks and public areas established around wetland areas

25-415 0 - 84 - 4

42 •Wetlands: Their Use and Regulation

units) have substantial wetland components (90).These 19 refuges represent approximately 50 per-cent of the total visitation to all U.S. NationalWildlife Refuge units. Several of these refuges arepredominantly wetland environments: J. N. DingDarling Refuge in Florida, considered one of thebest birdwatching sites in the United States, had671,000 visitors in 1981 (8th overall); LoxahatcheeRefuge in Florida had 333,329 visitors (19th); Oke-fenokee Refuge, one of the oldest, largest, and wild-est swamps in the United States, had 257,927 visit-ors (21st); the Great Swamp Refuge, more thanhalf of which is wilderness within the New YorkCity Metropolitan Area, had 250,756 visitors (23d).Recreational use of the Everglades National Parkin Florida averaged 675,000 from 1979 to 1981 (60).

Wetlands also may provide learning opportuni-ties for the general public or sites for educationaland scientific purposes. Research on such subjectsas botany, ornithology, and anthropology frequent-ly is carried out in wetland areas. Environmentaleducation is a major theme in many parks and pub-lic areas established around wetlands. For exam-ple, the environmental center at Tinicum Marshon the outskirts of Philadelphia coordinates numer-ous public education programs. In 1981 it had32,730 visitors (60).

From a purely scientific standpoint, the conceptof the ecosystem has played an important role inenvironmental research and in the formal teachingof ecology. Because of the importance of water tothe biosphere, most ecosystem study areas are se-lected to include water bodies such as streams,lakes, and wetlands. Wharton, (97) for instance,describes the scientific opportunities availablethrough the Alcovy River Swamp:

The Alcovy River is ideally suited for educationaluses: it is essentially unpolluted, it is located withineasy driving distance of a large metropolitan areabut is unaffected by it; and it contains a uniqueswamp ecosystem found nowhere else in the Geor-gia Piedmont.

The river swamp has a diversity of habitats anda corresponding diversity of plants and animals.It offers aquatic communities of all types of water,both flowing and still. The periodically high bio-mass of certain plant and animal groups offers anapproach to community ecology and productivity.

The drying up of bodies of water imitates both Pa-leozoic and monsoonal climatic effects on life andcan illustrate the evolutionary transition from waterto land. The swamp shows rapid changes in physio-chemical conditions.

The yearly import of decomposed mineral mat-ter can involve both geological and cultural (agri-cultural) concepts. The processes of photosynthesisand decomposition can be readily demonstrated.Both the aquatic and the terrestrial segments of thisecosystem are subject to an annual series of plantand animal communities (succession), rapidly en-forced by the regimen of the hydrocycle. Inverte-brates such as clams, snails, leeches, adult aquaticinsects, and larvae of aerial forms are extremelyabundant— some of the species are ‘‘indicators’of the degree of pollution present.

Much of the swamp fauna (invertebrates, fish,salamanders, mammals, birds) are present in mid-winter, when other habitats are barren, Many ofthe vertebrate groups are yearly renewable by in-undation (fish), are fossorial (salmanders), or areextremely plentiful (frogs). Thus, the animal com-munity is not easily damaged or overcollected.There are few subsurface runways to crush, ordelicate layers of litter and humus to compress, asin a terrestrial forest. Most of the mammals arerenewable by migration from the river corridor ifaccidentally killed; the tracks, droppings, or otherevidence of most are readily observable on the bareswamp floor (raccoon, otter, mink, wildcat, beaver,rodents, shrews). The ecosystem is adjusted to whatmight be called ‘‘annual catastrophism."Even theforest floor is changed and renewed to some extentannually.

Other Intrinsic Values

In addition to those values previously discussed,there may be other less obvious but just as impor-tant reasons for preserving natural areas, includingwetlands (28). Many plants and animals may havegreat potential resource value for food, chemicals,drugs, and so forth, but are as yet undiscoveredor undeveloped. Some scientists believe that allspecies are an integral part of the natural environ-ment and contribute in some, perhaps unknown,way to its natural order and stability. The conserv-ative belief is that excessive manmade impact onthis natural system could cause irreversible changesin the natural order of the environment that may


carry an unknown risk of serious damage to hu-mans and their civilization. Natural systems canprovide baseline conditions that help determine theextent to which the environment has been affectedby man’s activities and pollution. They may pro-vide models for restoring or replacing habitats thathave been significantly affected or even models oflong-term survival for redesigning greatly modified,man-dominated systems that typically have notworked reliably over long periods of time.

Many people believe that unaltered naturalareas, including wetlands, are valuable in and ofthemselves, regardless of any tangible benefits orecological services society may receive from them.The reassurance that wetlands and other types ofnatural areas exist for both present and future gen-erations can be a strong motivation to preservewetlands in an undisturbed state. The Nature Con-

servancy, an organization whose goal is ‘‘the pres-ervation of natural diversity by protecting landscontaining the best examples of all components ofthe natural world, has devoted 50 percent of itspast preservation efforts to the protection of wet-lands. In the future, it plans to expand this to ap-proximately 75 percent (53). Similarly, the NorthCarolina Natural Heritage Program gives top pri-ority to protection of Carolina bays (bog swamps),bottom land swamps, and peat bogs (80). Underthe South Carolina Heritage Trust Program, 60percent of the areas preserved are shallow impound-ments, marshes, flood plains, and wetland depres-sions (80). In the Wisconsin Scientific Areas Pro-gram, which inventories unique natural areas, ap-proximately 50 percent of all inventoried areas arewetlands (36).

ECOLOGICAL SERVICES OR RESOURCEVALUES OF WETLANDS

The interaction between the hydrologic regimeand the wetland topography, saturated soil, andemergent vegetation largely controls the generalcharacteristics and the significance of the processesthat occur in wetlands. The processes are in turnresponsible for the ecological services the wetlandmay perform (fig. 4).

Isolated wetlands may temporarily store runoff,and flood plain wetlands may provide additionalconveyance capacity for flood waters, thereby re-ducing floodpeaks in downstream areas. During pe-riods of inundation, water flows over and throughthe wetland, depositing nutrient-rich organic andinorganic material suspended in the water. Thissuspended material is “trapped” along with anytoxic materials that may be bound onto this sus-pended material. The nutrients and their substancesthus become involved in many complex biochemicalcycles within the wetland system. These nutrientshelp fuel the relatively high plant productivitycharacteristic of most wetlands during the growingseason. The leaves of plants provide food and hab-itat for many forms of wildlife and endangered spe-

cies during the growing season. At the end of thegrowing season, when the vegetation dies back,some of the leaf material remains in the wetlandto support future plant growth in the coming sea-son. Other leaf material is flushed into adjacentwater bodies where it provides a nutrient-richsource of food for many aquatic organisms in thefood chain. The plant roots anchor the wetland soilsand prevent their erosion in some flood plain andcoastal environments. The ecological services ofwetlands are described in more detail below.4

Floodpeak

The ability of wetlands

Reduction

to store and convey flood-water is primarily a function of their topography.Many isolated freshwater and river wetlands are

‘Recent reviews of the scientific literature have been completed by:1) P. R. Adamus and L. T. Stockwell, “A Method for Wetland Func-tional Assessment, U.S. Department of Transportation, FederalHighway Administration, Office of Research, Environmental Divi-sion, Washington, D. C., 1983, p. 176; and 2) J. H. Sather andR. P. Smith, ‘ ‘An Overview of Major Wetland Functions, ” U.S. Fishand Wildlife Service, Washington, D. C., 1983.

44 ● Wetlands: Their Use and Regulation

Figure 4.—Relationship Between Wetland Processes and Values

Periodic inundation Wetland processes Ecological services

SOURCE: Office of Technology Assessment.

topographic depressions that retain runoff flowinginto them, at least until they are full. Also, duringflooding, the river overflows its banks and spreadslaterally across the flood plain, increasing its cross-sectional area and conveyance capacity. By tem-porarily storing storm water and providing capacityto convey floodwaters, wetlands can reduce flood-peaks and the frequency of flooding in downstreamareas. Vegetation in flood plain wetlands furtherreduces the flow velocity of the river, thereby reduc-ing potential floodpeaks in downstream areas andriverbank erosion. If the soil in a wetland is un-saturated, the soil itself will provide some storagecapacity during periods of flooding. While the valueof some wetlands for flood storage and conveyanceis well known, analytical techniques for predicting

the magnitude of this service still are being devel-oped, The value of inland wetlands to reduce flood-ing in downstream areas generally depends on thearea of the wetland, its location downstream, themagnitude of flooding, and the degree of encroach-ment on the wetland (16,31 ,67,88).

Inflow-Outflow Measurements

Only two studies were found that actually deter-mined the storage capacity of a wetland during floodconditions. One study measured water levels of acypress-tupelo swamp adjacent to the Cache Riverin southern Illinois before and after flooding to cal-culate the amount of flood water storage. The 90-acre swamp, which is separated from the river by

Ch. 3—Wetland Values and the Importance of Wetlands to Man . 45

a natural levee, stored 80,131 cubic meters (m3)of water. If this amount of storage were extrapolatedto the entire area of swampland in the watershed,total wetland storage would equal 8.4 percent ofthe total flood runoff as measured at a downstreamgage (52).

Bernet found that flow was about 5,000 cubicfeet per second (ft3/s) into the Thief Run WildlifeManagement Area and the Agassiz National Wild-life Refuge, while outflow was approximately 1,400ft3/s. He calculated that the flood storage capacityand losses due to the other factors of these two wet-land areas reduced the floodpeak at Grand Forks,by about 0.5 foot and at Crookston by about 1.5feet (8).

Comparison of Floodpeaks From Wetlandand Nonwetland Watersheds

By studying floodpeaks in 15 watersheds, No-vitzki found that floodpeaks may be as much as 80percent lower in watersheds with large lake andwetland areas than in similar basins with little ornone. Watersheds with 40-percent lake and wetlandarea have floodpeaks only 20 percent as large asthose with little or no wetland area. While flood-peaks were found to be lower in watersheds witha large percentage of wetlands, total streamflow inthe spring was higher in basins with large lake andwetland areas (63).

Analysis of Flood Hydrographs

Flood hydrographs—graphs of the time distribu-tion of runoff from a drainage basin—of perchedpeat bogs and peatlands indicate that these wetlandstemporarily store and slowly release storm waters(5,9). Long-term hydrography from the PassaicRiver, N.J., and the Ipswich River, Mass., showedthat the wetlands adjacent to the rivers play an im-portant role in delaying runoff (31). Synthetic hy-drographs (not calculated on historical data) foreight wetland areas also showed reductions in peakflows (94).

Actual flood-storage capacity often will dependon environmental conditions prior to flooding oron the relationship of a particular wetland to theregional hydrology. For example, when evapo-transpiration rates are low and water is ponded inwetlands, runoff during periods of heavy precipita-

tion may be greater from wetlands than from up-land areas (because the soil is saturated and the sur-face storage capacity quickly is exceeded) (51 ,77,92). On the other hand, high rates of evapotran-spiration and low water tables favor storage of flood-waters. In some cases, wetlands provide no stor-age capacity for floodwaters. For example, a hy-drographic analysis of two Massachusetts swampsindicated that both wetlands contributed signifi-cantly to floodpeaks because of their rapid dischargeof ground water (64).

The Role of Vegetation in Flooding

There have been a few attempts to isolate the ef-fect of vegetation on flooding. The frictional dragon runoff flowing through wetland vegetation is rep-resented by a roughness coefficient called ‘‘Man-ning’s ‘n. ‘‘ The higher the value of “n,” thegreater the drag and the slower the flow velocityof floodwaters. Values of n’ vary widely and arehighly dependent on the type and amount of vege-tative cover. In general, the value of ‘n” for a riverwetlands in or adjacent to it can be approximatelytwice the value of channels without associated wet-lands (15).

