Large freshwater and marine ecosystems suffer from a variety of anthropogenic stressors which include eutrophication, chemical contamination, coastal degradation and overexploitation of fisheries to name only a few. Attempts at remediation are often confounded by the multitude of local, regional, national and international governments and agencies that exercise jurisdiction over smaller parts of these ecosystems. In the North American Great Lakes, there exists a (nearly) 40 year track record for international cooperation in managing anthropogenic stressors that emphasizes sound ecosystem based science. Among these efforts was the designation of 42 severely polluted coastal regions as Areas of Concern (AoCs) which were deemed to have at least 1 of 14 possible Beneficial Use Impairments. The Bay of Quinte, Lake Ontario, is one AoC with 10 listed impairments. We used a “battery of tests” strategy to assess the health of the bay with respect to the impairments of “eutrophication or undesirable algae” and “degradation of phytoplankton and zooplankton communities” in the bay. This strategy integrates structural, functional and chemical parameters into established ecosystem health models. The results of the battery of tests showed continued eutrophication of the bay and not coincidentally, continued degradation of the phytoplankton community. We also found that point sources of phosphorous do not account for all of the (pelagic) primary production observed in the bay and suggest that non-point sources of phosphorous contribute significantly to eutrophication. Our results further suggest that the battery of tests strategy is a sensitive science-based tool for assessing ecosystem health. These tests could also be applied to the evaluation of ecosystem health in other Great Lakes AoCs as well as large lakes and marine environments where cultural eutrophication is a problem.

Introduction

The North American Great Lakes are an immense global aquatic resource, covering 245,000 km2 and accounting for an estimated 20% of the global supply of freshwater (Beeton, 1984). The lakes are shared by Canada and the United States, are home to over 30 million people in both countries and have been estimated to contribute more than $2 trillion U.S. to the regional and global economy (Environment Canada and the United States Environmental Protection Agency, 1995). The Great Lakes have also been subject to multiple anthropogenic stressors including chemical pollution, eutrophication, exotic species, overfishing, loss of biodiversity and climate change (Vollenweider et al., 1974; Mills et al., 1993; Kerr and Ryder, 1997; Trumpickas et al., 2009). Managing these multiple anthropogenic stressors in the Great Lakes has required international cooperation in addition to a shared commitment to maintain the ecosystemic integrity of this enormous global resource.

Concern over eutrophication in the Great Lakes became widespread in the 1950s and 1960s with the problem being most evident in the densely populated coastal zones of Lakes Erie and Ontario, as well as the southern shores of Lake Michigan. External phosphorus loadings, primarily from detergents and agricultural wastes, were identified as the probable cause of widespread algal blooms associated with eutrophication (Vollenweider, 1968; Vallentyne, 1974; Schindler, 1978). The governments of Canada and the United States signed the Great Lakes Water Quality Agreement (GLWQA) in 1972 which committed both governments “to restore and maintain the chemical, physical and biological integrity of the Great Lakes basin ecosystem” (Article II: IJC, 1988) using science based management.

The relationship between phosphorus loadings, primary production and algal standing crop (chlorophyll a) was modelled by Vollenweider et al. (1974) and served as the basis for establishing targets for phosphorous load reductions into the Great Lakes under the auspices of the GLWQA. The governments of Canada and the United States agreed to meet these targets beginning in 1978 by banning phosphates in soaps and detergents and by improving municipal wastewater treatment (IJC, 1988). Success in alleviating eutrophic conditions in the lower Great Lakes, especially Lake Erie, demonstrated that the ecosystem approach to management enshrined in the GLWQA–that put sound science ahead of national interests–was a viable model for the rehabilitation of shared aquatic resources (Burns, 1985; Vallentyne, 1993).

Phosphorous loadings were not the only issue affecting the health of the Great Lakes. Severe pollution and degradation of various coastal regions, embayments, harbours, river mouths and tributaries of the Great Lakes led to the designation of 42 Areas of Concern (AoCs) (IJC, 1989). AoCs were selected based on a criterion of having at least 1 of 14 Beneficial Use Impairments (BUIs), although multiple impairments are the norm (Hartig and Zarull, 1992). BUIs included: “degraded fish and wildlife populations,” “fish tumours or other deformities,” “degradation of benthos,” “eutrophication or undesirable algae” and “degradation of phytoplankton and zooplankton populations,” to name a few. Although symptomatic in nature, the established list of BUIs was representative of environmental degradation at all trophic levels in keeping with the ecosystem approach adopted by the GLWQA.

