Eutrophication Thresholds -- Assessment, Mitigation and Resilience in Landscapes and Lakes

7. Project Summary: Eutrophication, a persistent environmental problem characterized by turbid water, toxic algae, fish kills, waterborne disease, and loss of aquatic ecosystem services, may be related to important thresholds in the phosphorus (P) cycle. We will address two main questions: (1) What thresholds in the transport and recycling of P in linked terrestrial-aquatic ecosystems cause lakes to switch between clear-water and eutrophic states? (2) How can thresholds for transport and recycling of P be manipulated to mitigate eutrophication, or increase resilience of clear water lakes against eutrophication? The research will conduct a retrospective analysis of the Yahara watershed and its major lakes (near Madison, Wisconsin), using a substantial historical data base of land characteristics and limnology. Changes in this watershed-lake system are emblematic of those in many agricultural, urbanizing regions of the United States. Approaches include statistical analyses of three different types of lake models and simulation studies using a Terrestrial-Aquatic P model. The project will describe thresholds related to eutrophication with respect to landscape, biogeochemical, and statistical characteristics. We will (1) establish whether the thresholds are likely to produce important changes in eutrophication, (2) determine how key controlling variables such as climate, landscape characteristics, land use/cover change, agricultural practices, and management actions affect thresholds, (3) evaluate prospects for mitigating eutrophication through interventions that utilize thresholds, and (4) assess changes in controlling variables that would increase or decrease resilience of clear-water and eutrophic regimes. Better understanding of thresholds related to eutrophication is a prerequisite for correcting this persistent problem in order to improve ecosystem condition, human health, and livelihoods.