FIELD STUDIES OF PHOSPHORUS AND CLADOPHORA IN LAKE

ONTARIO ALONG THE AJAX, ONTARIO WATERFRONT

Martin T. Auer, PhD, 2014

FIELD STUDIES OF PHOSPHORUS AND CLADOPHORA

IN LAKE ONTARIO ALONG THE AJAX, ONTARIO WATERFRONT

Martin T. Auer, Ph.D.

Submitted to the Town of Ajax, Ontario 23 January 2014

2

Summary Based on the experience gained through decades of scientific, peer-reviewed research about attached algae in the Great Lakes, with particular attention to Cladophora, I was asked by the Town of Ajax to assess whether the phosphorus discharged to the Ajax nearshore from the Duffin Creek Water Pollution Control Plant (“Duffin Creek WPCP”) was causing or contributing to the nuisance algae problem occurring along the Ajax waterfront.

Cladophora requires four conditions in order to grow: sufficient light, a suitable substrate (or bottom) to attach to, the right water temperature, and a food source (phosphorus). In Lake Ontario, the optimal water temperatures occur from late-May until mid-June (the Cladophora “growing season”). Algal growth will occur over this interval, and continue at sub-optimal rates for several months, provided that the alga’s needs for substrate for attachment, light and a supply of bioavailable phosphorus are met.

During the summer of 2013, field work was carried out to examine each of these three variables in the Ajax nearshore. Sonar surveys of the lake bottom were undertaken by a team from Michigan Technological University to characterize the suitability of the substrate for Cladophora growth. Measurements of the underwater light field were made by Ecometrix to determine the extent of light penetration.

The results of this field work indicate that there is a band of lake bottom along the Ajax nearshore, extending lakeward to a distance of ~1 km, where both suitable substrate and sufficient light exist to support Cladophora growth (“Cladophora Habitat Zone”).

The Cladophora Habitat Zone (green) at Ajax, Ontario and adjacent lake bottom where the alga is either irregularly present (green patches) or absent (tan). The yellow triangle points to the location of the Duffin Creek WPCP outfall.

3

Underwater video surveys of the Ajax nearshore, performed by Michigan Technological University, confirmed the presence of Cladophora, often covering 100% of the bottom of this Cladophora Habitat Zone. The existence of habitat (substrate, light, temperature) alone, however, will not create a nuisance algae problem. Algae can exist in nearshore areas without causing nuisance conditions. The difference between the mere presence of algae and nuisance conditions is productivity, i.e, how fast algal biomass is being generated.

Still image of algal biomass at a depth of 5 m derived from video obtained during a survey of the Cladophora Habitat Zone in August of 2013.

The supply of phosphorus, specifically bioavailable phosphorus, is the factor that controls Cladophora productivity. Soluble reactive phosphorus (“SRP”) is 100% bioavailable and is commonly found present in WPCP effluents and nonpoint source runoff. The effluent plume of the Duffin Creek WPCP was delineated and sampled on two occasions by a team from Upstate Freshwater Institute to quantify the impact of that discharge on SRP concentrations in the Cladophora Habitat Zone.

The highest concentrations of SRP were observed immediately adjacent to the Duffin Creek WPCP outfall with dramatic elevations above baseline SRP levels occurring throughout the Cladophora Habitat Zone. Currents traversing the Ajax nearshore have the potential to carry the plume and its SRP-enriched water to the east and to west across the Cladophora Habitat Zone.

A direct connection between the SRP-enriched plume and stimulation of growth and production within the Cladophora Habitat Zone was established by making measurements of algal tissue phosphorus across the Ajax nearshore and at a control site near Cobourg, Ontario.

4

The rate of Cladophora growth and thus the potential for production is directly related to its tissue phosphorus content, i.e. the amount of food stored by the alga. The tissue P metric also helps to smooth out the variability in SRP concentrations (difficult to track by water sampling) attending movement of the plume across the Cladophora Habitat Zone. This provides a more accurate picture of SRP availability and algae productivity over the course of the growing season.

The highest tissue phosphorus concentration was observed in the immediate vicinity of the Duffin Creek WPCP outfall with levels decreasing with distance from that location. Cladophora at Ajax is phosphorus-enriched to the extent that maximum rates of growth and production are approached and, proximate to the outfall, are achieved. This pattern of tissue phosphorus distribution is consistent with the conclusion that the Duffin WPCP outfall is the driving force for Cladophora growth and production at Ajax. The results also confirm that Cladophora at Ajax is among the most phosphorus-enriched, and therefore most productive, in Lake Ontario.

Based on the results of the field investigations and analysis summarized above, there is no doubt that the effluent being discharged to Lake Ontario from the Duffin Creek WPCP is the primary contributor to nuisance conditions of Cladophora growth at Ajax. The Duffin Creek WPCP is not yet operating at its maximum approved flow rate and is, therefore, not delivering its maximum allowable phosphorus load. The amount of phosphorus being discharged to the Ajax nearshore has the potential to increase by almost a factor of 3 under the EAC approved for the Duffin Creek WPCP. This increase in phosphorus loading has the potential to worsen the nuisance conditions presently experienced at Ajax and potentially extend the area affected along the regional shoreline.

The field program described here has conclusively demonstrated that the more than 100 kg of bioavailable phosphorus discharged daily to Lake Ontario by the Duffin Creek WPCP are received directly within the Cladophora Habitat Zone along the Ajax waterfront. Analysis of the results of the field program as set out above lead to several primary conclusions:

• The Duffin Creek WPCP discharge to Lake Ontario at Ajax establishes an effluent plume of bioavailable phosphorus that overlies lake bottom having physical conditions capable of supporting the growth of attached algae and stimulates the growth of the alga Cladophora glomerata (“Cladophora”) across the Ajax nearshore.

• The bioavailable phosphorus supplied by the Duffin Creek WPCP plume leads to enrichment of the stored phosphorus (tissue P) content of Cladophora, achieving levels supporting nuisance conditions. The degree of phosphorus enrichment, and thus Cladophora growth and productivity, is highest in proximity to the Duffin Creek WPCP outfall and decreases with distance from that nutrient source.

• The level of phosphorus enrichment, and the resulting levels of Cladophora biomass and productivity, associated with the Duffin Creek WPCP outfall are well above those characteristic of sites on Lake Ontario less impacted by urban activity.

5

• Based on all of the foregoing, and given that the Duffin Creek WPCP effluent is by far the largest phosphorus input to the Ajax nearshore, that source may be considered the proximal cause of the Cladophora problem and the appropriate focus for efforts to remediate conditions of nuisance algal growth.

• The Duffin Creek WPCP is slated to substantially increase the amount of phosphorus that it discharges to Lake Ontario. The impact of this increase, absent a reduction in effluent phosphorus concentrations and/or relocation of the outfall, will be greater stimulation of Cladophora growth and exacerbation of the nuisance algae problem.

The position of the Duffin Creek WPCP effluent plume (red and pink) on 8/9/2013 overlain on the Cladophora Habitat Zone (green) at Ajax, Ontario. There was no area unimpacted by plume SRP within the survey limits. The yellow triangle points to the location of the Duffin Creek WPCP outfall.

6

1. Motivation and Problem Definition

The filamentous, green alga Cladophora glomerata grows attached to solid substrate in

the Great Lakes nearshore and is widely distributed in Lake Ontario (Michigan Tech Research

Institute; http://geodjango.mtri.org/static/sav/). However, Cladophora biomass and the

occurrence of bloom conditions are highly variable around the lake and phosphorus loading from

local watersheds has been identified as the underlying driver for this spatial variability (Higgins

et al. 2012). A particularly robust presence of Cladophora has been observed in waters adjacent

to urban centers, i.e. those having elevated levels of dissolved salts, measured as electrical

conductivity (Higgins et al. 2012). Among seven stations in Lake Ontario representing a range

of urban impacts, levels of conductivity and Cladophora biomass were highest at Ajax, Ontario

(Higgins et al. 2012).

