Jan Ciborowski - Academia.edu (original) (raw)
Papers by Jan Ciborowski
Journal of Great Lakes Research, 2007
Fish community composition often varies across ecoregions and hydrogeomorphic types within ecoreg... more Fish community composition often varies across ecoregions and hydrogeomorphic types within ecoregions. We evaluated two indices of biotic integrity (IBIs) developed for fish in Great Lakes coastal wetlands dominated (> 50% cover) by Typha (cattail) and Schoenoplectus (formerly Scirpus) (bulrush) vegetation. Thirty-three coastal wetlands dominated by either Typha or Schoenoplectus vegetation were sampled using fyke nets set overnight. These sites were selected to span anthropogenic disturbance gradients based on population density, road density, urban development, point-source pollution, and agricultural inputs (nutrients, sediments), measured using a GIS-based analysis of Great Lakes coastal land use. Sites subject to low levels of anthropogenic influence had high IBI scores. The Typhaspecific IBI showed a marginally significant negative correlation with population density and residential development (r = -0.54, p < 0.05; n = 21). The Schoenoplectus-specific IBI negatively correlated most strongly with nutrient and chemical inputs associated with agricultural activity and point-source pollution (r = -0.66 and -0.52, respectively; p < 0.01; n = 30). However, some relationships between IBI and disturbance scores were non-linear and likely exhibit a threshold relationship, particularly for Schoenoplectus dominant sites. Once a certain level of disturbance has been exceeded, a sharp change in fish community's composition and function occurs which is symptomatic of a degraded site. The IBI indices appear to indicate effects of some, but not all classes of anthropogenic disturbance on fish communities. † Current address: Watershed Ecosystems Graduate Program, Trent University, Peterborough, Ontario K9J 7B8 Canada 705.748-1011, ext. 7341, f 705.748.1026
Journal of Great Lakes Research, 2007
Watersheds represent spatially explicit areas within which terrestrial stressors can be quantifie... more Watersheds represent spatially explicit areas within which terrestrial stressors can be quantified and linked to measures of aquatic ecosystem condition. We delineated thousands of Great Lakes watersheds using previously proven and new watershed delineation techniques. These were used to provide summaries for a variety of anthropogenic stressors within the Great Lakes. All delineation techniques proved useful, but each had applications for which they were most appropriate. A set of watershed delineations and stressor summaries was developed for sampling site identification, providing relatively coarse strata for selecting sites along the U.S. Great Lakes coastline. Subsequent watershed delineations were used for high-resolution site characterization of specific sites and characterizing the full coastal stressor gradient. For these delineations we used three general approaches: 1) segmentation of the shoreline at points midway between adjacent streams and delineation of a watershed for each segment; 2) specific watershed delineations for sampled sites; and 3) a Great Lakes basin-wide, high-resolution approach wherein sub-basins can be agglomerated into larger basins for specific portions of the coast. The third approach is unique in that it provides a nested framework based on hierarchies of catchments with associated stressor data. This hierarchical framework was used to derive additional watershed delineations, and their associated stressor summaries, at four different scales. Providing anthropogenic stressor metrics in such a format that can quickly be summarized for the entire basin at multiple scales, or specifically for particular areas, establishes a strong foundation for quantifying and understanding stressor-response relationships in these coastal environments.
Canadian Journal of Fisheries and Aquatic Sciences, 1996
Hexagenia nymphs are sensitive to hypoxia, and their abundance has been proposed as an ecosystem ... more Hexagenia nymphs are sensitive to hypoxia, and their abundance has been proposed as an ecosystem indicator for assessing the recovery from eutrophication of shallow, mesotrophic lakes. Acute oxygen tolerance limits are known for Hexagenia spp., but effects of prolonged exposure to sublethal levels of hypoxia are not. A series of 21-day laboratory experiments was conducted to determine the influence of
Canadian Journal of Fisheries and Aquatic Sciences, 1983
ABSTRACT By releasing live and dead nymphs of two mayfly species, Baetis tricaudatus Dodds and Ep... more ABSTRACT By releasing live and dead nymphs of two mayfly species, Baetis tricaudatus Dodds and Ephemerella inermis Eaton, into the water column of a river and catching them downstream in a series of contiguous nets, I estimated settling and lateral dispersal rates. Live animals settled over shorter distances than dead individuals, and became more widely laterally dispersed for any given distance downstream and mean current velocity. Transport of suspended organisms in a river in which mean current velocity increases with increasing distance from shore may produce a skewed cross-river benthic distribution of animals. The degree of skewness will depend on the current velocity gradient and on suspended animals' settling behavior.
