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Assessment of habitat impairments impacting the aquatic resources of Lake Ontario W.-D.N. Busch and S.J. Lary
Abstract: A habitat classification system was used to describe aquatic habitat and evaluate habitat degradation in Lake Ontario. Primary consideration was given to physical loss or disruption of habitat availability; because habitat availability was treated as a functional entity, disruptions or stresses caused by chemical or biological sources were included. Data on biological, chemical, and physical anthropogenic changes were scattered, patchy, and disjointed. Therefore, the Delphi technique was used to evaluate the degree of functional habitat impairment for 29 habitats. The criteria for the impairments were the severity of the ecological impact (shift in trophic transfer efficiency) and its permanence (short > decades > permanent). The amounts of functional degradation were averaged by habitat categories (N = 88) for each habitat and multiplied by the estimated areal proportion of that habitat in the ecosystem. We estimated that during 1970–1990, Lake Ontario’s ecosystem health was degraded by 58%. Impairments were caused almost equally by anthropogenic stresses from biological (loss of indigenous and introduction of exotic species), chemical (persistent toxins), and physical (dredge–fill, damming, and water-level regulations) sources. Our finding is consistent with a late 1980s study that used lake trout (Salvelinus namaycush) as an indicator of ecosystem health. Résumé : Nous avons appliqué un système de classement des habitats à la description d’habitats aquatiques dans le lac Ontario et à l’évaluation de leur détérioration. Nous nous sommes occupés surtout de la destruction physique ou de la perte d’utilisation d’habitats; puisque les habitats utilisables sont traités sous l’angle d’entités fonctionnelles, nous avons inclus tout stress ou source de perturbation d’origine chimique ou biologique. Les données sur les changements physiques ou biochimiques d’origine anthropique étaient éparses, fragmentaires ou inordonnées. C’est pourquoi nous avons eu recours à la technique Delphi pour l’évaluation de la détérioration du fonctionnement de 29 habitats. Les critères retenus étaient la gravité de l’impact écologique (changement observé en termes d’efficacité des transferts trophiques) et sa durée (courte durée, dJcennies, caractère permanent). Nous avons calculé la moyenne par catégorie d’habitats (N = 88) du degré de détérioration des habitats étudiés sur le plan de leur fonctionnement, et multiplié le résultat obtenu par le pourcentage de la superficie estimée que cet habitat occupe dans son écosystème. Nous avons estimé qu’entre 1970 et 1990, l’écosystème global du lac Ontario s’est détérioré de 58 %. Les sources de détérioration, d’importance sensiblement égale, étaient les stress anthropiques à caractère biologique (perte d’espèces indigènes et introduction d’espèces exotiques), chimique (substances toxiques persistantes) et physique (dragage/remplissage, endiguement et régulation du niveau de l’eau). Nos observations confirment les résultats d’une étude faite à la fin des années 1980 qui utilisait le touladi comme indicateur de l’état des écosystèmes. [Traduit par la Rédaction]
Introduction A restoration or rehabilitation activity requires an understanding of the impairments to an ecosystem or the cause of deviation from the “healthy” state (Evans et al. 1990; Environment Canada and U.S. EPA 1995). Some efforts have been made to evaluate the state of the Lake Ontario ecosystem (Christie et al. 1986; LOPCHIC 1993). The overall decline in condition and its present degraded state has been documented. However, the specific condition indicators, such as changes in fish and wildlife species diversity, harvest rates, nutrient abundance, chemical loadings, human population growth, land clearing, and shoreline modifications, have not been measured
consistently, and the data have not been evaluated holistically (Christie 1973; Crowder and Painter 1991; Luckey 1994; Hartig and Law 1994). The Great Lakes Water Quality Agreement (GLWQA 1987) states that “impairment of beneficial use(s) means a change in the chemical, physical, or biological integrity of the Great Lakes System sufficient to cause any of the following (italics added for emphasis): (1) restrictions on fish and wildlife consumption; (2) tainting of fish and wildlife flavor; (3) degradation of fish and wildlife populations;
Received November 1994. Accepted December 4, 1995. J13213 W.-D.N. Busch1 and S.J. Lary. U.S. Fish and Wildlife Service, Lower Great Lakes Fish and Wildlife Resources, 405 North French Road, Amherst, NY 14228, U.S.A. 1
Author to whom all correspondence should be addressed. e-mail: r5ffa
[email protected]
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(4) fish tumors or other deformities; (5) bird or animal deformities or reproduction problems; (6) degradation of benthos; (7) restrictions on dredging activities; (8) eutrophication or undesirable algae; © 1996 NRC Canada
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Fig. 1. Lake Ontario basins (modified from Sly and Prior 1984).