The field program described in this report was designed to clarify the provenance of

phosphorus in the nearshore waters at Ajax, Ontario and to explore the degree to which those

sources may contribute to Cladophora blooms.

2. Study Site and Description of the Field Program

The study site at Ajax, Ontario consisted of three transects extending lakeward to

distances of 4.5 km, 3.0 km and 3.0 km (Figure 1). Each transect included seven stations having

water depths ranging from 2.5 to 30 m. The sampling program (Table 1) characterizes:

• Cladophora growth habitat; • Cladophora distribution and nutritional status; and • Sources of phosphorus supporting Cladophora growth

Table 1. Date, objectives and the nature of measurements made during 2013 field surveys.

Date Survey Focus Measurements

8/9 Phosphorus sources Nitrate plume surveys

8/20-23 Cladophora growth habitat, distribution and nutritional status

Side scan sonar; remotely operated vehicle video surveys;

8/29 Phosphorus sources Nitrate plume surveys; nitrate – soluble reactive phosphorus correlation

10/9 Light environment Depth profiles of light intensity

7

Duffin CreekWPCP

DuffinCreekWPCP

City ofPickering

Town of Ajax

Figure 1. The study site at Ajax, Ontario with water depth and station locations.

8

At Ajax, Ontario, lake bottom conditions well suited for supporting Cladophora beds are present lakeward from the shore to depths of 10-15 m, a distance of ~0.75-1.5 km. A sandy bottom type, also suitable for support of Cladophora beds when colonized by mussels, is observed at depths of 25-30 m, a distance of ~2.5-4.0 km offshore. However, the amount of light available at this offshore location is insufficient to support Cladophora growth. Thus the area physically capable of supporting the development of Cladophora beds at Ajax is limited to waters having the solid substrate to which the alga attaches at depths less than ~10 m. Given the necessary physical conditions (light and hard substrate for attachment), the presence and level of production of Cladophora depends on phosphorus availability. Cladophora beds are not a common feature of Great Lakes ecosystems featuring SRP concentrations < 0.5 µgP/L. Above this level, growth is stimulated and production increases with increasing SRP concentration, approaching its maximum growth rate at ~2 µgP/L. Above this level, Cladophora growth is largely insensitive to additional increases in SRP. Thus, SRP concentrations from 0.5 – 2.0 µgP/L, defines the range of interest in managing Cladophora blooms and attendant nuisance conditions.

Analysis of survey results drew upon additional resources including the TRCA Peer Review,

data obtained from Environment Canada and the U.S. National Oceanic and Atmospheric

Administration, interpreted satellite imagery from the Michigan Tech Research Institute, the

peer-reviewed primary scientific literature, agency and university reports, stakeholder images of

nearshore conditions and Dr. Auer’s 30 years of experience in the study of phosphorus and

Cladophora in the Great Lakes.

3. Fundamental Requirements for Cladophora Growth

As with most plants and animals, Cladophora colonizes habitat providing a particular set

of environmental conditions, e.g. hard substrate for attachment, adequate light at the lake bottom

and seasonally optimum temperatures. These features determine the suitability of a site to host a

Cladophora bed. Whether or not a suitable site will be colonized, and the degree to which the

bed will develop, depends on the availability of the limiting nutrient, in this case phosphorus.

Here we describe the physical environment and nutrient conditions that mediate Cladophora

growth, explore the importance of distinguishing algal standing crop and production in assessing

that growth and describe the various forms of phosphorus and their utility in understanding the

Cladophora growth dynamic.

9

3.1 Physical Conditions

The fundamental requirement for establishment of a Cladophora bed is the presence of

solid substrate for attachment, e.g. bedrock, boulders and cobbles (Figure 2). Substrate of human

origin (e.g. piers and breakwalls), and beds of invasive mussels (Higgins et al. 2005), may also

serve this purpose. Sand, silt and clay bottoms are not sufficiently stable to support attachment.

At Ajax, the nature and suitability of the lake bottom for supporting Cladophora beds varies in

both the longshore and offshore directions. In the longshore direction, Cladophora beds are

widely distributed (Figure 3; http://geodjango.mtri.org/static/sav/), with some patchiness

reflecting the presence of unsuitable bottom types (primarily sand). A side scan sonar and high

definition video survey of the Ajax waterfront (Figure 4) served to confirm satellite-derived

information and to characterize the distribution of Cladophora beds with distance offshore and

thus increasing depth. The lake bottom at Ajax consists of boulders, cobbles, sand and mussel

beds. Cobbles and boulders are dominant from the shore to a depth of 10-15 m, a distance of

0.75-1.5 km. This bottom type becomes mixed with sand at depths of 15-20 m (~1.25-2.0 km

offshore), with cobbles and boulders being less prominently featured than in shallower

environments. At depths of 25-30 m (offshore distances of 2.5-4.0 km and beyond), the lake

bottom is predominately sand, colonized by mussel beds (Figure 5). The presence of patches of

sandy bottom in waters <10 m deep, and the transition from cobble-bounder bottom to sand as

depth increases, results from differences in water turbulence and the ability of wave action to

keep cobbles and boulders washed free of sand. Based on the side scan sonar and high definition

videos, lake bottom types suitable for supporting Cladophora beds at Ajax are present from the

shore to depths of 30 m (and likely beyond). The true suitability of these locations is influenced

as well by light availability, the second physical condition examined here.

As for all plants, light plays a critical role in mediating the growth of Cladophora. Only

light with wavelengths between 400 and 700 nanometers can support photosynthesis. Thus, in

applications relating to Cladophora, light is quantified only over that wavelength range and is

termed photosynthetically available radiation (PAR), expressed as a photon flux, i.e. moles of

photons (elementary particles of light) incident on a unit surface area per unit time. One mole

of photons is termed an Einstein and a microEinstein (µE) is one millionth of a mole, leading to

units for PAR of µE·m-2·s-1. Three metrics of PAR are important here: incident light on a cloud-

free day (~2000 µE·m-2·s-1), an optimum intensity (~550 µE·m-2·s-1; calculated from Tomlinson

10

Figure 2. Cobble and boulder lake bottoms from Lake Huron (left) and Lake Erie (right). Both have the required substrate for attachment and light environment and both experience seasonal temperature regimes that include the optimum for Cladophora growth. The absence/presence of Cladophora beds at the two sites results from differences in phosphorus supply. Note that the Cladophora bed at right would be submerged below a meter or more of water under typical conditions, but has been exposed here by seiche activity.

11

Figure 3. The distribution of Cladophora beds in the Ajax/Pickering/Whitby, Ontario nearshore as determined from satellite sensing data ( http://geodjango.mtri.org/static/sav/). Cladophora beds are indicated by a green color with the darkness reflecting bed density as sensed by satellite instrumentation. Areas not supporting Cladophora beds, typically sand bottom, are indicated by a tan color. Satellite sensing penetrates to the optical depth of the water, here ~8 m. Thus, Cladophora beds may extend further out in the lake, as confirmed by ground truth monitoring.

12

(a) (b)

(c) (d)

Figure 4. Remotely operated vehicle (ROV) survey of bottom type and the nature and distribution of Cladophora beds in the Ajax nearshore of Lake Ontario: (a) deployment, (b) submersal, (c) descent and (d) retrieval. Images by Dave Dean, Michigan Tech Research Institute.

13

cobbles and boulders

cobbles and boulders

cobbles and boulders

cobbles and boulders

2.5 m

5 m

10 m

15 m

Figure 5. High definition video and side scan sonar tracks of Cladophora bed development (left) and lake bottom type (right) at various depths in the Ajax nearshore.

14

cobbles and boulders

mottled – mussel beds

mottled – mussel beds

20 m

25 m

30 m

Figure 5. Continued. High definition video and side scan sonar tracks of Cladophora bed development (left) and lake bottom type (right) at various depths in the Ajax nearshore.