Impact of Wetland Filling andDevelopment on Flooding

The Corps has used model-generated hydro-graphs to estimate the volume of storm water thatcould be stored in the basin wetlands of the CharlesRiver, Mass., and to determine the reduction instorage, assuming future encroachment (89). Fol-lowing a storm in 1955, approximately 50,000 acre-ft of storm water flushed past the Charles RiverVillage gaging station with a peak flow of 3,220ft3/s. This amount is equivalent to 5 inches of runofffrom the 184-square-mile drainage basin. On theadjacent Blackstone River, which has few, if any,wetlands, the storm discharge peaked at 16,900 ft3/sand the bulk of the storm water was discharged ina much shorter time period than on the Charles.Based on this analysis, it was predicted that a 40-percent reduction in wetland area along the riverwould result in a 2- to 4-foot increase in floodpeaksand would increase flood damages by at least $3million annually.

Hydrographs of the Neponset River Basin,Mass., were used to determine the impact of en-

46 Ž Wetlands: Their Use and Regulation

croaching on the basin’s flood plains and wetlands(l). The study predicted that the basinwide floodlevel for the 100-year flood would increase 0.5 feetif 10 percent of the flood plain/wetland storagecapacity were lost, and 3 feet if 50 percent of theflood plain/wetland storage capacity were lost. Fill-ing a wetland will reduce its storage capacity; if thefill material rises above the level of the flood plain,flood conveyance value also may be reduced.

The effects of drainage on floodflows are slightlymore complicated. One point of view is that drain-age increases floodpeaks by synchronizing andspeeding the runoff of water and by eliminating thepotential storage of runoff in wetlands. A contrast-ing viewpoint is that drainage channels may reducefloodpeaks by draining away heavy rains that other-wise would have left the soil saturated through thewinter, reducing the storage available during criticalspring rain and snowmelt. Research to date has notyet resolved this controversy.5

Shoreline Erosion Control

Shoreline erosion is a natural process caused byriver currents during flooding, tidal currents in thecoastal areas, and wind-generated waves along theshores of large lakes, broad estuaries, and ocean-facing barrier islands. Boat wakes also can causeconsiderable shoreline damage.

Four characteristics of vegetated wetlands areresponsible for reducing erosion: 1) the low-gradientshore that absorbs and dissipates wave energy (70);2) the dampening and absorption of wave energyby the plants themselves (44,95); 3) the root struc-ture and peat development in wetlands that bindand stabilize the shore (71, 76); and 4) the deposi-tion of suspended sediment that is encouraged bydense growth of wetland plants. s

5See the following references for reviews of information pertainingto the impacts of wetlands draining on flooding: 1) L. J. Brunn,J. L. Richardson, J. W. Enz, and J. K. Larsen, “Streamflow Changesin the Southern Red River Valley of North Dakota, North DakotaFarm Research Bimonthly Bulletin, vol. 38, No. 5, 1981, pp. 11-14;2) John M. Malcolm, “The Relationship of Wetland Drainage toFlooding and Water Quality Problems and Its Impact on the J. ClarkSalyer National Wildlife Refuge, ” FWS, Upham, N. Dak., 1979; and3)J. E. Miller and D. L. Frink, “Changes in Flood Response of theRed River of the North Basin, North Dakota-Minnesota, ” U.S. Geo-logical Survey, C)pen File Report 82-774, 1982.

bRecent reviews of the scientific literature have been completed byP. R. Adamus and L. T. Stockwell, “A Method for Wetland Func-

Vegetated freshwater or saltwater wetlands lo-cated adjacent to open but usually sheltered bodiesof water significantly reduce shoreline erosioncaused by large waves generated by occasionalstorms and boat traffic.7 Wetlands adjacent to riversalso may reduce riverbank erosion from strong cur-rents during major flooding. Although it general-ly is agreed that wetland vegetation does not nat-urally establish itself in high-energy environmentswhere the potential for erosion is greatest, wetlandplants, once established, do help to control erosion,stabilize the soil, encourage deposition of sediments,and dampen wave energy. Isolated wetlands notassociated with larger bodies of water will not havesignificant value for erosion control.

Potential Economic Importance

Shoreline erosion is a major problem in manycoastal areas. In Virginia, for instance, it has beenestimated that 1,476 hectares of tidal shorelineeroded away between 1850 and 1950. This amountrepresents approximately 20 percent of the 5 millionmetric tons of silt and clay that wash into Virginia’sestuaries annually (39). The impacts of shorelineerosion include: loss of public and private proper-ty and the subsequent loss of taxable income forlocalities, filling of navigable waters with erodedsediment, increased turbidity of waters, siltationof fish and wildlife habitat, and loss of recreationallyvaluable sand beaches. Millions of dollars are spenteach year to reduce shoreline erosion and main-tain the navigability of channels.

Ability of Wetlands to Control Shoreline Erosion

Wetlands not only resist erosion themselves, butalso protect the more easily eroded upland areasshoreward of the wetland. Three studies have com-

tional Assessment, ’ U.S. Department of Transportation, FederalHighway Administration, OffIce of Research, Environmental Divi-sion, Washington, D. C., 1983, p. 176.

‘Most of the existing literature on this f“unction has been reviewedin the following: 1) H. H. Allen, “Role of Wetland Plants in ErosionControl of Riparian Shorelines, ” Wetlands Functions and Values:The State of Our Understanding, P. E. Greeson, J. R. Clark, andJ. E. Clark (eds. ) (Minneapolis, Minn.: American Water ResourcesAssociation, 1979), pp. 403-414; 2) Carter, et al. (15); 3) R. G. Dean,‘‘Effects of Vegetation on Shoreline Erosional Processes, WedandFunctions and Values: The State of Our Understanding, P. E.Greeson, J. R. Clark, and J. E. Clark (eds. ) (Minneapolis, Minn.:American Water Resources Association, 1979), pp. 415-426; and 4)Institute for Water Resources (88).


pared the rate of erosion of uplands buffered bywetlands to that of unbuffered uplands.

In a study of two similar sites on the Hacken-sack River in New Jersey, the marsh vegetation atone site was cut; at the other site, the marsh wasleft in its natural condition (26). Both sites weresubjected to waves generated by heavy boat traf-fic. While the uncut site exhibited only a negligi-ble retreat of the bank over the year of monitor-ing, the bank at the second site retreated nearly 2meters, with most of the change occurring imme-diately after the marsh was cut.

In a second study, the rate of erosion of uplandareas at three sites on the Chesapeake Bay over a20-year period was measured with aerial photo-graphs. Wetlands eroded as fast as adjacent up-lands; however, erosion of uplands buffered by thewetlands was negligible (70).

In a third study the retreat/advance of the shore-lines of an artificially planted marsh (Juncus roe-merianus, Phragmites australis, Typha latifolia,and Spartina alterniflora) and of an adjacent un-planted area were measured over a period of 8 years(7). Initial erosion of the planted area was followedby a period when the shoreline actively expandedbefore it appeared to reach equilibrium. In general,the volume of sediment eroded from the unplantedshore averaged 2.3 m3 per lineal meter-year (m3/lineal m-yr. ), nearly four times the average rateobserved in the planted marsh. In addition, the un-planted shore retreated at a rate that was more thantwice that observed for the marsh-fringed shore,

Limitations of Wetlands to Control Erosion

Natural wetlands are typically found in low-en-ergy environments, sheltered from extensive waveaction (4, 17). Artificial wetlands, however, often areconstructed in higher wave-energy environmentswhere natural wetlands would not typically occur.Young rooted plants are used rather than allow-ing the shoreline to seed itself naturally. In addi-tion, with many artificial plantings, a ‘‘toe’ or lowridge is constructed below the marsh to contain themarsh soil and to reduce the impact of incomingwaves until the plants are established firmly. Mostof the literature citing the erosion-control functionsof wetlands is based on observations of marshes spe-cifically planted to control erosion. For example,

in a 1981 survey of 86 marshes planted to controlshoreline erosion in 12 coastal States, 33 plantingswere found successful, 25 were partially successful,and 28 failed (43). Even planted marshes, however,were more frequently successful under less severewave environments.

Ground Water Recharge

Ground water recharge is the ability of a wetlandto supplement ground water through infiltration/percolation of surface water to the saturated zone(88). Some wetlands that are connected hydrolog-ically to a ground water system do recharge groundwater supplies and assume an important local orregional role in maintaining ground water levels.However, owing to the low permeability of organicsoils or the relatively impermeable layers of claytypically found in wetlands, adjacent upland areasoften have a greater potential to recharge groundwater ( 16). In addition, wetlands may often serveas discharge rather than recharge areas. 8

Ground water recharge can occur in isolated(basin) wetlands, such as cypress swamps, prairiepotholes, Midwestern and Northeastern glaciatedwetlands, and flood plain wetlands. CedarburgBog, adjacent to Milwaukee, Wis., is an exampleof a high-value recharge area (58). Much of theprecipitation falling on this basin percolates down-ward through the soil and enters openings in a dolo-mite aquifer. Since the bog occupies the basin ofa former postglacial lake on a high point in the sur-rounding topography, the water percolates radial-ly away from the bog, influencing ground watersupply over an area of 165 mi2.

While some wetlands may recharge groundwater, their recharge value relative to upland areasmay be low. In three watersheds in Minnesota, forinstance, the greatest amount of ground water re-charge was found to occur on upland sands, andthe least in wetland peats (93). In addition, thequantity of water recharged may vary widely. Forexample, in one wetland studied only 39 gallonsper day (gal/d), or 0.05 percent of the annual waterbudget, infiltrated the wetland (12). On the otherhand, the average yearly natural recharge calcu-lated for Lawrence Swamp in Massachusetts was

‘Adamus and Stockwell, op. cit.

48 . Wetlands: Their Use and Regulation

8 million gal/d (assuming 44 inches of precipita-tion/yr) (56).

The quality of the ground water resource alsodetermines the value of a particular recharge area.While Lawrence Swamp recharges large quantitiesof water to the shallow aquifer directly underneathit, this aquifer has a high content of fine sands, iron,and manganese and cannot be used as a water sup-ply (56). -

Water Quality Improvement

By temporarily retaining pollutants, such as sus-pended material, excess nutrients, toxic chemicals,and disease-causing micro-organisms, it is generallybelieved that wetlands improve, to varying degrees,the quality of the water* that flows over andthrough them. Dissolved nutrients (i. e., nitrogenand phosphorous) may be taken up directly byplants during the growing season and by chemicalabsorption and precipitation at the wetland soil sur-face. Organic and inorganic suspended materialalso tends to settle out and is trapped in the wetland.Some pollutants associated with this trapped ma-terial may be converted by biochemical processesto less harmful forms; some may remain buried.Others may be taken up by the plants growing inthe wetland and either recycled or transported fromit.

The accumulation of toxic chemicals, such asheavy metals and petroleum and chlorinated hydro-carbons by wetlands may be only temporary (fromdays to years). On the other hand, some toxicchemicals have accumulated in many wetlands overa much longer time. With some toxic chemicals,like degradable pesticides, the fact that thesepollutants are secured in the wetland long enoughto degrade is important. Other toxics either remainburied or are taken up by the wetland plants.

While wetlands may, under natural circum-stances, retain nutrients on a net annual basis, thevalue of a particular wetland for water quality im-provement depends on the effect of the nutrientstorage on an adjacent or connected body of water.However, even if a wetland does not retain large

amounts of nutrients on a net annual basis, it mayinfluence the timing of nutrient inputs into adja-cent waters. By retaining nutrients during the grow-ing season, for instance, and exporting them afterthe growing season, wetlands may have a positiveinfluence on water quality. Freshwater wetlandshave been used successfully for secondary treatmentof sewage effluents.