Canadian Journal of Fisheries and Aquatic Sciences, 1987
Journal of Great Lakes Research, 2005
Environmental Monitoring and Assessment, 1993
Pennsylvania-style light traps were used to capture adult Trichoptera from the St. Marys, St. Cla... more Pennsylvania-style light traps were used to capture adult Trichoptera from the St. Marys, St. Clair, Detroit and Niagara rivers, Canada. Adequate biomass was acquired in single, 2-h collections to permit triplicate gas chromatographic analyses of 1–4 g samples for 36 organochlorine contaminants. Contaminant levels varied unpredictably but relatively little among samples taken at monthly intervals over the summer. Samples collected simultaneously from the two sides of the Detroit R. reflected local sediment contaminant patterns, suggesting limited dispersal by adults. Genus-specific differences in contaminant concentrations within the Hydropsychidae and Leptoceridae probably reflect differences in larval habitats and manner of feeding. Contaminant concentrations and relative composition paralleled published reports of contaminants in sediments from collection locations. St. Marys R. caddisflies contained contaminant levels indistinguishable from samples collected at reference sites. St. Clair R. samples contained high levels of compounds associated with petrochemical industries located in the river's upstream reaches. High levels of polychlorinated biphenyls (PCBs) and most other contaminants in Detroit R. samples reflected industrial loadings near Detroit, Michigan. Niagara R. samples contained elevated concentrations of PCBs and pesticides. Cluster analysis grouped samples into five clusters each with unique contaminant composition. These also corresponded to geographic origin: St. Marys, St. Clair, Detroit and upper and lower Niagara rivers. The relative ease of collection and consistent results obtained render adult Trichoptera potentially valuable candidates for surveys of aquatic contamination over a broad range of geographical and ecological conditions.
Freshwater Biology, 1977
SUMMARY. Experiments conducted in an artificial stream showed that significantly more nymphs drif... more SUMMARY. Experiments conducted in an artificial stream showed that significantly more nymphs drifted from an inorganic substrate at a mean current velocity of 28.5 cm s−1 than at 18.5 cm s−1. Drift density, however, was not affected. Disproportionately large numbers of nymphs drifted while current velocities were being increased from 18.5 to 28.5 cm s−1.Both drift numbers and drift density were greater in turbid water, after the addition of large amounts of inorganic sediment, than under clear-flowing conditions during dark periods but not in the light. The interaction of increasing current velocity and sediment levels resulted in a significantly greater number of drifting nymphs under lighted conditions.Minor spates which do not seriously disturb the stream bed may initiate significant increases in macroinvertebrate drift.
Canadian Journal of Fisheries and Aquatic Sciences, 1989
Aka. T6G 2 E3 Ciborcswski, 8. 1. H., and D. A. Craig. 1989. Factors influencing dispersion sf lar... more Aka. T6G 2 E3 Ciborcswski, 8. 1. H., and D. A. Craig. 1989. Factors influencing dispersion sf larval black flies (Qiptera: Sirnuliidae): effects of current velocity and food concentration. Can. 1. Fish. Aquat. Sci. 46: 1329-1 341.
Canadian Journal of Zoology-revue Canadienne De Zoologie, 1977
and substrate on the distribution and drift of two species of mayflies (Epherneroptera). Can. J. ... more and substrate on the distribution and drift of two species of mayflies (Epherneroptera). Can. J. Zool. 55: 1970-1977. The effects of substrate type and current velocity on the distribution and drift of Baetis vagans McDunnough and Paraleptophlebia mollis (Eaton) were examined in an artificial stream. Of those B. vagans (swimming nymphs) remaining on the substrates, most were retrieved from branches while few were found in inorganic substrates. In all cases, numbers of B. vagans remaining on the substrates increased as current velocit~es increased. Paraleptophlebia mollis (crawling nymphs) were most frequently associated with grave1 (11.2-16 mm diameter), whereas branches were of less importance.
