Weather whiplash in agricultural regions drives deterioration of water quality

Abstract

Excess nitrogen (N) impairs inland water quality and creates hypoxia in coastal ecosystems. Agriculture is the primary source of N; agricultural management and hydrology together control aquatic ecosystem N loading. Future N loading will be determined by how agriculture and hydrology intersect with climate change, yet the interactions between changing climate and water quality remain poorly understood. 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 wet spring in 2013 was abrupt; the media dubbed this ''weather whiplash''. We use recent (2010)(2011)(2012)(2013)(2014)(2015) and historical data to connect weather whiplash (drought-to-flood transitions) to increases in riverine N loads and concentrations. The drought likely created highly N-enriched soils; this excess N mobilized during heavy spring rains (2013), resulting in a 34% increase (10.5 vs. 7.8 mg N L -1 ) in the flow-weighted mean annual Biogeochemistry (2017) 133:7-15 DOI 10.1007 nitrate concentration compared to recent years. Furthermore, we show that climate change will likely intensify weather whiplash. Increased weather whiplash will, in part, increase the frequency of riverine N exceeding E.P.A. drinking water standards. Thus, our observations suggest increased climatic variation will amplify negative trends in water quality in a region already grappling with severe impairments.

Precipitation as the Primary Driver of Variability in River Nitrogen Loads in the Midwest United States

“…An example of this was the Minnesota River in 1991 when N-load was much higher even though SF and BF were near normal (Table 2). This is similar to the observation of Loecke et al (2017) who characterized large changes in weather patterns as "weather whiplash" and showed that these changes led to deterioration of water quality. Therefore, these analyses suggest that if current climate trends of higher precipitation and larger storms continue (Melillo 2014), it will not only lead to higher SF, BF, and NLOADS in Midwestern Rivers, but also to more fluctuations in these hydrologic and N loss parameters.…”

“…Comparatively, N loss was a smaller fraction of NANI (16%) below this threshold. Loecke et al (2017) developed a "Weather Whiplash Index" to characterize climate impacts on the deterioration of water quality from agricultural regions. In reporting the climate impact, Howarth et al (2012) followed up on their earlier analysis of 16 major watersheds in northeastern U.S. that suggested 10%-15% of N input was exported from drier watersheds as compared to over 35% from wetter watersheds (Howarth et al 2006).…”

Ensemble modeling informs hypoxia management in the northern Gulf of Mexico

“…There is also uncertainty in predicting the impacts of climate change on meteorological and hydrological patterns, and how those impacts may affect the system's susceptibility to hypoxia. For example, the frequency, intensity, and timing of droughts and storms are predicted to shift as a result of global climate change (42), with potential interacting effects on the timing and amount of nutrient delivery, the intensity and duration of stratification, the solubility of oxygen, and biogeochemical cycling (43,44). More research is needed to enhance our predictive understanding of how these and other processes may cause shifts in internal feedbacks and complex nonlinearities in response to management actions (45)(46)(47).…”

Fate and consequence of nutrients at an abandoned feedlot, Glacial Ridge National Wildlife Refuge, Minnesota, USA

“…Dry springs following wet autumns in the upper Mississippi River basin have been shown to decrease nitrate concentrations in streams and rivers. Conversely, a wet spring following a dry autumn results in elevated spring nitrate concentrations (Loecke et al 2017). Although unusually dry conditions during 2006 correlate with the sudden drop in groundwater nitrate at the feedlot, concentrations did not recover even partially when normal weather conditions and water-table levels returned (Figure 10), nor is there evidence for transport of nitrate to nearby drains (Figure 9).…”

“…Alternatively, recent work indicates that large changes in nitrate loss to streams can be triggered by a strong change in prevailing precipitation, or "weather whiplash" (Loecke et al 2017). Dry springs following wet autumns in the upper Mississippi River basin have been shown to decrease nitrate concentrations in streams and rivers.…”