Trapping Suspended Sediment

Excessively high levels of suspended material inthe water column can be detrimental. By increas-ing turbidity, suspended sediment can interfere withfishing, swimming, and the esthetic appeal of water.Reduction in light penetration due to increased tur-bidity can kill aquatic plants, and settling of thesuspended sediment can smother bottom-dwellinginvertebrates and impair fish spawning. If sus-pended sediment has a high organic content, thedissolved oxygen level in the water column may de-crease to levels that may adversely affect many or-ganisms.

One of the major water quality functions of wet-lands is the removal of suspended sediment. By re-ducing wave energy and the velocity of water flow-ing through the wetland, wetland plants encouragethe deposition of suspended sediment. In fact, sedi-mentation rates are related directly to the densityof marsh vegetation (7). Measurements of sedimentaccretion, most of which are for marine or estuarineenvironments, range from 0.04 centimeters (cm)to 1,100 cm/yr.9

The ability of vegetated wetlands to trap sus-pended sediment more effectively than similar un-vegetated areas was shown clearly in an 8-yearstudy on Currituck Sound in North Carolina. Dur-ing the first 5 years, planted marsh lost an averageof 1.4 m3/linear m of beach/yr, while an adjacentunplanted area lost 3.3 m3/yr. Between 1978 and1979 the planted areas, however, captured an av-erage of 1.5 m3 of sediment/yr; the unplanted arealost an additional 1.3 m3. From 1979 to 1980, theplanted area gained 0.6 m3 and the unplanted arealost 0.4 m3. During the last year of the study, theplanted area appeared relatively stable, while theunplanted area lost 1.0 m3 (7).

*The term “water quality” is defined here as the chemical, physical,and biological condition of the water itself and not more broadly asthe condition of the wetland and its associated habitat. 9Adamus and Stockwell, op. cit.


As the elevation of wetlands increases, accretionof sediment will slow. In one study, for instance,a Spartina marsh near the mean high-water levelannually accreted from 2.0 to 4.25 millimeters(mm) of sediment. An area of colonizing Spartinaat a lower elevation, however, accreted sedimentat the rate of 9.5 to 37.0 mm/yr (10). Marshes tendto trap sediment as long as they are inundated bysediment-laden waters.

Suspended organic and nonorganic material hasa strong tendency to adsorb other pollutants, in-cluding nutrients, pathogens, and toxics, such asheavy metals and chlorinated and petroleum hydro-carbons, that then are deposited with the sedimentin wetlands (10). The ability of wetlands to ‘‘trap’suspended material greatly influences the fate ofpollutants associated with the suspended materialand the potential ability of a particular wetland toimprove water quality.

Removing Toxic Substances

Heavy metals, chlorinated and petroleum hydro-carbons, radionuclides, and other potentially harm-ful toxic substances may persist for many years.Because they tend to adsorb onto suspended ma-terial, toxics can be trapped in wetlands, either tem-porarily or permanently. At the sediment surface,these metals remain immobilized. Once buried andexposed to the anaerobic conditions that typicallyprevail in sediment, metals again can become mo-bile; however, they will be trapped within the sedi-ment by the oxygenated zone at the sediment sur-face (54,55). Heavy-metal-removal efficiencies ofwetlands vary from 20 to 100 percent, dependingon the metals involved and the physical and bio-logical variations that exist in wetland habitats (85).

For compounds such as heptachlor, lindane, orenderin, which degrade readily in soils, the trap-ping of the sediment results in a very efficient andpermanent process for removing these contami-nants from the water. (Natural or manmade altera-tions of the wetland caused by lowering the watertable, dredging, and the like, however, could mo-bilize large quantities of toxic materials. ) However,in general, it is not known yet to what extent wet-lands processes are capable of removing toxic ma-terials over the long term.

Some toxics may be taken up from the sedimentby wetland plants and transferred through the foodchain to higher trophic levels when the plant ma-terial is consumed, either directly by herbivores oras detritus. Food chain transfer will depend on thetoxic chemical and its form as well as the charac-teristics of the plant species and the chemical’s loca-tion in the plant. For example, food chain transferis known to occur with some metals, such as mer-cury or cadmium, but may not occur with others,such as lead. Synthetic materials, including chlor-inated hydrocarbons, are taken up by wetlandplants, but food chain effects are not known. Thereprobably is some selectivity of uptake of toxics byparticular wetland plant species, but the availabledata are insufficient to indicate any universaltrends. In summary, though wetlands may removetoxics from water, it is possible that such removalof heavy metals eventually may lead to contamina-tion of higher trophic levels by passage up the foodchain (42).

Influencing Nitrogen and Phosphorus

Nitrogen and phosphorus are two nutrients thatare necessary for the growth of algae. In excess,however, they can cause “blooms” of algal growththat can impart an unpleasant taste to drinkingwater and can interfere with recreational uses ofwater. In addition, the decomposition of algae canreduce levels of dissolved oxygen in the water col-umn to levels that may be harmful to other orga-nisms that need oxygen for survival.

Nutrients are retained in wetland by similarmechanisms as other pollutants (85). Both nitrogenand phosphorus readily adsorb to sediment andthereby tend to become trapped in the anaerobicsediment of wetlands. As with other toxics, how-ever, nutrients are not necessarily permanentlytrapped; they may, for instance, be rapidly assim-ilated by rooted wetland plants. In fact, the bulkof the nitrogen and phosphorus for plant growthapparently comes from the sediment. At the endof the growing season, much of the assimilated nu-trients may be leached from the plants. Boyd, forinstance found that about 50 percent of the phos-phorus in dead cattail tissue was leached over a


20-day period. * Another fraction of the nutrientsin the plant is exported from the wetland as detritus;this fraction is probably highly variable, dependinglargely on the hydrology of the wetland. The deadplant tissue remaining in the wetland is rapidly col-onized by bacteria and the byproducts of the de-composition process, including inorganic nutrients,are released into the water column. Nitrogen storedin the plant, for example, is converted by these de-composes to ammonia. Plant material remainingin the wetland is eventually reincorporated into thesediment. It has been hypothesized that a signifi-cant amount of the nitrogen and phosphorus avail-able from the sediment for plant uptake is recycledfrom the plant growth of the previous year (42).

Water Quality Considerations

Aggregate Effect. —Present understanding of theprocesses described above is not sophisticatedenough to predict their aggregate effect on waterquality. Nitrogen fixation, for instance, the oppositeprocess of denitrification (atmospheric nitrogen isfixed by certain bacteria and algae), can contributesignificant amounts of nitrogen to the wetland ni-trogen budget and therefore cancel the effects ofdenitrification, Some wetland studies havemeasured the quantity of all pollutants entering thewetland from all sources—ground water, surfacewater, precipitation, and so forth-and the amountleaving the wetland. The aggregate effect of allwetland processes on water quality is reflected bythe difference between the amount of pollutantentering and leaving the wetland. In this manner,it can be determined whether wetlands act as a sinkor a source of pollutants.

Thirty-nine input-output studies, focusing for themost part on nitrogen and phosphorus, were re-viewed. These studies were screened carefully tomeet a number of stringent criteria. First, since thebehavior of the wetland varies greatly during dif-

● The fate of nitrogen is more complicated than that of other pol-lutants thus far discussed. Nitrogen occurs in several forms in naturalwater: nitrite, nitrate ammonia, and organic nitrogen (proteins andother large molecules). In addition, the air contains over 78 percentnitrogen gas, which is exchanged continuously through the surfacewaters. Relatively large populations of micro-organisms in wetlands,under the right circumstances, can convert nitrogen from one formto another. Thus, nitrogen can be removed ultimately from water bymicrobial conversion to gas through the process of denitrification, orconversely, fixed from the atmosphere and converted to inorganic ni-trogen.

ferent seasons, only those studies sampling month-ly for at least a year were selected. Second, all chem-ical forms of nitrogen and phosphorus had to bemeasured: measurement of both organic and in-organic forms is necessary since the various formsare interconvertible. For nitrogen, total nitrogen(Kjeldahl) must have been measured in unfilteredsamples and in nitrate and nitrite. For phosphorus,measurement of total phosphorus from unfilteredsamples was required. Third, for studies of undis-turbed wetlands, all reasonable input and outputsources had to be measured, including intermittentor temporary sources of surface runoff, groundwater, and precipitation. In the case of an artificialpollution source, such as a sewage outfall, thefailure to measure natural sources of nutrients wasoverlooked on the assumption that such sourceswere comparatively trivial. Measurement of all sig-nificant sources and sinks of water, however, wasrequired, even if the quantity of naturally occur-ring nutrients was overlooked.

Freshwater Systems. —Of 30 freshwater input-output studies reviewed, only seven (12,23,27,52,62,98,99), met all the criteria listed above. A ma-jor drawback of these studies is that large quan-tities of pollutants doubtlessly flow into and out ofwetlands during storms or floods. The chance ofgetting a good sample of nutrients flowing into awetland during a major flood is small if outflow issampled only monthly. One study (52), for in-stance, found that 99 percent of the nutrient flowinto a flood plain swamp occurred during a singleflood. The swamp floods approximately once every1.13 years.

Although Crisp (23) found a net export of nitro-gen and phosphorus in an eroding British peatland,all other authors found net reductions of nutrientsin freshwater wetlands. Large percentage reduc-tions generally were observed where sewage wasapplied (12,27,98) and small percentage reductionswere observed where nutrient sources were natural(52,62). One study (99) was unusual in that sewageand natural water were applied to artificially enclos-ed marsh plants so that surface outflow was pre-vented. Water that had filtered through the marshsediments was sampled in outside wells. Since thenatural hydrology of the marshes had been altered,the large percentage reductions in both the naturaland sewage-treated marshes may not be represent-ative of activity of natural marshes.


Estuarine Systems. —Input-output studies aremore difficult to conduct in estuarine or marine en-vironments owing to tidal fluctuations. Nine estua-rine studies were screened using the same criteriaused for the freshwater studies. Findings from asingle acceptable study (91) are reported in table4. These results suggest that nitrogen was exportedfrom a Massachusetts salt marsh.

Evaluating Wetlands for Water Quality.—To evaluate the value of a wetland for improvingwater quality, a number of factors must be con-sidered. First is the condition of water in the waterbody adjacent to the wetlands. In many lakes,estuaries, and rivers, excessive nutrient concentra-tions cause undesirable algal blooms. In otherbodies of water, however, desirable levels ofprimary productivity may be limited by a lack ofthese nutrients. If these waters have phytoplankton-based food chains, low nutrient concentrations canresult in low productivity at all levels of the foodchain. In this case, nutrients would be consideredbeneficial and not pollutants.

The reduction of excess nutrients necessary tobring about an improvement in water quality isanother consideration. For instance, an evaluationof a proposal to reconstruct wetlands along the Kis-simmee River in Florida and thereby reduce nutri-

ent loadings to Lake Okeechobee, concluded thata 50-percent reduction in phosphorous loadingswould improve water quality, but a 10-percent re-duction would have little effect (41). In anotherstudy, lake-edge wetlands in Wisconsin did retainnitrogen and phosphorus; however, the levels of nu-trients flowing out of the wetland still were highenough to cause excessive algal growth (47).

The timing of nutrient inputs and outputs alsois important. A study of phosphorus inputs and out-puts from a forested riverine wetland in Illinoisfound that while the swamp took in 11 times morephosphorus than was discharged, nearly all of it wasretained during flood periods (52).