Areas of Concern were intended to serve as focal points for remediation efforts, but some controversy has arisen because objective, quantitative and scientifically defensible parameters for beneficial use impairments were never fully defined (Krantzberg, 2004; George and Boyd, 2007). Researchers and managers are faced with the question of what constitutes an impaired beneficial use and at what point is it no longer impaired? These are known as “listing” and “delisting” criteria. There is an obvious need for researchers to develop and deploy relevant ecological indicators in order for managers to objectively define impairments of ecosystem health and to measure potential recovery.

The Bay of Quinte is one such AoC located on the northeastern shore of Lake Ontario, with 10 Beneficial Use Impairments including: “Eutrophication or undesirable algae” and “degradation of phytoplankton and zooplankton communities” (BQ RAP, 1993). Fisheries and Oceans Canada in partnership with the Ontario Ministry of Natural Resources, Ontario Ministry of the Environment and Environment Canada began monitoring the bay in 1972 as part of the initial efforts to control eutrophication in the Great Lakes which included regular measurements of nutrients, chlorophyll a, phytoplankton and zooplankton. Because of this effort, an enormous, long term (almost 40 years) data set was developed which in itself provides unique opportunities for addressing ecological questions in a robust manner.

The current article employs a “battery of tests” strategy to assess the status of beneficial use impairments (BUIs) of “eutrophication or undesirable algae” and “degradation of phytoplankton and zooplankton communities” in the Bay of Quinte. This strategy integrates structural (chlorophyll a, phytoplankton biomass and taxonomy, zooplankton biomass and taxonomy), functional (primary production) and chemical (phosphorous loadings) parameters and applies them to established ecosystem health models and scales which include:

  • The trophic ladder (phytoplankton biomass) of Munawar and Munawar (1982)

  • A qualitative assessment of phytoplankton composition (Hutchinson, 1967)

  • Vollenweider's eutrophication models (Vollenweider et al., 1974)

  • The Planktonic Index of Biotic Integrity (P-IBI) (Kane et al., 2009)

Collectively, these metrics incorporate a large body of the long term monitoring data from Project Quinte (2000–2008). Our goal is to assess the current state of BUIs in the Bay of Quinte and offer scientific guidance towards the development of delisting criteria that are founded upon sound ecosystem-based science.

Materials and Methods

Study area and sampling program

The Bay of Quinte is a large Z – shaped embayment (254 km2) that is also relatively shallow (4–8 m), but is much deeper at the interface with Lake Ontario. One shallow station in the upper bay (Belleville–5m) was sampled bi-weekly from May 1st to October 31st in each year (Figure 1) from 2000 to 2008. Integrated epilimnetic water was collected and subsamples were drawn for primary production, chlorophyll a, and phytoplankton. Zooplankton was sampled from discrete depths.

Chemical, structural and functional measurements

Point source phosphorous loadings were compiled by P. Kintsler, Ontario Ministry of the Environment, Kingston, Ontario (pers. comm.). Chlorophyll a concentrations were determined by filtering up to 1 litre of water through Whatman GF/C filters followed by cold acetone pigment extraction and spectrophotometric analysis (Strickland and Parsons, 1968).

Phytoplankton samples were fixed immediately with Lugol's iodine. Identification and enumeration followed the Utermöhl (1958) inverted microscope technique as described in Nicholls et al. (2002) which are broadly compatible with the established techniques of Munawar et al. (1987). All species names were verified with either the Integrated Taxonomic Information Service (ITIS) (http://www.itis.gov) or algaeBASE (Guiry and Guiry, 2012) prior to publication. The listing on ITIS was given preference.

The zooplankton data used in this article were obtained from Bowen and Johannsson (2011). Samples were collected using a 41 litre Schindler–Patalas trap fitted with a 64 μm mesh. Three depths were sampled at Belleville (1m, 2m and 3m) and preserved immediately with 4% sugared formalin. A single composite sample was constructed for each station-date by combining 50% of the sample from each depth. Biomass of each taxon was determined in each sample from length–weight regressions.

Annual primary production was estimated by 14carbon uptake. Samples from each cruise were spiked with Na14CO3 and incubated for 2–4 h at irradiance levels ranging from 10–120 μE s−1 m−2. Following incubation, acidification and bubbling was used to remove excess 14C and radioactivity was determined by liquid scintillation counting (Millard et al., 1999). Seasonal areal primary production (SAPP) was then estimated according to the model of Fee (1990). The original estimates of SAPP were provided by E.S. Millard and M. Burley of Fisheries and Oceans Canada, Burlington, Ontario (pers. comm.). These estimates were increased by 10% in order to account for winter primary production (Vollenweider et al., 1974; Fitzpatrick et al., 2007).