Ecological Applications, 2002
Defining objectives for ecological rehabilitation requires consideration of how an ecosystem resp... more Defining objectives for ecological rehabilitation requires consideration of how an ecosystem responds to management. Validated quantitative models of physical, chemical, and biological processes are the best way to project such impacts; however, time, data, and model limitations often make these approaches impractical. An alternative is to encode expert knowledge about interactions among ecosystem components in a fuzzy cognitive map (FCM), which then translates that subjective, qualitative information into predictions of ...
Canadian Journal of Zoology-revue Canadienne De Zoologie, 1990
Journal of Great Lakes Research, 2005
Canadian Journal of Zoology-revue Canadienne De Zoologie, 1992
ABSTRACT Natural populations of the burrowing mayfly belonging to the genus Hexagenia are charact... more ABSTRACT Natural populations of the burrowing mayfly belonging to the genus Hexagenia are characterized by unusually broad size-frequency distributions. Environmental features are often invoked to explain among-populations growth differences. We used a 4 × 4 factorial design to investigate differences in mean larval size and mortality of Hexagenia reared at different densities and food levels over four time intervals (30, 60, 90, and 120 d) in the laboratory. Larvae were hatched from eggs collected from imagoes at the Detroit River near Windsor, Ontario. Although neither density nor food limitation influenced larval growth at either 30 or 60 d growth, the number of days required for eggs to hatch did significantly influence larval growth at this time. At 30 d growth, larvae that hatched after 6 d incubation were significantly smaller than larvae that required an additional day to hatch (7 d). At both 30 and 60 d, larvae that hatched after 6 d incubation had lower mortality than larvae that hatched after 7 d. At 90 and 120 d growth, density and food significantly influenced larval size and mortality. Larvae reared at low density and with a high food level attained the largest size. Mortality increased under stressed conditions (high density and (or) low food level). Since endogenous features (day of hatch) can be important early in larval development (at 30 or 60 d), such features may contribute to the outcome of competitive events that occur later in development (at 90 or 120 d), when exogenous factors (density and food) become significant.
Canadian Journal of Fisheries and Aquatic Sciences, 1984
... To determine the influence of decreasing velocity, the order of August readings was reversed.... more ... To determine the influence of decreasing velocity, the order of August readings was reversed. We also evaluated expected colonization pattern with current velocity constant, set at the overall mean value observed dufing August trials (38.25 cm . ...
Environmental Toxicology and Chemistry, 1996
ABSTRACT
1983. Life histories, microdistribution and drift of two mayfly (Ephemeroptera) species in the Pe... more 1983. Life histories, microdistribution and drift of two mayfly (Ephemeroptera) species in the Pembina River, Alberta, Canada. -Holarct. Ecol. 6; 3-10.
Journal of Great Lakes Research, 1989
Journal of Great Lakes Research, 2005
A lake-wide benthic survey of Lake Erie during summer 2002 indicated that Dreissena bugensis is t... more A lake-wide benthic survey of Lake Erie during summer 2002 indicated that Dreissena bugensis is the dominant dreissenid in Lake Erie, especially in the east basin where this species was found at every station but no Dreissena polymorpha were collected. Mean (±SD) densities of dreissenid mussels were comparable between the west (601 ± 2,110/m 2 ;n = 49) and central (635 ± 1,293/m 2 ; n = 41) basins, but were much greater in the east basin (9,480 ± 11,173/m 2 ; n = 17). The greater variability in mussel density among stations and replicate samples in the central and west basins than in the east basin is attributable to the preponderance of fine-grained substrata in the nearshore, higher episodic rates of sediment deposition, and periodic hypoxia in bottom waters. Although there was little change in lake-wide mean dreissenid densities between 1992 and 2002 (declining from ca. 2,636 individuals/m2 to 2,025 individuals/m 2 ), basin-averaged shell-free dry tissue mass increased by almost four-fold from ca. 6.8 ± 15.6 g /m 2 to 24.7 ± 71.3 g/m 2 in the same interval. Up to 90% of this biomass is in the eastern basin. Other changes in 2002 include the virtual absence of mussels in the 3 to 12 mm size range, probably because of predation by round gobies, and an increase in the average size of mature mussels. The substantial changes observed between 1992 and 2002 suggest that dreissenid populations in Lake Erie were still changing rapidly in abundance and biomass, as well as species composition. The results of this survey suggest that a direct link between Dreissena spp. and hypolimnetic hypoxia in the central basin is unlikely.
