2019/11/07 Dr. Laura Johnson- "The effects of phosphorus management in the Lake Erie watershed from 1969 to today"

Historically, cultural eutrophication of Lake Erie was a major concern and through efforts by the United States and Canada starting with the Great Lakes Water Quality Agreement (GLWQA), Lake Erie largely recovered by the mid-1990s.  However, over the past decade 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 45 years.  In the agricultural watersheds (e.g., Maumee and Sandusky Rivers), long-term trends in loads and concentrations indicate that total phosphorus (TP), which consists of particulate and dissolved P, has decreased since the mid-1970s, whereas dissolved reactive P (DRP) has been increased drastically in the mid-1990s. Trends in the Cuyahoga River, which is dominated by point-source inputs of P, are quite different– TP and DRP decreased in the mid-1970s and have since remained consistently low.  Thus, increased DRP and HABs appear to be associated with recent patterns in agriculture such as broadcasting surface fertilizers, build-up of P at the soil surface, unnecessary fertilizer application, increased soil compaction from large equipment, and increased tile drainage intensity.  Encouraging best management practices (BMPs) on farmland focused on DRP loss, such as the 4Rs and nutrient management, rather than particulate P and erosion should help decrease the severity of HABs in the future.