Lake Erie Basin Phosphorus Concentration Trends

Figure 1. Lake Erie Basin Phosphorus Concentration Trends

Each year the USEPA Great Lakes National Program Office (GLNPO), collects water samples from an established monitoring network around Lake Erie. Spring sampling data reflect major loading events caused by spring runoff and allow predictions of the expected size of the annual plankton crop. Summer data are much less variable and more representative of the ambient water.quality in the lake. Therefore, summer phosphorus concentrations are used to summarize lake water quality trends. For each sampling year a basinwide average was computed using data from each of the individual stations. Only offshore stations were used to reduce the influence of shoreline effects.

Due to phosphorus controls at sewage treatment plants, a ban on the use of phosphorus detergents, and agricultural conservation practices, the phosphorus concentration target for the central Lake Erie basin was met in the mid-1980s. Concentrations in the western basin continue to fluctuate but are very near maintaining the target. In 2001, the 5-year average phosphorus concentration for the western basin was 16.2 g/l. The central basin average was 6 g/l. However , overall, spring concentrations and loadings to the lake seem to be rising raising the need for continued monitoring and research on that issue.