Spatial Variability in Nutrient Transport by HUC8, State, and Subbasin Based on Mississippi/Atchafalaya River Basin SPARROW Models

Abstract

Nitrogen (N) and phosphorus (P) loading from the Mississippi/Atchafalaya River Basin (MARB) has been linked to hypoxia in the Gulf of Mexico. With geospatial datasets for 2002, including inputs from wastewater treatment plants (WWTPs), and monitored loads throughout the MARB, SPAtially Referenced Regression On Watershed attributes (SPARROW) watershed models were constructed specifically for the MARB, which reduced simulation errors from previous models. Based on these models, N loads/yields were highest from the central part (centered over Iowa and Indiana) of the MARB (Corn Belt), and the highest P yields were scattered throughout the MARB. Spatial differences in yields from previous studies resulted from different descriptions of the dominant sources (N yields are highest with crop-oriented agriculture and P yields are highest with crop and animal agriculture and major WWTPs) and different descriptions of downstream transport. Delivered loads/yields from the MARB SPARROW models are used to rank subbasins, states, and eight-digit Hydrologic Unit Code basins (HUC8s) by N and P contributions and then rankings are compared with those from other studies. Changes in delivered yields result in an average absolute change of 1.3 (N) and 1.9 (P) places in state ranking and 41 (N) and 69 (P) places in HUC8 ranking from those made with previous national-scale SPARROW models. This information may help managers decide where efforts could have the largest effects (highest ranked areas) and thus reduce hypoxia in the Gulf of Mexico.

The impact of source water quality on the cost of nitrate treatment

“…Agricultural activities have been identified as the primary contributor of nitrogen across the Mississippi River Basin (Robertson et al, ) and other watersheds such as western Lake Erie (Betanzo et al, ; Robertson & Saad, ). The same was true across the four study watersheds, where farm fields and confined manure contributed a majority of the nitrogen runoff in the source waters.…”

Reducing Nitrogen Export from the Corn Belt to the Gulf of Mexico: Agricultural Strategies for Remediating Hypoxia

“…In this study, we focus on the challenges and opportunities associated with Gulf hypoxia; however, we believe that our conclusions are applicable to the Chesapeake Bay, Lake Erie, and many other hypoxic areas worldwide. Early studies of hypoxia in the GoM identified nitrogen and phosphorus loss from agricultural areas in the Corn Belt region of the Midwestern U.S. as a dominant source of nutrients (Goolsby et al ., ), and this has been corroborated by later studies (USEPA, ; Robertson and Saad, ; Robertson et al ., ). Meanwhile, the hypoxic zone has grown in size, affecting an area of 20,000 km 2 in August 2010 (National Research Council, ).…”

Nutrient delivery to Lake Winnipeg from the Red—Assiniboine River Basin – A binational application of the SPARROW model

“…Remediation of eutrophication and its symptoms requires reduction of nutrients from surface waters, but not all parts of most watersheds and sources of nutrients contribute equally (University of Wisconsin-Madison, College of Agricultural and Life Sciences [UW-CALS] 2005; Robertson et al 2014). To support the development of water quality objectives and nutrient management policies, credible estimates of the distribution of nutrient loads from across the RARB are needed as well as robust methods for apportionment of nutrient sources.…”