(9) restrictions on drinking water consumption, or taste and odor problems; (10) beach closings; (11) degradation of aesthetics; (12) added costs to agriculture or industry; (13) degradation of phytoplankton and zooplankton populations; and (14) loss of fish and wildlife habitat.” Some of the criteria listed above are stand-alone measurements of impairment. However, criteria 3, 4, 5, 6, 8, and 13 are subsets or symptoms of criterion 14 if habitat is defined as the biological, chemical, and physical setting needed to support all life functions of the organisms (Sly and Busch 1992a). Therefore, anthropogenic chemical, physical, or biological stressors may disrupt the integrity of the system through impairments to ecosystem functions, such as trophic transfer. These impairments to the health of the ecosystem are in addition to the more commonly identified, acute effects caused when habitats are physically destroyed (Sly and Busch 1992a). Along these lines, this study assessed the functional impairments to the habitats of the Lake Ontario ecosystem in terms of anthropogenic changes to chemical, physical, or biological integrity (GLWQA 1987; Environment Canada and U.S. EPA 1995). Data on physical changes to the basin were identified and inventoried. Information on chemically caused stresses were reviewed. The biological impacts caused by exotic species on the health of the ecosystem were also evaluated. The results from these assessments were combined to obtain an index of ecosystem health for Lake Ontario. This index can be used as a tool for understanding the specific impairments to the ecosystem and to assist in the development of concise, achievable restoration options for the ecosystem.
Geographic area and hydrology Lake Ontario, with a surface area of 19 010 km2, is the smallest of the Laurentian Great Lakes (Fig. 1). Its longest dimension, in an east–west direction, is approximately 306 km. The width is about 85 km. The mean depth is 84 m, while maximum depth is 245 m. Despite the small surface area, Lake Ontario is the twelfth largest lake in the world by volume. Lake Ontario is divided into four basins. The three major basins, the Niagara, Mississauga, and Rochester, going from west to east, are separated by the Whitby–Olcott and Scotch Bonnet sills, respectively. The easternmost basin, the Kingston, is separated from the Rochester basin by the Duck–Galoo sill. The sediments follow a gradient of sands and gravels in the nearshore areas to silts and clays in the deeper portion of the basins. The Niagara basin has a maximum depth of 128 m, while the Mississauga basin’s maximum is about 201 m deep, and the Rochester basin’s maximum depth is approximately 245 m. The Kingston basin has a maximum depth of 30 m. Islands and extensive littoral areas are common in the Kingston basin (Eckert 1984; Martini and Bowlby 1991; Sly 1991). Lake Ontario receives the outflow from the upper four Great Lakes via the Niagara River at the average annual rate of 5520 m3⋅s-1. Direct inflow from all other major tributaries total only an additional 540 m3⋅s-1 (Sly 1991). Despite the lake’s great depth, the theoretical water retention time is only 6 yr because of the high inflow from the Niagara River (IJC 1989). Fluctuations in the water level of Lake Ontario are less than 2 m⋅yr-1, far less than historical fluctuations (Sly 1991). This is largely a result of artificial water-level regulation coupled with a relatively small surface area, which limits evaporation effects. Limnology and biota Lake Ontario is a dimictic lake, undergoing vernal and autumnal mixing. Summer stratification results in classical zonation. © 1996 NRC Canada
