PHOSPHORUS INTERCEPTION FOR EFFECTIVE WATERSHED MANAGEMENT: A BROADENED APPROACH FOR GREEN LAKE, WISCONSIN

In 2014, the Wisconsin Department of Natural Resources classified Green Lake (2,948 ha) as an impaired waterbody for a worsening metalimnetic oxygen minimum. Subsequently, the Green Lake Association (GLA), a nonprofit organization committed to safeguarding Wisconsin’s deepest natural inland lake, initiated extensive research to comprehensively understand the issues and propose viable solutions to measurably improve the water quality of this 72-m-deep, mesotrophic drainage lake. The findings of these studies—facilitated by the GLA and completed in collaboration with universities, government entities, and consultants—revealed that the lake's primary challenge is excessive phosphorus loading. To remove the lake's impairment listing, the baseline phosphorus load would need to be reduced from 8,440 to 4,060 kg/yr (approximately a 60% reduction). These studies further identified that approximately 80% of the lake’s annual tributary-based phosphorus load—stemming from its 277 km², agriculturally-dominated watershed—enters the take from two primary inlets. Recognizing the inadequacy of solely relying on the voluntary adoption of best management practices to achieve these substantial phosphorus reductions, the GLA is exploring additional strategies and technologies to manage phosphorus loading at these crucial inlets. Concurrently, efforts are underway to test a pilot project to intercept dissolved phosphorus from an agricultural retention pond outlet. This proactive approach attempts to prevent Green Lake’s transition from mesotrophic to eutrophic status. Through the integration of innovative techniques and collaborative partnerships, the GLA aims to improve the water quality of this unique ecological resource.

Primary Presenter: Stephanie Prellwitz, Green Lake Association (stephanie@greenlakeassociation.org)

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