Assessment of hydrology and nutrient losses in a changing climate in a subsurface-drained watershed

Authors: MEHAN, SUSHANT - Formation Environmental Llc; AGGARWAL, RUCHIR - University Of Michigan; GITAU, MARGARET - Purdue University; Flanagan, Dennis; WALLACE, CARLINGTON - Interstate Commission On The Potomac River Basin; FRANKENBERGER, JANE - Purdue University

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2019
Publication Date: 6/23/2019
Citation: Mehan, S., Aggarwal, R., Gitau, M.W., Flanagan, D.C., Wallace, C.W., Frankenberger, J.R. 2019. Assessment of hydrology and nutrient losses in a changing climate in a subsurface-drained watershed. Science of the Total Environment. 688:1236-1251. https://doi.org/10.1016/j.scitotenv.2019.06.314.
DOI: https://doi.org/10.1016/j.scitotenv.2019.06.314

Interpretive Summary: Projections from climate models indicate that temperature and precipitation values may increase in the future, and this could have negative effects on water quality. This computer simulation study used measured weather, stream flow and nutrient losses from an agricultural watershed in northeastern Indiana to calibrate a hydrologic and water quality model (Soil and Water Assessment Tool – SWAT), and then used future climate predictions as model inputs to assess the effects on surface and tile flows, and nutrient losses, particularly soluble phosphorus (P) losses. We found that the extreme precipitation events and temperatures across the watershed were predicted to increase to the end of this century (2099). The SWAT model predicted increased nutrient losses because of the increase in large storm events, and more soluble P losses were predicted in surface runoff. P losses from subsurface tile drains were projected to decrease. Also corn yields were predicted to decrease to the end of the century, while soybean yields could increase. The use of nine different individual climate models provided a range of inputs to SWAT, and a range of model outputs for flow, nutrient losses, and crop yields. This study impacts scientists, conservation agency personnel, extension agents, other federal, state, and local natural resource agency staff, farmers, and others with interest in Phosphorus losses from agricultural areas to Lake Erie or other water bodies. Projections from this and similar studies can be used to plan for the possible effects of future climate change, and development of strategies to minimize negative effects on crop growth and water quality.

Technical Abstract: Studies assessing the impact of subsurface drains on hydrology and nutrient yield in a changing climate are limited, specifically for Western Lake Erie Basin. This study aimed to evaluate the impact of changing climate on hydro-climatology and nutrient loadings in agricultural subsurface-drained areas on a watershed in northeastern Indiana. The study was conducted using a hydrologic model - the Soil and Water Assessment Tool (SWAT) - under two different greenhouse gas emission scenarios (RCP 4.5 and RCP 8.5). Based on analysis, annual subsurface drain flow totals could increase by 70% with respect to the baseline by the end of the 21st century. Surface runoff could increase by 10 to 140% and changes are expected to be greater under RCP 8.5. Soluble phosphorus yield over the basin in a year via subsurface drains could decrease by 30 to 60% under either emission scenarios. Annual total soluble phosphorus yield (soluble phosphorus loading to stream) from subsurface drains and surface runoff could vary from 0.041 to 0.058 kg/ha under RCP 4.5 and 0.035 to 0.064 kg/ha under RCP 8.5 by the end of the 21st century while the values from the baseline model were 0.051 kg/ha. This was attributable to the fact that future climate could have a greater increase in surface runoff than subsurface drain flow based on analysis of the different climate scenarios. Outputs from individual climate model data rather than ensembles provided a band of influence of watershed responses, while outputs from different timelines provided details for evaluating management practice suitability with respect to anticipated differences in climate. Results provide valuable information for stakeholders and policy makers for planning management practices to protect water quality.