Murray N. Charlton

Temporal Trends in Lake Erie Plankton Biomass: Roles of External Phosphorus Loading and Dreissenid Mussels

Abstract We compare the results of lakewide plankton studies conducted during 1996–2002 with data reported in the literature from previous years to evaluate the effectiveness of continued nutrient control, the relationship between external phosphorus loading and plankton abundance, and the many predicted outcomes of the dreissenid invasion. We found that although recent external annual phosphorus loading has not changed since reaching mandated target levels in the early- to mid-1980s, phytoplankton communities have. Total phytoplankton biomass, measured through enumeration and size-frequency distributions has increased since minima were observed in 1996 or 1997, with summer (July–September) biomasses generally greater than before the dreissenid establishment in the late 1980s. Cyanobacteria biomass also increased during summer in all basins after the dreissenid invasion. In contrast, chlorophyll a concentration has decreased in all basins during both spring and summer. However chlorophyll a concentration was poorly correlated with total phytoplankton biomass. Relative to the mid-1980s, crustacean zooplankton biomass during the years 1996–2002 increased in the western basin during spring and summer, increased in the central basin during spring but remained the same during summer, and decreased to low levels in the eastern basin. Several of these observations are consistent with predictions made by previous researchers on the effects of reduced total external phosphorus loading and the stimulatory or inhibitory effects of dreissenid mussels. However, several were not. Results from this study, particularly the inconsistencies with tested predictions, highlight the need for further research into the factors that regulate plankton community dynamics in Lake Erie.

Seasonal Phosphate Demand for Lake Erie Plankton

From April to mid-October 1979, in the eastern and central basins of Lake Erie, the pattern for phosphate demand was assessed by four independent methods: conventional monitoring, measurements of polyphosphate, phosphate turnover time, and a newly developed phosphate deficiency index. Thermal stratification and P limitation occurred faster in the central than in the eastern basin and the plankton remained P limited throughout most of the stratified season. This condition relaxed as the thermocline deepened in the central basin, exposing the epilimnion to a greater area of sediments. In September, when mixing of the entire water column occurred, the plankton were no longer P limited. In contrast, as the thermocline deepened in the eastern basin, metalimnetic water was entrained but the plankton remained P limited until mid-October. These observations support the view that a reduction of phosphorus in Lake Erie would probably affect the phytoplankton biomass during the periods of P limitation.

Lake Erie Offshore in 1990: Restoration and Resilience in the Central Basin

Abstract The Great Lakes Water Quality Agreement (GLWQA) of 1972 resulted in large expenditures to build and operate treatment plants to remove phosphorus from sewage. Technology is available to remove even more phosphorus than is customary now. Thus, it is important to the eutrophication issue to document and understand the effects of management in order to diagnose the efficacy and appropriateness of present and future controls. The ground-breaking Canada-U.S. “Project Hypo” study of 1970 resulted in phosphorus reduction targets for Lake Erie in the GLWQA. Research cruises in the offshore of the central basin during 1979, 83, 84, and 85 were complemented by a series of cruises in 1990. Chemical and biological water quality variables were measured in the relatively stable months of July and August. Chlorophyll and phosphorus concentrations and secchi disk readings suggest that exemplary surface water quality was already apparent in 1979. Based on scaling arguments, relatively small chemical changes are expected in the offshore and these are consistent with observations. Sediment phosphorus regeneration and dissolved oxygen depletion were similar in 1970 and 1990 despite 20 years of nutrient reductions. The delayed improvement in the hypoUmnion may be consistent with delayed or avoided damage due to mechanisms of system resilience. The GLWQA may have prevented a sediment response that would take many decades to reverse.

Trends in spatial and temporal levels of persistent organic pollutants in Lake Erie sediments.

A Lake Erie sediment survey was conducted in 1997 to characterize spatial trends in contamination, and for comparison with a 1971 survey to assess any changes in environmental quality since the advent of measures to reduce contaminant sources. Contaminant data for some contaminant classes in 1971 was based on analysis of frozen archived samples, thereby allowing a direct comparison between surficial sediment contamination in 1971 and 1997 based on modern analytical methods. Lake-wide contaminant concentrations of polychlorinated biphenyls (PCBs) and organochlorine compounds including hexachlorobenzene and the DDT compounds in 1997 were substantially lower, compared to levels in samples collected in 1971. Lake-wide average sediment PCB levels were found to have decreased roughly 70% from 136 ng/g in 1971 to 43 ng/g in 1997. Similarly, reductions in other compound classes ranged from 40% to 80%. In 1997, some individual contaminants classes including PCBs exhibited a spatial trend toward increasing sediment contamination from the eastern basin to the western basin, and from the north-central basin to the south-central basin. Levels of organic contaminants in sediments in some areas of Lake Erie still exceeded the strictest Canadian Federal and Ontario Provincial guidelines. However, exceedances of guidelines describing contaminated environments in 1997 were predominantly restricted to the western basin and near-shore sites in the southern part of the central basin.

The re-eutrophication of Lake Erie: Harmful algal blooms and hypoxia

Lake Erie supplies drinking water to more than 11 million consumers, processes millions of gallons of wastewater, provides important species habitat and supports a substantial industrial sector, with >

Freshwater mussels as biomonitors for organic industrial contaminants and pesticides in the St. Lawrence River.

