Water Quality and Nutrient Management Extension Programs in Ohio

摘要

Lake Erie is the shallowest, smallest by volume, and southernmost of the Laurentian Great Lakes (Millie et al. 2009). The lake is bounded by the Canadian Province of Ontario to the north and the US States of Michigan to the west, and Ohio, Pennsylvania and New York to the south and east. As with all the Great Lakes, Lake Erie is a vital source of drinking water, international and interstate commerce, recreation, tourism, and industry for the nearly 12 million residents living near the lake. Because of its relatively small size and shallow depth, Lake Erie is more susceptible to disturbance due to natural and human influences than the other Great Lakes (Millie et al. 2009).The lake has experienced significant nutrient loading, especially phosphorus, from a number of point and non-point sources for most of the 20th century. Excessive loading of nutrients in agricultural run-off has long been associated with a myriad of water quality issues around the world, including the Great Lakes region (Makarewicz 1993). In the Great Lakes region, Lake Erie has consistently been the most affected by excessive nutrient loading (Baker 1985) with excessive phosphorus and nitrogen in run-off waters cited as the most damaging (Forster and Rausch, 2002; Richards et al. 2013). Since phosphorus is the primary limiting nutrient for harmful algal bloom (HAB) development, the cumulative addition of phosphorus over time has enhanced the development of HABs and significantly impaired the water quality of the lake (Bertram 1993; Taft 1945). HABs create taste and odor problems within the water, degrade overall environmental quality, and make the lake less aesthetically pleasing. In addition, certain HAB species release toxins in the water, which pose a significant health hazard to humans and wildlife (Dove and Chapra 2015).To address these issues, an international commission was formed in the 1970s to develop and implement strategies for reducing nutrient loading in the lake. These strategies included upgrading municipal water treatment systems, reducing the phosphorus content of soaps, detergents, and lawn fertilizers, and promoting agricultural practices that reduced tillage and increased residue cover. These actions resulted in a decrease in phosphorus runoff into Lake Erie, and for a time, a cessation of HAB formation (Chesters et al. 1980).HABs appeared again in Lake Erie in the 1990s. Causes cited for this resurgence included increased nutrient loading from point and non-point sources, and a warming of the lake (Baker 1992; Millie et al. 2009). Zebra and quagga mussels (Dreissena polymorpha and D. rostriformis bugensis) were also found in Lake Erie during this time. These mussels are non-native invasive species brought into Lake Erie through the ballast of ocean going ships. These invasive mussels have caused numerous environmental problems in the Lake, including changes in the trophic structure of the lake and a clarification of the water column (Holland 1993). This clarification is allowing sunlight to penetrate deeper, and is believed to be contributing to the resurgence of HABs (Wynne et al. 2010).HABs are scums of green algae which form on the surface to a depth of 2–3 feet and can produce the toxin microcsystin. When present in large enough quantities, microcsystin can cause significant human and environmental health problems (Millie et al. 2009). HABs are considered to be one of the most significant issues threatening water quality in the Great Lakes Basin, and Lake Erie in particular (Dove and Chapra 2015). The potential damage HABs can cause was highlighted on August 4, 2014. On this date, the close proximity of HABs to the city of Toledo water intake facilities resulted in microcsystin levels exceeding the 1 ppm threshold for safe drinking water set by the U.S. Environmental Protection Agency. This threshold, combined with the outdated city water intake and treatment system, shutdown Toledo's water supply to over 400,000 residents. This shu