Ecosystem health indices

The trophic ladder (Munawar and Munawar, 1982) defines trophic state as a function of phytoplankton biomass along a linear scale, where the lowest levels (<1 g m−2) being indicative of ultra-oligotrophic conditions and the highest levels (>5 g m−2) indicative of hyper eutrophic conditions. Phytoplankton species composition is also used to make assumptions about trophic state based on well established patterns in community structure (Hutchinson, 1967).

Vollenwieder's eutrophication models (Vollenweider et al., 1974)

formula
where

A = Annual Primary Production (g C m−2 y−1)

P = Annual Phosphorus Loadings (g m−2 y−1)

formula
where

A = Annual Primary Production (g C m−2 y−1)

C = Annual Mean Chlorophyll a (μg l−1)

Planktonic index of biotic integrity (P-IBI) (Kane et al., 2009)

formula
where:

  • EAjk = June biomass of edible algae taxa metric score,

  • CBjk = June % Microcystis, Anabaena, and Aphanizomenon of total phytoplankton biomass metric score,

  • RJjk = June zooplankton ratio (Calanoida/ (Cladocera + Cyclopoida)) metric score,

  • LMjk = July Limnocalanus macrurus density metric score,

  • RAjk = August zooplankton ratio (Calanoida/ (Cladocera + Cyclopoida)) metric score,

  • ZBjk = August crustacean zooplankton biomass metric score,

  • M = number of metrics,

  • S = number of sites (within a basin), and

  • B = number of basins.

Results and Discussion

The earliest efforts at remediation in the Bay of Quinte included reductions in point source phosphorus loads from >200 kg d−1 in 1972 to <70 kg d−1 in 1978 (Minns et al., 1986) with reductions continuing to the present. Following the Bay of Quinte's designation as an Area of Concern, target levels were established for total phosphorus concentrations (30 μg l−l), phytoplankton biomass (4–5 g m−3) and chlorophyll a (12–15 μg l−l) (BQ RAP, 1993). Current research suggests that while these targets have been achieved, the bay is still eutrophic and the remediation targets are not robust enough to affect a change in trophic state (Munawar et al., 2011).

In previous work, we recommended that a “battery of tests” strategy be adopted to assess Beneficial Use Impairments using a variety of structural and functional measurements (Munawar et al., 2011). The battery of tests can be applied to test relevant impairments with multiple indicators being available to add confidence to the results. These tests range from simple structural indicators which would include estimation of phytoplankton biomass and its species composition based on microscopic analysis and functional/experimental assessments of primary productivity. Also included in the battery are integrated mathematical models that combine multiple structural, functional and chemical parameters. We chose a subset of the complete battery for consideration in this article.

Trophic ladder/phytoplankton biomass

The trophic ladder approach of Munawar and Munawar (1982) uses the structural measurement of total phytoplankton biomass to define a trophic gradient. Ultra-oligotrophic conditions at one extreme are defined as occurring where phytoplankton biomass is below 1 g m−3 and at the other extreme hyper-eutrophic conditions are defined when biomass exceeds 5 g m−3. According to this scale, the Bay of Quinte could be classified as either eutrophic (>3 g m−3 of phytoplankton) or hypereutrophic (>5 g m−3) from 2001–2008, with only a single year (2000) observed where the biomass was low enough to result in mesotrophic conditions (Figure 2). Phytoplankton biomass has also been used as a Remedial Action Plan target and we have previously noted that based on the trophic ladder approach, achieving the interim RAP target of 4–5 g m−3 will still result in a eutrophic embayment (Munawar et al., 2011). While not presented here, long term data shows that annual mean phytoplankton biomass never fell below the threshold of 3 g m−3 from 1972–1999 (Nicholls and Carney, 2011) and indicates that eutrophic and hyper eutrophic conditions were the norm both before and after the imposition of phosphorus controls.

Actually, our results are rather understated, since phytoplankton biomass was calculated as the weighted mean of 13 observations from May to October, whereas the original scale was based on single observations, so this model could be applied to each individual sampling date. For example, in 2000 when mean biomass was observed to be at its lowest historical level, eutrophy was observed on 3 (of 13) sampling dates (Table 1). At the other extreme, in 2007 eutrophy was observed on 9 sampling dates. Phytoplankton biomass suggests a consistent long term pattern of eutrophication in the upper Bay of Quinte.

