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Title: Regional effects of agricultural conservation practices on nutrient transport in the Upper Mississippi River Basin

item GARCIA, ANA - Us Geological Survey (USGS)
item ALEXANDER, RICHARD - Us Geological Survey (USGS)
item Arnold, Jeffrey
item NORFLEET, LEE - Natural Resources Conservation Service (NRCS, USDA)
item White, Michael
item ROBERTSON, DALE - Us Geological Survey (USGS)
item SCHWARZ, GREGORY - Us Geological Survey (USGS)

Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2016
Publication Date: 5/31/2016
Publication URL:
Citation: Garcia, A.M., Alexander, R.B., Arnold, J.G., Norfleet, L., White, M.J., Robertson, D.M., Schwarz, G. 2016. Regional effects of agricultural conservation practices on nutrient transport in the Upper Mississippi River Basin. Journal of Environmental Science and Technology. 50:6991-7000. doi:10.1021/acs.est.5b03543.

Interpretive Summary: USDA has assisted land owners across the U.S. in installing and implementing conservation practices for decades. Due to changing climate and management, it is difficult to measure the impact of these practices on water quality in large river systems. An additional complication is the variability of additional pollutant sources from municipal, industrial, and non-agricultural land uses. In an attempt to quantify the impact of conservation practices in the Upper Mississippi River Basin, we applied the USGS—SPARROW model with output from the USDA-CEAP project. Results from the combined model show reductions in nitrogen and phosphorus entering the Mississippi River with nitrogen loads strongly correlated with the intensity of conservation. The study confirmed the positive impacts of conservation practices in large river systems.

Technical Abstract: Despite progress in the implementation of conservation practices, related improvements in water quality have been challenging to measure in larger river systems. In this paper we quantify these downstream effects by applying the empirical U.S. Geological Survey water-quality model SPARROW to investigate whether spatial differences in conservation intensity were statistically correlated with variations in nutrient loads. In contrast to other forms of water quality data analysis, the application of SPARROW controls for confounding factors such as hydrologic variability, multiple sources and environmental processes. A measure of conservation intensity was derived from the USDA-CEAP regional assessment of the Upper Mississippi River and used as an explanatory variable in a model of the Upper Midwest. The spatial pattern of conservation intensity was negatively correlated (p = 0.003) with the total nitrogen loads in streams in the basin. Total phosphorus loads were weakly negatively correlated with conservation (p = 0.25). Regional nitrogen reductions were estimated to range from 5 to 34% and phosphorus reductions from 1 to 10% in major river basins of the Upper Mississippi region. The statistical associations between conservation and nutrient loads are consistent with hydrological and biogeochemical processes such as denitrification. The results provide empirical evidence at the regional scale that conservation practices have had a larger statistically detectable effect on nitrogen than on phosphorus loadings in streams and rivers of the Upper Mississippi Basin.