Environmental Management, 2007
Integrated, quantitative expressions of anthropogenic stress over large geographic regions can be... more Integrated, quantitative expressions of anthropogenic stress over large geographic regions can be valuable tools in environmental research and management. Despite the fundamental appeal of a regional approach, development of regional stress measures remains one of the most important current challenges in environmental science. Using publicly available, pre-existing spatial datasets, we developed a geographic information system database of 86 variables related to five classes of anthropogenic stress in the U.S. Great Lakes basin: agriculture, atmospheric deposition, human population, land cover, and point source pollution. The original variables were quantified by a variety of data types over a broad range of spatial and classification resolutions. We summarized the original data for 762 watershed-based units that comprise the U.S. portion of the basin and then used principal components analysis to develop overall stress measures within each stress category. We developed a cumulative stress index by combining the first principal component from each of the five stress categories. Maps of the stress measures illustrate strong spatial patterns across the basin, with the greatest amount of stress occurring on the western shore of Lake Michigan, southwest Lake Erie, and southeastern Lake Ontario. We found strong relationships between the stress measures and characteristics of bird communities, fish communities, and water chemistry measurements from the coastal region. The stress measures are taken to represent the major threats to coastal ecosystems in the U.S. Great Lakes. Such regional-scale efforts are critical for understanding relationships between human disturbance and ecosystem response, and can be used to guide environmental decision-making at both regional and local scales.
Journal of Great Lakes Research, 2007
Fish community composition often varies across ecoregions and hydrogeomorphic types within ecoreg... more Fish community composition often varies across ecoregions and hydrogeomorphic types within ecoregions. We evaluated two indices of biotic integrity (IBIs) developed for fish in Great Lakes coastal wetlands dominated (> 50% cover) by Typha (cattail) and Schoenoplectus (formerly Scirpus) (bulrush) vegetation. Thirty-three coastal wetlands dominated by either Typha or Schoenoplectus vegetation were sampled using fyke nets set overnight. These sites were selected to span anthropogenic disturbance gradients based on population density, road density, urban development, point-source pollution, and agricultural inputs (nutrients, sediments), measured using a GIS-based analysis of Great Lakes coastal land use. Sites subject to low levels of anthropogenic influence had high IBI scores. The Typhaspecific IBI showed a marginally significant negative correlation with population density and residential development (r = -0.54, p < 0.05; n = 21). The Schoenoplectus-specific IBI negatively correlated most strongly with nutrient and chemical inputs associated with agricultural activity and point-source pollution (r = -0.66 and -0.52, respectively; p < 0.01; n = 30). However, some relationships between IBI and disturbance scores were non-linear and likely exhibit a threshold relationship, particularly for Schoenoplectus dominant sites. Once a certain level of disturbance has been exceeded, a sharp change in fish community's composition and function occurs which is symptomatic of a degraded site. The IBI indices appear to indicate effects of some, but not all classes of anthropogenic disturbance on fish communities. † Current address: Watershed Ecosystems Graduate Program, Trent University, Peterborough, Ontario K9J 7B8 Canada 705.748-1011, ext. 7341, f 705.748.1026
Journal of Great Lakes Research, 2007
Watersheds represent spatially explicit areas within which terrestrial stressors can be quantifie... more Watersheds represent spatially explicit areas within which terrestrial stressors can be quantified and linked to measures of aquatic ecosystem condition. We delineated thousands of Great Lakes watersheds using previously proven and new watershed delineation techniques. These were used to provide summaries for a variety of anthropogenic stressors within the Great Lakes. All delineation techniques proved useful, but each had applications for which they were most appropriate. A set of watershed delineations and stressor summaries was developed for sampling site identification, providing relatively coarse strata for selecting sites along the U.S. Great Lakes coastline. Subsequent watershed delineations were used for high-resolution site characterization of specific sites and characterizing the full coastal stressor gradient. For these delineations we used three general approaches: 1) segmentation of the shoreline at points midway between adjacent streams and delineation of a watershed for each segment; 2) specific watershed delineations for sampled sites; and 3) a Great Lakes basin-wide, high-resolution approach wherein sub-basins can be agglomerated into larger basins for specific portions of the coast. The third approach is unique in that it provides a nested framework based on hierarchies of catchments with associated stressor data. This hierarchical framework was used to derive additional watershed delineations, and their associated stressor summaries, at four different scales. Providing anthropogenic stressor metrics in such a format that can quickly be summarized for the entire basin at multiple scales, or specifically for particular areas, establishes a strong foundation for quantifying and understanding stressor-response relationships in these coastal environments.
