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USGS presentation: Pheasant Branch supplies about 15% of Lake Mendota phosphorus; Confluence Pond traps roughly 30%
Summary
USGS hydrologist Todd Stuntebeck told Middleton officials that long-term monitoring shows Pheasant Branch contributes roughly 15% of annual phosphorus to Lake Mendota, the Confluence Pond traps about 30% of incoming phosphorus (≈3,300 lb/yr on average), and monitoring and sample-analysis costs and contract terms are under review.
Todd Stuntebeck, a hydrologist with the U.S. Geological Survey(USGS) Upper Midwest Water Science Center, presented the agency—s monitoring data for Pheasant Branch and other tributaries to Lake Mendota at the Middleton stormwater committee meeting. He said USGS—s Parmenter Street gauge has daily flow records dating to 1975 and that the agency—s measurements focus on phosphorus because of its role in algal growth.
Stuntebeck said the four primary tributaries feeding Lake Mendota delivered roughly 55,000 pounds of phosphorus over the 2024 water year and that, using a 30-year average and modeled estimates to fill data gaps, Pheasant Branch accounts for about 15% of the annual load. "Pheasant Branch contributes about 15% of the overall, annual load to the lake," he said.
Why it matters: phosphorus drives nuisance algal blooms and beach closures in the Madison-area lakes. Stuntebeck emphasized that a combination of weather variability and long-term land-use change complicates…
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