Disease-Causing Micro-Organisms

Viruses and bacteria from sewage effluent or run-off from pastureland may contaminate drinking wa-ter, recreational water, and commercial fisheries.Because these micro-organisms are adsorbed ontoparticles suspended in the water column, they maybe trapped along with the suspended material bywetlands. Pathogens can remain for many monthsin the soil matrix where they may be exposed toultraviolet radiation or attacked by chemicals andother organisms, or they may naturally die off.

Table 4.—Summary of Input-Output Studies

Artificial/ Input output PercentReference Wetland type Location natural Sampling frequency/duration Pollutant (kg/ha/yr) changeCrisp (1966) . . . . . . . . . . . . . . . . Peat bog Britain N Weekly/l year N 745 4,864 + 552

P 38-57 71 + 25 - -87Mitsch, et al. (1977) . . . . . . . . . . Flood plain Illinois N Monthly and bimonthly P 8,127 7,694 - 5

swam D

Boyt, et al. (1977) . . . . . . . . . . . . Riverine Florida A Monthly/l year P 90.0 11.5 -87swamp

Dierberg and Brezonik (1978) . . Cypress Florida A Monthly/2 years N 144 12 -91swamp P 113 4 -96

Novitzki (1978). . . . . . . . . . . . . . . Fresh marsh Wisconsin N Monthly (stream, wells); N 233 183 -21periodically (runoff)/3 years P 5.0 4.6 -8

Sediment 3,909 735 -81Yonika and Lowry (1979) . . . . . . Fresh marsh Massa- A Monthly and bimonthly/ N 4,782 1,817 - 6 2

shrub swamp chusetts 1 year P 859 205 - 7 6

Zoltek and Bayley (1979) . . . . . . Fresh marsh Florida A/N Monthly/2 years N 3,565 2 , 2 8 4a - 3 6

P(art.) 4,575 343a -93N(art.) 645 315a -51P(nat.) 46 16a -65

Valiela, et al. (1975) ., . . . . . . . . Salt marsh Massa- N Monthly/l year N(nat.) 26,252 31,604 + 20chusetts

alncluding ground water dilution calculated W chloride budget.

SOURCE: References cited in column 1.


There is little published information on the fate ofpathogens in wetland systems (3).

Fish and Wildlife Values

Wetlands are important to many species of fishand wildlife for food, habitat, and support of thefood chain. The importance of plant productivityis reflected in the relatively high carrying capacityof wetlands for certain species. Bottom land hard-wood forests, for instance, have been found to sup-port nearly twice as many whitetail deer per unitarea as do upland forests, owing, it is thought, tothe abundance of food. Wetland vegetation alsoprovides nesting material and sites for numerousbirds and mammals; some freshwater fish rely onclumps of vegetation for depositing their eggs.Finally, emergent wetland plants provide the covernecessary for protection from predators or for stalk-ing prey for species of birds as well as fish andshellfish. Some species spend their entire life withina particular wetland; others are residents only dur-ing a particular lifecycle or time of year.

Because of their value for food and habitat, wet-lands often become a focal point for varied wildlifepopulations within a particular region. The impor-tance of wetlands is reflected by the relatively largeproportion of wetland in the National Wildlife Re-fuge System. While only 5 percent of the Nation’sarea (excluding Alaska) is wetland, nearly 40 per-cent of the area protected under the refuge systemis wetland. In turn, these areas attract hunters,birdwatchers, and many other wildlife enthusiasts.Of the top 25 wildlife refuges most visited, 19 havea significant wetland component. Refuges contain-ing wetlands attracted nearly 14 million visitors in1981, approximately 50 percent of the number visit-ing all of the national wildlife refuges (90).

Because of their numbers, it is impossible to de-scribe adequately all the different species that usewetlands. This section focuses on recreational andcommercial species of prime importance to man andon endangered species that depend to varying de-grees on the food and habitat found uniquely inwetlands. Some species, termed ‘‘wetland special-ists, are heavily dependent on wetlands. They in-clude migratory waterfowl, mammals, the alligator,freshwater game fish, crayfish, and 35 endangered

species. Because of the direct link between wetlandsand these species, wetland losses will cause signifi-cant and adverse impacts on these indigenous pop-ulations.

This section also identifies other wildlife thatheavily use wetlands as well as other nonwetlandareas. Deer, for instance, browse in bottom landhardwoods, but they are not limited to these areas.Wetland resources may, however, be a critical orlimiting factor in their survival. Because theseanimals are not linked as strongly to wetlands asare wetland specialists, wetland losses would ad-versely affect populations of nonspecialists to a lesserextent.

Finally, this section discusses the food chain val-ues of wetlands. Many commercially and recrea-tionally important species that do not directly usewetlands for feeding, nesting, or protection mayfeed on animals lower in the food chain that do relydirectly either on wetlands or on detritus that floatsfrom the wetland into adjacent bodies of water. Themost important example of this food chain effectin terms of commercial and recreational value isthe link between coastal wetlands and estuarine-dependent fish.

Food and Habitat

Migratory Waterfowl.—Wetlands are vital tomany species of the duck, geese, and swan familyof North America for nesting, food, and cover.These birds primarily nest in Northern freshwaterwetlands in the spring and summer, but use wet-lands for feeding and cover in all parts of the coun-try during migration and overwintering. The sur-vival, return, and successful breeding of manyspecies, therefore, depend on a wide variety of wet-land types distributed over a large geographic areaof the country (fig. 5). The major migratory routes,breeding and nesting areas, and overwinteringareas roughly correspond with regions of greatestwetland concentration (see fig. 1).

The most important areas for ducks and geeseare the breeding areas of the North, like the prairie-pothole region, Canada, and Alaska. For over-wintering, the Chesapeake Bay, the gulf coast, thecentral valley of California, and the MississippiRiver stand out (fig. 5). Also essential, but not in-


Figure 5.— General Pattern of Duck Distribution in North America


The mallard, for instance, the most commonlyhunted waterfowl in the United States, is a dab-bling duck and feeds on plants and food just underthe surface of the water. Bulrush, smartweed, andwildrice are the emergent wetland plants, and pond-weed and wild celery are submerged plants favoredby the mallard. In contrast, the canvasbacks, a div-ing duck, typically feeds in deeper water. They pre-fer submerged plants, such as pondweed, wild cel-ery, and widgeon grass to emergent vegetation butstill may feed on emergents when preferred foodsare not available. Geese and swans, on the otherhand, favor emergent wetland vegetation to sub-merged plants. Canadian and snow geese, in par-ticular, feed on the rootstock of salt marsh cord-grass as well as on cultivated crops (81).

Waterfowl also depend on wetlands for nestingsites. Inland freshwater and saltwater marshes andcoastal tundra are the most important wetland typesfor waterfowl breeding (96). In general, waterfowlprefer wetlands where open water and vegetationare interspersed. Temporarily flooded wetlandshave been known to have high breeding-pair densi-ties, probably because of plentiful invertebrates,which breeding waterfowl require for egg produc-tion (96). Northern freshwater tidal marshes areused to a more limited extent for breeding, andwooded swamps and bottom land hardwoods areused by wood ducks for nesting (66,78).

Of the 44 species of waterfowl that use NorthAmerican wetlands, 4 species of geese and 10 to15 species of ducks are hunted in sizable numbers(6,59). In the 1980-81 season, for instance, 1.9million people killed 12.9 million ducks and 1.7million geese (13). FWS estimated that 50 percentof all hunters 16 years and older, or 5.3 millionhunters, hunted migratory birds (includes non-waterfowl) in 1980, spending $638 million, or 11percent of all hunting expenditures (32). In addi-tion, FWS estimated that of 100 million Americans16 years and older who participated in outdoor ac-tivities related to fish and wildlife, 83.2 million par-ticipants spent $14.8 billion on observing andphotographing fish and wildlife. Sixty-six percentof these participants were involved directly withobserving or photographing waterfowl.

Other Birds. —There are several other types ofbirds that are found commonly in wetlands (48).The American coot is physically and ecologically

similar to the duck and is shot in considerablenumbers. Coots have diets similar to those of ducksbut build floating nests in emergent vegetation.Snipe also inhabit freshwater marshes and wetmeadows and are strictly carnivores, feeding onaquatic invertebrates they pull from mud with theirlong bills. The four rail species and the gallinules,which have special adaptations to wetlands, arecommonly found there and are hunted to some ex-tent. Herons, egrets, cranes, storks, and ibises nestcolonially in wetlands. Herons and egrets feed onfish, frog, and invertebrates in shallow marshwaters. Ibises and storks nest over water in pro-tected sites of deep marshes but feed in wet mead-ows and uplands.

Mammals. —A number of mammals live in wet-lands. For example, muskrats may live in bank bur-rows or “houses” constructed of wetland vegeta-tion along the banks of freshwater and saltwatermarshes, rivers, and streams. 10 In freshwater theirdiets may consist of cattail, bulrushes, waterlilies,

10The fo]]owing discussion is based on four sources of in fOrrnatiOn:

1 ) Schamberger, et al. (80); 2) W. H. Burt and R. P. Grossenheider,A Field Guide to the Mammals, 3d ed. (Boston: Houghton-Mif?lin,1976); 3) F. C. Daibner, Animals of the Tidaf Marsh (New York:Van Nostrand Reinhold, 1982); 4) Odum, et al. (68).

Photo credit: U.S. Fish and Wildlife Service, Jim Leupold

A white-faced bis ends its young in a marsh at BearRiver National Wildlife Refuge. Many water birds

depend on marsh vegetation for nesting sites


wildrice, and pondweed. In salt marshes, they feedheavily on cordgrasses. They occasionally eat in-sects, clams, and crayfish. In coastal areas, musk-rats reach their highest densities in brackish marshesdominated by bulrushes and cordgrasses.

Another mammal, the nutria, is a related rodentthat first was introduced from South America intoLouisiana in 1938 for its fur. It is twice the sizeof the muskrat but is ecologically similar. Nutriaprefer freshwater marshes, though they also maybe found in low- to high-salinity marshes.

Mink that inhabit wetlands usually rely on cray-fish and frogs in the North-Central States and preyheavily on muskrats during droughts and periodsof muskrat overpopulation. However, fish are themost important food for a North Carolina popula-tion of mink, and crayfish are most important formink in Louisiana. Mink appear to use the differentcoastal wetlands with equal success. In general,however, densities of these mammals are higher infreshwater rather than saltwater marshes,

Nutria are harvested for their fur in Louisiana,Maryland, the Carolinas, Texas, Oregon, andWashington. Mink and muskrat are taken in almostall States, though the majority are trapped in thewetland-rich States of the upper Midwest, theDakotas, and Louisiana (68). In 1979-80, for in-stance, these species represented 32 percent of thetotal mammal-harvest value of approximately $295million (for unfinished pelts). 11 This is a significant

i 11~fO~~~tion on the economic value of wetland furbearers comesfrom two sources: 1 ) Fur Resources Committee, International Associa-tion of Fish and Wildlife Agencies, fur harvest chart for the United

Photo credit: U.S. Fish and Wildlife Service

A nutria wading in a marsh at Belle Isle, La. Thesefurbearers reach their greatest density in freshwatermarshes, though they may also be found in low-to-high

salinity marshes

contribution to the fur industry, which recordedsales of almost $1 billion in 1980.

N u m b e r Average Total valueharvested* pelt price (rounded)

Muskrat 8,634,753 $ 8 . 6 3 $74,526,548Nutria . . 1,344,652 7.25 9,748,727Mink . . . 394,214 22.42 8,838,277

“ 1979-1980 season

While mammals are harvested primarily for theirpelts, they also are valuable for meat and variousbyproducts. During the 1979-80 season in Loui-siana alone, 582,000 lbs of nutria and 18,000lbs of muskrat, both valued at $0.04/lb, wereharvested for meat; their combined value was$24,000.