Canadian Journal of Fisheries and Aquatic Sciences, 1996
Hexagenia nymphs are sensitive to hypoxia, and their abundance has been proposed as an ecosystem ... more Hexagenia nymphs are sensitive to hypoxia, and their abundance has been proposed as an ecosystem indicator for assessing the recovery from eutrophication of shallow, mesotrophic lakes. Acute oxygen tolerance limits are known for Hexagenia spp., but effects of prolonged exposure to sublethal levels of hypoxia are not. A series of 21-day laboratory experiments was conducted to determine the influence of
Canadian Journal of Fisheries and Aquatic Sciences, 1983
ABSTRACT By releasing live and dead nymphs of two mayfly species, Baetis tricaudatus Dodds and Ep... more ABSTRACT By releasing live and dead nymphs of two mayfly species, Baetis tricaudatus Dodds and Ephemerella inermis Eaton, into the water column of a river and catching them downstream in a series of contiguous nets, I estimated settling and lateral dispersal rates. Live animals settled over shorter distances than dead individuals, and became more widely laterally dispersed for any given distance downstream and mean current velocity. Transport of suspended organisms in a river in which mean current velocity increases with increasing distance from shore may produce a skewed cross-river benthic distribution of animals. The degree of skewness will depend on the current velocity gradient and on suspended animals' settling behavior.
Canadian Journal of Fisheries and Aquatic Sciences, 1987
Journal of Great Lakes Research, 2005
Environmental Monitoring and Assessment, 1993
Pennsylvania-style light traps were used to capture adult Trichoptera from the St. Marys, St. Cla... more Pennsylvania-style light traps were used to capture adult Trichoptera from the St. Marys, St. Clair, Detroit and Niagara rivers, Canada. Adequate biomass was acquired in single, 2-h collections to permit triplicate gas chromatographic analyses of 1–4 g samples for 36 organochlorine contaminants. Contaminant levels varied unpredictably but relatively little among samples taken at monthly intervals over the summer. Samples collected simultaneously from the two sides of the Detroit R. reflected local sediment contaminant patterns, suggesting limited dispersal by adults. Genus-specific differences in contaminant concentrations within the Hydropsychidae and Leptoceridae probably reflect differences in larval habitats and manner of feeding. Contaminant concentrations and relative composition paralleled published reports of contaminants in sediments from collection locations. St. Marys R. caddisflies contained contaminant levels indistinguishable from samples collected at reference sites. St. Clair R. samples contained high levels of compounds associated with petrochemical industries located in the river's upstream reaches. High levels of polychlorinated biphenyls (PCBs) and most other contaminants in Detroit R. samples reflected industrial loadings near Detroit, Michigan. Niagara R. samples contained elevated concentrations of PCBs and pesticides. Cluster analysis grouped samples into five clusters each with unique contaminant composition. These also corresponded to geographic origin: St. Marys, St. Clair, Detroit and upper and lower Niagara rivers. The relative ease of collection and consistent results obtained render adult Trichoptera potentially valuable candidates for surveys of aquatic contamination over a broad range of geographical and ecological conditions.
