Heavy Precipitation Impacts on Nitrogen Loading to the Gulf of Mexico in the 21st Century: Model Projections Under Future Climate Scenarios

Abstract

While spatial heterogeneity of riverine nitrogen (N) loading is predominantly driven by the magnitude of basin‐wide anthropogenic N input, the temporal dynamics of N loading are closely related to the amount and timing of precipitation. However, existing studies do not disentangle the contributions of heavy precipitation versus non‐heavy precipitation predicted by future climate scenarios. Here, we explore the potential responses of N loading from the Mississippi Atchafalaya River Basin to precipitation changes using a well‐calibrated hydro‐ecological model and Coupled Model Intercomparison Project Phase 5 climate projections under two representative concentration pathway (RCP) scenarios. With present agricultural production and management practices, N loading could increase up to 30% by the end of the 21st century under future climate scenarios, half of which would be driven by heavy precipitation. Particularly, the RCP8.5 scenario, in which heavy precipitation and drought events become more frequent, would increase N loading disproportionately to projected increases in river discharge. N loading in spring would contribute 41% and 51% of annual N loading increase under the RCP4.5 and RCP8.5 scenarios, respectively, most of which is related to higher N yield due to increases in heavy precipitation. Anthropogenic N inputs would be increasingly susceptible to leaching loss in the Midwest and the Mississippi Alluvial Plain regions. Our results imply that future climate change alone, including more frequent and intense precipitation extremes, would increase N loading and intensify the eutrophication of the Gulf of Mexico over this coming century. More effective nutrient management interventions are needed to reverse this trend.

Understanding the Shift of Drivers of Soil Erosion and Sedimentation Based on Regional Process‐Based Modeling in the Mississippi River Basin During the Past Century

“…Fortunately, the increased occurrence of extreme rainfall from the 1980s to the 2000s has predominantly been concentrated in the MRB’s southern region, primarily characterized by forested areas, except the Mississippi Alluvial Plain. However, as climate changes toward a more vigorous hydrological cycle (Allan & Soden, 2008), more frequent EP events are projected to occur in the Upper Mississippi sub‐basin, where cropland is the dominant land use type (J. Zhang et al., 2022). The intensified EP in the future may amplify soil erosion, as has already been exhibited in the 2010s (Segura et al., 2014).…”

“…However, as climate changes toward a more vigorous hydrological cycle (Allan & Soden, 2008), more frequent EP events are projected to occur in the Upper Mississippi sub-basin, where cropland is the dominant land use type (J. Zhang et al, 2022). The intensified EP in the future may amplify soil erosion, as has already been exhibited in the 2010s (Segura et al, 2014).…”

Soil legacy nutrients contribute to the decreasing stoichiometric ratio of N and P loading from the Mississippi River Basin

“…However, measures to reduce nutrient loading have been degraded by the mineralization/release of legacy P, given that the TP loading from the Mississippi River Basin continued to increase. Future climate change with increased storm density and accelerated hydrologic cycle in the Mississippi River Basin is likely to exacerbate legacy nutrient loss as well (Zhang et al, 2022). Nutrient control measures need to better address the challenges of legacy P, to meet nutrient reduction goals.…”

An Approach for Prioritizing Natural Infrastructure Practices to Mitigate Flood and Nitrate Risks in the Mississippi-Atchafalaya River Basin

“…Spatial targeting is typically conducted at a finer resolution within small watersheds [22,23] where it can be better used by local community planners. Larger regional spatial targeting is more often carried out using county-or state-level data or lumped parameters [24,25].…”