Alligators. —Alligators are found in the wetlandsof the Southeast, from North Carolina to Texas,preying on a variety of vertebrates, including mam-mals, birds, fish, and other reptiles. Alligators needshallow waters and banks for rest and warming inthe sun. They use wetland vegetation for cover,protection, and nest construction. Controlled har-vest of wild alligators for their hides and meat ispermitted in some areas of Louisiana. In 1979, over16,000 alligators worth about $1.7 million were har-vested in the Louisiana coastal region (40).

States and Canada (27 species), 1979-80. Figures in text for the UnitedStates alone; and 2) Eugene F. Deems, Jr., and Duane Pursely, “NorthAmerican Furbearers, A Contemporary Reference, InternationalAssociation of Fish and Wildlife Agencies, 1982,

Photo credit: U.S. Fish and Wildlife Service

Alligators need shallow water and banks for rest andwarming in the Sun. They use wetland vegetation for

cover and nest construction


Crayfish.— Crayfish require the fluctuatingwater levels found in wetlands for mating and egglaying. Crayfish also feed primarily on wetlandvegetation (46). Although there are commercialcrayfish fisheries in Wisconsin and the PacificNorthwest, the most valuable crop comes from theLower Mississippi River Basin, particularly Loui-siana. Approximately 25 million lbs, representingrevenues of $11 million, are harvested annually. *

Fish and Shellfish. —Many freshwater and salt-water fish require wetlands at some stage of theirlifecycle. l2 Pike, pickerel, and muskellunge seemto prefer vegetated shallow water for broadcastingtheir eggs and may even spawn on land that is onlytemporarily flooded in the spring.13 Large mouthbass spawn in the temporarily flooded zones of bot-tom land hardwoods. An abundant supply of in-vertebrates in these areas supply necessary foodduring a critical period after the fish eggs hatch (38).The alewife and the blueback herring spawn infreshwater tidal marshes and flood plain forestsalong the east coast (18).

Members of the perch family (including wall-eyes), the sunfish family (including bluegill, bass,and crappie), and the pike family (including pick-erel and muskellunge) commonly are found in veg-etated wetlands, owing to the protection from pred-ators afforded by the vegetation, strong currents,sunlight, and the fact that the prey of all these fishoften take refuge in the wetland. Grey snapper,sheepshead, spotted sea trout, and red drum moveinto mangroves after spending their first few weeksin submerged seagrass beds. These fish feed heavilyon either small fishes or amphipods (86).

Juvenile marine fish and shellfish also use coastalmarshes, particularly marshes of intermediate sa-linity, because this salinity excludes both marineand freshwater predators (2). (See table 5 for a listof species. ) Pacific coast wetlands probably do notserve the same nursery function as do the Atlanticcoast and gulf coast wetlands (68).

● Calculation of the crayfish catch ($11 million, 25 million lbs), basedon data supplied by Larry Delabreteonne.

IZAdamus and Stockwell, op. cit.‘Information comes from two sources: 1) C. L. Hubbs and K. F.

Lagler, ‘ ‘Fishes of the Great Lakes Region, Cranbrook Institute ofScience, Bulletin No. 26, Bloomfield Hills, Mich,, 1958; 2) M. B.Trautman, ‘ ‘The Fishes of Ohio, ” Ohio State University Press, Col-umbus, 1957,

Table 5.—Selected Commercial or Sport Fish andShellfish Utilizing Coastal Marshes as Nurseries

Sand seatroutWeakfishCroakerspotMenhadenStriped mulletBay anchovyStriped bassWhite perchSilver perchSummer flounderBrown and white shrimp

SOURCE: Odum, at. al., 1979, op. cit., note 68.

Endangered Species. —Approximately 20 per-cent of all plant and animal species found on theFederal Government’s list of endangered orthreatened species heavily depend on wetlands forfood and/or habitat (table 6). Many other plant andanimal species not included on the Federal list arefound on State lists. A number of endangeredspecies not listed in table 6 also may use wetlandresources to a greater or lesser extent. 14

Other Wildlife. —While relatively few animalsdepend entirely on resources found only inwetlands, many animals heavily exploit wetlandresources. Foxes and raccoons, for instance, mayprefer den sites in wetlands, owing to their closeproximity to the water (72). In fact, the availabili-ty of wetland resources may determine the healthand survival of many animals during critical times.Wetlands, for instance, are preferred by deer,pheasants, and other animals as winter cover be-cause of the presence and availability of food. Cedarswamps, for example, are the only feeding groundsthat can sustain white-tailed deer through northernMichigan winters. In Minnesota, white-tailed deerspend 80 percent of their time in wetlands betweenDecember and April (79).

During droughts and dry years, wetlands serveas reservoirs that are extremely important to re-gional wildlife stability. Southeastern swamps pro-vide food resources when upland resources are un-available (57). In a survey conducted by FWS, State

14 For a more Comp]ete review of the species that use Wdands, SeeJohn Kusler, “Our National Wetland Heritage: A Protection Guide-book, ” Environmental Institute, Washington, D. C,, 1978. The tablewas prepared by the OffIce of Endangered Species and subjected toapproximately 30 reviews.

Ch. 3—Wetland Values and the Importance of Wetlands to Man ● 57

Table 6.—Endangered Wetland Species on the FederalEndangered and Threatened Species List

Species (including subspecies,Range groups of similar species, and genera)

Alaska, Northwest California . . . . . . . . . . . . .

California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

California, Arizona

Carolinas to Texas,

. . . . . . . . . . . . . . . . . . . . . .

California. . . . . . . . . . . . .

Rocky Mountains east to Carolinas. . . . . . . .

lowa. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Southeast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Carolinas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Florida. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Appalachians . . . . . . . . . . . . . . . . . . . . . . . . . . .

Massachusetts . . . . . . . . . . . . . . . . . . . . . . . . .

Maine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Guam, Marianas Islands . . . . . . . . . . . . . . . . .

Aleutian Canada goose

Saltmarsh harvest mouseCalifornia clapper railLight-footed clapper railSan Francisco garter snakeDesert slender salamanderSanta Cruz long-toed salamanderDelta green ground beetleTruckee barberrySan Diego mesa mintCrampton’s Orcutt grassSaltmarsh bird’s beak (a snapdragon)

Yuma clapper rail

Brown pelican

Whooping crane

lowa Pleistocene snail

American alligatorHouston toadPine barrens tree frog

Bunched arrowhead

Everglades kiteCape Sable seaside sparrowDusky seaside sparrowAmerican crocodileAtlantic saltmarsh snake

Chittenango ovate amber snail

Plymouth red-bellied turtle

Furbish Iousewort

Hawaiian cootHawaiian duckLaysan duckHawaiian gallinuleHawaiian stilt

Marianas mallard

SOURCE Office of Technology Assessment

game managers identified the game and fur animalsthat use wetlands in their States (table 7). A largenumber of nongame species were found to use wet-lands.

Food Chain Support

The infusion of nutrients that comes with springflooding, combined with the nutrients alreadystored in wetland soils, results in wetland plant pro-

ductivity that often is significantly higher than theproductivity of adjacent open-water or uplandareas. For instance, the fertility of flood plains,resulting from the annual deposits of enriched sedi-ment carried by spring floods, is widely recognized.Similarly, coastal salt marshes and certain types ofinland freshwater wetlands that receive a regularsupply of nutrients achieve some of the highest ratesof plant productivity of any natural ecosystem,


Table 7.—Game and Fur Animals Identified by StateGame Managers as Found in Wetlands

Small game:Grouse, ruffedGrouse, sageGrouse, sharp-tailedHungarian partridgeMourning dovePheasantQuail, bobwhiteQuail, Gambel’sQuail, valleyRabbit, cottontailRabbit, swampSnowshoe hareSnipeSquirrels (gray and fox)Woodcock

Big game:AntelopeBlack bearBlack-tailed deerElkMouseMule deerWhite-tailed deer

Fur animals:BeaverBobcatFox (red and gray)OpossumOtterRaccoonsSkunkWeasel

SOURCE: S. T. Shaw and G. C. Fredina, wetlands of the United States, U.S. De-partment of the Interior, Fish and Wildlife Service, 1971

Plant material produced by wetlands may be animportant link in the food chain. In bottom landhardwood areas, decomposing leaves serve as thebase for springtime explosions in populations of in-vertebrates, which are an important source of pro-tein for egg-laying waterfowl. Many researchersalso have examined the importance of detritus fromestuarine marshes as food for commercially and rec-reationally valuable estuarine fish. Wetlands gen-erally produce a great deal of plant material, someof which is flushed into the estuary in the form ofdetritus. In some estuaries, such as those foundalong the Georgia and Louisiana coasts, where theratio of marsh to open water is high, detritus is amajor component of the diet of estuarine fish.

Potential Importance of Estuarine Fish andShellfish From Wetlands.—Table 8 shows the 10most recreationally important species of marinefish, judging by estimated number of fish landed.

Table 8.—The 10 Most Recreationally ImportantMarine Fish in the United States in 1979

Ranked by Number of Fish Landed

Thousands of fish

Estuarine Nonestuarine

Flounders (summer and winter) 38,649Bluefish a . . . . . . . . . . . . . . . . . . 27,332Seatrout (3 species) . . . . . . . . 22,440Sea catfishes . . . . . . . . . . . . . . 20,727spot . . . . . . . . . . . . . . . . . . . . . . 18,480Atlantic croaker . . . . . . . . . . . . 16,505Pinfish . . . . . . . . . . . . . . . . . . . . 12,811Perch (4 species) . . . . . . . . . . . 9,556Snappers (Several). . . . . . . . . . 9,363Grunts (several) . . . . . . . . . . . . 8,606

Total . . . . . . . . . . . . . . . . . . . 105,630 (57%) 78,839 (43%)aDi5agreement Owr estuarine dependence

SOURCE: National Marine Fisheries Service, “Fisherfes of the United States,1980,” Current Fishery Statistics No. 8100, 1981.

Out of an estimated 2.98 million marine fish caughtby recreational fishermen in the United States in1979, 5 out of the top 10 species, or 57 percent bynumber, were estuarine-dependent. By weight,they comprised about 62 percent of the total catchof 438.6 million lbs.

The percentage of estuarine-related fish andshellfish out of the total U.S. fisheries harvest ishigh. * Table 9 shows the 15 most important speciesor groups of species commercially harvested byU.S. fishermen in 1980, ranked by their docksidevalue. 15 Eight of these fifteen species commonly arefound in estuaries at least sometime during theirlifecycles. They represent 61 percent of the dock-side value and 77 percent of the total weight of thecatch of the 15 groups listed. Commercial landingsby U.S. fishermen for fish and shellfish in U.S.ports totaled 6.48 billion lb in 1980, with a dock-side value of $2.23 billion. Approximately 4.08 bil-

*It should be noted that there is disagreement on which fish shouldbe considered ‘‘estuarine. ” This rises partially from different defini-tions of the term and partially from lack of knowledge regarding manyof the details of marine fish life histories. For this discussion, we haveused Stroud’s ( 1971) survey of 15 fisheries biologists on the estuarinedependence of nearly 100 fishes.

1 JEstimated tot~ catch, al] regions, from National Marine FisheriesService, 1981. Estuarine dependence based on McHugh (1966) andStroud (1971). 1 ) National Marine Fisheries Service, ‘‘Fisheries ofthe United States, 1980, ” Current Fishery Statistics No. 8100, 1981;2) J. L. McHugh, ‘ ‘Management of Estuarine Fisheries, A Sym-posium on Estuarine Fisheries, American Fisheries, Soc. Spec. Pub].No. 3, 1966, pp. 133-154; 3) R. H. Stroud, “Introduction to Sym-posium, A Symposium on the Biological Significance of Estuaries,P. A. Douglas and R, H. Stroud (eds. ) (Washington, D. C.: SportFishing Institute, 1971).