50 billion annual income to tourism, recreational boating, shipping, fisheries, and other industries. These and other key ecosystem services are currently threatened by an excess supply of nutrients, manifested in particular by increases in the magnitude and extent of harmful planktonic and benthic algal blooms (HABs) and hypoxia. Widespread concern for this important international waterbody has been manifested in a strong focus of scientific and public material on the subject, and commitments for Canada-US remedial actions in recent agreements among Federal, Provincial and State agencies. This review provides a retrospective synthesis of past and current nutrient inputs, impairments by planktonic and benthic HABs and hypoxia, modelling and Best Management Practices in the Lake Erie basin. The results demonstrate that phosphorus reduction is of primary importance, but the effects of climate, nitrogen and other factors should also be considered in the context of adaptive management. Actions to reduce nutrient levels by targeted Best Management Practices will likely need to be tailored for soil types, topography, and farming practices.

Downflux of Sediment, Organic Matter, and Phosphorus in the Niagara River Area of Lake Ontario

Native mussels (Elliptio complanata and Lampsilis radiata radiata) were collected from 17 stations in the St. Lawrence River between Lake Ontario and Trois Rivières and from three stations in a major tributary, the Ottawa River, in October, 1985. Mussels were solvent-extracted and analyzed individually by dual capillary column gas chromatography for seven organochlorine pesticides, 11 chlorobenzenes, octachlorostyrene and 63 PCB congeners. Bioconcentration patterns for contaminants in mussel tissues implicated Lake Ontario as the source of Mirex and DDT derivatives to the system and the Grass River as the major source of PCBs. Numbers of PCB congeners in mussels increased from 21-27 in the upper river to 56-59 in the Cornwall/Massena industrial core, mainly due to the appearance of di-, tri- and tetrachlorobiphenyls; an average of 43 congeners persisted as far downstream as Lac Saint-Pierre. Concentrations of most contaminants in mussels from the Ottawa River were 50-75% lower than the lowest values reported for the St. Lawrence River. This study provides information on the origin, bioavailability and persistence of organic contaminants in the St. Lawrence River ecosystem.

Water quality trends in Hamilton Harbour: Two decades of change in nutrients and chlorophyll a

Vertical arrays of sediment traps were installed near the mouth of the Niagara River and at nearshore and offshore sites. Surveys of temperature, turbidity, and conductivity were used to establish that the traps nearest the river mouth were under the river outflow plume. A single offshore array in 1980 indicated downfluxes of 1-2 g · m−2 · d−1 of dry matter in the mid-water column. These fluxes were similar to those of small lakes but much higher fluxes were found near the bottom of Lake Ontario. More extensive work in 1981 confirmed the presence of a near-bottom nepheloid layer and the effect it has on increasing downflux extimates. Sediment traps near shore and at the river mouth caught substantially more material at all depths than did traps at the offshore stations. Downfluxes of phosphorus and sediment were consistent with independent estimates of loading and retention.

Lake Erie Oxygen Revisited

ABSTRACT Systematic water quality research and monitoring has been on-going in Hamilton Harbour since 1987 in response to the Remedial Action Plan (RAP) for this Area of Concern (AOC). Here we present a spatiotemporal analysis of water quality in the harbour and its biological response from 1987 to 2007. Overall nutrient concentrations have decreased by 16 (SRP), 26 (NH3-Tot) and 36% (TP) in the harbour, chl a concentrations have decreased by 16% and NO3/2 concentrations have increased by 27%. Hypoxia in the hypolimnion of Hamilton Harbour remains a common occurrence despite improvements in surface water quality conditions. Seasonal patterns in water quality in Hamilton Harbour are mainly driven by biological activity and show typical patterns observed in dimictic nutrient rich lakes. There is systematic spatial variability in water quality in the harbour which is related to the proximity of point and non-point sources; however, there is coherence among all stations sampled and similar temporal trends were observed for all stations. The biological response in the harbour suggests that phosphorus limited algal growth is becoming more prevalent in Hamilton Harbour and the rate of improvements in water quality should accelerate in the near future following further reductions in phosphorus loadings.

Sedimentation, Resuspension, and Oxygen Depletion in Lake Erie (1979)

The problem of predicting the future hypolimnion oxygen regime in Lake Erie from past records is reassessed. Instead of comparing oxygen depletion rates, the data were manipulated to reveal comparable concentrations at the end of August each year. By removing confusion caused by variable concentrations at the beginning of stratification, the expected change of 0–2 mg/Lfrom the 1950s to present was revealed. The oxygen regime of the east basin has changed little if at all; the year-to-year variability being as large as possible trends in concentration. A water sampling device used in the earliest samplings was found to produce incorrect samples under certain conditions, thereby lessening confidence in the early data. The trajectory of oxygen concentration after stratification is independent of epilimnion productivity. It is proposed that oxygen depletion depends on average trophic conditions proceeding each stratified season. Modestly improved O2 concentrations can be expected with, periodically, low concentrations due to lake levels and weather after nutrient loading reductions. The lag of O2 response to loading reductions is at least 10 years. Lag phenomena may have prevented full O2 response to loading increases.