15

et al. 2010) and the compensation point (25-35 µE·m-2·s-1; based on Graham et al. 1982), where

positive net production by Cladophora ceases.

The amount of light that reaches a Cladophora bed depends on depth and the

transparency of the water column at a particular site. As light moves through the water, some is

reflected back to the surface and the balance is absorbed, resulting in a cumulative attenuation of

the light received at the surface (Figure 6a). Changes in light with depth are well described by a

first order decay with an attenuation coefficient, ke (m-1). The magnitude of ke increases as

levels of dissolved color, chlorophyll (phytoplankton) and sediment increase. Light attenuation

is typically greatest at shallower depths where waves and wind mixing resuspend bottom

sediment. For the sites visited in the Ajax nearshore, light levels at the lake bottom were highest

at depths of 2.5 and 5 m, about 60% of the optimum intensity (Figure 6b). As depth increased

with increasing distance from shore, light at the lake bottom decreased in an essentially

exponential manner (Figure 6b). Application of the Great Lakes Cladophora Model (Tomlinson

et al. 2010; Auer et al. 2010) demonstrated that, at depths >10 m (offshore distance of ~1 km),

net production (growth minus loss to respiration) was negligible (Figure 6c).

With respect to temperature, Cladophora is considered to be primarily a spring species,

exhibiting optimal growth at temperatures between 13 and 17 °C (Graham et al. 1982). These

temperatures typically occur from late May to mid-June in the Lake Ontario nearshore at Ajax

(NOAA Coastwatch, Great Lakes Surface Environmental Analysis, 2009-2012). The alga is

physically robust and able to maintain attachment in the turbulent nearshore environment under

optimal growth conditions. However, later in the summer, the physical integrity of Cladophora

declines due to self-shading (Higgins et al. 2008a) and/or a transition to sub-optimal light and

water temperature conditions (Tomlinson et al. 2010). At this point, and continuing forward into

the fall, wind-driven detachment (sloughing) may occur and lead to the accumulation of

windrows of algal material on beaches. Deposits of sloughed Cladophora are known to host the

bacteria responsible for avian botulism, contribute to the persistence of human pathogens

(Verhougstraete and Rose 2014) and create conditions (e.g. odor) that interfere with human use

of the ecosystem. When entrained in cooling water intakes at power plants, algal biomass may

clog screens and filters and require suspension of operations at a cost of as much as $1 million

per day.

Taken together then, Cladophora will colonize solid bottom types to depths determined

16

0

50

100

150

200

250

300

2.5 5 10 15 20 25 30

0

0.5

1

1.5

2

2.5

3

2.5 5 10 15 20 25 30Depth (m)

Ligh

t at B

otto

m (P

AR)

Prod

uctio

n (k

gDW

/m2 /

yr)

0

5

10

15

20

25

30

0 500 1000 1500

Dept

h (m

)

Light (PAR)

30m

15m

2m

(a)

(b)

(c)

Figure 6. The underwater light field in Lake Ontario at Ajax: (a) vertical profiles at depths of 2 m, 15 m and 30 m; dashed line is compensation point, (b) light at the lake bottom for various depths across a nearshore – offshore transect and (c) model-calculated net production of Cladophora at various depths. The optimum light intensity for Cladophora is ~550 µE·m-2·s-1.

by the transparency of the water column, exhibiting maximum growth at depths of optimum light

intensity over periods of optimum water temperature. In the Ajax nearshore of Lake Ontario,

this means that Cladophora beds may develop broadly along a shore-parallel axis wherever solid

bottom types exist and extend offshore to the depth at which the requirement for light is no

longer met; for this species, at Ajax ~10 m (~1 km offshore). These characterizations of the

physical environment help to define the region potentially supporting the development of

Cladophora beds and thus area vulnerable to stimulation of growth by phosphorus addition.

3.2 Phosphorus

Phosphorus is the nutrient limiting Cladophora growth in the Great Lakes (i.e., the alga

requires a certain concentration of phosphorus in lake water in order to grow). Cladophora beds

may thus be expected to develop at sites offering favorable physical conditions (Section 3.1)

where the alga’s minimum demand for phosphorus is met. As phosphorus supplies increase at

these sites, the annual production of algal biomass increases, as does the potential to produce

nuisance conditions. Development of an understanding of the phosphorus – Cladophora

dynamic sufficient to support efficient phosphorus management decisions requires attention to

the various forms of phosphorus present and their relative abilities to support Cladophora growth

(i.e. their bioavailability).

Analytically, the entire complement of phosphorus present in the water (total phosphorus,

TP; Figure 7) consists of three fractions: soluble reactive phosphorus (SRP), dissolved organic

phosphorus (DOP) and particulate phosphorus (PP); all three forms are found in tributary and

point source discharges and the lakes and rivers that receive them. SRP is directly and

completely bioavailable and includes dissolved inorganic P (the orthophosphate ion, −34PO ) and

that portion of the DOP analyte that is easily converted (hydrolyzed) to SRP. In addition to

direct discharges, DOP may be produced through in-lake processes (e.g. excretion by plankton

and decomposition of organic detritus). DOP is not directly available to algae, but a fraction of it

(~67%; Lambert 2012) is bioavailable and may be converted to SRP through enzymatic

hydrolysis. PP is discharged directly and produced in the lake through uptake and incorporation

of SRP by the phytoplankton. PP is not directly available to Cladophora, a portion (~36%;

Lambert 2012) may be converted to SRP through physical (desorption of P from Fe/Al-rich

solids) and biological (solubilization and hydrolysis of organic-P) processes. PP may also be

transformed to SRP through the metabolic activity of mussels. Here, the potential for PP to

18

Total PhosphorusParticulate Phosphorus

Dissolved OrganicPhosphorusSoluble Reactive

Phosphorusfbio

fbiofassim

microbialtransformation

microbialtransformation

transformationby mussels

Figure 7. The total phosphorus analyte, its components and their transformation. Soluble reactive phosphorus (SRP) is the form directly available to Cladophora. A fraction of the dissolved organic P (fbio,DOP) may be made bioavailable through microbial conversion to soluble reactive P. A fraction of the particulate P (fbio,PP) may also be made bioavailable through microbial conversion to SRP. Mussels filter particulate P from the water, rejecting some as pseudofeces prior to processing and assimilating the balance (fassim) and converting it to soluble reactive phosphorus.

19

become bioavailable is determined by the degree of mussel selection (e.g. phytoplankton) or

rejection (e.g. terrigenous solids) of particulate matter (MacIsaac 1996).

When absorbed from the water by Cladophora, SRP is incorporated into biomass (tissue-

P or cell quota), partitioned for use providing physical structure and in supporting plant growth.

The fraction of tissue-P providing structure (also referred to as the minimum cell quota) has been

shown to remain constant at ~0.035% of the dry weight (DW) of the alga (Tomlinson et al. 2012;

see also Table 2). Growth rate and production increase as tissue-P increases above that

minimum, eventually approaching the maximum growth rate. Tissue-P maxima of 0.230 and

0.136 %DW have been reported for Lakes Erie and Ontario (Table 2).

Table 2. Cladophora tissue-P in Lakes Erie and Ontario.

Lake Year(s) Min (P, %DW)

Max (P, %DW)

Mean (P, %DW)

Reference

Erie 1995-2002 0.028 0.230 0.066 Higgins et al. 2005

Ontario 2008 0.044 0.136 0.072 Higgins et al. 2012

Relationships between phosphorus dynamics and Cladophora growth become

increasingly reliable as the analyte of choice becomes more closely related to the mechanisms of

growth. For example, the total phosphorus analyte, commonly applied to set trophic state

objectives (i.e. relationship between nutrients and algal abundance) in open lake environments, is

of little or no use with respect to Cladophora. This is the case because its bioavailability, and the

transformations of its component parts contributing to that bioavailability, is poorly defined.

