The re-emergence of large blooms of benthic filamentous algae in the lower Great Lakes during the late 1990s and early 2000s seemed to run counter to evidence of ecosystem recovery from eutrophication after point-source phosphorus controls were enacted under the Great Lakes under the Great Lakes Water Quality Agreement. Despite clear linkages between increases in dissolved P inputs from non-point sources and harmful algal blooms in places such as western Lake Erie, the proximate triggers of these expansive blooms of benthic algae are more challenging to decipher, in part because loading information is not sufficient, and the response of benthic algae to non-point source inputs of P may be modulated by recent ecosystem changes mediated by exotic filter feeding mussels. Consequently, revised phosphorus loading targets for eastern Lake Erie have not been set, and remain a priority objective under the revised Great Lakes Water Quality Agreement of 2012. Research findings from Environment and Climate Change Canada’s Great Lakes Nutrient Initiative program will be presented as well as other illustrative examples from other locations in the Great Lakes to demonstrate the complexity of the challenge and potential implications for nutrient management strategies.
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