Since the early 2000s, Lake Erie has been experiencing a recurrence of harmful algal blooms (HABs) in the western basin and an increase in hypoxia in the central basin. The National Center for Water Quality Research at Heidelberg University has been monitoring major tributaries to Lake Erie for up to 42 years. A minimum of one sample and, during storm runoff, up to three samples a day are analyzed for all major nutrients and suspended sediments from six major tributaries to Lake Erie (Maumee, Sandusky, Portage, Raisin, Huron, and Cuyahoga). The return of western basin HABs corresponds to a 2-fold increase in dissolved reactive phosphorus (DRP) loading from western basin tributaries from the mid-1990s to today. Furthermore, the size of the western basin HABs from 2002-2017 was best correlated with the discharge and total bioavailable P loads from March 1 – July 31 from the Maumee River and these relationships are the basis of the current HAB forecast produced by NOAA each year. These two major findings have since formulated a series of management decisions for the Lake Erie watershed.
Results/Conclusions
Current recommendations developed as part of Annex 4 of the Great Lakes Water Quality Agreement require a 40% reduction in March – July total P and DRP loads to reduce the frequency of HABs in western Lake Erie. This is the first time DRP has been explicitly identified in load reduction recommendations for Lake Erie. Domestic action plans to meet these reductions goals now include practices to reduce DRP losses instead of focusing primarily on soil erosion prevention. Similarly, the 4R nutrient certification program was developed in this region due to the issues associated with DRP losses and the link to fertilizer rate and placement. Although it never was fully enacted, last summer former Ohio Governor Kasich signed an executive order to declare half of the Maumee River watershed as distressed, essentially requiring that each farmer have a nutrient management plan. Finally, there has been a massive increase in monitoring stations throughout the Lake Erie watershed, so that management plans can be tested for efficacy and to enable an adaptive management approach. Yet, one of the biggest challenges remaining is communicating the possible time lag in achieving desired results in tributary water quality and subsequent lake health.