Integrated assessment modeling reveals near-channel management as cost-effective to improve water quality in agricultural watersheds

Authors: HANSEN, AMY - University Of Kansas; CAMPBELL, TODD - Iowa State University; CHO, SE JONG - Us Geological Survey (USGS); CZUBA, JONATHON - Virginia Tech; Dalzell, Brent; DOLPH, CHRISTINE - University Of Minnesota; HAWTHORNE, PETER - University Of Minnesota; RABOTYAGOV, SERGEY - University Of Washington; LANG, ZHENGXIN - University Of Washington; KUMARASAMY, KARTHIK - Utah State University; BELMONT, PATRICK - Utah State University; FINLAY, JACQUES - University Of Minnesota; FOUFOULA, EFI - University Of California; GRAN, KAREN - University Of Minnesota; KLING, CATHY - Cornell University; WILCOCK, PETER - Utah State University

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2021
Publication Date: 7/13/2021
Citation: Hansen, A.T., Campbell, T., Cho, S., Czuba, J.A., Dalzell, B.J., Dolph, C.L., Hawthorne, P.L., Rabotyagov, S., Lang, Z., Kumarasamy, K., Belmont, P., Finlay, J.C., Foufoula, E., Gran, K.B., Kling, C., Wilcock, P. 2021. Integrated assessment modeling reveals near-channel management as cost-effective to improve water quality in agricultural watersheds. Proceedings of the National Academy of Sciences (PNAS). 118(28). Article e2024912118. https://doi.org/10.1073/pnas.2024912118.
DOI: https://doi.org/10.1073/pnas.2024912118

Interpretive Summary: Water quality is severely degraded in cultivated landscapes that are dominated by corn and soybean production. Current water quality policy focuses on reducing nutrient and sediment losses from agricultural fields yet recent studies have highlighted important roles of near-channel areas as sources of sediment and sinks for nitrogen nutrients. We developed a novel integrative modeling approach to assess water quality benefit-to-cost tradeoffs for watershed management scenarios that include a wide range of both field and near-channel management actions, yielding estimates of reductions in sediment and nitrate loads and associated costs for alternative management actions. Our results indicate that near-channel management, most notably fluvial wetland restoration, were most effective for achieving long-standing policy goals for sediment and nitrate reduction.

Technical Abstract: Despite decades of policy that strives to reduce nutrient and sediment export from agricultural fields, water quality in intensively managed agricultural landscapes remains highly degraded. Recent analyses show that current conservation efforts are not sufficient to reverse widespread water degradation in Midwestern agricultural systems. Intensifying row-crop agriculture and increasing climate pressure require a more integrated approach to water quality management that addresses diverse sources of nutrients and sediment and off-field mitigation actions. We used multi-objective optimization analysis and a novel integrated biophysical model to evaluate the cost-effectiveness of alternative portfolios of watershed management practices to achieve nitrate and suspended sediment reduction goals in an agricultural basin of the Upper Midwestern U.S. By integrating three watershed-scale models to capture both field and riverine processes, we included near-channel management actions alongside more typical field management actions to directly compare benefit-to-cost ratios across diverse portfolios. This optimization analysis revealed that fluvial wetlands, i.e. wide, slow flowing, vegetated water bodies within the riverine corridor, are the single most cost-effective management action to reduce nitrate and sediment loads, and essential for meeting moderate to aggressive water quality targets. Because wetland construction was costly compared to other practices, it was not selected in portfolios at low investment levels. Wetland performance was sensitive to placement, emphasizing the importance of watershed scale planning to realize potential benefits of wetland restorations. We conclude that extensive inter-agency cooperation at a watershed scale is required to achieve substantial, economically viable improvements in water quality under intensive row-crop agricultural production.