SRP, the completely bioavailable component, serves more effectively in this regard (Figure 8a)

when concentrations are evaluated in a pseudo-steady state context, i.e. ignoring short term,

temporal dynamics. Given that SRP concentration drives algal uptake, it is not surprising that

long term exposure to SRP is well related to tissue-P content (Figure 8b). Thus the relationship

between tissue-P and growth provides the best representation of nutrient conditions driving

growth within a Cladophora bed (Figure 8c). Compared with the dynamic nature of SRP in the

water column, especially at locations proximate to point source discharges, tissue-P levels are

quite stable and thus serve well in providing an integrated representation of the nutrient

environment to which Cladophora is exposed. Both the SRP- and tissue-P growth (production)

20

0.0

0.2

0.4

0.6

0.8

1.0

0.00 0.05 0.10 0.15 0.20 0.25

Nor

mal

ized

Prod

uctio

n

Tissue-P (%DW)

0.0

0.2

0.4

0.6

0.8

1.0

0 2 4 6 8 10

Nor

mal

ized

Prod

uctio

n

SRP (µgP/L)

0.00

0.05

0.10

0.15

0.20

0.25

0 2 4 6 8 10

Tiss

ue-P

(%DW

)

SRP (µgP/L)

(a)

(b)

(c)

Figure 8. Phosphorus nutrition relationships in Cladophora as determined using the the Great Lakes Cladophora Model (Tomlinson et al. 2010): (a) SRP and growth, (b) SRP and tissue-P and (c) tissue-P and growth.

21

Cladophora is widely distributed in the Lake Ontario nearshore, with its abundance ranging from a simple presence to levels capable of creating blooms and attendant nuisance conditions. Physical conditions at the Ajax site (i.e. solid bottom for attachment, penetration of sufficient light to the lake bottom) are such that 100% coverage by Cladophora is common over a depth range of 2.5 – 10 m. In contrast to many locations on Lake Ontario, the Ajax nearshore is impacted by urban activity, and thus supports some of the highest levels of phosphorus enrichment and Cladophora biomass and production observed.

curves take the form of a rectangular hyperbola (Figures 8a and c) with the growth rate

approaching its maximum as SRP (2 µgP/L) and tissue-P (0.15 %DW) concentrations reach

saturating levels.

4. Cladophora Occurrence, Distribution and Abundance

Cladophora is a member of the community of attached algae which occupy physically-

suitable nearshore habitat across the Great Lakes. Ulothrix is common in the phosphorus-poor

waters of Lake Superior, Chara in extreme northern Lake Michigan and Lake Huron and

Cladophora in parts of Lake Huron, the balance of Lake Michigan and in Lakes Erie and

Ontario. Cladophora is broadly distributed across the Lake Ontario nearshore, with its presence

clearly evident in interpreted satellite images (Figure 9). However, presence alone provides little

information regarding Cladophora abundance (standing crop, gDW·m-2) or production (gDW·m-

2·yr-1) and it is these, not presence, that fouls beaches and clogs water intakes.

The presence and distribution of Cladophora in the Great Lakes may be driven by local

phosphorus sources, by whole lake levels of phosphorus or by combinations of the two. In the

1970s and 1980s, Cladophora growth was driven by local sources in Lakes Huron and Michigan

(i.e. open water phosphorus concentrations were insufficient to support development of

Cladophora beds) and by whole lake conditions in Lakes Erie and Ontario (i.e. phosphorus

concentrations in the open lake water were sufficient to support development of Cladophora

beds). Today, management efforts have reduced SRP concentrations in Lake Ontario to levels

where the system is in transition from whole lake to local source forcing. This change is

particularly evident in differences in the mean and maximum abundance of Cladophora in Lakes

Erie and Ontario (Table 3), and in the strong correlation between Cladophora abundance and

urban influences (as represented by conductivity levels) recently documented for Lake Ontario

22

Oak Orchard, NY

Ajax, Ontario

Mexico Bay, NY

Figure 9. Distribution of Cladophora at selected sites on Lake Ontario (light and dark green = Cladophora beds present; tan = Cladophora beds absent. Images obtained from Michigan Tech Research Institute: http://geodjango.mtri.org/static/sav/.

23

(Figure 10, Higgins et al. 2012). The strength of this relationship (r2 = 0.8964, n=7; Higgins et

al. 2012) clearly points to the importance of local sources of phosphorus in stimulating the

development of Cladophora beds in certain nearshore waters.

Table 3. Standing crop of Cladophora (gDW·m-2) in Lakes Erie and Ontario.

Lake Year(s) Min Max Mean Reference

Erie 1995-2002 1 600 197 Higgins et al. 2005

Ontario 2008 19 93 47 Higgins et al. 2012

Of the seven sites on Lake Ontario surveyed by Higgins et al. (2012; Figure 5), the Ajax

nearshore ranked 1st in urban influence (conductivity), 1st in Cladophora biomass and 2nd in

phosphorus nutritional status (tissue P; behind Toronto).

The spatial distribution of Cladophora beds in the Ajax nearshore is consistent with what would

be predicted based on satellite imagery (Figure 3), bottom type (side scan sonar surveys; Figure

5) and levels of light penetration (Figure 6). High definition video acquired through remotely

operated vehicle surveys (Figure 4) show that Cladophora blankets the lake bottom along the

Ajax nearshore, achieving ~100% coverage to a depth of between 10 and 15 m (1.0 - 1.4 km

offshore) wherever solid substrate is available. Cladophora beds are sparsely populated at 15

and 20 m and the alga is absent at depths of 25 m and beyond despite the presence of extensive

mussel beds. Here, Cladophora has become light limited (Figure 6). The occurrence of

nuisance conditions, anticipated given the work of Higgins et al. (2012) and the more spatially

extensive monitoring results presented here, is well documented (Figure 11).

Thus, it may be concluded that Cladophora is widely distributed in the Ajax nearshore,

achieving 100% bottom coverage over a depth range of 2.5 – 10 m wherever solid substrate is

present and resulting in the occurrence of nuisance conditions on the beaches. Field observations

reported here are consistent with the local source, urban phosphorus enrichment paradigm of

Higgins et al. (2012). Management of these conditions suggests quantification of the provenance

of that phosphorus enrichment as an appropriate next step.

24

0

20

40

60

80

100

120

0.00 0.05 0.10 0.15

R2 = 0.8964

Tissue-P (%DW)

Clad

opho

raBi

omas

s (gD

W·m

-2)

minimumcell

quota

Figure 10. The relationship between Cladophora biomass and tissue-P for samples collected from Lake Ontario by Higgins et al. (2012).

25

(a)

(c)

(b)

(d)

Figure 11. Sloughed, decomposing Cladophora at the Ajax waterfront. Images (a-c) by Paul Wealleans, Ajax; image (d) by Jamey Anderson, Michigan Tech.

26

As the nutrient limiting the growth of Cladophora in the Great Lakes, phosphorus (particularly bioavailable phosphorus, is the appropriate focus for management of nuisance. Identification of the provenance of the phosphorus stimulating growth in the Ajax nearshore is the necessary first step in supporting management. The Duffin WPCP discharges 85% of the total phosphorus (TP) and 98% of the SRP to the Ajax nearshore and does so at a location where physical conditions (solid bottom type, light environment) are as required to support development of Cladophora beds.

Tributary inputs make up most of the balance of phosphorus loads, but are minor in their contribution and would be expected to have a lesser bioavailability than WPCP effluent. Phosphorus levels in the open waters of Lake Ontario have decreased markedly since 1980 and today support the presence, but not nuisance growth, of the alga. There is no evidence that phosphorus sources in adjacent communities impact conditions at Ajax.

Mussels certainly contribute to the areal extent and vigor of Cladophora growth, but they do so through modification of physical conditions and through transformation of phosphorus from various sources; mussels are not, in and of themselves, a source of phosphorus.

The Duffin Creek WPCP effluent is, therefore, the appropriate focus for remediation of nuisance conditions of Cladophora growth in the Ajax nearshore.