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Winter stratification is rather weak since the lake usually remains free of ice, with the exception of inshore shallow areas and sheltered embayments. Hypolimnetic upwellings are common, even during maximum summer stratification (Johannsson and O’Gorman 1991). Vertical thermal bars are a feature of the warming and cooling processes of the lake and serve to temporarily segregate inshore and offshore waters, particularly at the outset of summer stratification. The isolation of inshore waters serves to restrict dispersion of nearshore pollutants, nutrients, and other loadings (Eckert 1984). Circulation is typically wind driven, and is frequently of several cells, corresponding generally with the sub-basins. The period of time that was examined for this study (1970–1990) was one of significant and rapid change in water quality and in species composition, abundance, and condition (Smith and Lange 1994). However, it was also a period of relative stability in the physical attributes of the basin (Whillans et al. 1992). Most tributary damming for hydro-power production had occurred prior to 1970, although these dams still prevent up- or down-stream movement of biota. The rate of other shoreline alterations such as shoreline protection, dredging, or filling decreased, in part due to restrictions caused by governmental regulations. Until the middle to late 1980s, the trophic status of Lake Ontario was considered mesotrophic based on average phosphorus concentrations (IJC 1989; Leach and Herron 1992). Yet, many inshore areas and embayments were decidedly eutrophic. The phytoplankton community of Lake Ontario was dominated (90%) by diatoms, green algae, dinoflagellates, and flagellates. Cladophora sp. was the predominant attached algae. The zooplankton community was dominated by Bosmina longirostris and Daphnia retrocurva (Johannsson and O’Gorman 1991). Diporeia hoyi and Mysis relicta dominated the deepwater benthos, while the more eutrophic, nearshore regions were predominantly occupied by oligochaetes, particularly Potamothrix sp. and Aulodrilus sp. Fish species in the epilimnion, in order of numerical abundance, were alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax), yellow perch (Perca flavescens), white sucker (Catostomus commersoni), and lake chub (Couesius plumbeus) (LOPCHIC 1993; Smith and Lange 1994). Alewife, rainbow smelt, and slimy sculpin (Cottus cognatus) dominated the deep waters (Jones et al. 1993). Native lake whitefish (Coregonus clupeaformis) abundance was very low. Top cold-water predators were hatchery supported populations of rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta), lake trout (Salvelinus namaycush), Pacific salmon (Oncorhynchus sp.), and a limited number of Atlantic salmon (Salmo salar). Embayments supported local populations of northern pike (Esox lucius), largemouth bass (Micropterus salmoides), smallmouth bass (Micropterus dolomieu), yellow perch, white perch (Morone americana), and brown bullhead (Ameiurus nebulosus) (Eckert 1984). Commercial harvest was limited by management regulations and species availability during 1970–1990. Catches were chiefly catfish (Ictalurus sp.), bullhead, walleye (Stizostedion vitreum), white perch, American eel (Anguilla rostrata), and, by the late 1980s, included increasing numbers of lake whitefish (Eckert 1984; IJC 1989; Sly 1991). During this time, a very active offshore sports harvest had been established. The harvest included exotic and native salmon and trout.
In the late 1980s to early 1990s, the return to more natural conditions in water quality caused changes in primary and secondary production, and consequently in the fish community (Smith and Lange 1994). Significant reductions in the artificially high levels of nutrients, as a result of improved sewage treatment, combined with the changes in energy flow caused by the zebra mussel (Dreissena polymorpha), reduced primary productivity in the “open waters” (Smith and Lange 1994; Environment Canada and U.S. EPA 1995). Consequently, the trophic status of Lake Ontario’s fish community shifted from mesotrophic to oligotrophic (Jones et al. 1993; Smith and Lange 1994). The primary forage species, the exotic alewife, appeared to be declining in both abundance and condition (Jones et al. 1993). Yet, native fish species such as lake whitefish and burbot (Lota lota) increased greatly in abundance and efforts to reestablish naturally reproducing lake trout are showing signs of success. For example, 1995 offshore stock assessment by New York State Department of Environmental Conservation and the National Biological Service indicated that the 1994 year class of lake trout in Lake Ontario included 8% naturally produced fish (C. Schneider, New York State Department of Environmental Conservation, personal communication).
