The Impact of Climate Variability and Land Management Practices on Water Quality in Iowa at the Watershed Scale

Abstract:

The Raccoon River Basin plays a major role to the Mississippi River Basin’s high nutrient exports. Future climate change (increases in temperature, humidity, and or precipitation) may have major impacts on the biological, physiological, and agronomic processes imposing a threat to ecosystem services. Acts to reduce nitrogen loads within this basin have included local lawsuits and the implementation of the Iowa Nutrient Reduction Strategy (INRS). To reach the INRS goal of a 41% reduction in nitrate loads, one strategy suggests incorporating bioenergy crops (i.e., miscanthus) within the current corn-soybean landscape. In this study, we focus on simulating nitrogen export and streamflow for historical and future land use scenarios by using an agroecosystem model (Agro-IBIS) and a hydrology model (THMB). Agro-IBIS has been updated to include Iowa-specific soil texture, land use, climate data sets at the 500-m resolution similar to the scale of agricultural fields, as well as the implementation of reproductive heat stresses on both corn and soybean that allow for a more accurate representation of the effects of future temperatures on crop productivity. Data from CMIP5 for historical (1987-1996), mid-century (2047-2058), and late century (2087-2096) under the RCP 4.5 and 8.5 warming projections are used to drive our climate scenarios. Using recent crop profit analyses for the state of Iowa, we use a profitability map as well as a nitrogen leaching thresholds to determine which grid cells are replaced with miscanthus. This new land use scenario is then simulated through the models and nitrogen export and streamflow output are compared to the historical levels. We hypothesize that increasing climate variability will decrease cropping system resilience (with respect to changes in yield and profit) and water quality and strategically implemented conservation practices will have a greater impact on water quality improvement under future climate conditions than under current weather conditions.