Changes in Grand Lake St. Mary's Watershed: Moving Towards an Improved Understanding of Water Quality Over the Past Decade

Grand Lake St Marys (GLSM) is a hypereutrophic lake situated in the primarily agricultural GLSM watershed of northwest Ohio. Over the past decade, numerous surveys have characterized the environmental quality of the lake as highly impaired. Elevated nutrient rich runoff levels coupled with the physical characteristics of the watershed have acted as catalysts for frequent harmful algal blooms resulting in no contact warnings and drinking advisories which have impacted the region environmentally and economically. In 2011, the watershed was officially declared distressed by the state of Ohio. Following this designation, a series of voluntary and obligatory best management practices, conservation initiatives, and rules were implemented in an effort to reduce nutrient loading on a watershed scale. These efforts included constructing wetlands and in-lake littoral areas, increasing the use of filter strips, riparian buffers, cover crops, improving manure management practices, such as transferring manure out of the watershed and increasing covered manure storage, and the implementation and enforcement of policies encompassing the maintenance of nutrient management plans and a watershed wide ban on winter manure application. Since 2011, nitrogen and phosphorus concentrations have greatly declined during the winter months (16-57%) as well as the remainder of the year (12-41%; with exception of spring SRP) during critical medium and high flow loading periods. Despite these impressive declines, however, nutrient levels remain too high. Thus, conservation work in GLSM is ongoing and includes the continued expansion of existing BMPs as well as addition of new wetlands to continue improving water quality region wide.