labs_title

Eutrophication will increase during the 21st century as a result of precipitation changes

E. Sinha, A.M. Michalak and V. Balaji

Excessive nitrogen input from rivers is a major cause of eutrophication in estuaries and coastal waters. Impacts of eutrophication include the formation of harmful algal blooms and hypoxic dead zones. These problems are widely expected to intensify with climate change. Here, we use projections of precipitation derived from climate models to explore riverine nitrogen loading for the continental United States under future climate scenarios. Anticipated changes in precipitation patterns are found to cause large and robust increases in nitrogen fluxes by the end of the century. It is therefore imperative that water quality management strategies take into account the interactions between land management and climate change.


Figure: Projected changes in mean total nitrogen flux for watersheds within the continental United States for the RCP8.5 "business-as-usual" emission scenario.(A) Total nitrogen flux for the historical period (1976–2005), averaged across 30 years and 21 CMIP5 models. (B and C) Projected change in mean total nitrogen flux for the near future (2031–2060) and far future (2071–2100) relative to the historical period. For (B) and (C), stippling highlights watersheds with a robust change in total nitrogen flux (i.e., more than 50% of the models show a significant change and more than 80% of the models agree on the sign of change). Watersheds with inconsistent projections (i.e., more than 50% of the models show significant change but fewer than 80% of the models agree on the sign of change) are shown in white. Remaining watersheds are shown in color without stippling. The black outlines highlight the upper Mississippi Atchafalaya River Basin and the Northeast region.

Abstract

Eutrophication, or excessive nutrient enrichment, threatens water resources across the globe. We show that climate change–induced precipitation changes alone will substantially increase (19 ± 14%) riverine total nitrogen loading within the continental United States by the end of the century for the “business-as-usual” scenario. The impacts, driven by projected increases in both total and extreme precipitation, will be especially strong for the Northeast and the corn belt of the United States. Offsetting this increase would require a 33 ± 24% reduction in nitrogen inputs, representing a massive management challenge. Globally, changes in precipitation are especially likely to also exacerbate eutrophication in India, China, and Southeast Asia. It is therefore imperative that water quality management strategies account for the impact of projected future changes in precipitation on nitrogen loading.

Sinha, E., A.M. Michalak, V. Balaji (2017) "Eutrophication will increase during the 21st century as a result of precipitation changes", Science, 357 (6349), 405-408, doi: 10.1126/science.aan2409.