E. Sinha, A.M. Michalak, K.V. Calvin and P.J. Lawrence
Excessive nitrogen runoff can lead to degraded water quality that impacts both human and natural systems. Some human activities, such as conversion of land to cropland, can have direct impacts on nitrogen runoff. In order to examine the impacts that land use and land management changes have on nitrogen loading, we studied different combinations of socioeconomic development pathways both with and without the associated natural climate outcomes. We found that societal choices have a significant impact on nitrogen loading in the contiguous United States and even larger regional impacts. These results have important implications for developing strategies for managing water quality as both societal and climatic trends need to be taken into consideration.
Figure: The range of socioeconomic pathways considered here result in large differences in future nitrogen loading, both with and without associated changes to the climate. Change in mean total nitrogen flux by the end-of-the-century (2071–2100) relative to the historical period (1976–2005) for the different scenarios based on projected land use and fertilizer application rates, both without and with impact of associated changes in total annual and springtime extreme precipitation.
Excessive nitrogen runoff leads to degraded water quality, harming human and ecosystem health. We examine the impact of changes in land use and land management for six combinations of socioeconomic pathways and climate outcomes, and find that societal choices will substantially impact riverine total nitrogen loading (+54% to −7%) for the continental United States by the end of the century. Regional impacts will be even larger. Increased loading is possible for both high emission and low emission pathways, due to increased food and biofuel demand, respectively. Some pathways, however, suggest that limiting climate change and eutrophication can be achieved concurrently. Precipitation changes will further exacerbate loading, resulting in a net increase of 1 to 68%. Globally, increases in cropland area and agricultural intensification will likely impact vast portions of Asia. Societal and climate trends must therefore both be considered in designing strategies for managing inland and coastal water quality.
Sinha, E., A.M. Michalak, K.V. Calvin, P.J. Lawrence (2019) "Societal decisions about climate mitigation will have dramatic impacts on eutrophication in the 21st century," Nature Communications, 10 (939), doi:10.1038/s41467-019-08884-w.