Freshwater Biology, 1977
SUMMARY. Experiments conducted in an artificial stream showed that significantly more nymphs drif... more SUMMARY. Experiments conducted in an artificial stream showed that significantly more nymphs drifted from an inorganic substrate at a mean current velocity of 28.5 cm s−1 than at 18.5 cm s−1. Drift density, however, was not affected. Disproportionately large numbers of nymphs drifted while current velocities were being increased from 18.5 to 28.5 cm s−1.Both drift numbers and drift density were greater in turbid water, after the addition of large amounts of inorganic sediment, than under clear-flowing conditions during dark periods but not in the light. The interaction of increasing current velocity and sediment levels resulted in a significantly greater number of drifting nymphs under lighted conditions.Minor spates which do not seriously disturb the stream bed may initiate significant increases in macroinvertebrate drift.
Canadian Journal of Fisheries and Aquatic Sciences, 1989
Aka. T6G 2 E3 Ciborcswski, 8. 1. H., and D. A. Craig. 1989. Factors influencing dispersion sf lar... more Aka. T6G 2 E3 Ciborcswski, 8. 1. H., and D. A. Craig. 1989. Factors influencing dispersion sf larval black flies (Qiptera: Sirnuliidae): effects of current velocity and food concentration. Can. 1. Fish. Aquat. Sci. 46: 1329-1 341.
Canadian Journal of Zoology-revue Canadienne De Zoologie, 1977
and substrate on the distribution and drift of two species of mayflies (Epherneroptera). Can. J. ... more and substrate on the distribution and drift of two species of mayflies (Epherneroptera). Can. J. Zool. 55: 1970-1977. The effects of substrate type and current velocity on the distribution and drift of Baetis vagans McDunnough and Paraleptophlebia mollis (Eaton) were examined in an artificial stream. Of those B. vagans (swimming nymphs) remaining on the substrates, most were retrieved from branches while few were found in inorganic substrates. In all cases, numbers of B. vagans remaining on the substrates increased as current velocit~es increased. Paraleptophlebia mollis (crawling nymphs) were most frequently associated with grave1 (11.2-16 mm diameter), whereas branches were of less importance.
Ecological Applications, 2002
Defining objectives for ecological rehabilitation requires consideration of how an ecosystem resp... more Defining objectives for ecological rehabilitation requires consideration of how an ecosystem responds to management. Validated quantitative models of physical, chemical, and biological processes are the best way to project such impacts; however, time, data, and model limitations often make these approaches impractical. An alternative is to encode expert knowledge about interactions among ecosystem components in a fuzzy cognitive map (FCM), which then translates that subjective, qualitative information into predictions of ...
Canadian Journal of Zoology-revue Canadienne De Zoologie, 1990
Journal of Great Lakes Research, 2005
Canadian Journal of Zoology-revue Canadienne De Zoologie, 1992
ABSTRACT Natural populations of the burrowing mayfly belonging to the genus Hexagenia are charact... more ABSTRACT Natural populations of the burrowing mayfly belonging to the genus Hexagenia are characterized by unusually broad size-frequency distributions. Environmental features are often invoked to explain among-populations growth differences. We used a 4 × 4 factorial design to investigate differences in mean larval size and mortality of Hexagenia reared at different densities and food levels over four time intervals (30, 60, 90, and 120 d) in the laboratory. Larvae were hatched from eggs collected from imagoes at the Detroit River near Windsor, Ontario. Although neither density nor food limitation influenced larval growth at either 30 or 60 d growth, the number of days required for eggs to hatch did significantly influence larval growth at this time. At 30 d growth, larvae that hatched after 6 d incubation were significantly smaller than larvae that required an additional day to hatch (7 d). At both 30 and 60 d, larvae that hatched after 6 d incubation had lower mortality than larvae that hatched after 7 d. At 90 and 120 d growth, density and food significantly influenced larval size and mortality. Larvae reared at low density and with a high food level attained the largest size. Mortality increased under stressed conditions (high density and (or) low food level). Since endogenous features (day of hatch) can be important early in larval development (at 30 or 60 d), such features may contribute to the outcome of competitive events that occur later in development (at 90 or 120 d), when exogenous factors (density and food) become significant.
