The Madison-based Clean Lakes Alliance says climate change is offsetting efforts to reduce phosphorus pollution in the Yahara lakes system. 

The environmental advocacy group yesterday released its 2022 State of the Lakes report, which covers the latest findings on conservation practices, shifting weather patterns and their impact on phosphorus runoff in the five-lake system in south-central Wisconsin. 

Phosphorus is responsible for the growth of blue-green algae, which can pose a threat to human health and reduce biodiversity. The group says one pound of phosphorus entering a body of water can lead to 500 pounds of algae growth. 

While the amount of concentrated phosphorus per gallon of water entering the Yahara watershed has declined, according to U.S. Geological Survey data, higher levels of rainfall linked to climate change are causing more phosphorus overall to enter the lakes. 

“The good news is that if runoff and streamflow volumes had not changed, modeling indicates a significant decline in phosphorus loadings would have occurred over the last 30 years,” Matt Diebel, a scientist with the USGS, said in the report. “This is due, in part, to increased adoption of conservation practices that have decreased the concentration of phosphorus in runoff.” 

The report references figures from the Wisconsin Initiative on Climate Change Impacts, showing a “region that is getting wetter and warmer.” The last 20 years have been the warmest on record for the state, while the last decade has seen the most rainfall. Per the report, average annual precipitation has increased about 17 percent since 1950. 

“Increasing rainfall volume and intensity represent an unwelcome trend that can negatively affect the performance of many conservation practices,” report authors wrote. “In addition, warmer winters are leading to greater runoff and phosphorus delivery as liquid precipitation falls across frozen soils, especially where winter manure spreading occurs.” 

The group also highlights a positive trend in land conservation, as more farmers and other landowners in the area are adopting practices aimed at reducing soil erosion and preserving water quality. That includes promoting grasslands and natural growth by limiting conversation to “row crop” production or urban development, planting more cover crops on farm fields and more. 

“Considerable progress has been achieved to-date with the adoption of conservation practices throughout the watershed … the cumulative effect of these actions is largely holding the line against several growing headwinds described in this report,” report authors wrote. 

See the full report: 

See the release: 

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