Methods Definition of aquatic habitat(s) In classical biological usage, habitat is generally described as a geographical entity, such as a coastal marsh or the littoral zone of a lake. Little emphasis is placed on other life-support functions needed by the biota (Cowardin et al. 1979) and, therefore, lacks the focus needed for a detailed analysis and evaluation of the functional health of a complex, multiple habitat ecosystem. Margalef (1981) and Ryder and Edwards (1985), for example, have identified the need for a more functional ecosystem-based approach to habitat evaluation, especially from a management viewpoint. A process using a functional-based habitat application was recently provided by Sly and Busch (1992a). Under this approach, habitat is defined as the sum total of the biological, chemical, and physical attributes of a specific location, which constitutes a distinct fish or wildlife refuge, feeding site, or breeding location. For the current project, habitat units were described and assigned biological, chemical, and physical descriptors to provide the means for evaluation of the availability and functional health of these habitats (Busch et al. 1993). A list of impairments, with descriptors, was also developed (Busch et al. 1993). These are stresses (biological, chemical, or physical) that interfere with the normal functions of the habitat unit and, therefore, affect life processes of organisms living within that habitat unit. Habitat classification methodology: identification and justification The Aquatic Habitat Classification System (AHC) was used to inventory and assess the Lake Ontario ecosystem. The complete methodology is described in Busch and Sly (1992). The selection of potential habitat units was based on well-defined physical factors, such as topography, stratigraphy, and other classical landform descriptors. These habitats were then considered from the perspective of biological interactions and community structure, whether actual or potential. The habitat information inventory available from Busch et al. (1993) provided the habitat information base and a list of functionally distinct habitat units. The information and supportive literature were identified, obtained, and organized according to its biological, chemi© 1996 NRC Canada
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Fig. 2. The hierarchy of aquatic habitat classification.
cal, and (or) physical application. An “expert system” or Delphi technique (Zuboy 1981; Crance 1987) was used to evaluate the anthropogenic stresses to determine major impairments to habitat functions. Applying the AHC hierarchy as a model, all lake habitats fall under two major categories, or subsystems (Fig. 2). The open water subsystem includes the circulatory basins and major embayments and extends shoreward to either the sand–silt sediment boundary or the attached plant boundary, whichever reaches the greater depth. Shoreward of this boundary is the nearshore subsystem that includes all coastal features as well as islands and shallow water features such as reefs and shoals. These are included here since they, like the shore, are dominated by edge or interface effects. The nearshore subsystem area from the shore to the 25-m contour constitutes a separate zone from deeper waters. This is based on the following criteria: (i) wave activity exerts its influence to a maximum depth of approximately 25 m (Sly 1991), and (ii) thermocline development in Lake Ontario is restricted to the top 25 m (Sly 1991). Thus,
the major, wind-driven physical forces defining this habitat exert their effects above the 25-m contour. The nearshore subsystem is described from a classical geological basis. Since subsequent definitions of habitat units rely on an understanding of coastal morphology, the following definitions were adopted. The shore is that zone from the low-water mark landward to the base of a cliff, large or small, which marks the landward limit of effective wave action. A cliff, in this sense, refers to the abrupt change in gradient, no matter how small, indicating where wave erosional forces cease, and is usually demarcated by a change in vegetation and substrate. Wetlands are described by Cowardin et al. (1979). Criteria to evaluate stresses on aquatic habitats Criteria were developed from literature sources and from consultations with natural resource managers to evaluate stress (Busch et al. 1993). The goal was to identify and describe stress factors capable of impairing the functions performed by a habitat unit in support of © 1996 NRC Canada
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Busch and Lary Table 1. Estimated anthropogenic impairments (stresses) affecting habitat functions in Lake Ontario. Habitats combined by general categoriesa Open water (67%) Shoreline (100 m inland) and littoral area (3 m) (15%) Wetlands (4%) Tributary and embayments (12%) Special features (2%) Total stress impact by type
Biological stresses
Chemical stresses
0.11 0.03 0.04 0.01 0.21
Total stress impact by habitats
0.03
Physical stresses 0.02
0.03 0.01 0.09 0.01 0.17
0.03 0.02 0.12 0.01 0.20
0.09 0.05 0.25 0.03 0.58
0.16
Note: Habitats were combined into five general categories. Estimated impact was multiplied by its estimated percent of total surface area for watershed effect. a Values in parentheses are the percentage of the basin surface area for each category.
