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Nitrogen Pollution in the Upper Mississippi River Basin

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The amount of nutrients contained in fertilizer, livestock manure, municipal wastewater. atmospheric deposition, and legume residues were quantified in each of the major drainage basins within the Upper Mississippi River Basin study unit as part of the U.S. Geological Survey's National Water-Quality Assessment Program

These sources of nutrients may potentially affect surface- and ground-water quality, so knowledge about the relative importance of each source may assist in the management of surface and ground waters within the study unit.

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Fertilizer and livestock manure were potentially large sourcesof nitrogen and phosphorus in each of the four drainage basins. However, nitrogen in legume residues was a more importantsource in the Upper Mississippi, St

Croix, and Lower Missis-sippi River Basins because hay comprised a larger part of thetotal acreage of crops grown in these basins. Atmospheric deposi-tion comprised a larger percentage of the nitrogen sources in theSt. Croix River Basin compared to the other three drainage basinsprobably because amounts of the other sources are relatively low.Nitrogen and phosphorus yields in streams were greatest in theLower Mississippi River Basin and the Minnesota River Basin,where amounts of nonpoint sources of these constituents alsowere the greatest per square mile. Land use varies among these four drainage basins. The Minne-sota River Basin (MRB) consists primarily of agricultural land.Soybeans and corn are the principal crops grown, and pigs are thedominant type of livestock raised in this basin. Data obtainedfrom the state agricultural censuses.

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There is some variety in nutrient concentrations across strata, as described in detail by UMRBA’s draftdesignated uses report (UMRBA 2011). For example, in spring, total phosphorus mean concentrationsare generally higher in the main channel than in backwaters (see Figure 3-20). However, in the summerthe opposite is true – the main channel has lower TP concentrations than the backwaters. Also, totalnitrogen mean concentrations are higher in the main channel than in backwaters.Historically, backwaters may have removed significant amounts of nitrogen from the UMR viadenitrification. However, recent work suggests that backwaters do not currently fulfill that role to anysubstantial degree (Cavanaugh et al. 2006; James et. al. 2008; Kreiling et al. 2010). Nitrogen and phosphorus concentrations in surface waters are tied to both naturally occurring andhuman-related sources

Research and modeling indicate that agricultural land use is the primarydeterminant of nutrient loading in the UMR, followed by urban areas. Additionally, both nitrogen andphosphorus loads to the UMR are largely tied to contributions from major tributaries

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Finally, nutrient pollution in the Mississippi river watershed is a challenging issue and USGS is working with numerous partners to apply monitoring, modeling and other science expertise, and leverage resources needed to address this complex issue. Using an adaptive management decision-making process, nutrient reduction practices can be monitored and assessed and management actions adjusted as needed for improvement.

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Cavanaugh, Jennifer C. et al. "Nitrogen Dynamics in Sediment During Water Level Manipulation on theUpper Mississippi River." River Research and Applications, Vol. 22 (2006): 651-666.

Donner, Simon D. et al. "Modeling the impact of hydrological changes on nitrate transport in theMississippi River Basin from 1955 to 1994." Global Biogeochemical Cycles, Vol. 16, No. 3 (2002): 1-19.

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