Impacts of climate and land-use on freshwater nitrogen loading during storms across the United States

<p style="font-weight: 400;">Although freshwater-draining watersheds in urbanized areas generally receive higher nitrogen (N) loading because of impacts of development like impervious surfaces and increased contaminants in runoff, the exact drivers and implications of this finding on different climates is understudied. Increased anthropogenic and natural loading of nitrogen into freshwater systems is associated with eutrophication and degraded water quality, and N loading is effectively studied using concentration-discharge (c-Q) relationships. During storm events, periods of elevated precipitation lead to increased quick-moving flows into waterways which in turn alter surface water pathways for N loading. Historically, nitrate concentrations and discharge during storm events have been observed to have a hysteretic relationship. The study of this hysteresis provides insight into which variable is driving the other and the observed magnitude of this effect. Using NSF-funded high-frequency data acquired from the NEON online database, I studied nitrate c-Q relationships on a storm-by-storm basis to provide insight into loading patterns during storms in different sites across the United States and investigate how land use and climate variables impact hysteretic behavior. Building upon previous hysteretic analyses, I quantified the direction and magnitude of hysteresis loops, as well as characterize the chemo-dynamic behavior present in relation to the developed land area, sanitation infrastructure trends, and the climate zone in each site. My analysis will provide a more holistic understanding of storm-based N loading in different contexts across the United States, which used in conjunction with c-Q analyses based in other timescales can inform local nutrient management strategies to be more targeted and context-specific, which is especially important as climate change increases the frequency and severity of extreme weather.