Is Lake Erie a resilient ecosystem?

Abstract

Lake Erie has a long history of natural and cultural perturbations ranging from glacial origins, arrival of Europeans, exploration-early colonization, degradation, exotic invasion, and phosphorus reduction to its recent recovery. Is Lake Erie a resilient ecosystem responding to phosphorus abatement and exotic invasion? It is believed that Erie was an oligotrophic system when glaciers receded followed by a long period of mesotrophic conditions. It has been classified from mesotrophic to eutrophic ecosystem during the past three decades. In the 1970s the Great Lakes Water Quality Agreement was signed between Canada and the United States and steps were taken to reduce the phosphorus loading to the Great Lakes including Lake Erie. Total phosphorus and chlorophyll a levels in the eutrophic west have dropped from 41 µg L −1 and 13.8 µg L −1 in the 1970s to <20 µg L −1 and 5.6 µg L −1 in the 1990s. Similarly a significant decrease in phytoplankton biomass was recorded from 1970 to 1992 in the western basin. During the same period Diatomeae decreased markedly from 55% to 10% whereas Chlorophyta increased from 8% to 55%. Similar trends were evident in the other biota. Primary production rates in the 1990s were dominated by small sized organisms (picoplankton and nanoplankton) similar to Lake Superior—a pristine oligotrophic ecosystem. Based on several criteria such as reduction of biomass and primary production, high species diversity, decrease of eutrophic and increase of mesotrophic-oligotrophic species and prevalence of picoplankton-nanoplankton, Lake Erie appears to be a rapidly changing and resilient ecosystem altering from eutrophic to meso-oligotrophic conditions. These observations are also supported by the response of other biota such as zooplankton and benthos. For example during 1993 the non-zebra mussel benthic biomass in the western basin had returned to a similar composition observed earlier in 1952 including the recovery of the mayfly. On the other hand eastern basin benthos has not shown the same extent of recovery as the west. Fish community trends are very complex, but the return of the walleye and whitefish in the western and eastern basins respectively are encouraging signs of recovery. The changes observed at various trophic levels are indicative of a meso-oligotrophic environment.

Mesozooplankton and microzooplankton grazing during cyanobacterial blooms in the western basin of Lake Erie

“…Over the past several decades these systems have been subject to a series of anthropogenic pressures such as the introduction of non-native species (i.e., dreissenid mussels) and eutrophication. Of the Great Lakes, Lake Erie is the most socioeconomically important (Fuller et al, 2002;Munawar et al, 2002) serving the recreational, commercial, and drinking water needs of over ten million people (Fuller et al, 2002). It is divided into the physically, chemically, and biologically distinct eastern, central, and western basins.…”

Late-summer phytoplankton in western Lake Erie (Laurentian Great Lakes): bloom distributions, toxicity, and environmental influences

“…Although the magnitude of the Pandorina bloom event was surprising, accumulations of chlorophytes and cyanobacteria, or both, throughout the western basin were not unexpected. Both phylogenetic groups thrive in nutrient-enriched waters (Moss 1977;Paerl 1988) and historically have been abundant throughout western Lake Erie (Munawar and Munawar 1996;Nicholls 1997;Makarewicz et al 1999). Chlorophytes are characterized by high growth/loss rates and a high demand for nutrients, whereas cyanobacteria typically have lower growth/loss rates and a lower nutrient demand (than chlorophytes; Jensen et al 1994;see Paerl and Millie 1996).…”

“…Lake Erie, the shallowest and smallest of the Lakes by volume, is divided into eastern, central, and western basins, each quite different in physical, chemical, and biological aspects. Lake Erie has a long history of anthropogenic perturbation (Burns 1985;Munawar et al 2002). Excessive nutrient loading during the mid-twentieth century [e.g., 1.61 9 10 5 and 2.73 9 10 4 metric tons of total nitrogen (N) and phosphorus (P), respectively, from 1966 to 1967 alone; Sly 1976] resulted in eutrophic waters in the western and central basins.…”

Diversity of Microcystin-Producing Cyanobacteria in Spatially Isolated Regions of Lake Erie

“…Lake Erie is the most productive of these lakes, and it maintains a position of regional socioeconomic importance (3,9). Although the annual appearance of Microcystis in the western basin of Lake Erie since 1995 is well documented (2,11,14,15), the presence of other microcystin producers has garnered less attention.…”