Phytoplankton species composition

The species composition of the phytoplankton is another example of a structural ecological parameter that can be directly measured and is also instructive about trophic state and overall health. It is impossible to give a thorough treatment to phytoplankton species composition for all of our observations (n = 104), so we have selected two examples from 2006 for intensive analysis. As previous work has indicated, 2006 was the second consecutive year of recurring late summer algal blooms (Munawar et al., 2011; Nicholls and Carney, 2011) and we selected two dates where eutrophic conditions were observed (i.e. phytoplankton biomass >3 g m−3). We chose 26 July, the first occurrence of eutrophic conditions that year and 19 September, the last sampling date of the summer.

The species composition and relative abundance are shown in Table 2. The July bloom was dominated by species of Cyanophyta, namely Anabaena spiroides, A. circinalis, A. planktonica and Microscystis aeruginosa which are all strongly associated with eutrophic conditions (Munawar and Munawar, 1996; Hutchinson, 1967). Centric diatoms (e.g. Cyclotella sp.) and phytoflagellates (Cryptomonas caudata, C. erosa, C. ovata and Rhodomonas minuta) were also abundant. The late summer bloom was dominated by blue-greens including Lyngbya limnetica, Anabaena spiroides, A. circinalis and Microscystis aeruginosa. A similar assortment of centric diatoms and phytoflagellates to the July sample was also found in September. The presence of nitrogen—fixing species of Anabaena and Microcystis is characteristic of nutrient enriched habitats (Hutchinson, 1967; Munawar and Munawar, 1982; Stockner and Shortreed, 1988). On the other hand, Lyngbya limnetica (observed here in late summer) tend to out-compete other groups of phytoplankton for nitrogen when there is ample phosphorus and therefore thrive in turbid, light limited environments (Reynolds, 1984; Scheffer et al., 1997; Salmaso, 2000). The composition of the phytoplankton community provides hard evidence that the observed blooms are the consequence of external phosphorus loadings and that cultural eutrophication is a continuing threat to the Bay of Quinte ecosystem.

The presence of algal toxins, including microcystins and anatoxins, has become an increasingly important issue in the Great Lakes and other watersheds and is closely related to eutrophication. In Areas of Concern, however, the specific beneficial use impairment is often considered to be taste and odour (Watson et al., 2008), although Microcystin levels have been used as an indicator of phytoplankton health in other AoCs (Irvine and Murphy, 2009; Gillett and Steinman, 2011). Many of the dominant species observed during both blooms are known to produce Microcystin and other algal toxins. For example, Anabaena spiroides, A. planktonica, Micocystis aeroginosa and A. flos-aquae were the major toxin producers observed in July and A. spiroides, Lyngbya diguettii, A. planktonica and Aphanizomenon flos-aquae were found in September. While the occurrence of these species does not imply the production of algal toxins, it does present an obvious risk. More work is needed to link phytoplankton taxonomy with toxin production and other physiological properties including photosynthesis and respiration rates in order to better understand the hazard posed by algal blooms.

Vollenweider's eutrophication models

Phosphorus loadings were identified early on as the probable cause of eutrophication in the Bay of Quinte (Johnson and Owen, 1971) and a phosphorus abatement program was implemented beginning in 1978. Currently, point source phosphorous loads are in the range of 9–22 kg d−1 (equivalent to 0.01 – 0.03 g m−2; Table 3) and generally fall below the recommended cap of 15 kg d−1 (Minns and Moore, 2004). Vollenweider's eutrophication models (Vollenweider et al., 1974) were developed to predict the relationship between phosphorus loadings, primary production and algal standing crop and provide a scale for classifying lakes and embayments based on any of the 3 parameters. With these models, managers could calculate the magnitude of reductions in external phosphorus loads needed to alleviate eutrophic conditions. It is worth noting that Vollenweider's models provided the scientific basis for the phosphorus abatement provisions of the Great Lakes Water Quality Agreement (Bruce, 2011). Although the models were intended to be applied on a lakewide basis, recent work has demonstrated that they can also be applied to smaller embayments, providing a valuable tool for assessing AoCs (Munawar and Fitzpatrick, 2011).

