Glenn J. Warren

The U.S. EPA Lake Erie Indicators Monitoring Program 1983–2002: Trends in Phosphorus, Silica, and Chlorophyll a in the Central Basin

During the past 20 years, Lake Erie has exhibited a series of complex chemical changes resulting from changing anthropogenic influences and introductions of exotic species. Since 1990, some apparent trends in nutrient concentrations have been inconsistent with the predictions of models originally used to guide Lake Erie water quality management. We performed time trend analysis on total phosphorus (TP), chlorophyll a (Chl a), and dissolved reactive silica (DRS) measurements collected during spring and summer in the central basin of Lake Erie between 1983 and 2002. Three distinct time trends in basin-specific, station-averaged open-water TP concentrations were observed over the 20-year period: 1983–1989 decreases, 1990–1997 increases, and 1997–2001 decreases. Exceptionally high levels of turbidity and TP were observed in spring 2002, possibly reflecting increasing frequency of winter storm events. Open-water concentrations of TP declined during the 1980s as annual TP loadings to Lake Erie declined below the 11,000 metric ton target level that had been expected to reduce central basin eutrophication. This was accompanied by a significant increase in available silica and in Chl a concentrations. During the period 1990–2002, when dreissenid mussels were abundant, spring TP concentrations increased but summer TP concentrations declined. Unexpected increases in spring central basin concentrations of DRS (exceeding 1 mg/L) were observed. During the same period, Chl a concentrations declined in the spring and rose slightly during summer.

Young-of-the-Year Coregonus Hoyi in Lake Michigan: Prey Selection and Influence on the Zooplankton Community

Young-of-the-year bloater, Coregonus hoyi, 16 to 71 mm standard length, were collected from an offshore reference station 100 m deep in southern Lake Michigan during July-August, 1985 and 1986. Gut contents of the fish were examined for prey taxa and prey size. Small bloaters (<20 mm) ate Cyclops copepodids almost exclusively. Bloaters between 20 and 35 mm had increasing proportions of Daphnia in their diets as a function of increased body length. Daphnia, especially D. pulicaria, was the most important component in the diets of the largest fish (<35 mm). Larger YOY bloaters preyed selectively on large individuals of D. pulicaria. Abundance of Coregonus increased during 1985 and 1986 subsequent to a decrease in the population of alewife (Alosa pseudoharengus) in Lake Michigan. Planktivory by bloaters may have been an important selective influence on the summer plankton community in offshore regions of the lake, contributing to a decrease in D. pulicaria.

Ecological monitoring for assessing the state of the nearshore and open waters of the Great Lakes

The Great Lakes Water Quality Agreement stipulates that the Governments of Canada and the United States are responsible for restoring and maintaining the chemical, physical and biological integrity of the waters of the Great Lakes Basin Ecosystem. Due to varying mandates and areas of expertise, monitoring to assess progress towards this objective is conducted by a multitude of Canadian and U.S. federal and provincial/state agencies, in cooperation with academia and regional authorities. This paper highlights selected long-term monitoring programs and discusses a number of documented ecological changes that indicate the present state of the open and nearshore waters of the Great Lakes.

Assessment and Management of Fish Community Health in the Great Lakes: Synthesis and Recommendations

Abstract Our objective was to provide a perspective on fish community health to serve as a conceptual framework for assessing the effects of toxic chemicals and other anthropogenic influences on fish communities in the Great Lakes. We discuss the hierarchical structure and homeostatic mechanisms of aquatic ecosystems, and describe a general ecosystem stress syndrome (GESS) that characterizes patterns of ecosystem response in terms of alarm, resistance, and exhaustion. Anthropogenic stressors operate at various levels within the organizational hierarchy of aquatic ecosystems, and their effects are filtered and propagated throughout the system by physical, chemical, and biological processes. Determination of causal relationships between stressors and system responses has proven difficult because of the multiplicity of factors that influence system behavior. Methods employed for fish health investigations in the Great Lakes span molecular to ecosystem approaches, reflecting the diversity of stressors operating on the fish communities, but have tended to be applied within relatively narrow disciplinary perspectives. We perceive a need for broader perspectives and interdisciplinary investigation of the effects of toxic chemicals and other stressors. Attainment and maintenance of healthy fish communities, which we define as relatively stable, self-sustaining assemblages of fishes providing sustained economic, social, aesthetic, and ecological benefits, requires an ecosystem-based fisheries management strategy. The strategy must incorporate the integral roles of humans and other terrestrial species in the Great Lakes ecosystem in recognition of feed-back mechanisms involving resource utilization and waste and material inputs, thereby incorporating health concerns for all high risk populations including humans. We recommend adoption of a field-oriented epidemiological approach for monitoring and assessment of fish community health, supported by transdisciplinary investigative teams for ecosystem problems requiring diagnostic and remedial activities. We suggest that Areas of Concern under Annex 2 of the 1978 Great Lakes Water Quality Agreement be used as sites for comparative management experiments involving deliberate manipulation of ecosystem processes, not only to rehabilitate these areas, but also to improve understanding of the structural and functional properties of these systems, and to provide feedback for adjustment of the selected management options.