fish or wildlife in the Lake Ontario basin. From this information, criteria were established to assess the degree of degradation of specific habitat units (Schindler 1987). The evaluation of the degree of habitat degradation (biological, chemical, and physical) necessitated several considerations. After a specific habitat unit was delineated, the degree of impairment was determined using the Delphi technique (Zuboy 1981; Crance 1987). An effort was made to separate the natural from the anthropogenic restrictions. The functional concerns were addressed by comparing impacted areas to reference sites within the basin that have maintained their structure and are able to support ecosystem functions needed for a healthy state (Martin 1994). Functional impairments of 88 habitat categories (class level; Sly and Busch 1992b) were evaluated for biological, chemical or physical stresses. The criteria were the severity of the ecological impact, defined as a significant change or shift in the efficiency or direction of the energy flow between trophic levels, and the expected permanence of the stress defined by time (weeks, season, year, decades, or permanent). The application of the Delphi technique to the assessment used a scale of 0.1 to 1.0 to estimate the degree of disturbance for each of the two criteria and the 88 habitat categories (Fig. 2). The assessment process was repeated and applied to address the biological, chemical, and physical stress factors causing functional impairments. The results were combined and averaged for five habitat groups and were multiplied by an approximation of the size of the habitat’s area (percentage of the water-surface area of the system) to relate the impairment to the total health of the ecosystem. Procedure for the inventory of aquatic habitat information The aquatic habitat data are from Busch et al. (1993). The data were obtained in 1991–1992. The information search was not restrained by information type, format, source, or national borders. It included raw data, scientific papers and reports, interviews, office visits, and information requests using all applicable media. Ideally, assessment of ecosystem condition should focus, like a snapshot, on a narrow time period. The length of time allowed for the assessment window is especially relevant if the system is going through major changes. Throughout the information gathering phase, it became increasingly clear that Lake Ontario habitat information was scattered, patchy, and disjointed. Some portions of the lake system have been studied in detail, while other areas have not been studied. Therefore, to obtain the best applicable understanding, a lengthy time frame was allowed, 1960–1990, with the major focus on the 1970–1990 period.
