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A Study of the Boone River Watershed: Linking an Agroecosystems Model with a Process-based Hydrologic Model

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INRC Fall 2021 Water Quality Research Seminar Series: New Technologies, New Tools and Emerging Concerns 
Nov. 10, 2021
Presenter: Antonio Arenas, assistant professor in the Department of Civil, Construction and Environmental Engineering at Iowa State University

Arenas discusses linking a column agroecosystems model (APSIM) with a process-based hydrologic model (GHOST) to explore the effects of cover crops, small grains, and reduced fertilizer rates on flooding and nitrogen export in the Boone River Watershed. The linked models were modified to simulate the hydrologic and water quality benefits of alternative scenarios: corn-soybeans with a winter wheat cover crop (CSW), corn-soybeans-oats (CSO), and corn-soybeans-oats-alfalfa (CSOA). All three scenarios reduced the number of flood peaks exceeding the 2-year exceedance threshold from 18 to nine. Nitrate concentrations in groundwater and tile drainage from APSIM were used with discharges from GHOST in an end-member mixing analysis (EMMA) to estimate the nitrate load of the baseline corn-soy scenario, which we validated using measured nitrate loads in the Boone River between March 2012 and September 2017. The simulated total six-year nitrate load was only 2.8% larger than the observed load. EMMAs were then conducted on the alternative scenarios, and total six-year loads decreased 41% for CSW, 53% for CSO, and 47% for CSOA. Applying fertilizer at the recommended rate reduced the total nitrate load by 22%. Furthermore, crop yields simulated by APSIM were not observed to drop significantly under the alternative rotation and reduced fertilizer rate scenarios.  

Arenas has been working with computational models applied to water resources management for more than 10 years. His current research focuses on the development and application of fully coupled surface-subsurface watershed models to evaluate flood mitigation strategies and study the fate and transport of nutrients.

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