Weather Whiplash in Agricultural Regions Drives Deterioration of Water Quality

Abstract:

Excess nitrogen (N) impairs water quality and creates hypoxic zones in downstream, coastal ecosystems. Agriculture is the primary source of reactive N loading to aquatic ecosystems; agricultural management together with hydrology controls landscape N runoff. Future N loading to aquatic ecosystems will be determined by how agriculture and hydrology intersect with climate change, yet the interactions between climate change and water quality remain poorly understood. Given the implications for local and continental-scale water quality, it is critical to understand how intensive landscape management and a changing climate will alter N loading to aquatic ecosystems. Here, we show that changing precipitation patterns, resulting from climate change, interact with agricultural land use to deteriorate water quality. We focus on the 2012-2013 Midwestern U.S. drought as a “natural experiment”. The transition from drought conditions in 2012 to a historically wet spring in 2013 was abrupt; the popular media dubbed this “weather whiplash”.  We use new and historical data to connect weather whiplash (drought-to-flood transitions) to increases in riverine N loads and concentrations. The 2012 U.S. drought created highly N-enriched soils; excess N mobilized during heavy spring (2013) rains, resulting in record-high riverine N concentrations. Furthermore, we demonstrate that climate change is likely to increase weather whiplash, driving increased frequencies of riverine N concentrations exceeding E.P.A. drinking water standards. Thus, our observations may be a harbinger of a future in which increased climatic variation amplifies negative trends in water quality in a region already grappling with severe impairments.