title: Regional Effects of Agricultural Conservation Practices on Nutrient Transport in the Upper Mississippi River Basin.
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.
authors.affiliation: U.S. Geological Survey, 3916 Sunset Ridge Rd., Raleigh, North Carolina 02906, United States.
authors.forename: Ana María
authors.initials: AM
authors.lastname: García
authors.affiliation: U.S. Geological Survey, 432 National Center, Reston, Virginia 20192, United States.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Alexander
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Grassland Soil and Water Research Laboratory, 808 East Blackland Rd. Temple, Texas 76502, United States.
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Arnold
authors.affiliation: U.S. Department of Agriculture, Natural Resources and Conservation Service, 101 East Blackland Rd. Temple, Texas 76502, United States.
authors.forename: Lee
authors.initials: L
authors.lastname: Norfleet
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Grassland Soil and Water Research Laboratory, 808 East Blackland Rd. Temple, Texas 76502, United States.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: White
authors.affiliation: U.S. Geological Survey, 8505 Research Way, Middleton, Wisconsin 53562, United States.
authors.forename: Dale M
authors.initials: DM
authors.lastname: Robertson
authors.affiliation: U.S. Geological Survey, 432 National Center, Reston, Virginia 20192, United States.
authors.forename: Gregory
authors.initials: G
authors.lastname: Schwarz
mesh_terms: D000383:Agriculture; D004784:Environmental Monitoring; D008922:Mississippi; D009584:Nitrogen; D010758:Phosphorus; D045483:Rivers
chemical_list: D010758:Phosphorus; D009584:Nitrogen