5. Phosphorus Provenance

Satellite mapping of Cladophora beds, near bottom ROV imaging of algal abundance and

stakeholder reports of deposits of malodorous, decomposing algal biomass confirm the existence

of nuisance conditions at Ajax, Ontario predicted from the observations of Higgins et al. (2012).

Where the required physical conditions are present (Section 3.1), the presence of Cladophora,

the density of algal biomass within Cladophora beds and the amount of Cladophora biomass

produced annually is governed by the availability of phosphorus, the growth limiting nutrient in

the Great Lakes. Management of nuisance conditions of Cladophora growth requires that the

sources of phosphorus, i.e. their provenance, be identified. For Lake Ontario at Ajax, Ontario,

these sources potentially include exchange with offshore waters, delivery by longshore transport

and inputs from point and nonpoint discharges (Figure 12).

27

Figure 12. Examples of phosphorus sources to the Ajax, Ontario nearshore.

offshore exchange

nonpointsource(tributary,Duffins Creek)

nonpointsource(stormwater)

point source(Duffin CreekWPCP outfall)

Duffin CreekWPCP

City ofPickering

Town of Ajax

Lake Ontario

28

5.1 Offshore Boundary

Where concentrations of SRP are high lakewide, such as Lake Erie, nuisance levels of

Cladophora growth are considered to be whole lake forced, i.e. such conditions occur wherever

suitable physical conditions are present (Section 3.1). The whole lake forcing of Cladophora

growth characteristic of the 1970s and 1980s is now in transition to local source forcing as a

result of successful efforts to manage phosphorus loads to Lake Ontario (Figure 13). SRP

concentrations at an open lake Environment Canada station 22 km offshore of Ajax, Ontario

have fallen from 9.6 µgP/L in 1980 to as low as 1.0 µgP/L in 2001-2003 (Figure 13a) and are

averaging 1.5 µgP/L since 2001. While additional sampling is necessary to more clearly

define SRP boundary conditions at Ajax, it is clear that offshore concentrations are now in the

region of P-limitation (Figure 8a) and Lake Ontario has shifted from being driven by whole lake

phosphorus levels to being driven by local and regional inputs.

Successful phosphorus management achieved at a whole lake level for Lake Ontario is

evident at sites in the nearshore not impacted by urban influences. For example, Cladophora

beds at Oak Orchard and Mexico Bay, New York exhibit low algal biomass and P-stressed

physiologies (Higgins et al. 2012). Even at Ajax, Ontario, a location with urban impacts, low

SRP levels have been reported: 50-75% of the SRP values measured in the Ajax nearshore by

Leon et al. (2008) fell within the P-limiting concentration range characteristic of offshore waters

(Figure 14).

Thus, while SRP levels in the offshore waters of Lake Ontario are sufficient to support

the presence of Cladophora, they are no longer able to support nuisance growth. Higgins et al.

(2012) recognized this, proposing that “effective management of Cladophora blooms in Lake

Ontario should occur through managing P loading at local scales while ensuring lake-wide P

concentrations do not increase.”

5.2 Longshore Boundary

Substances such as phosphorus, discharged at one point along the Lake Ontario shoreline,

may be moved in a shore-parallel (longshore) manner by the action of currents and diffusive

mixing (mass transport). Currents in the Ajax, Ontario portion of the Lake Ontario nearshore are

move most often west → east (35-40% of the time) and east → west (25-30% of the time; Figure

15). Candidate sources for phosphorus exchange would include the Corbett Creek WPCP (13

km east of Ajax; annual TP load 0.12 times that of the Duffin Creek WPCP) and the Highland

29

Figure 13. Long term variation in the spring (Mar-Apr) SRP offshore boundary condition in Lake Ontario. Solid and dashed lines are the mean ± S.D. for the 2001-2010 interval. Environment Canada data provided by Alice Dove.

0

2

4

6

8

10

solu

ble

reac

tive

P (µ

gP/L

)

1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

30

0

1

2

3

4

5

6

7

8

0

1

2

3

4

5

6

7

8

solu

ble

reac

tive

P (µ

gP/L

)so

lubl

e re

activ

e P

(µgP

/L)

2007

2008

Figure 14. Spring soluble reactive phosphorus concentrations across the Ajax nearshore of Lake Ontario (data of Leon et al. 2008). Lines represent the mean ± 1 S.D. offshore SRP concentration for 2001-2010.

31

N

NE

E

SE

S

SW

W

NW

40%

30%

20%

10%

Figure 15. Direction of transport by currents in the Ajax nearshore of Lake Ontario, May-Aug 2010. Compass direction indicates the heading of the current, e.g. E = current heading west to east.

32

Creek WPCP (10 km west of Ajax; annual TP load 1.69 times that of the Duffin Creek WPCP).

Auer (2011) reviewed a conservative substance tracer database (conductivity, 23 dates in 2007-

2008) developed by the Toronto Region Conservation Authority and partners and found no clear

evidence of longshore exchange. A similar review of a soluble reactive phosphorus database

developed by Leon et al. (2008; 8 dates in 2007) noted that SRP levels at a single station on the

eastern boundary of the Ajax nearshore exceeded concentrations meaningful for Cladophora

management (0.5-2 µgP/L) on six of eight occasions and were saturating for Cladophora growth

(>2 µgP/L) on two occasions. Given the magnitude of the Corbett Creek WPCP TP load (8%

that of the Duffin Creek WPCP) and its distance from the Ajax nearshore, it is unlikely that

longshore transport would be responsible for elevated SRP Levels near Ajax; it is more likely

that the SRP elevation in the Ajax nearshore was due to a local source, e.g. the Duffin Creek

WPCP discharge. No elevations in SRP concentration were observed at the western boundary,

suggesting that the Highland Creek WPCP had no effect on SRP conditions in the Ajax

nearshore.

5.3 Nonpoint Source Inputs

Nonpoint source inputs to the Ajax nearshore include direct runoff, stormwater outfalls

and discharges from Duffins and Carruthers Creeks. At the recommendation of TRCA and its

partners, Auer (2011) focused on Duffins and Carruthers Creeks, calculating TP loads during

periods favorable for Cladophora growth in the summer (Jun → Sep) of 2007-2009. The

resulting TP loads were 34.3 and 3.7 kgP/d for Duffins and Carruthers Creeks, respectively.

These values compare favorably with the annual TP loads in 2008 calculated for Duffins (40.5

kgP/d) and Carruthers (3.0 kgP/d) Creeks by Makarewicz et al. (2012) and for Duffins Creek

(45.2 kgP/yr) calculated for the 1990-2010 interval by Malkin et al. (2010). Annual loads would

be expected to be higher than summer loads, as the annual timeframe would include more wet

weather events (see Malkin et al., 2010, Figure 7b).

Booty et al. (2013) used an event-based data set to calculate annual TP loads for Duffins

Creek. The annual estimate for TP loads in a normal to dry year (41 kgP/d, 2007) was similar to

loads described above, however, loads for a wet year (2008, 178 kgP/d) and a wet year with an

extreme event (2009, 221 kgP/d) were much higher. While an annual, event-based approach

may improve the quality of loading estimates for Lake Ontario as a whole, their application may

be misleading when applied to understanding phosphorus provenance related to Cladophora. In

33

particular, the wet weather events that contribute to high annual loads occur most frequently

during months where conditions are unfavorable for Cladophora growth (e.g. Dec-Apr, Figure

16) and the phosphorus so delivered is transported from the nearshore within a few days of its

receipt at current velocities characteristic of the region (NOAA Great Lakes Coastal Forecasting

System). It is concluded that the summer TP load of 34.3 kgP/d (Auer 2011) most appropriately

characterizes the contribution of Duffins Creek during the period of active Cladophora growth.

