The impact of agricultural intensification on hydrologic disconnectivity in the Mississippi Delta area of the Mississippi Alluvial Plain, USA

Authors: Langendoen, Eddy; Heintzman, Lucas; Witthaus, Lindsey; Moore, Matthew; GREENWOOD, KILLI - University Of Texas At Arlington; LI, DANIEL - University Of Texas At Arlington; FANG, NICK - University Of Texas At Arlington

Submitted to: European Geosciences Union General Assembly Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2024
Publication Date: 4/14/2024
Citation: Langendoen, E.J., Heintzman, L.J., Witthaus, L.M., Moore, M.T., Greenwood, K., Li, D., Fang, N. 2024. The impact of agricultural intensification on hydrologic disconnectivity in the Mississippi Delta area of the Mississippi Alluvial Plain, USA. European Geosciences Union General Assembly Proceedings. pp. EGU24-20677. In EGU General Assembly Abstracts, Vienna, Austria, April 14-19, 2024.

Interpretive Summary: ABSTRACT ONLY.

Technical Abstract: The landscape of the Mississippi Delta, the Mississippi portion of the Mississippi Alluvial Plain, USA, has experienced significant agricultural intensification, primarily through a rapid increase in irrigated cropland, since the early to mid 1970s. The Mississippi Alluvial Plain overlies the Mississippi River Valley Alluvial Aquifer, which currently is the second most heavily pumped aquifer in the USA (~46 million cubic meters per day). The increased irrigation demand has supported a six- to seven-fold increase in irrigated farmland; about 70% of all cropland is irrigated. The irrigation intensification has resulted in similar increases in crop yield. The predominant irrigation application is furrow irrigation, which has been facilitated by precision land leveling. Berms are typically placed around the lower elevations of the leveled field to detain runoff and slowly release the water through an outlet (or multiple outlets) into a ditch or other types of manmade or modified natural drainages. As a result, the current topography and hydrography of the Mississippi Delta is vastly different from that in the 1960s. The changes in surface hydrology and hydrologic connectivity will also affect how fine sediments, nutrients and other agrochemicals are transported and transformed. The vast size of the Mississippi Delta (~18,000 square kilometers) does not accommodate extensive monitoring of runoff, transport, and transformation processes across the entire landscape. Scientists at the U.S. Department of Agriculture, Agricultural Research Service, National Sedimentation Laboratory are therefore developing computer models and supporting databases to evaluate the controlling processes at the basin scale. Current US national databases of surface hydrography in the Mississippi Delta (e.g., the National Hydrography Dataset Plus High Resolution; NHDPlus HR) are based on elevation data (10 m resolution digital elevation model) collected before land leveling. Hence, the NHDPlus HR drainage system significantly differs from the actual drainage system. Using machine learning (ML) technology we have characterized the drainage system from high-resolution lidar data (average point density > two points per square meter) collected during the period 2018-2020. The ML-derived drainage system includes ditches as narrow as three meters and identifies field outlets. To assess how surface hydrology and connectivity have changed, and possible implications on water quantity and quality, we are building two HEC-RAS models using the pre-1970 hydrography and the 2018-2020 hydrography of the 12-digit hydrologic unit code (huc) subwatershed Roundaway Bayou-Quiver River (huc # 080302070805; surface area is ~162 square kilometers), which is located in the central portion of the Mississippi Delta. Because HEC-RAS accounts for the effects of subgrid-scale topography on surface runoff, we can accurately describe the 2018-2020 topography and hydrography at larger spatial resolution; in our simulations we used a grid of 10 m horizontal resolution. We will present results on the changes in surface runoff (magnitude, direction, retention, and connectivity) and implications for water quantity and quality in the Mississippi Delta region.