Climate change impacts on the nutrient losses of two watersheds in the Great Lakes region

Authors: WANG, LILI - Purdue University; Flanagan, Dennis; CHERKAUER, KEITH - Purdue University

Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2018
Publication Date: 4/8/2018
Citation: Wang, L., Flanagan, D.C., Cherkauer, K. 2018. Climate change impacts on the nutrient losses of two watersheds in the Great Lakes region. Water. 10:442. doi:10.3390/w10040442.
DOI: https://doi.org/10.3390/w10040442

Interpretive Summary: Production of agricultural crops can have serious side-effects, most notably off-site water pollution by sediment, nutrients, and pesticides that can leave farms fields in runoff water. The amounts of runoff and pollutant losses are driven by the amount and intensity of rainfall that occurs, as well as the soils, topography, and land management systems at each field’s location. Some projections of future climate changes (due to global warming) indicate that the depths, frequency and intensity of rainfall events will increase in the future. In this study we used a coupled water erosion and water quality model (WEPPWQ – Water Erosion Prediction Project Water Quality model) as well as downscaled future climate predictions to determine what effects changes in future climate may have on nutrient (N – Nitrogen, P – Phosphorus) losses from two small watersheds located in Wisconsin: Green Lake (790 ha) and Walworth (1124 ha). We found that changes in rainfall and intense storms were greatest towards the end of this century, and there were consistent increases in air temperatures. Runoff and stream flow were predicted to increase by between 10 and 54% over the next century, depending upon the future period selected and the greenhouse gas emissions scenario used. Soil loss increases ranged from 21 to 103%, while predicted increases in total P losses ranged from 25 to 109% for the two watersheds. Predicted future changes in soluble N (nitrate-N) losses ranged from 1 to 96%, again depending upon the future period selected and emissions scenario used. These results impact scientists, university faculty, students, conservation agency personnel and others involved in environmental assessment and control practices to reduce losses of pollutants from agricultural production areas. Indications are that climate change in at least part of the Great Lakes Basin in the U.S. has the potential to increase losses of pollutants to off-site water bodies, which may affect algal growth and eutrophication there. Application of additional, different, or new land management practices may be necessary to reduce pollutant losses to acceptable levels.

Technical Abstract: Non-point sources (NPS) of agricultural chemical pollution are one major reason for the degradation of water quality in the Great Lakes. This study focuses on quantifying the impacts of climate change on nutrient (Nitrogen and Phosphorus) losses from NPS in the Great Lakes region through the end of this century (comparing the nutrient loss prediction of three future periods from 2015-2099 with 30 years for each period against the historical nutrient estimation data from 1985 to 2008). Effects on total phosphorus and nitrate-nitrogen losses due to changes in precipitation amount, intensity, and frequency as well as air temperature are evaluated for two small watersheds in the Great Lakes Region, under three special report emission scenarios (SRES A2, A1B, B1). The newly developed Water Erosion Prediction Project-Water Quality (WEPPWQ) model is utilized to simulate nutrient losses with downscaled and bias corrected future climate forcings from two General Circulation Models (GFDL, HadCM3). Total phosphorus loss is projected to increase by 28% to 72% for the Green Lake watershed and 31% to 108% for the Walworth watershed mainly due the increase of precipitation quantity, and intensity and frequency of extreme storm events. Nitrate-nitrogen losses are projected to increase by 5% to 38% for Green Lake watershed and 8% to 95% for the Walworth watershed as a combined result of increase in precipitation quantity and intensity and frequency of extreme storm events, however the major influencing factors are different in each future period.