Summer SRP loads for 2007-2009 were calculated by Auer (2011) to be 2.09 and 0.35

kgP/d for Duffins and Carruthers Creeks, respectively. Malkin et al. (2010) estimated annual

SRP loads for Duffins Creek to be 4.7 kgP/d (1990-2010); again, higher because they were

calculated over an interval that would include more wet weather events. The TP and SRP loads

from Duffins Creek have declined dramatically (55% and 92%, for TP and SRP, respectively)

since the 1980s. Decommissioning of two WPCPs previously discharging to Duffins Creek

(flow transferred to Duffin Creek WPCP in 1980) and implementation of nonpoint source

controls are likely reasons for the documented reductions.

Based on the estimates of Auer (2011), loads from Duffins and Carruthers Creeks account

for 16% and <3% of the TP and SRP loads to the Ajax nearshore, with the balance contributed

by the Duffin Creek WPCP’s contemporary discharge (see Section 5.4 following). Using the

approved ECA loading limit for the Duffin Creek WPCP (311 kgP/d; CH2M Hill 2013), the

tributary contribution to phosphorus loads would drop to 10% for TP and 2% for SRP, assuming

a constant SRP:TP ratio). Of a relatively small magnitude on a mass basis, the tributary loads

were also calculated to be negligible in their impact on an areal basis (two dimensional model;

Auer 2011).

5.4 Point Source Input

The Ajax nearshore receives input from a single point source, the Duffin Creek WPCP.

This facility discharges 358,805 m3/d (average, Jan-Jun 2013) of treated effluent to Lake Ontario

via an outfall located ~1 km offshore of the WPCP at a depth of 9 m. Average effluent TP and

SRP concentrations for the Jan-Jun 2013 interval were 303 and 156 µgP/L, respectively.

5.4.1 Loading to the Ajax nearshore

The summer and annual average TP loads for the Duffin Creek WPCP are 217 (Auer

2011) and 249 (Makarewicz et al. 2012) kgP/d, respectively. The summer SRP load is 107

kgP/d (Auer 2011). Including Duffins and Carruthers Creeks as contributors to the Ajax

34

0

10

20

30

40

50

60

0

10

20

30

40

50

60

0

10

20

30

40

50

60

Flow

(m3 /

s)Fl

ow (m

3 /s)

Flow

(m3 /

s)

J F M A M J J A S O N D

J F M A M J J A S O N D

J F M A M J J A S O N D

2007

2008

2009

Figure 16. Duffins Creek hydrologic record for 2007-2009 illustrating reduced frequency of wet weather events contributing to annual phosphorus loads during the Cladophora growing season (green overlay). Source: Environment Canada, Water Survey of Canada.

35

nearshore, the Duffin Creek WPCP accounts for 85% of the TP and 98% of the SRP load. With

the approved ECA TP loading limit (311 kgP/d; CH2M Hill 2013), the Duffin Creek WPCP

contribution would be 89% for TP and 98% for SRP (assuming a constant SRP:TP ratio). No

calculations were performed for the 2010-2012 interval (a period of reduced phosphorus

discharge at the Duffin Creek WPCP) because the required information was not included in the

ESR.

5.4.2 Mass transport

The Duffin Creek WPCP is, by an overwhelming margin, the largest contributor of TP

and SRP to the Ajax nearshore. The offshore outfall discharges effluent directly to habitat with

the solid substrate and light environment required to support development of Cladophora beds

(Figure 17). Beyond this immediate point discharge, the impact of the Duffin Creek WPCP is

determined by the extent to which phosphorus is transported along the lakeshore through

diffusive (dilution) and advective (currents) mass transport.

The role of mass transport is examined here through the results of mapping studies of the

Duffin Creek WPCP plume conducted in August of 2013. Three dimensional mapping was

performed by acquiring spatially intensive vertical profiles at 117 (9 August 2013) and 55 (29

August 2013) stations, yielding a database of 1891 and 1031 observations for the two dates,

respectively. The target analyte for the mapping surveys was nitrate (Satlantic ISUS sensor), a

substance considered conservative in this application and thus useful in tracking the transport

and dilution of this nitrate-rich discharge. Measurements were made along eight transects

extending outward from the buoy marking the Duffin Creek WPCP discharge. The contribution

of the effluent to water column nitrate concentrations (termed % effluent) was calculated by,

100%min,max,

min,

33

33 ⋅−

−=

//

//

ONON

ONON

CCCC

where 3NOC is the nitrate concentration (µgN/L) measured at a particular site, max,3NOC is the

maximum nitrate concentration (µgN/L) measured in proximity to the Duffin Creek WPCP

outfall and min,3NOC (µgN/L) is the minimum nitrate concentration measured lakeward of the

Duffin Creek WPCP outfall. Values for max,3NOC and min,3NOC varied between surveys: 2454 and

266 µgN/L on 8/9/2013 and 1345 and 203 µgN/L on 8/29/2013.

36

Figure 17. Cladophora habitat in the Ajax nearshore as categorized by depth and offshore distance. From the shore lakeward to a depth of 10-15 m, the lake bottom is largely populated by cobbles and boulders with 100% colonization by Cladophora Some patches of sand exist in this region (see Figure 3). Continuing lakeward to a depth of ~25 m, less solid bottom material is observed (more sand), light at bottom becomes sub-optimal and Cladophora beds are sparse. From a depth of 25 m offshore, the bottom is sand with mussel beds and no Cladophora is present due to light limitation. The yellow triangle indicates the position of the Duffin Creek WPCP outfall.

Duffin Creek WPCP outfall

Duffin CreekWPCP

Town of Ajax

37

In addition, paired samples were collected at 11 stations/depths during the 8/29/2013 survey for

SRP. These results were regressed against the nitrate concentration measured at that

station/depth (Figure 18). The equation describing that regression was then applied to the nitrate

data base from 8/9 and 8/29 to yield companion estimated SRP data sets. Those data were

interpolated in space and assigned to bins representing (1) conditions unimpacted by the plume,

i.e. those associated with offshore waters, (b) conditions where the plume stimulated Cladophora

growth, i.e. increased growth rates above those of the unimpacted condition and (c) conditions

where the phosphorus nutrition of Cladophora is saturated and growth can be increased no

further.

Survey results are presented here as discrete station/depth measurements (spider plots,

Figures 19 and 20), as interpolated nitrate plots describing the distribution of the effluent plume

(Figures 21 and 22) and as interpolated estimated SRP plots describing the impact of the plume

of phosphorus nutrition and Cladophora growth (Figures 23 and 24). Four findings have

emerged from analysis of these measurements. Examination of survey results presented as

‘spider plots’ (8/9, Figure 19; 8/29, Figure 20), demonstrates that mass transport conditions

during the two surveys were similar and revealed that,

Finding 1. The location and shape of the plume on these survey dates reflect east → west mass transport of the effluent discharge along the Ajax waterfront; and

Finding 2. On these dates, the Duffin Creek WPCP plume is most prominently positioned at depths of 5.5 – 7 m, a phenomenon termed “interflow’.

Interpolation of the nitrate data set (Figures 21 and 22) makes it further evident that,

Finding 3. Plume-enriched lake water (5-15% effluent) is, during these surveys, resident at locations having bottom types and a light climate that support the development of Cladophora beds. Further, this plume extends completely to the shoreline.

Finally, based on interpolations of estimated SRP levels (Figures 23 and 24), it is apparent that,

Finding 4. Phosphorus delivered by the plume stimulates Cladophora growth above that supported by contact with offshore waters and, at some locations, supports nutrient-saturated growth.

38

R² = 0.7634

0

2

4

6

8

10

0 200 400 600 800Nitrate (µgN/L)

Solu

ble

Reac

tive

P (µ

gP/L

)

Figure 18. The relationship between measured values of nitrate and soluble reactive phosphorus used to develop estimates of SRP for plume mapping.

39

(a) 0.5 – 1.0 m

(b) 5.5 – 6.0 m

Figure 19. Spider plots, nitrate plume survey, 8/9/2013: (a) surface water, (b) mid-depth and (c) all depths.