The effects of power plant passage on zooplankton mortalities: Eight years of study at the Donald C. Cook nuclear plant

Zooplankton mortalities resulting from passage through the Donald C. Cook Nuclear Plant (southeastern Lake Michigan) were studied over an 8-year (1975-1982) period. The power plant operated at a low AT (< 12°C) and discharge water temperatures did not exceed 35°C (except September 1978). While zooplankton mortalities were significantly greater in discharge than intake waters, differences were small, averaging < 3%. There was no evidence of additional delayed effects on zooplankton mortality following plant passage. Calanoid copepods (Diaptomus spp, Eurytemora affinis and Limnocalanus macrurus) were most sensitive to plant passage, cyclopoid copepods least sensitive, while cladocerans (Daphnia spp, Eubosmina coregoni) were intermediate in sensitivity. There was no relationship between zooplankton mortalities and temperature (AT, discharge water temperature), suggesting that thermal stresses were not the major source of mortality. The single exception was September 1978 when discharge water temperatures exceeded 35°C and there were large differences between intake and discharge water zooplankton mortalities (net mortality differences of 14-22% for the two units). Mechanical stresses appeared to be the major cause of zooplankton mortality. However, there was only a weak relationship between mortality as a result of plant passage and zooplankton size. Based on our long-term preoperational (1970-1974) and operational (1975-1982) ecological studies in the vicinity of the power plant, we hypothesize that fish predation, rather than power plant operation, probably was the major source of zooplankton mortality in inshore waters during much of the year.

Biomonitoring using invasive species in a large Lake: Dreissena distribution maps hypoxic zones

Due to cultural eutrophication and global climate change, an exponential increase in the number and extent of hypoxic zones in marine and freshwater ecosystems has been observed in the last few decades. Hypoxia, or low dissolved oxygen (DO) concentrations, can produce strong negative ecological impacts and, therefore, is a management concern. We measured biomass and densities of Dreissena in Lake Erie, as well as bottom DO in 2014 using 19 high frequency data loggers distributed throughout the central basin to validate a three-dimensional hydrodynamic-ecological lake model. We found that a deep, offshore hypoxic zone was formed by early August, restricting the Dreissena population to shallow areas of the central basin. Deeper than 20 m, where bottom hypoxia routinely develops, only young of the year mussels were found in small numbers, indicating restricted recruitment and survival of young Dreissena. We suggest that monitoring Dreissena distribution can be an effective tool for mapping the extent and frequency of hypoxia in freshwater. In addition, our results suggest that an anticipated decrease in the spatial extent of hypoxia resulting from nutrient management has the potential to increase the spatial extent of profundal habitat in the central basin available for Dreissena expansion.

Life after Dreissena : The decline of exotic suspension feeder may have significant impacts on lake ecosystems

It is well documented that the introduction of dreissenid bivalves in eutrophic lakes is usually associated with decreases in turbidity and total phosphorus concentrations in the water column, concomitant increases in water clarity, as well as other physical changes to habitat that may have cascading effects on other species in the invaded waterbody. In contrast, there is a paucity of data on the ecological ramifications of the elimination or decline of dreissenids due to pollution, bottom hypoxia, or other mechanisms. Using data collected by the U.S. Environmental Protection Agency Great Lakes National Program Offices Long-Term Biology and Water Quality Monitoring Programs, we analyzed the impacts of the hypoxia-induced declines in Dreissena densities in the central basin of Lake Erie on major water chemistry and physical parameters. Our analysis revealed that the decline in Dreissena density in the central basin was concomitant with a decrease in spring dissolved silica concentrations and an increase in total phosphorus and near bottom turbidity not seen in the western or eastern basins. In contrast, opposite patterns in water quality were observed in the eastern basin, which was characterized by a high and relatively stable Dreissena population. We are the first to report that dreissenid-related shifts in water quality of invaded waterbodies are reversible by documenting that the sharp decline of Dreissena in the central basin of Lake Erie was concomitant with a shift from clear to turbid water.

Lake Michigan (USA) Mass Balance Study: modeling fate, transport and bioaccumulation of PCBs, atrazine, trans-nonachlor and mercury

Development of effective strategies for toxics management requires a quantitative understanding of the relationships between contaminant sources, concentrations, sinks and effects on the ecosystem. The mass balance approach integrates environmental monitoring, load estimation and research efforts within a modeling framework that is compatible with both scientific and management objectives. Mass balance was chosen for Lake Michigan in order to understand the complex pathways through the system so that effective management strategies can be designed to reduce the threats from toxic chemicals. A key to mass balance is the estimation of the magnitude of mass fluxes of toxic chemicals between environmental media. Computer models evaluate environmental data to estimate the flow of pollurants between water, sediments, air and the food web. Based on these estimates, the mass balance can determine how changes in inputs from atmospheric deposition or tributary streams affect concentrations and inventories of toxic chemicals. Thus, the mass balance can serve as a useful too! to understand the current environmental concentrations of toxic chemicals and to predict future concentrations based on various management scenarios.