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Assessing the Impacts of Recent Crop Expansion on Water Quality in the Missouri River Basin Using the Soil and Water Assessment Tool
Citation:
Chen, P., Y. Yuan, W. Li, S. LeDuc, T. Lark, X. Zhang, AND C. Clark. Assessing the Impacts of Recent Crop Expansion on Water Quality in the Missouri River Basin Using the Soil and Water Assessment Tool. Journal of Advances in Modeling Earth Systems. John Wiley & Sons, Inc., Hoboken, NJ, 13(6):e2020MS002284, (2021). https://doi.org/10.1029/2020MS002284
Impact/Purpose:
This is a large¿scale environmental assessment of how land use/land cover changes impact water quality. The US Midwest has undergone a cropland increase of corn and soybean production from 2008 to 2016. Most of this cropland increase has displaced grasslands, which has raised concerns on water quality and ecosystems. In this study, a large¿scale watershed model, the Soil and Water Assessment Tool (SWAT), was applied to the Missouri River Basin (MORB), where some of the highest rates of grassland conversion to cropland have occurred. The SWAT model was used to quantify water quality changes resulting from grassland conversion to cropland. Results from this study showed that conversion from grassland to cropland increased nutrient loading to waterbodies. In addition, this study identified MORB areas within states such as Iowa, Missouri, Nebraska, and Kansas as producing the greatest amounts of nutrient loading due to a combination of grassland conversion, high precipitation, and high percentage of pre¿existing cropland.
Description:
The Missouri River Basin (MORB) has experienced a resurgence of grassland conversion to crop production, which raised concerns on water quality. We applied the Soil and Water Assessment Tool (SWAT) to address how this conversion would impact water quality. We designed three crop production scenarios representing conversion of grassland to: 1) continuous corn; 2) corn/soybean rotation; and 3) corn/wheat rotation to assess the impact. The SWAT model results showed: 1) the lower MORB produced high total nitrogen (TN) and total phosphorus (TP) load before conversion (baseline) due mainly to high precipitation and high agricultural activity; 2) the greatest percentage increases of TN and TP occurred in the North and South Dakotas, coinciding with the highest amount of grassland conversion to cropland; and 3) grassland conversion to continuous corn resulted in the greatest increase in TN and TP loads, followed by conversion to corn/soybean and then conversion to corn/wheat. Although the greatest percentage increases of TN and TP occurred in the North and South Dakotas, these areas still contributed relatively low TN and TP to total basin loads after conversion. However, watersheds, predominantly in the lower MORB continued to be “hotspots” that contributed the greatest amounts of TN and TP to the total basin loads—driven by a combination of grassland conversion, high precipitation, and loading from pre¿existing cropland. At the watershed outlet, the TN and TP loads were increased by 6.4% (13,800 t/yr) and 8.7% (3,400 t/yr), respectively, during the 2008 – 2016 period for the conversion to continuous corn scenario.
URLs/Downloads:
DOI: Assessing the Impacts of Recent Crop Expansion on Water Quality in the Missouri River Basin Using the Soil and Water Assessment Tool