Ch. 3—Wetland Values and the Importance of Wetlands to Man ● 59

Table 9.—The 15 Most Important Fish and Shellfish Harvested by U.S. Fisheries in 1980

Thousands of dollars Thousands of pounds

Nonestuarine Estuarine Nonestuarine Estuarine

Shrimp (several species, all coasts) . . . — $ 402,697 — 339,707Salmon (5 species) . . . . . . . . . . . . . . . . . . 532,277 —

$233,125613,811

Tuna (6 species) . . . . . . . . . . . . . . . . . . . . — 399,432King crab . . . . . . . . . . . . . . . . . . . . . . . . . .

—168,694 — 185,624

Menhaden (Atlantic and Gulf) . . . . . . . . .—

— 112,012 — 2,496,649Sea scallops . . . . . . . . . . . . . . . . . . . . . . . 110,429 28,752 —Flounders (several species, all coasts) . — 82,4& — 216,920American lobster. . . . . . . . . . . . . . . . . . . . 75,233 — 36,952Oyster . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

—— 70,075 — 49,081

Snow, or tanner crab . . . . . . . . . . . . . . . . 55,161 — 121,674Sea herring (Atlantic and Pacific) . . . . .

—44,955 — 291,069

Hard clam. . . . . . . . . . . . . . . . . . . . . . . . . .—

— 44,068 — 13,370Blue crab . . . . . . . . . . . . . . . . . . . . . . . . . . 55,167 — 163,206Atlantic cod . . . . . . . . . . . . . . . . . . . . . . . . 31,883 — 118,245 —Dungeness crab . . . . . . . . . . . . . . . . . . . . — 21,613 — 38,025

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . $719,480 $1,120,397 1,181,748 3,930,769Percent . . . . . . . . . . . . . . . . . . . . . . . . . . 390/0 61 0/0 230/o 77 ”/0

SOURCE: National Marine Fisheries Service, “Fisheries of the United States, 1980,” Current Fishery Statistics No, 8100, 1981,

lion lbs of estuarine fish and shellfish species werelanded by U.S. commercial fishermen in 1980. Thisrepresented 63 percent of total U.S. commerciallandings at U.S. ports, with a dockside value of$1.15 billion, 51.5 percent of the value of the totalcatch. The retail value of the estuarine-related catchis more speculative.

Factors Affecting Production of Plant Mate-rial. —The production of plant material in wetlandsgenerally is high relative to other upland ecosys-tems, such as grasslands (table 10), largely becauseof the flux of nutrients and water through wetlands(75), In general, production of plant material willbe greatest in wetlands of flowing or regularly fluc-tuating water and lowest in stillwater wetlands (un-less enriched by nutrients) (14), Approximately 15percent or less of the annual plant growth of coastalmarshes* is harvested by direct feeding by macro-invertebrates such as fiddler crabs, snails, amphi-pods, and polychaete worms (49). After the grow-ing season, most standing plant material onmarshes dies.

Up to 70 percent of the net primary productivi-ty of coastal wetlands may be exported from thewetland to open-water areas (49). The amount ex-ported will vary—in the ‘‘high marsh, only 10

*’I’his discussion pertains to coastal marshes, Limited research in-dicates that dlssol~.ed organic compounds and decaying plant materialarc exported from inland wetlands at a greater rate than from uplandsof equivalent area.

percent may be exported, while areas adjacent tothe water’s edge may export much more. In somecases, there may be no net export. Any detrital par-ticles exported from the marsh rapidly are colonizedby bacteria, fungi, and other micro-organismswhich increase the concentration of protein and fat-ty acid content, enhancing caloric value. These mi-crobes also adsorb dissolved organic compoundsfrom the surrounding water. As a result, the orig-inal plant material is transformed into a nutritiousfood source for filter feeders. 16

16 Sather and Smith, OP. cit.

Table 10.—Wetland Plant Productivity(metric tons per hectare per year)

Range

Coastal:Salt marshes (aboveground only):

Louisiana and Georgia . . . . . . . . . . . . . . . . . 22North Atlantic . . . . . . . . . . . . . . . . . . . . , . . . . 4-7Pacific coast . . . . . . . . . . . . . . . . . . . . . . . . . . 3-19

Freshwater tidal wetlands(above and below ground). . . . . . . . . . . . . . . 13-16

Inland:Freshwater marshes (above and below ground):

Sedge-dominated marshes . . . . . . . . . . . . . . 9-12Cattail marshes . . . . . . . . . . . . . . . . . . . . . . . 20-34Reed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-27Bogs (above and below ground) . . . . . . . . . 4-14Wooded swamps . . . . . . . . . . . . . . . . . . . . . . 7-14

SOURCE: Wet/and Functiorrs and V#ues The State of Our Understanding, P, E,Greeson, J. R. Clark and J. E. Clark (eds.) (Minneapolis, Minn. AmericanWater Resources Association, 1979), pp 146-161


Analysis of the stomach contents of estuarine fishand shellfish shows a wide variety of foods. For in-stance, the stomach contents of menhaden includeprimarily algae, but also detritus, small crustaceans,and even small fish and fish eggs (50). Commer-cial shrimp seem to have an even broader diet, con-sisting of single-celled algae, algal filaments, detri-tus, bacteria, protozoa, and easily captured ani-mals, including very small worms and crustaceans(25). Analysis of the stomach contents of oystersand hard clams often shows both detritus from vas-cular plants and phytoplankton, probably from theopen estuary. However, there is evidence that mostof the food value comes from the phytoplankton(37,69,84).

While commercially and recreationally impor-tant fish may not directly consume detritus as theirmajor food source, they may feed on invertebratesthat use detritus as a major food source. Newlyhatched Atlantic croaker, for instance, eat the smallcrustaceans found in the water column, particularlyvarious copepods commonly found in the tidalcreeks dissecting grassy salt marshes (2). As theygrow, they add larger items to their diets, such asamphipod crustaceans, mysid shrimp, small crabs,worms of all sorts, mollusks, and smaller fish (69,84). Also, opposum shrimp, a common marsh in-vertebrate, is a major component of the diet ofstriped bass on both the east and west coasts. Chi-ronomid midge larvae were found to account forover 80 percent of the diet of juvenile chum andchinook salmon (24).

Most coastal marshes export detritus to adjacentcoastal waters. While estuarine fish and shellfishmay directly and indirectly use detritus when avail-able, the quantitative significance of wetlands-derived detritus to the food supply of the estuaryrelative to contributions of detritus from other ter-restrial or open-water food sources generally is notknown, but probably varies widely with both speciesand estuary, If the estuary has very few marshesand much open water, such as in the North andMiddle Atlantic States and most areas in the Pacif-ic, the likelihood is increased that the ultimatesource of organic matter for fish is not the marshgrass, but the phytoplankton. For example, Chesa-peake Bay is the source of a great deal of commer-cially valuable seafood, but its ratio of marsh toopen water is only 0.04; the ratio at Sapelo Island,

Ga., is nearly 2.0. Given what is known about thephytoplankton production in the Chesapeake Bay,the annual contribution of salt marshes to totalavailable energy is only around 2 to 5 percent (61).In fact, the scientific literature lacks convincingevidence, at least for Atlantic and Pacific coasts,supporting the belief that coastal marshes play asignificant role in supporting fish and shellfish pro-ductivity through the export of detritus (68).

Climatic and Atmospheric Functions

Although there has been little research relatedto these functions, some wetland scientists havehypothesized that large wetlands help to maintainlower air temperatures in the summer and preventextremely low temperatures in the winter. They alsoare a source of water to the atmosphere, leadingto the formation of cumulus clouds, thunderstorms,and precipitation. Finally, wetlands, through proc-esses of microbial decomposition, either may storeor emit gaseous byproducts important to globalatmospheric stability.

Moderation of Local Temperatures

Water warms and cools slowly in comparisonwith land areas; thus, wetlands will have a moder-ating influence on daily atmospheric temperatures.Drained agricultural areas in Florida, for instance,were found to be 50 F colder in the winter thanwere surrounding, undrained areas (35). It has beensuggested that wetland drainage of the Evergladesmay have increased frost act ion (87). Becausedeeper water bodies contain more water than wet-lands with the same area, lakes will have a moremoderating influence on atmospheric temperaturethan will wetlands (35).

Maintaining Regional Precipitation

Wetlands contribute to rainfall through processesof evaporation and the release of water vapor fromplants (evapotranspiration). In a study of Floridacumulus clouds, for instance, lakes larger than 1mile in diameter exerted a noticeable effect onclouds in the area (35), It has been hypothesizedthat wetland drainage could reduce summer thun-derstorm activity in Florida by reducing evapo-transporation, leading in turn to regional rainfalldeficits (22).

Ch. 3—Wetland Values and the Importance of Wetlands to Man . 61

Maintain Global Atmospheric Stability

There is increasing concern now that increasesin atmospheric nitrous oxide from man’s activitiesmay adversely affect the stratosphere and mayinfluence the radiative budget of the troposphere.Studies on tidal salt marshes have shown thatmicrobial decomposition in wetland soils underanaerobic conditions can convert nitrous oxide toother chemical forms. The importance of this proc-ess on a global scale remains unclear (36).

Terrestrial detritus may form one of the largestbut least accurately known pools of carbon in thebiosphere. It generally is agreed that the world poolof detrital carbon is several times larger than thetotal carbon content of the atmosphere or of theworld biota. A significant fraction of detritus is

found as peat or in the highly organic soils of wet-lands (34). If left undisturbed, the carbon in theseorganic soils remains as reduced organic carbon.Since the mid-19th century, the conversion of wet-lands has resulted in the oxidation of organic mat-ter in the soil and the release of carbon dioxide tothe atmosphere (65). Many scientists feel that in-creasing levels of carbon dioxide in the atmospherewill lead to global warming.

Methane, a byproduct of microbial decomposi-tion of organic material in wetlands, also is thoughtto function as a sort of homeostatic regulator forthe ozone layer that protects modern aerobic lifefrom the deleterious effects of ultraviolet radia-tion (65).

CHAPTER 3 REFERENCES

1.

2.

3.

4.

5.

6.

7.

Anderson-Nichols & Co. , Inc. , ‘ ‘Neponset River

B a s i n F l o o d P l a i n a n d W e t l a n d E n c r o a c h m e n t

Study, ’ ‘ Massachusetts Water Resources Commis-sion, 1971, p. 61.Arnoldi, D. C., Herke, W. H., and Glairain, E.J., Jr., ‘ ‘Estimates of Growth Rate and Length ofStay in a Marsh Nursery of Juvenile AtlanticCroaker, Micropogon udulatus (1 .), ‘Sandblasted’

With Fluorescent Pigments, Gulf Caribb. Fish.Inst. Pmc., vol. 26, 1979, pp . 158 -172 .

Association of Bay Area Governments, ‘ ‘The Use

o f Wet lands f o r Water Po l lu t i on Contro l , c on -

tract report to the Municipal Environmental Re-

s e a r c h L a b o r a t o r y , Env i ronmenta l Pro tec t i on

A g e n c y , Cincinnati, O h i o , 1 9 8 1 .

Athearn, W. D., Anderson, G. L. , Byrne, R. J. ,

Hobbs, D. H., 111, and Ziegler, J. M., “Shoreline

Situation Report: Northampton County, Virgin-

i a , Chesapeake Research Consortium Report,No. 9, 1974.Bay, R. R., ‘‘Runoff From Small Peatland Water-sheds, ” Journal of Hydrology, vol. 9, 1969, pp.

90 -102 .