Canadian Journal of Fisheries and Aquatic Sciences, 1984
... To determine the influence of decreasing velocity, the order of August readings was reversed.... more ... To determine the influence of decreasing velocity, the order of August readings was reversed. We also evaluated expected colonization pattern with current velocity constant, set at the overall mean value observed dufing August trials (38.25 cm . ...
Environmental Toxicology and Chemistry, 1996
ABSTRACT
1983. Life histories, microdistribution and drift of two mayfly (Ephemeroptera) species in the Pe... more 1983. Life histories, microdistribution and drift of two mayfly (Ephemeroptera) species in the Pembina River, Alberta, Canada. -Holarct. Ecol. 6; 3-10.
Journal of Great Lakes Research, 1989
Journal of Great Lakes Research, 2005
A lake-wide benthic survey of Lake Erie during summer 2002 indicated that Dreissena bugensis is t... more A lake-wide benthic survey of Lake Erie during summer 2002 indicated that Dreissena bugensis is the dominant dreissenid in Lake Erie, especially in the east basin where this species was found at every station but no Dreissena polymorpha were collected. Mean (±SD) densities of dreissenid mussels were comparable between the west (601 ± 2,110/m 2 ;n = 49) and central (635 ± 1,293/m 2 ; n = 41) basins, but were much greater in the east basin (9,480 ± 11,173/m 2 ; n = 17). The greater variability in mussel density among stations and replicate samples in the central and west basins than in the east basin is attributable to the preponderance of fine-grained substrata in the nearshore, higher episodic rates of sediment deposition, and periodic hypoxia in bottom waters. Although there was little change in lake-wide mean dreissenid densities between 1992 and 2002 (declining from ca. 2,636 individuals/m2 to 2,025 individuals/m 2 ), basin-averaged shell-free dry tissue mass increased by almost four-fold from ca. 6.8 ± 15.6 g /m 2 to 24.7 ± 71.3 g/m 2 in the same interval. Up to 90% of this biomass is in the eastern basin. Other changes in 2002 include the virtual absence of mussels in the 3 to 12 mm size range, probably because of predation by round gobies, and an increase in the average size of mature mussels. The substantial changes observed between 1992 and 2002 suggest that dreissenid populations in Lake Erie were still changing rapidly in abundance and biomass, as well as species composition. The results of this survey suggest that a direct link between Dreissena spp. and hypolimnetic hypoxia in the central basin is unlikely.
Environmental Management, 2007
Integrated, quantitative expressions of anthropogenic stress over large geographic regions can be... more Integrated, quantitative expressions of anthropogenic stress over large geographic regions can be valuable tools in environmental research and management. Despite the fundamental appeal of a regional approach, development of regional stress measures remains one of the most important current challenges in environmental science. Using publicly available, pre-existing spatial datasets, we developed a geographic information system database of 86 variables related to five classes of anthropogenic stress in the U.S. Great Lakes basin: agriculture, atmospheric deposition, human population, land cover, and point source pollution. The original variables were quantified by a variety of data types over a broad range of spatial and classification resolutions. We summarized the original data for 762 watershed-based units that comprise the U.S. portion of the basin and then used principal components analysis to develop overall stress measures within each stress category. We developed a cumulative stress index by combining the first principal component from each of the five stress categories. Maps of the stress measures illustrate strong spatial patterns across the basin, with the greatest amount of stress occurring on the western shore of Lake Michigan, southwest Lake Erie, and southeastern Lake Ontario. We found strong relationships between the stress measures and characteristics of bird communities, fish communities, and water chemistry measurements from the coastal region. The stress measures are taken to represent the major threats to coastal ecosystems in the U.S. Great Lakes. Such regional-scale efforts are critical for understanding relationships between human disturbance and ecosystem response, and can be used to guide environmental decision-making at both regional and local scales.