40

% Effluent: 0-2% 2-5% 5-10% 10-15% 15-25% >25%

0.5-1.0 m 1.5-2.0 m 2.5-3.0 m

3.5-4.0 m 4.5-5.0 m 5.5-6.0 m

6.5-7.0 m 7.5-8.0 m 8.5-9.0 m

Figure 19. Spider plots, nitrate plume survey, 8/9/2013 - continued: (a) surface water, (b) mid-depth and (c) all depths.

41

(a) 0.5 – 1.0 m

(b) 5.5 – 6.0 m

Figure 20. Spider plots, nitrate plume survey, 8/29/2013: (a) surface water, (b) mid-depth and (c) all depths (next page).

42

Figure 20. Spider plots, nitrate plume survey, 8/29/2013 - continued: (a) surface water, (b) mid-depth and (c) all depths.

0.5-1.0 m 1.5-2.0 m 2.5-3.0 m

3.5-4.0 m 4.5-5.0 m 5.5-6.0 m

6.5-7.0 m 7.5-8.0 m 8.5-9.0 m

43

(a) 0.5 – 1.0 m

(b) 4.5 – 5.0 m

Figure 21. 2D plots, nitrate plume survey, 8/9/2013: (a) surface water, (b) mid-depth and (c) all depths.

44

Figure 21. 2D plots, nitrate plume survey, 8/9/2013 - continued: (a) surface water, (b) mid-depth and (c) all depths.

0.5-1.0 m 1.5-2.0 m 2.5-3.0 m

3.5-4.0 m 4.5-5.0 m 5.5-6.0 m

6.5-7.0 m 7.5-8.0 m 8.5-9.0 m

45

(a) 0.5 – 1.0 m

(b) 6.5 – 7.0 m

Figure 22. 2D plots, nitrate plume survey, 8/29/2013: (a) surface water, (b) mid-depth and (c) all depths.

46

Figure 22. 2D plots, nitrate plume survey, 8/29/2013 - continued: (a) surface water, (b) mid-depth and (c) all depths.

0.5-1.0 m 1.5-2.0 m 2.5-3.0 m

3.5-4.0 m 4.5-5.0 m 5.5-6.0 m

6.5-7.0 m 7.5-8.0 m 8.5-9.0 m

47

(a) 0.5 – 1.0 m

(b) 5.5 – 6.0 m

Figure 23. Impact of the Duffin Creek WPCP plume on soluble reactive phosphorus concentrations in the Ajax nearshore on 8/9/2013. Three levels of impact are identified: unimpacted (SRP levels are those of offshore waters); stimulated (SRP levels are increased above those of offshore waters within the range sensitive to elevation of phosphorus concentration); and saturated (SRP levels are increased above those of offshore waters to concentrations supporting the maximum possible rate of Cladophora growth).

48

0.5-1.0 m 1.5-2.0 m 2.5-3.0 m

3.5-4.0 m 4.5-5.0 m 5.5-6.0 m

6.5-7.0 m 7.5-8.0 m 8.5-9.0 m

Figure 23. Continued. Impact of the Duffin Creek WPCP plume on soluble reactive phosphorus concentrations in the Ajax nearshore on 8/9/2013. Three levels of impact are identified: unimpacted (SRP levels are those of offshore waters); stimulated (SRP levels are increased above those of offshore waters within the range sensitive to elevation of phosphorus concentration); and saturated (SRP levels are increased above those of offshore waters to concentrations supporting the maximum possible rate of Cladophora growth). Legend as in Panels (a) and (b) of this figure.

49

(a) 0.5 – 1.0 m

(b) 6.5 – 7.0 m

Figure 24. Impact of the Duffin Creek WPCP plume on soluble reactive phosphorus concentrations in the Ajax nearshore on 8/29/2013. Three levels of impact are identified: unimpacted (SRP levels are those of offshore waters); stimulated (SRP levels are increased above those of offshore waters within the range sensitive to elevation of phosphorus concentration); and saturated (SRP levels are increased above those of offshore waters to concentrations supporting the maximum possible rate of Cladophora growth).

50

0.5-1.0 m 1.5-2.0 m 2.5-3.0 m

3.5-4.0 m 4.5-5.0 m 5.5-6.0 m

6.5-7.0 m 7.5-8.0 m 8.5-9.0 m

Figure 24. Continued. Impact of the Duffin Creek WPCP plume on soluble reactive phosphorus concentrations in the Ajax nearshore on 8/29/2013. Three levels of impact are identified: unimpacted (SRP levels are those of offshore waters); stimulated (SRP levels are increased above those of offshore waters within the range sensitive to elevation of phosphorus concentration); and saturated (SRP levels are increased above those of offshore waters to concentrations supporting the maximum possible rate of Cladophora growth). Legend as in Panels (a) and (b) of this figure.

51

It is concluded from these findings that,

Conclusion 1. The effluent plume from the Duffin Creek WPCP discharge stimulates Cladophora growth in the Ajax nearshore and, at certain times and locations, saturates the phosphorus reserves of the alga, resulting in maximum rates of growth and production.

Less well defined is the shore-parallel (east-west) extent of phosphorus stimulation of

Cladophora growth associated with the Duffin Creek WPCP plume. The definition of the plume

provided here is for two dates, however, the distribution of the effluent in the nearshore is acted

upon by diffusive and advective mass transport over longer (e.g. weekly, monthly) time frames.

In addition, phosphorus-enriched effluent is distributed vertically in a non-homogenous manner

(see cross-section, Figure 25) due to differences in density between the effluent plume and

ambient lake water (the interflow phenomenon). The potential for distribution of phosphorus

across the Ajax nearshore may then be visualized as being analogous to that of a lawn sprinkler

turning on its axis (Figure 25) to distribute phosphorus across Cladophora beds in the onshore,

shore-parallel and offshore directions (Figure 26). Thus the ability to directly observe and

document the Duffin Creek WPCP plume’s presence along the Ajax nearshore requires water

sampling conducted for the full range of current direction scenarios. However, a memory of

plume presence is retained in, and reflected by, the stored phosphorus (tissue-P) content of the

alga.

5.4.3 Tissue-P distribution

While plume surveys provide a direct and definitive characterization of effluent impact,

the position and distribution of the plume is dynamic, potentially changing on a daily basis as the

winds driving mass transport shift. Here, the integrative capacity of tissue-P (Section 3.2) can

provide valuable insight. Cladophora has the capacity for luxury uptake, i.e. it can take up and

store phosphorus beyond its immediate requirement for growth. Because the rate of phosphorus

uptake (minutes to hours) greatly exceeds that for depletion due to growth (days to weeks), the

tissue-P content of the alga provides an integration of the ambient nutrient environment, which is

difficult if not impossible to obtain through conventional water column monitoring.

Higgins et al. (2012) successfully utilized tissue-P as a metric of the phosphorus nutrition

of Cladophora at sites on Lake Ontario having different degrees of urban impact. A tissue-P

52

% Effluent

shore open lake →

Duffin WPCP discharge(1 km offshore, 9 m depth)

Figure 25. Cross-sectional representation of the plume from the Duffin WPCP on 8/9/2013. Differences in temperature (density) dictate the vertical position of the plume: at the surface when the lake water is cool (overflow) and at mid- or bottom-depths when the lake water is warm (interflow, underflow). The case presented here illustrates the interflow condition.

53

currents moving east → west currents moving west → east

currents moving onshore

currents moving offshore

Figure 26. Illustration of how the plume from an offshore discharge point such as a WPCP outfall may migrate in response to changes in current direction. The red oval identifies the discharge locations; warmer colors (orange, yellow, green) indicate higher concentrations.

54

survey was conducted in August 2013 along the Ajax nearshore and at a control site near

Cobourg, Ontario, a location characterized by Higgins et al. (2012) as having low urban impact.