Results The results indicate that the habitats making up the Lake Ontario ecosystem, during the 1960–1990 (focus 1970–1990), were functionally impaired by 58% (Table 1). The impair-
ments were caused almost equally by biological (21%), chemical (17%), and physical (20%) stressors. Biological stresses were most severe in the open water habitat category, which comprises 67% of the basin’s surface area. Its functional performance was determined to be impaired by the dramatic increase in distribution and abundance of exotic species, most notably the sea lamprey (Petromyzon marinus) and zebra mussel (Environment Canada and U.S. EPA 1995). Other contributing factors included artificial changes in primary production and instability within the native fish community caused by loss of native species such as lake trout, Atlantic salmon, blue pike (Stizostedion vitreum glaucum), and deepwater sculpin. This change in the open-water community and the loss of native species resulted in management agencies stocking Lake Ontario with exotic predator species to provide fishing opportunities and to control the high production of exotic prey species. The wide geographic and trophic distribution of the exotics and their permanence resulted in the high stress indicator (Table 1). Chemical stresses were highest in the tributary and embayments habitat category (Table 1). Most of the larger tributaries and embayments are also harbors with extensive shoreline development and historic chemical loadings, with high levels of point and nonpoint contributions (Rang et al. 1992; Luckey 1994). Some of these areas have been labeled Areas of Concern as a result of determinations that their degraded state is impacting the lake–ecosystem. The impacts include fish tumors, wildlife deformities, and degradation of aquatic biota caused by chemical accumulation from the sediments or watershed (Hartig and Law 1994; Koonce et al. 1996). Physical stresses were primarily from physical and waterflow changes caused by hydro-power development, construction of harbor facilities, and maintenance dredging for harbors in the tributaries (Smith 1995). They, combined with the chemical stresses, resulted in the finding of the tributary and embayments habitat category as the most heavily stressed habitat type of Lake Ontario (Table 1). Surprisingly, shoreline–littoral and wetland habitats were not identified as being heavily stressed habitats during the study period (Table 1). This was partially the result of the time frame; governmental regulations for protection of lake-connected wetlands and the shoreline and littoral zone have strengthened so that the physical area of these habitat units had not decreased significantly in the last 20 yr. Prior to government restrictions, shoreline–littoral and wetland habitats were © 1996 NRC Canada
118 Fig. 3. Dichotomous key scores, by stress category, for Lake Ontario. The vertical line extending from each bar indicates percent uncertainty (from Edwards et al. 1990).
greatly altered. In addition to agriculture, extensive urbanization, particularly in the vicinities of Toronto, Hamilton, and Rochester, has significantly impacted the shoreline and associated wetlands. Local loss of urban wetlands is estimated to be greater than 80%, with an overall total loss of 50% (Whillans et al. 1992).
Discussion and recommendations The impacts by society on the Lake Ontario ecosystem have been severe. The aquatic resources are impaired and anthropogenic stresses continue to have significant negative impacts on the ecosystem (Colborn et al 1990; EOWG 1990; IJC 1989; LOPCHIC 1993; Luckey 1994; Environment Canada and U.S. EPA 1995). The estimated overall impairment reported in Table 1 is very similar to the health condition of 50% reported for Lake Ontario by Edwards et al. (1990). Their results described the conditions in the mid-1980s using a dichotomous key, with lake trout as the index species (Ryder and Edwards 1985; Ryder 1990; Marshall, Ryder, and Edwards 1992). Edwards et al. (1990) include “exploitation and production” as a significant stressor since their assessment focused on lake trout performance (Fig. 3). Conversely, in our aquatic habitat assessment, the focus was on the impairments to the functional performance of the habitats. Both this and the Edwards et al. (1990) ecosystem health assessments indicate that the chemical stresses in Lake Ontario, although still of concern, are less important than the physical and biological impairments, which are the most significant restoration impediment. The goal of restoration of the Lake Ontario ecosystem is the same as that defined in the GLCPA (1990) for the entire Great Lakes system: “of restoring and maintaining the chemical, physical, and biological integrity of the waters of the Great Lakes Basin.” Furthermore, the specific requirement for implementation of lakewide management plans (LaMPs) in GLCPA (1990) mandate “a systematic and comprehensive ecosystem approach to restoring and protecting the beneficial uses of the waters.” Protection of the beneficial uses of these waters is also required by the Boundary Waters Treaty (1909), and restoration is the goal of the GLWQA (1987).
