Predicting the impacts of intensifying heavy precipitation on nitrogen loading to the Gulf of Mexico during the 21st Century

Abstract:

The temporal dynamics of riverine nitrogen (N) loading are closely controlled by the amount and timing of precipitation events. Future changes in precipitation are expected to strongly influence N loading, with consequences for estuarine and coastal ecosystems and economies. However, it remains unknown how future precipitation events with various intensities, occurring places, and timings, together with temperature change, are likely to impact land-to-aquatic N export. In this study, we estimate the potential responses of N loading in the Mississippi Atchafalaya River Basin (MARB) to three precipitation regimes—heavy precipitation, non-heavy precipitation, and no-rainfall days—under two future climate scenarios. We use the projections of future climate and atmospheric CO₂ concentrations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) and time-series gridded data of other environmental drivers to force a well-calibrated hydro-ecological model. Our results suggest that, by the end of this century, the annual total heavy precipitation in the MARB would on average increase by 8% and 15% under the RCP4.5 and RCP8.5 scenarios, respectively. N loadings from the MARB to the Gulf of Mexico are projected to increase up to 30% under future climate scenarios, and about half of this increase would be driven by heavy precipitation. Notably, the RCP8.5 scenario would likely cause higher N loading than RCP4.5 in the northern MARB, in which heavy precipitation and drought events are projected to be more frequent. Our results imply that anthropogenic inputs of N will be increasingly susceptible to loss under future climate scenarios. Our results reveal the impacts of future extreme climatic events on N loading over this coming Century and have implications for agriculture sustainability, nutrient management, and efforts made to reduce water pollution in estuaries and coastal waters.