TRENDS IN SEDIMENT AND NUTRIENT CONCENTRATIONS IN MAJOR LAKE ERIE TRIBUTARIES, 1975–2004

During the period 1975–1995, two major Lake Erie tributaries, the Maumee and Sandusky Rivers in northwest Ohio, showed substantial and statistically significant decreases in concentrations of suspended sediment, total phosphorus, soluble reactive phosphorus, and total Kjeldahl nitrogen, but increases in nitrate plus nitrite. Research currently underway has documented generally similar trends for the same period for the Raisin, Cuyahoga, and Grand (OH) Rivers. This research also shows that during the period 1995–2004, many of the earlier trends toward improved water quality have either reversed or the rate of improvement has slowed. Increased loadings to Lake Erie coincide with increased in-lake concentrations of phosphorus, renewed problems with hypoxia in the Central Basin, and increased blooms of cyanobacteria. Trend results will be presented for phosphorus and related parameters, and we will explore possible causes for the trends, including weather effects, population growth, exurbanization, and changes in agricultural practices.