Final Report and Synthesis Paper

Forecasting the Causes, Consequences and Remedies for Hypoxia in Lake Erie

Download Full Report: Ecofore-Lake Erie Project Final Report (PDF)

Download the Synthesis paper: Assessing and addressing the re-eutrophication of Lake Erie: Central Basin Hypoxia

Executive Summary

spraying 192Relieving excessive phosphorus loading is a key management tool for controlling Lake Erie eutrophication. During the 1960s and 1970s, excessive phosphorus inputs degraded water quality and reduced central basin hypolimnetic oxygen levels, which in turn, eliminated thermal habitat vital to cold-water organisms and contributed to the extirpation of important benthic macroinvertebrate prey species for fishes. In response to load reductions under the 1978 Great Lakes Water Quality Agreement (GLWQA) between the U.S. and Canada, Lake Erie responded quickly with reduced water-column phosphorus concentrations, phytoplankton biomass, and bottom-water hypoxia (dissolved oxygen < 2 mg/l). However, since the mid-1990s, cyanobacteria blooms increased and extensive hypoxia and excessive benthic algae returned.

We built and synthesized long term and recent trends in key nutrient loads and indicators of eutrophication, assessed their likely ecological impacts, and developed load response curves to guide revised hypoxia-based loading targets called for in the 2012 protocol amending the Great Lakes Water Quality Agreement.

Our results showed that reducing central basin hypoxic area to levels observed in the early 1990s (ca. 2,000 km2) requires cutting total phosphorus loads by 46% from the 2003-2011 average or reducing dissolved reactive phosphorus loads by 78% from the 2005-2011 average. Reductions to these levels are also protective of fish habitat. We provide potential approaches for achieving those new loading targets under current and potential future climates, and suggest that recent load reduction recommendations focused on western basin cyanobacteria blooms may not be sufficient to reduce central basin hypoxia to ≤2,000 km2.