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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #359140
Title: Soil Vulnerability Index assessment as a tool to explain annual constituent loads in a nested watershed

Author
item LOHANI, SAPANA - University Of Nevada
item Baffaut, Claire
item THOMPSON, ALLEN - University Of Missouri
item Sadler, Edward

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: The Soil Vulnerability Index (SVI) was developed by the NRCS to identify vulnerability of cropland to runoff and leaching. It is a simple index that can be used with basic knowledge of ArcGIS. The goal of this study was to investigate a possible relationship between sediment and nutrients transported by the streams and fraction of the watershed in each SVI class. SVI maps were developed for each of the 7 sub-watersheds of the Mark Twain Lake watershed in Missouri. SVI assessment was performed by considering how slope, hydrologic soil group and erodibility K-factor affected SVI; and investigating if the distribution of SVI for cropland in each sub-watershed could help explain measured 2006-2010 sediment and nutrient loads better than crop distribution alone. A regression analysis was performed between annual loads of sediment and nutrients exported from the watersheds and a composite number that reflected crop distribution with and without SVI. Integrating SVI in the explanatory variable improved the ability to explain loads in the watersheds for sediment and nutrients. These results support the application of SVI at watershed scale to identify cropland of greatest vulnerability and the link between these and transported pollutant loads.

Technical Abstract: The Soil Vulnerability Index (SVI) was developed by the USDA-NRCS to identify inherent vulnerability of cropland to runoff and leaching. It is a simple index that relies on the SSURGO database and can be used with basic knowledge of Arc GIS. The goal of this study was to investigate a possible relationship between nutrient loadings and fraction of the watershed in each SVI class. The SVI maps were developed for each of the 7 sub-watersheds of the Mark Twain Lake watershed in Missouri, which were similar in soil conditions and climatic variability. The SVI assessment was performed by investigating if the distribution of SVI for cropland in each sub-watershed could help explain measured 2006-2010 sediment and nutrient loads better than crop distribution alone. Regression analyses were performed between annual loads of sediment and nutrients exported from the watersheds and a composite number that included cropland distribution alone on one hand, and cropland distribution combined with SVI on the other hand. Coefficients of determination and p-values were compared to assess the ability of land use and SVI distributions to explain stream loads. Integrating SVI in the land cover variable improved the ability to explain loads in the watersheds for sediment, total nutrients, and dissolved nitrogen. Results with and without SVI were identical for dissolved phosphorus. These results support the application of SVI at watershed scale to identify cropland of greatest vulnerability and the link between these and transported pollutant loads.