Promoting Science-Based Management of Wisconsin's Natural Resources

WGF Analysis: Nitrogen Pollution and The Need to Develop Nitrogen Criteria for Wisconsin’s Surface Waters

Dave Marshall, John Sullivan & Jim Baumann, April 30, 2019

Background: Considerable research – both in Wisconsin and across the county – supports the need to control both phosphorus and nitrogen to adequately manage water quality problems in surface waters. In many lakes and streams, both nitrogen and phosphorus contribute to eutrophication and water quality degradation. However, nitrogen itself may be the most important nutrient in certain types of lakes, such as floodplain lakes along rivers across the state.

Both nitrogen and phosphorus can be the limiting nutrients causing dense blankets of freefloating plants that cover lake surfaces. The dense free-floating plant blankets not only
undermine recreational uses but can literally smother lakes as dissolved oxygen declines to critically low levels without sufficient photosynthesis. Nitrogen, in the form of nitrate, not only threatens human health but has also been shown through research studies to be acutely toxic to young fish, amphibians and early life stages of other aquatic life forms.

Based on monthly sampling at the Wisconsin Department of Natural Resources (WDNR) long term trend site on the Pecatonica River at Martintown and Sugar River at Brodhead, nearly all of the samples dating back to the late 1980s exceeded recommended chronic toxicity level. Where agriculture dominates a surrounding landscape, affected streams often have excessive nitrogen levels along with widespread chronically toxic NO3-N and nitrite nitrogen (NO2-N) concentrations. While no action has been proposed to reduce surface water NO3-N levels in Wisconsin, Minnesota is developing criteria for protection of fish and aquatic life.

Often nitrogen reaches surface waters though groundwater discharges, such as springs and seeps. Rain may infiltrate into the soil and transport nitrogen from fertilizers and manure “laterally” to surface waters. Thus, nutrient management on farms is vital for the quality of Wisconsin lakes, wetlands and streams. However, current management practice standards, such as Natural Resources Conservation Service (NRCS) Nutrient Management Code 590, are insufficient for the level of management needed. The primary goals of the 590 are agronomic and not for water quality protection; the primary reason why nitrate levels across Wisconsin often exceed the Drinking Water Standard.

Prepared by Wisconsin’s Green Fire Work Group: Nitrogen in Surface Waters – Dave Marshall,
John Sullivan and Jim Baumann

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