Modeling and prioritizing interventions using pollution hotspots for reducing nutrients, atrazine and E. coli concentrations in a watershed

Authors: ABIMBOLA, OLUFEMI - University Of Nebraska; MITTELSTET, AARON - University Of Nebraska; MESSER, TIFFANY - University Of Nebraska; Berry, Elaine; VAN GRIENSVAN, ANN - Free University Of Brussels

Submitted to: Sustainability
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2020
Publication Date: 12/24/2020
Citation: Abimbola, O., Mittelstet, A., Messer, T., Berry, E., van Griensvan, A. 2020. Modeling and prioritizing interventions using pollution hotspots for reducing nutrients, atrazine and E. coli concentrations in a watershed. Sustainability. 13:103. https://doi.org/10.3390/su13010103.
DOI: https://doi.org/10.3390/su13010103

Interpretive Summary: Excess nutrients, herbicides, and fecal bacteria are major causes of waterbody impairment globally. As part of a program to assist agricultural producers with the implementation of best management practices (BMPs) for successful remediation of pollutants, a watershed-scale Soil and Water Assessment Tool (SWAT) was used to assess the effectiveness of proposed BMPs in the Big Sandy Creek Watershed, Nebraska. Streams in this watershed are impaired by high concentrations of the fecal bacterium Escherichia coli, the herbicide atrazine, and nitrogen and phosphorus, and previous work identified target subwatersheds or “hotspots” for these pollutants. Using SWAT with incorporated pollution hotspots and fund limitations, the objectives were to (1) simulate proposed BMPs within target subwatersheds to determine reductions in pollutant loads and (2) determine if water-quality standards were met at the watershed outlet. Proposed BMPs included no-till, crop rotation, filter strips, grassed waterways, terraces, and reduced atrazine application rate. Overall, a combination of filter strips, grassed waterways, and reduction in the rate of atrazine use was determined to likely yield measurable water quality improvements both at the hotspots and the watershed outlet. However, even in the best-case scenario, atrazine and E. coli target concentrations at the watershed outlet were not met. In addition to the hotspots, a reduction or elimination of atrazine use in upland subwatersheds, and treatment of manure in subwatersheds with high number of animals and feedlots, would benefit the water quality of the whole watershed. This work demonstrated that SWAT can be used to assess the effectiveness of various BMPs in agricultural watersheds.

Technical Abstract: Excess nutrients and herbicides remain two major causes of waterbody impairment globally. In an attempt to better understand pollutant sources in the Big Sandy Creek Watershed (BSCW) and the prospects for successful remediation, a program was initiated to assist agricultural producers with the implementation of best management practices (BMPs). The objectives were to (1) simulate BMPs within hotspots to determine reductions in pollutant loads and (2) to determine if water-quality standards are met at the watershed outlet. Regression-based load estimator (LOADEST) was used for determining sediment, nutrient and atrazine loads, while artificial neural networks (ANN) were used for determining E. coli concentrations. With respect to reducing sediment, total nitrogen and total phosphorus loads at hotspots with individual BMPs, implementing grassed waterways resulted in average reductions of 97%, 53% and 65% respectively if implemented all over the hotspots. Although reducing atrazine application rate by 50% in all hotspots was the most effective BMP for reducing atrazine concentrations (21%) at the gauging station 06883940, this reduction was still six times higher than the target concentration. Similarly, with grassed waterways established in all hotspots, the 64% reduction in E. coli concentration was not enough to meet the target at the gauging station. With scaled-down acreage based on the proposed implementation plan, filter strip led to more pollutant reductions at the targeted hotspots. Overall, a combination of filter strip, grassed waterway and atrazine rate reduction will most likely yield measureable improvement both in the hotspots (>20% reduction in sediment, total nitrogen and total phosphorus pollution) and at the gauging station. Despite the model’s uncertainties, the results showed a possibility of using Soil and Water Assessment Tool (SWAT) to assess the effectiveness of various BMPs in agricultural watersheds.