Bellrose, F . C . , “Ducks , Geese , and Swans o f

North America, Wildlife Management Institute,

Stackpole Books, Harrisburg, Pa., 1976, p. 544.

B e n n e r , C . S . , K n u t s o n , P . L . , B r o c h u , R . A . ,

a n d H u r m e , A . K . , “Vege ta t ive Eros i on Con -

trol in an Oligohaline E n v i r o n m e n t , C u r r i t u c k

Sound, North Carolina, ” Third Annual Meeting

8.

9.

10.

11.

12.

13.

14.

of the Society of Wetland Scientists, WrightsvilleBeach, N. C., May 16-19, 1982.Bernet, C., “Water Bank: Keeping WetlandsWet, ’ The Minnesota Volunteer, vol. 42, No.246, SeptemberlOctober 1979, p. 4.Boelter, D. H., and Verry, E. S., “Peatland andWater in the Northern Lake States, ” USDA For-est Service General Technical Report NC-3 1,North-Central Forest Experiment Station, St.Paul, Minn . , 1977 .

Boto , K . G . , and Patr i ck , W. H . , J r . , “Ro le o f

W e t l a n d s in t h e R e m o v a l o f S u s p e n d e d S e d i -

merits, ” WetZand Functions and Values: The Stateof Our Understanding, P. E. Greeson, J. R.Clark, and J. E. Clark (eds. ) (Minneapolis, Minn.:American Water Resources Association, 1979),pp. 479-489.Boyd, C. E., ‘ ‘Losses of Mineral Nutrients Dur-ing Decomposition of Typha latifolia, ‘‘ Arch.Hydrobiol., vol. 66, No. 4, 1970, pp. 511-517.Boyt, F. L., Bayley, S. E., and Zoltek, J., “Re-moval of Nutrients From Treated MunicipalWastewater by Wetland Vegetation, Journal ofthe Water Pollution Control Federation, vol. 49,1977, Pp. 789-799.Brackhage, G., OffIce of Migratory Bird Manage-ment, Fish and Wildlife Service, personal commu-nication with OTA, May 3, 1982.Brinson, M. M., Lugo, A. E., and Brown, S.,“Primary Productivity, Decomposition and Con-


15,

16.

17

18.

19.

204

21.

22.

23.

24.

sumer Activity in Freshwater Wetlands, AnnualReview ofEco]ogy and Systematic, vol. 12, 1981,pp. 123-161.Carter, V., Bedinger, M. S., Novitzki, R. P., andWilen, W. O., ‘‘Water Resources and Wetlands, ”Wetland Functions and Values: The State of OurUnderstanding, P. E. Greeson, J. R. Clark, andJ. E. Clark (eds.) (Minneapolis, Minn.: Ameri-can Water Resources Association, 1979), pp.334-376.Cernohous, L., ‘‘The Value of Wetlands as FloodControl, unpublished manuscript compiled forthe U.S. Fish and Wildlife Service, Bismarck AreaOffice, Bismarck, N. Dak., 1979,Clairain, E. J., Cole, R. A,, Diaz, R. J., Ford,A. W,, Huffman, R. I., and Wells, B. R., “Habi-tat Development Field Investigations, Miller SandsMarsh and Upland Habitat Development Site, Co-lumbia River, Oregon, ” Summary Report, Tech-nical Report D-77-38, U.S. Army EngineerWaterways Experiment Station, Vicksburg, Miss.,1978.Clark, J., “Freshwater Wetlands: Habitats forAquatic Invertebrates, Amphibians, Reptiles, andFish, Wetland Functions and Values: The Stateof Our Understanding, P. E. Greeson, J. R.Clark, and J. E. Clark (eds. ) (Minneapolis, Minn.:American Water Resources Association, 1979),pp. 330-343.Clark, J. R., and Benforado, J., “Report on a Bot-tomland Hardwood Wetlands Workshop, LakeLanier, Ga., June 1-5, 1980.Coordinating Council on Restoration of theKissimmee River Valley and Taylor Creek-Nub-bin Slough Basin, “Symposium Summary, Re-gional Influence of Drainage of the Hydrologic Cy-cle in Florida, ” July 1982.Council on Environmental Quality, “Our Na-tion’s Wetlands, ” An Interagency Task Force Re-port, 1978, p, 70.Cowardin, L. M., Carter, V., Golet, F. C., andLaRoe, E. T., “Classification of Wetlands andDeepwater Habitats of the United States, ” U.S.Fish and Wildlife Service, 1979, p. 103.Crisp, D. T., ‘‘Input and Output of Minerals foran Area of Pennine Moorland: The Importanceof Precipitation, Drainage, Peat Erosion, and Ani-ma.ls, ’’~ourn~ of Applied Ecology, VO1. 3, 1966,pp. 327-348.Crow, J. H., and MacDonald, K. B., “WetlandValue: Secondary Production, ” Wetland Func-tions and Values: The State of Our Understand-ing, P. E. Greeson, J. R. Clark, and J. E. Clark(eds.) (Minneapolis, Minn.: American Water Re-sources Association, 1979), pp. 146-161.

25

26

27.

28.

29.

30.

31

32.

33.

34!

35.

36,

Dan, W., ‘‘Food and Feeding of Some AustralianPenaeid Shrimp, ” Proc. World Su. Conf Biol,and Culture of Shrimps and Prawns, Fish. Rep,F. A. D., vol. 57, 1968, pp. 251-258.Dibner, P. C., “Response of a Salt Marsh to OilSpill and Cleanup: Biotic and Erosional Effects inthe Hackensack Meadowlands, New Jersey, ”NTIS Report No. PB-285-211, 1978.Dierberg, F. E., and Brezonik, P. L., ‘‘The Ef-fect of Secondary Sewage Effluent on the SurfaceWater and Groundwater Quality of CypressD o m e s , Cypress Wetlands for Water Manage-ment, Recycling, and Conservation, 4th AnnualReport to the National Science Foundation, H. T.Odum and K. C. Ewel (eds. ) (Gainesville, Fla.:University of Florida, 1978), pp. 789-799.Ehrenfeld, D. W., “The Conservation of Non-Re-sources, ” American Scientist, vol. 64, 1976, pp.648-656.Elder, J. F., and Cairns, J., “Production and De-composition of Forest Litter Fall on the Appalach-icola River Floodplain, Florida, U.S. GeologicalSurvey Water-Supply Paper 2196, 1983.Elkins, J. W,, Wofsy, S. C., McElroy, M. B.,Kolb, C. E., and Kaplan, W. A., “AquaticSources and Sinks for Nitrous Oxide, ” Nature,vol. 275, 1978, pp. 602-606.Fagan, G. L., Jr., “Analysis of Flood Hydro-graphy From Wetland Areas, ” Ph. D. dissertation,available from University Microfilms, No. 81-18860, 1981.Fish and Wildlife Service, “The 1980 NationalSurvey of Fish, Hunting and Wildlife-AssociatedRecreation, Portland, Oreg., 1982.Flake, L. D., “Wetland Diversity and Water-fowl, ” Wetland Functions and Values: The Stateof Our Understanding, P. E. Greeson, J. R.Clark, and J. E. Clark (eds. ) (Minneapolis, Minn.:American Water Resources Association, 1979),pp. 312-319.Friedman, R. M., and DeWitt, C. B., “Wetlandsas Carbon and Nutrient Reservoirs: A Spatial,Historical, and Societal Perspective, ” WedandFunctions and Values: The State of Our Under-standing, P. E. Greeson, J. R. Clark, and J. E.Clark (eds.) (Minneapolis, Minn.: AmericanWater Resources Association, 1979), pp. 175-185.Gannon, P. T., Barthdic, J. F., and Bill, R. G.,“Climatic and Meteorological Effects on Wet-lands, ” Wetland Functions and Values: The Stateof Our Understanding, P. E. Greeson, J. R.Clark, andJ, E. Clark (eds. ) (Minneapolis, Minn.:American Water Resources Association, 1979),pp. 576-588.Gerrnain, C., Wisconsin Scientific Areas Program,


37.

38.

39.

40.

41.

42

43

44.

45.

46.

47.

48.

personal communication with Joan Ham, OTA,Dec. 14, 1981.Haines, E. B., and Montague, C. L., “FoodSources of Estuarine Invertebrates Analyzed Using1 sC/1 ZC Ratios, Ecology, V O1. 60, 1979, Pp.48-56.Hall, D. H., ‘‘A Synopsis of the Values of Over-flow in Bottomland Hardwoods to Fish and Wild-l i f e , U.S. Fish and Wildlife Service, EcologicalServices, 1979.Hobbs, C. H., Byrne, R. J., Kerns, W. R., andBarber, N. J., ‘ ‘Shoreline Erosion: A Problem inEnvironmental Management, ” CoastaJ Zone i’t4an-agernentjournaJ, vol. 9, No. 1, 1981, pp. 89-105.Jantzen, R. , Director, U.S. Fish and WildlifeService, testimony before House Subcommittee onFisheries, Wildlife Conservation, and the Environ-ment, Nov. 20, 1981.Jones, R. A., and Lee, G. F., ‘‘An Approach forthe Evaluation of Efilcacy of Wetlands-Based Phos-phorus Control Programs for Eutrophication-Re-lated Water Quality: Improvement in DownstreamWaterbodies, ” VVater, Air and Sod Pollution, vol.14, 1980, pp. 359-378.Kadlec, R. H., and Kadlec, J. A., “Wetlands andWater Quality, Wetland Functions and VaJues:The State of Our Understanding, P. E. Greeson,J. R. Clark, and J. E. Clark (eds. ) (Minneapolis,Minn.: American Water Resources Association,1979), pp. 436-456.Knutson, P. L., Ford, J. C., Inskeep, M. R., andOyler, J., “National Survey of Planted SaltMarshes, Wetlands, September 1981.Knutson, P. L., and Selig, W. N., “Wave Damp-ing in Spartina AJterniflora Marshes, Third An-nuaJ Meeting of the Society of WetJand Scientists,Wrightsville Beach, N. C., May 16-19, 1982.Kroodsma, D. E., (‘Habitat Values for Non gameWetland Birds, ” Wetland Functions and VaJues:The State of Our Understanding, P. E. Greeson,J. R. Clark, and J. E. Clark (eds.) (Minneapolis,Minn.: American Water Resources Association,1979), pp. 320-329.LaCraze, C., “Crawfish Farming, ” Louisiana De-partment of Wildlife and Fisheries, Baton Rouge,La., Fisheries Bulletin No. 7, 1981.Lee, C. R., Bentley, E., and Amundson, R., “Ef-fects of Marshes on Water Quality, ” CouplingLand and Water Systems, A. D. Hader (cd.) (NewYork: Springer-Verlag, 1975), pp. 105-127.Leopold, A. S., Gutierrez, R. J., and Bronson,M. T., North American Game Birds and Mam-maJs (New York: Scribner, 1981).

49.

50.

51.

52.

53.

54.

55.

56.

57.

58.

59.

60.

61.

