Nutrients

Beginning in the 1970s, the trend to increasing nutrient loads and worsening algal conditions in Lake Erie was reversed, consistent with the GLWQA (Great Lakes Water Quality Agreement) objectives. During that period,most of the damage occurred in Lake Erie’s western basin and, subsequently, water quality improvements were most prevalent there. By the 1990s, phosphorus concentrations were one half of their former levels in the western basin with smaller improvements in the central and eastern basins. However, despite tremendous efforts, total phosphorus concentrations in the western basin remained high enough to stimulate occasional algal blooms. In recent years,these blooms seem to have become worse.

Recent algal problems in Lake Erie prompted a brief review of stimulatory nutrients in the lake. Changes in the lake’s biological components seem to render the nutrient controls of decades past insufficient for today’s conditions in some areas. Offshore algal problems are most prevalent in the western basin. There is a west to central to east basin gradient of improving water quality, consistent with the presence of the largest total phosphorus loads in the west basin. Phosphorus continues to be the limiting nutrient. There is enough nitrogen present that it is not usually limiting algae, although almost any nutrient can be shown to appear limiting to algae on a given day. Nitrogen warrants watching as the ecological implications of ongoing increases are unknown. The relationship between phosphorus and algae as indicated by chlorophyll remains strong in offshore waters.

Nearshore, there is a serious problem with attached filamentous algae in the east basin and parts of the west basin. Algal problems are usually associated with elevated nutrient supplies but Dreissenid mussels seem mostly responsible for attached algae. At the same time, more research is needed to determine whether whole lake and/or shoreline source control, if possible, would be effective at ameliorating the problem.

For the lands draining to Lake Erie, the LaMP called for aquatic habitat improvements (land use modifications) that would cause a concomitant reduction of phosphorus loads. Those reductions now seem desirable even if, individually, they may not be capable of effecting large changes in the lake. There is evidence that the agricultural losses of nutrients to the lake, after initial reductions, have become more serious. Total phosphorus concentrations in some rivers such as the Maumee are so high that, despite many actions to date, further strong remedial measures are needed for long-term improvement of algal problems.

Overall reductions in total phosphorus to the lake are still needed. Great Lakes Water Quality Agreement goals and targets are not consistently being met. Agricultural and municipal sources of phosphorus remain mitigation targets, because they have the highest loads at the highest concentrations with the highest availability to algae. A strong nutrient research and monitoring program is needed to address unknowns and to evaluate progress.

US and Canadian governments are working on “The Lake Erie Binational Nutrient Management Strategy”, This strategy identifies the strategic actions required to move towards the achievement of these endpoints. The success of the Lake Erie Binational Nutrient Management Strategy will depend on the commitment from various stakeholders to join forces and to change how nutrients are currently used, applied, transported and discharged. Multiple jurisdictions, in both Canada and the United States, will be responsible for on the ground implementation actions.As the implementation of the Nutrient Management Strategy moves forward, new research and monitoring will continue to fill knowledge gaps and may lead to the refinement of these targets. This will help to ensure that the targets are ecologically credible and sustainable to meet the vision, goals and objectives of the Lake Erie Binational Nutrient Management Strategy.