The question remains as to whether or not the models are suitable for a shallow, largely riverine embayment, such as the Bay of Quinte, with relatively high flushing rates and long phosphorous retention times. The models were developed from surveys of over 150 temperate watersheds which varied greatly in their physical, biological and chemical characteristics and included riverine systems (Vollenweider, 1968; Janus and Vollenweider, 1981). Importantly, the models include critical P loading estimates for watersheds as shallow as 5m (mean depth), as well as much deeper lakes (Vollenweider, 1968). P retention in the Bay of Quinte (0.55 g m−2 y−1; Johnson and Owen, 1971) was in the middle of the range (0.11–1.08 g m−2 y−1) of the lakes surveyed by Vollenweider. Similarly, flushing rates in the Bay of Quinte (2.6–26.8 y−1; Minns et al., 2004) were well within the range of 0.26–62.7 y−1 observed in various southern Ontario watersheds to which the models were applied (Vollenweider and Dillon, 1974).

As a practical matter, high flushing rates have the effect of diluting the total phosphorous (TP) concentration and thereby reducing primary production and algal stranding crop, whereas high P retention would have the effect of increasing the TP concentration and result in increased primary production and a larger standing crop (Vollenweider and Dillon, 1974; Schindler, 1978). In terms of applying Vollenweider's model to the Bay of Quinte as a tool for predicting P loads, we would expect that the dilution effect of high flushing rates will be mitigated by the high P retention capacity and thus not hinder our estimates.

In the Bay of Quinte, Vollenweider's models (Figure 3) show that: (1) annual primary production is higher than predicted from phosphorus loadings and (2) eutrophic conditions persist in the bay based on primary production and chlorophyll a concentrations. The annual primary production observed (282–425 g m−2) was much higher than predicted by phosphorus loadings (0.01–0.03 g m−2) as was the algal standing crop (11–26 μg l−1 of chlorophyll a). The reason for this disparity is that only point sources of phosphorus were considered, whereas the model was calibrated to include both point and non-point sources. In fact, point source phosphorus loads, according to the model, account for only 10–14% of the annual primary production and 3–8% of the algal standing crop (Table 3). By implication, the models suggest that non-point sources (tributaries, storm sewer overflows, etc.) contribute significantly to the total phosphorous loadings in the bay and are a major factor behind the persistent eutrophic conditions. In fact, Minns et al. (2004) estimated tributary loadings to the Bay of Quinte to be >600 kg d−1 – roughly 40 x greater than point source loads–which would account for a significant amount of the observed primary production.

The predicted values of chlorophyll a and primary production from point source loads using Vollenweider's models (Table 3) suggest that the bay would be oligotrophic if there were no other sources of phosphorus. As past management plans have focused on reductions in point source loads, it is apparent that future management strategies must consider ways of reducing non-point sources of phosphorus. The use of Vollenweider's models indicates that the Beneficial Use Impairment of eutrophication is likely to continue into the future without reductions in non-point phosphorus loadings.

Planktonic index of biotic integrity (P-IBI)

Degradation of phytoplankton and zooplankton communities is also listed as a Beneficial Use Impairment for the Bay of Quinte, so metrics which assess the relative health of both organisms are also needed. One such metric is the Planktonic Index of Biotic Integrity (Kane et al., 2009) which considers the biomass and composition of phytoplankton and zooplankton populations however the index does not directly consider the impacts of predators. The P-IBI was originally developed for another ecosystem in the Great Lakes basin, Lake Erie, which shares some major stressors with the Bay of Quinte including eutrophication and invasive species (Johnson and Owen, 1971; Vollenweider et al., 1974; Nicholls et al., 2002). From 2000–2008, we found that P-IBI scores in the Bay of Quinte ranged from 1.67–3.57 (Figure 4) with scores of less than 2 considered hyper-eutrophic, 2–3 eutrophic and >3–4 mesotrophic. In 6 of 9 years, the bay was eutrophic according to the P-IBI, mesotrophic for two of the years and hyper-eutrophic during one year. Overall, the P-IBI model indicates the continuance of eutrophication in the bay some 25–30 years after the implementation of point source phosphorous controls.

While the P-IBI model explicitly addresses eutrophication, it is built on the implicit linkages between phytoplankton and zooplankton communities and the results can therefore be useful in addressing the related BUI of “degradation of phytoplankton and zooplankton communities.” This is because some of the driving factors behind low P-IBI scores include a high proportion of Cyanophyta relative to other phytoplankton (i.e. blue-green algal blooms), a relatively small biomass of edible phytoplankton (which would include centric diatoms and smaller phytoflagellates) and a reduced zooplankton population, especially among Cladocerans. These findings are consistent with our recently published work on the Bay of Quinte (Munawar et al., 2011) which concluded that organic carbon was likely being sequestered by other micro-organisms (i.e. heterotrophic nanoflagellates) indicating a potential lack of energy transfer from phytoplankton to zooplankton resulting in an impaired zooplankton community.

