The re-eutrophication of the Laurentian Great Lakes and the potential influence of changes in agricultural land use, climate, and transport pathways

English Abstract:

Agricultural land use has a variety of effects on material and energy flow of receiving waters, some of which can be highly local, while others may be far reaching, with cumulative impacts extending to large, distant receiving waters such as oceans or large lakes. The impacts of land use, including agriculture, on the Laurentian Great Lakes (LGL) became a topic of intense study during the eutrophication of the lower LGL that occurred in the late 1960s and early 1970s. The Pollution from Land Use Reference Group (PLUARG) was formed to examine the relationships between land use and their impacts on the LGL, then to develop recommendations for changes in these practices to reduce impacts on the LGL. The agricultural studies of the PLUARG examined the interaction between types of agricultural land use and the sensitivity of those landscapes to lose nutrients and other materials to the streams that drain them, as well as to develop recommendations to mitigate these losses. In the ensuing years, water quality in the LGL improved dramatically, driven primarily by improvements in sewage treatment. More recently, there has been a resurgence of eutrophication in the western basin of Lake Erie, as well as widespread nearshore algal fouling occurring in all of the lower LGL. The mechanisms causing the re-eutrophication of the LGL are not yet quantified. However, it is known that a major driver is a shift in the food webs of the LGL, while changes in climate and tributary loading may also be important. On the agricultural landscape, several changes such as artificial drainage, climate change, and other land use practices have occurred that may influence not only the magnitude, but also the nature and timing of nutrient loss to watersheds. In this work, we provide an overview of the PLUARG approaches to examining the connection between agricultural land use and their impacts on the LGL as well as possible changes in the magnitude, timing, and hydrological connectivity that have happened since those studies. We will also describe a new study that will revisit many of the goals of the PLUARG agricultural studies to examine how these changes may be influencing the re-eutrophication of the LGL.