Presentation on theme: "Great Lakes Offshore Biological Desert and the Nearshore Slime Around the Tub David Rockwell Monitoring Indicators and Reporting Branch US EPA, Great Lakes."— Presentation transcript:
Great Lakes Offshore Biological Desert and the Nearshore Slime Around the Tub David Rockwell Monitoring Indicators and Reporting Branch US EPA, Great Lakes National Program Office
Methods Great Lakes National Program Office Annual monitoring cruises, 1983-2005 –Spring unstratified (April) –Summer stratified (August)
GLNPO Biology Program Measures Phytoplankton –Community Composition, Biomass –Deep Chlorophyll Maximum –Historical Communities Crustacean Zooplankton and Benthos –Community Composition –Size Structure of Community
GLNPO Sampling Stations Different colors indicate regions assumed to be homogeneous
Methods 1984-1990: –Tows B-2 m –63 m mesh net with flowmeter –Biomass calculated from avg. length/spp generated from 20 m tows 1998-2005 –100 (or B-2 m) tows –153 m mesh net with flowmeter –20 individuals/spp measured/sample
Mary Balcer Richard P. Barbiero University of Wisconsin-SuperiorCSC, & Loyola University Chicago Zooplankton Communities in Lake Huron 1984-2005
Total crustacean biomass with standard error bars
Size distribution of crustacean biomass North Basin South Basin
Superior central basin Huron northern basin Diaptomus sicilis Limnocalanus macrurus Lake Huron and Lake Superior Zooplankton Communities
Phosphorus Loading Trends Recent Loads Dolan and McGunagle 2005 Michigan P Load (tonnes yr -1 ) Superior Erie Ontario Huron GLWQA Target
Total Phosphorus Trends (Spring) Harvey Bootsma SOLEC 2006 Michigan TP ( g L -1 ) ♦ ■ ■ ♦ Environment Canada USEPA-GLNPO Huron Ontario Erie Central Superior GLWQA Target
Plots of simulation results and data for TP ( gP/L) in the Upper Great Lakes: (a) Superior, (b) Michigan, and (c) Huron. The water-quality objectives are shown as dashed lines. (RWG D Annex 3 Technical Subgroup Report DePinto et al 2006) Schematic of a long-term, total phosphorus model for the Great Lakes (Chapra 1977).
Lake Erie Total Phosphorus, ug-P/L Pre(1983-1989)/Post (1990-2004)
Lake Erie Total Dissolved Phosphorus, ug-P/L Pre(1983-1989)/Post (1990-2004)
DRP/TP Maumee Sandusky Cuyahoga Grand Figure courtesy of Dr. Peter Richards, Heidelberg College
Sandusky and Maumee River Watersheds Lake Erie Figure courtesy of Dr. Peter Richards, Heidelberg College
Average [P] (ppm) P in Wisconsin Cropland Bundy and Sturgul 2001
P Input to soil Water [P] Soil [P] Sediment [P] Years Source: S.R. Carpenter, 2005 Long-term Influence of Soil P on Lake P Soil P inputs reduced after year 250 Phosphorus Density (g m -2 ) P Inputs to Soil (g m -2 y -1 )
Average [P] (ppm) Soil P Storage Change (kg ha -1 ) P in Wisconsin Cropland Bundy and Sturgul 2001
Phosphorus Density (g m -2 ) P Inputs to Soil (g m -2 y -1 ) Long-term Influence of Soil P on Lake P Soil P budget balanced at year 250 P Input to soil Water [P] Soil [P] Sediment [P] Years Source: S.R. Carpenter, 2005
Summary Offshore Declines in Zooplankton Biomass are observed Lake Huron. Phosphorus loads and open lake phosphorus concentrations have declined in the Great Lakes in response to controls Top down effects are observed to contribute to decline in the lower food web. Nearshore Cladophora increases appear to be link to Dreissena invasion via increased water clarity and cycling of nutrients Total phosphorus loading has increased soluble fraction and open lake concentrations in Lake Erie have a significant increase in soluble fraction in the spring. Total phosphorus concentrations in the Upper Great Lakes appear to below levels modeled to exist in 1800.
In the nearshore zone, increased water clarity has altered the relationship between P supply and algal abundance. More P abatement would benefit the nearshore zone, but would it benefit pelagic zone? Dissolved Reactive Silica increases in Lakes Michigan and Huron are linked to TP declines. Dissolved Reactive Silica increases in Lake Erie are linked to predation by Dreissena Nearshore shunt of nutrients redirected to the nearshore zones of the Lakes contributing to the reemergence of Cladophora while offshore P concentrations remain low. Continued addition of P to soils may pose a challenge to the lakes well into the future.