In defining the zooplankton impairment, Johannsson and Nicholls (2002) noted that increases in the relative densities of Bosmina longirostris, Daphnia pulicaria, total calanoid copepods, littoral cladocerans, Leptodiaptomus minutus and Diacyclops thomasi would be expected before the zooplankton community could be considered unimpaired. Furthermore, Bowen and Johannsson (2011) have observed that while zooplankton biomass did increase in the early 1980s following nutrient load reductions, significant reductions in zooplankton biomass followed the establishment of dreissenid mussels in the 1990s—particularly among Cladocerans, Cyclopoids and Calanoids—suggesting continued impairment in the zooplankton community. However, more work is needed to address the current state of the zooplankton impairment.

The concept of Beneficial Use Impairments was intended to provide robust, multi-trophic criteria for assessing ecosystem health however a consensus as to what constitutes impairment and recovery is still required (George and Boyd, 2007). Achieving this consensus requires proven ecological indicators that can be deployed as necessary in ecosystems facing anthropogenic stress. It is the responsibility of scientists to choose appropriate indicators to meet these needs. In this article, we chose our battery of tests in order to make optimum use of the long term Project Quinte database and included phosphorous loadings, primary production, chlorophyll a, phytoplankton and zooplankton in the various metrics.

We focused the battery of tests on measurements that address eutrophication in terms of phosphorus, algal standing crop and primary production; factors that were prevalent in the 1970s and that later contributed to the Bay of Quinte's listing as an AoC. To a lesser extent, we addressed potential bottom up impacts on the zooplankton community with the P-IBI model. We did not however, consider the synergistic impacts of other known stressors such as zebra mussels on the base of the food web nor did we consider top down stressors on the zooplankton community. We simply used an established set of criteria that clearly define eutrophication to determine the current state of the ecosystem.

Summary and Conclusions

In Figure 5, we summarized the results of the battery of tests with respect to the assessment of trophic state. Phytoplankton taxonomy was not included in this summary because it is only available on a limited basis. Nonetheless, our ecological indicators showed good agreement in concluding eutrophic or hyper eutrophic conditions in 7 of the 9 years studied. In 2000, 2 of 3 indicators (trophic ladder and P-IBI) suggested mesotrophic conditions, while Vollenweider's models suggested eutrophic conditions. Similarly in 2004, the P-IBI model suggested mesotrophic conditions, while the other 2 models showed eutrophic conditions. Although Vollenweider's models do not distinguish between eutrophic and hyper-eutrophic conditions, it would not be unreasonable to assume that higher levels of chlorophyll a and primary production were in fact indicative of hyper-eutrophic conditions. We conclude from the weight of evidence (24/27) that eutrophic conditions persist in the Bay of Quinte roughly 25 years after reductions in point source phosphorus loadings were first introduced.

With respect to Beneficial Use Impairments in the Bay of Quinte, specifically “eutrophication or undesirable algae” and “degradation of phytoplankton and zooplankton communities,” we conclude from the battery of tests that the Bay of Quinte remains eutrophic and that the phytoplankton community remains in a state of degradation. It is also apparent that future phosphorus abatement strategies will need to address the impact of non-point sources on primary production and algal standing crop. There is also evidence from the P-IBI model that the zooplankton community is also impaired, but our efforts were directed towards assessing the phytoplankton impairment. The battery of tests is composed of a mixture of structural, functional and chemical ecological indicators that are applicable to assessing the impact of multiple stressors in both marine and freshwater systems. The experiences and lessons learned from the Laurentian Great Lakes could be effectively applied towards assessing the health of the remaining Great Lakes Areas of Concern, as well as other freshwater and marine environments across the world, which have been impacted by cultural eutrophication.

Acknowledgements

We thank Drs. J. H. Leach, E. L. Mills and C. K. Minns, for their constructive reviews of the manuscript. A special thank you is due to J. Lorimer for the graphics and to S. Blunt and L. Elder (AEHMS) for technical editing. Finally, we gratefully acknowledge the hard work and perseverance of the DFO staff whose dedication to Project Quinte have made this research possible including: E. S. Millard, M. Burley, J. Gerlofsma, C. Timmins, R. Bonnell and A. Bedford.

The text of this article is only available as a PDF.

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