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Yet, anthropogenic impacts on Lake Ontario’s ecosystem health must be factored into restoration planning. Historical conditions or natural, undisturbed ecosystems are often suggested as targets or examples of ecosystem restoration benchmarks. This would appear applicable when humans are not a major component of the landscape. However, in ecosystems such as Lake Ontario where continuing human development is a major factor, humans have to be considered part of the landscape (Geller 1994). The use of undisturbed systems, or the predevelopment time frame, as comparison for today’s anthropogenically stressed systems, undermines the ecosystem approach by excluding the avoidable and unavoidable impacts of humans within that landscape. The current challenge for natural resource managers is to understand the ecosystem’s functional vitality within its structure, the interactions between trophic levels, and the effects of human use of the ecosystem on its restoration (Kerr 1974; Borgmann 1982; Sprules and Munawar 1986; Environment Canada and U.S. EPA 1995). The identification of obstructions to the functional vitality, for example, through disruptions in the energy flow by zebra mussels, is fundamental to assessing ecosystem vitality and the functional impairments caused by anthropogenic stresses (Rapport 1990; Steedman and Regier 1990). A focus on the ability to support “biological functions” allows for natural and (or) anthropogenic changes in species assemblages within an ecosystem that could still be described as “functionally healthy” even though stressed, for example, by extensive harvest (Schindler 1987; Ryder and Kerr 1990). Although a general ecosystem health assessment of Lake Ontario that describes an impaired system has been conducted, more data are needed to monitor and evaluate rehabilitation progress. The selection of data and geographic coverage should focus on the scale and specificity needed for the project. The detailed data collection could follow an organizational structure like that provided by the AHC, so that the information can be added to that available for improved system understanding and cost effectiveness. Based on our review of the state of the Lake Ontario information, priority areas include the following. (1) Protect the system from unintentional introductions or invasions of nuisance exotic species and limit the impacts of the exotic species already present. (2) Assess impairments to structure and productivity of the open-water biological resources by the following. (i) Continuing a bioindex program to collect lakewide lower trophic level data on total phosphorous, chlorophyll a, and zooplankton to describe spatial and temporal changes. The information will verify the accuracy of the nutrient loading objectives and allow improvements in the management of sustainable fish production. (ii) Assessing the strength and health of the fish community using a trophic and habitat guild approach to identify the effectiveness of habitat utilization. This activity should also identify the potential carrying capacity at the various trophic levels and estimate the differences between actual use and potential (Czapla et al. 1995). (3) Identify, quantify, remediate, and monitor the physical © 1996 NRC Canada
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and chemical impairments to biological functions in tributary–embayment habitats (Table 1), including the following. (i) Continue the progress for migratory, tributary fish to regain up- and down-stream passage and access to up steam habitats. (ii) Continue the remediation of impairments caused by chemicals accumulated in the sediments or watershed through regulatory processes so that fish and wildlife can safely occupy the tributary–embayment habitats. Obtain, through index organisms, data on normal background levels of natural chemicals and the frequency of deformities, at the whole, reproduction, cellular, and DNA level, to differentiate anthropogenic-caused stresses from those naturally occurring. (4) Develop a computerized data base with a Geographic Information System to fully integrate available information into a concise model of the Lake Ontario habitat inventory. While some historical impacts are reversible (i.e., toxic contaminant loading, excessive nutrients, overharvesting), others are not (i.e., exotic species introductions, drainage basin changes, native species extirpation). To implement ecosystem management, “desired” natural resource goals need to be identified and understood (Evans et al. 1990; Bertram and Reynoldson 1992). Society within the Lake Ontario basin is now debating the natural resource goals for this system. Although the theoretical options range from “a return to pristine conditions” to “intense aquaculture” (put–grow–take), neither extreme can be reached or sustained because of irreversible anthropogenic changes or economic limitations. There are a range of options in restoration initiatives to reach ecosystem goal(s), but these options need to be described so that society can evaluate the benefits. Ecosystem health models can clarify the options and benefits (Minns 1992). The information obtained from ecosystem health assessments provides a focus for action in restoring the health of the lake by assisting in identifying and ranking the numerous stresses affecting the system. This information is useful in recognizing the most significant problem (stress) areas and providing guidance for more detailed and quantifiable evaluations. Such a focus assists in improving the cost effectiveness of efforts towards rehabilitation of not only the Lake Ontario ecosystem but other aquatic systems as well.
Acknowledgments We thank the numerous persons who have contributed to the Lake Ontario habitat information assessment and data evaluation. This report also benefited from the critical review of a number of people including Tom Czapla, John R.M. Kelso, and Martha Balis-Larsen.
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