Cladophora samples were collected at a depth of 5 m by Remotely Operated Vehicle and by

hand at a buoy marking the Duffin Creek WPCP outfall. Tissue-P content at the outfall buoy

exceeded that of other locations in the Ajax nearshore by a factor of 4-8 (Figure 27a) and

exceeded maximum levels reported for Lakes Erie and Ontario (see Table 2) by factors of

approximately 2 and 4, respectively (Table 2). When viewed in the absence of the outfall buoy

measurement (Figure 27b), a clearer pattern of the distribution of tissue-P emerges. The highest

tissue-P concentration is observed in the immediate vicinity of the outfall and concentrations

then fall with distance from the outfall. The fact that tissue-P levels decrease, and do so

systematically, with distance from the outfall, calls into question the potential impact of sources

to the east and west of Ajax (the longshore boundary condition). The tissue-P content of

Cladophora remains above the minimum cell quota (see Section 3.2) at the east and west limits

of the Ajax nearshore, with a surplus phosphorus content (i.e. elevation above the minimum cell

quota) 1.4 – 1.8 times that of the Cobourg control. The pattern of the tissue-P distribution is

consistent with a conclusion that the Duffin Creek WPCP outfall is the driving force for

Cladophora growth and production in the Ajax nearshore.

Conclusion 2. Phosphorus contained in the effluent discharged by the Duffin WPCP increases the stored P content of Cladophora, stimulating growth potential across the entire Ajax nearshore and, at certain locations, saturating phosphorus reserves and supporting maximum algal growth.

Results from the Ajax tissue-P survey are examined within the context of similar

measurements made at various sites on Lake Ontario by Higgins et al. (2012) in Figure 28. It

was the conclusion of that study that higher levels of phosphorus reserves and a larger amount of

algal biomass would be associated with sites having a greater degree of urban impact. The

comparison offered in Figure 28 affirms the conclusion of Higgins et al. (2012) that phosphorus

reserves at Ajax are among the most enriched in Lake Ontario, far exceeding those at sites less

impacted by urban activity and thus representing a response to local P sources rather than whole-

lake nutrient conditions. Noting that Cladophora growth is proportional to tissue-P content

(Figure 8c), this elevation of phosphorus reserves is seen as the factor stimulating production and

the attendant potential for beach accumulation of algal biomass presently observed at Ajax.

55

Figure 27. Distribution of Cladophora tissue-P along the Ajax nearshore and at Cobourg, ON: (a) including and (b) excluding the measurement at the Duffin Creek WPCP outfall. Dashed line indicates minimum cell quota. Inset at center identifies sampling locations; the Duffin Creek WPCP outfall is located offshore of and between the W and WM stations.

0

0.1

0.2

0.3

0.4

0.5

W WPCP WM M EM E COB

Tiss

ue P

hosp

horu

s (P

as %

DW

)Ti

ssue

Pho

spho

rus (

P as

% D

W)

(a)

(b)

Tiss

ue P

hosp

horu

s (P

as %

DW

)

0.00

0.05

0.10

0.15

W WM M EM E COB

(a)

(b)

W5M WM5M

MID5MEM5M

E5MDuffin Creek

WPCP

Town of Ajax

56

AjaxDuffin WPCP Buoy

Ajax – WM, Toronto

Ajax - EM

Ajax - W

Oak Orchard

Ajax - E

Ajax - M

Cobourg

Mexico Bay

Ajax

Grimsby

Cobourg, Rochester

0.0

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4 0.6

Nor

mal

ized

Prod

uctio

n

Tissue-P (P as %DW)

Figure 28. Tissue-P content of Cladophora in Lake Ontario as measured by Higgins et al. (2012; yellow) and in the August 2013 survey of the Ajax, ON nearshore (white) identified on the tissue-P / production potential relationship originally presented as Figure 8c.

57

Conclusion 3. Phosphorus nutrition along the Ajax nearshore is enriched well above levels characteristic of sites on Lake Ontario less impacted by urban activity.

At present, the Duffin Creek WPCP plume overlays suitable habitat in a manner that stimulates,

and in some cases, P-saturates Cladophora growth (Figure 29). For the Jan-Jun interval of 2013,

the Duffin Creek WPCP discharge volume was 359 MLD, carrying a TP load of 109 kgP/d.

Under the approved EAC, the discharge volume can increase by 75% to 630 MLD and the TP

load by a factor of 2.85 to 311 kgP/d. A commensurate increase in SRP would be anticipated.

The impact of this would be to move levels of phosphorus nutrition at some presently impacted

sites from stimulated to saturated and to increase the extent over which Cladophora growth in

the Ajax lakefront will be influenced by the Duffin Creek WPCP discharge.

58

Figure 29. Cladophora habitat in the Ajax nearshore overlain with the Duffin Creek WPCP plume; 8/9/2013 at a depth of 4.5-5.0 m.

59

Literature Cited Auer, M.T. 2011. Monitoring, modeling and management of nearshore water quality in the

Ajax-Pickering region of Lake Ontario. Submitted to the Toronto Region Conservation Authority, 93 pp.

Auer, M.T., Tomlinson, L.M., Higgins, S.N., Malkin, S.Y., Howell, E.T. and H.A. Bootsma. 2010. Great Lakes Cladophora in the 21st Century: Same alga – different ecosystem. Journal of Great Lakes Research, 36: 248-255.

CH2M Hill. 2013. Class Environmental Assessment to Address Outfall Capacity Limitations at the Duffin Creek Water Pollution Control Plant. Prepared for the Municipalities of Durham and York, 318 pp.

Graham, J.M., Auer, M.T., Canale, R.P., and J.P. Hoffman. 1982. Ecological studies and mathematical modeling of Cladophora in Lake Huron: 4. Photosynthesis and respiration as function of light and temperature. Journal of Great Lakes Research, 8(1):100-111.

Higgins, S.N., Howell, E.T., Hecky, R.E., Guildford, S.J. and R.E. Smith. 2005. The Wall of Green: The status of Cladophora glomerata on the northern shores of Lake Erie’s eastern basin, 1995–2002. Journal of Great Lakes Research, 31: 547-563.

Higgins, S.N., Hecky, R.E. and Guildford, S.J. 2005. The collapse of benthic macroalgal blooms in response to self-shading. Freshwater Biology, 53(12): 2557-2572.

Higgins, S.N., Pennuto, C.M., Howell, E.T., Lewis, T.W. and Makarewicz, J.C. 2012. Urban influences on Cladophora blooms in Lake Ontario. Journal of Great Lakes Research, 38 (Supplement 4): 116-123.

Lambert, R.S. 2012. Great Lakes tributary phosphorus bioavailability. M.S. Thesis, Department of Civil and Environmental Engineering, Michigan Technological University, Houghton, MI, 39 pp.

Leon, L.F., Smith, R. and Hecky, R.E. 2008. 3D Hydrodynamic and Ecological Modelling. Report submitted to Ontario Power Generation and the Regions of York and Durham. University of Waterloo, Waterloo, Ontario.

MacIsaac, H.J. 1996. Potential abiotic and biotic impacts of zebra mussels on the inland waters of North America. American Zoologist, 36: 287-299.

Makarewicz, J.C., Booty, W.G. and Bowen, G.S. 2012. Tributary phosphorus loading to Lake Ontario. Journal of Great Lakes Research, 38 (Supplement 4): 14-20.

Malkin, S.Y., Dove, A., Depew, D., Smith, R.E., Guildford, S.J. and Hecky, R.E. 2010. Spatiotemporal patterns of water quality in Lake Ontario and their implications for nuisance growth of Cladophora. Journal of Great Lakes Research, 36: 477-489.

Tomlinson, L.M., Auer, M.T. and H.A. Bootsma. 2010. The Great Lakes Cladophora Model: Development and application to Lake Michigan. Journal of Great Lakes Research, 36: 287-297.

60

Verhougstraete, M.P. and Rose, J.B. 2014. Microbial investigations of water, sediment, and algal mats in the mixed use watershed of Saginaw Bay, Michigan. In Press. Journal of Great Lakes Research.