McCormick, J., and Somes, H. A., Jr., “TheCoastal Wetlands of Maryland, ” Maryland De-partment of Natural Resources, 1982.McHugh, J. L., “Estuarine Nekton, ” Estuaries,G. Lauff (cd.), publication 82 (Washington, D. C.:American Association for the Advancement of Sci-ence, 1967), pp. 581-620.Miller, E. G., “Effect of Great Swamp, New Jer-sey on Streamflow During Baseflow Periods,U.S. Geological Survey Professional Paper 525-B,1965, pp. B-177-179.Mitsch, W. J., Dorge, C. L., and Weimhoff, J.R., “Forested Wetlands for Water Resource Man-agement in Southern Illinois, University of Illi-nois at Urbana-Champaign Water Resources Cen-ter, Research Report No. 132, NTIS No. PS 276659, 1977.Morine, D., Vice President for Land Acquisition,the Nature Conservancy, and Lowe, G., ExecutiveVice President, the Nature Conservancy, personalcommunication with OTA, Apr. 19, 1983.Mortimer, C. H., ‘ ‘The Exchange of DissolvedSubstances Between Mud and Water in Lakes,Parts I and II,” J. Ecol., vol. 29, 1941, p p .280-329.Mortimer, C. H., “The Exchange of DissolvedSubstances Between Mud and Water and Lakes,Parts III and IV, ” J. EcoJ., vol. 30, 1942, pp.147-201.Motts, W. S., and O’Brien, A. L., “Geology andHydrology of Wetlands in Massachusetts, WaterResources Research Center, University of Mass-achusetts, Amherst, Publication No. 123, 1981.Mulholland, L. D., “Importance of SoutheasternSwamps to North American Birds and Mam-mals, presented at the Third Annual Meeting ofthe Society of Wetland Scientists, 1982.Mulica, W. S., and Lasca, N. P., “A Bog-Con-trolled Groundwater Recharge System in an Areaof Urban Expansion, Proceedings of SecondWorld Congress, International Water ResourcesAssociation, vol. 111, New Delhi, December 1974,pp. 175-194,National Academy of Sciences, Impacts of Emerg-ing Agricultural Trends on Fish and WildlifeHabitat (Washington, D. C.: National AcademyPress, 1982).National Park Service, “National Park StatisticalAbstract, available from the Statistical Office,Denver Service Center, U.S. Department of theInterior, 1981.Nixon, S. W., “Between Coastal Marshes andCoastal Rivers—A Review of Twenty Years of


62.

63

64

65.

66.

67.

68.

69.

70.

Speculation and Research on the Role of SaltMarshes in Estuarine Productivity and WaterChemistry, Estuarine and Wetland ProcessesWith Emphasis on ModeJing, Hamilton and Mac-Donald (eds. ) (New York: Plenum Press, 1979),pp. 437-511.Novitzki, R. P., “Hydrology of the Nevin Wet-land Near Madison, Wisconsin, ” U.S. GeologicalSurvey, Water Resources Investigation 78-48,NTIS No. PB-284 118, 1973.Notitzki, R. P., ‘‘The Hydrologic Characteristicsof Wisconsin’s Wetlands and Their Influence onFlood, Streamflow, and Sediment, ” WetlandFunctions and Values: The State of Our Under-standing, P. E. Greeson, J. R. Clark, and J. E.Clark (eds. ) (Minneapolis, Minn.: American Wa-ter Resources Association, 1979), pp. 377-388.O’Brien, A. L., “Hydrology of Two Small Wet-land Basins in Eastern Massachusetts, ” Water Re-sources Bulletin, vol. 13, No. 2, 1977, pp. 325-340.Odum, E. P., ‘ ‘The Value of Wetlands: A Hierar-chical Approach, Wetland Functions and Values:The State of Our Understanding, P. E. Greeson,J. R. Clark, and J. E. Clark (eds.) (Minneapolis,Minn.: American Water Resources Association,1979), pp. 16-25.Odum, W. E., Dunn, M. L., and Smith, T. J.,III, “Habitat Value of Tidal Freshwater Wet-lands, ” Wetland Functions and Values: The Stateof Our Understanding, P. E. Greeson, J. R.Clark, andJ. E. Clark (eds. ) (Minneapolis, Minn.:American Water Resources Association, 1979),pp. 248-255.Ogawa, H., “Evaluation Methodologies for theFlood Mitigation Potential of Inland Wetlands, ”Ph. D. dissertation, University of Massachusetts,Amherst, 1982.Onuf, C. P., Quammen, M. L., Shaffer, G. P.,Peterson, C. H., Chapman, J. W., Cermak, J.,and Holmes, R. W., ‘‘An Analysis of the Valuesof Central and Southern California Coastal Wet-lands, ” Wetland Functions and Values: The Stateof Our Understanding, P. E. Greeson, J. R.Clark, and J. E. Clark (eds. ) (Minneapolis, Minn.:American Water Resources Association, 1979),pp. 186-199.Overstreet, R. M., and Heard, R. W., “Food ofthe Atlantic Croker, Micropogonias undulatus,From Mississippi Sound and the Gulf of Mexico, ”Gulf Res. Rept. 6, 1978, pp. 145-152.Owens, R. E., III, “The Economic Value of theUse of Virginia’s Coastal Wetlands as an ErosionControl Strategy, Virginia Polytechnic Institute

71.

72.

73.

74.

75.

76.

77.

78.

79.

80.

81.

82.

and State University, M. S. thesis, Blacksburg,Va., 1980.Pestrong, R., ‘ ‘The Shear Strength of Tidal MarshSediments, NTIS No. AD-765 273, 1973.Porter, B. W., ‘ ‘The Wetland Edge as a Commu-nity and Its Value to Wildlife, Selected Pro-ceedings of the Midwest Conference on WetlandValues and Management, B. Richardson (cd.),1981.Reilly, W., “Can Science Help Save Interior Wet-lands?” Wetland Functions and Values: The Stateof Our Understanding, P. E. Greeson, J. R.Clark, and J. E. Clark (eds. ) (Minneapolis, Minn.:American Water Resources Association, 1979),pp. 26-30.Richardson, C. J., “Pocosin Wetlands” (Strouds-burg, Pa.: Hutchinson Ross Publishing Co.,1981).Richardon, C. J., ‘ ‘Primary Productivity Valuesin Freshwater Wetlands, ” Wetland Functions andValues: The State of Our Understanding, P. E.Greeson, J. R. Clark, and J. E. Clark (eds.) (Min-neapolis, Minn.: American Water Resources As-sociation, 1979), pp. 131-145.Ryan, J. D., and Everitt, T., “Investigations ofthe Plant Community-Soil-Soil Strength Micro-morphology Relationships in Coastal Marshes,NTIS No. AD-768 801, 1973.Sander, J. E., ‘ ‘Electric Analog Approach to BogHydrology, “ Groundwater, vol. 14, No. 1, 1976,pp. 30-35.Schamberger, M. L., Short, C., and Farmer, A.,“Evaluating Wetlands as Wildlife Habitat, ” Wet-land Functions and Values: The State of OurUnderstanding, P. E. Greeson, J. R. Clark, andJ. E, Clark (eds.) (Minneapolis, Minn.: AmericanWater Resources Association, 1979), pp. 74-83.Schitoskey, F., Jr., and Linder, R. L., “Use ofWetlands by Upland Wildlife, ” Wetland Func-tions and Values: The State of Our Understand-ing, P. E. Greeson, J. R. Clark, and J. E. Clark(eds.) (Minneapolis, Minn.: American Water Re-sources Association, 1979), pp. 307-322.School of Forestry and Environmental Studies,“Wetlands Trends and Policies in North andSouth Carolina, ” Duke University, OTA contractstudy, August 1982.Shaw, S. P,, and Fredine, C. G., “Wetlands ofthe United States: Their Extent and Their Valueto Waterfowl and Other Wildlife, Fish and Wild-life Service, U.S. Department of the Interior, Cir-cular 38, 1956, p. 67.Smardon, R. C., “Visual-Cultural Values of Wet-

Ch. 3—Wet/and Values and the Importance of Wetlands to Man ● 6 5

83.

84

85

86

87.

88.

89,

90

lands, Wetland Functions and Values: The Stateof Our Understanding, P. E. Greeson, J. R.Clark, and J. E. Clark (eds. ) (Minneapolis, Minn.:American Water Resources Association, 1979),pp. 535-544.Snyder, B. D., and Snyder, J. L., ‘ ‘Feasibility ofUsing Oil Shale Wastewater for Waterfowl Wet-lands, U.S. Fish and Wildlife Service, Office ofBiological Service, contract No. FWS 14-16-009-82-002, Fort Collins, Colo., 1982.Stickney, R. R., Taylor, G, L., and White, D.B., “Food Habits of Five Young SoutheasternUnited States Estuarine Sciaenidae, ChesapeakeSci., vol. 16, 1975, pp. 104-114.Tchobanoglous, G., and Culp, G. L., “WetlandSystems of Wastewater Treatment: An Engineer-ing Assessment, University of California, Davis,1980.Thayer, G. W., Stuart, H. H., Kenworthy, W.J., Ustach, J. F., and Hall, A. B., “Habitat Val-ues of Salt Marshes, Mangroves, and Seagrassesfor Aquatic Organisms, Wetland Functions andValues: The State of Our Understanding, P. E.Greeson, J. R. Clark, and J. E. Clark (eds. ) (Min-neapolis, Minn .: American Water Resources As-sociation, 1979), pp. 186-199.Thomas, T., “A Detailed Analysis of Climatolog-ical and Hydrological Records of South FloridaWith Reference to Man’s Influence Upon Ecosys-tem Evolution, report to U.S. National ParkService, 1970, p. 82.U.S. Army Corps of Engineers, Institute for WaterResources, ‘ ‘Analysis of Selected Wetlands Func-tions and Values, unpublished draft report 81 D-01, 1981.U.S Army Corps of Engineers, ‘ ‘Charles RiverWatershed, Massachusetts Natural Valley StorageProject, Design Memorandum No. 1, HydrologicAnalysis, New England Division, Waltham,Mass., 1976.U.S. Fish and Wildlife Service, ‘ ‘Refuge Visita-tion Figures, available from Division of RefugeManagement, Branch of Resource Management,1981.

91.

92.

93.

94,

95.

96.

97<

98<

99.

Valiela, I., Teal, J. M., and Sass, W. J., “Pro-duction and Dynamics of Salt Marsh Vegetationand the Effects of Experimental Treatment WithSewage Sludge, ’’Journal of Applied Ecology, vol.12, No. 3, 1975.Vecchiolo, J., Gill, H. E., and Land, S. M.,“Hydrologic Role of the Great Swamp and OtherMarshland in the Upper Passaic River Basin, ”Jour-nalofthe American Water WorksAssociation,vol. 54, No. 6, 1962, Pp. 695-701.Verry, E. S., and Boelter, D., “Peat and Hydrol-ogy, ’ Wetland Functions and Values: The Stateof Our Understanding, P. E. Greeson, J. R.Clark, and J. E. Clark (eds. ) (Minneapolis, Minn.:American Water Resources Association, 1979),pp. 389-402.Wadleigh, R. S., ‘‘Effects of Swamp Storage UponStorm Peak Flows, ’ M.S. thesis, Department ofAgricultural Engineering, University of Massachu-setts, Amherst, 1965.Wayne, C. J., ‘ ‘Sea and Marshgrasses: Their Ef-fect on Wave Energy and Nearshore Transport,M.S. thesis, Florida State University, College ofArts and Sciences, Tallahassee, Fla., 1975.Weller, M., “Freshwater Marshes: Ecology andWildlife Management” (Minneapolis, Minn.:University of Minnesota Press, 1981.Wharton, C. H., ‘ ‘The Southern River Swamp—A Multiple Use Environment, ” Bureau of Busi-ness and Economic Research, School of BusinessAdministration, Georgia State University, Atlanta,Ga., 1970.Yonika, D., and Lowry, D., “Feasibility Studyof Wetland Disposal of Wastewater TreatmentPlant Effluent, ” final report, Commonwealth ofMassachusetts Water Resources Commission, Re-search Project 78-104, 1979.Zoltek, J., and Bayley, S. E., “Removal of Nu-trients From Treated Municipal Wastewater byFreshwater Marshes, ” University of FloridaCenter for Wetlands, Gainesville, Fla., 1979.

wetland values and the importance of wetlands to man

Documents