Hydrologic Management Convolutes Expected Spatiotemporal Patterns of Dissolved Organic Matter in the Hudson River

Riverine dissolved organic matter (DOM) is a vector for nutrient cycling and elemental exchange between terrestrial and oceanic reservoirs. The quality and quantity of DOM transported in rivers are determined by a complex interplay of watershed-specific conditions (e.g., land use and discharge). In many temperate rivers, the frequency and intensity of hydrologic events are expected to increase with continued climate change, which would result in an overall increased export of terrestrial DOM. However, the presence of dams and other impoundments increase water residence time and could dampen these effects. Here, we examine DOM biogeochemistry in the Hudson River (New York, USA), which experiences intermittent periods of elevated discharge and receives a seasonally varied series of inputs from urban, agricultural, and forested landscapes. DOM was quantified and characterized using optical spectroscopic techniques, including parallel factor analysis (PARAFAC) modeling of fluorescent DOM components. Our findings indicate that the influence of land cover on DOM composition is secondary to that of hydrologic management. We also found DOM pulse-shunt effects to be more muted in the upper Hudson River watershed, where more water is retained by dams and reservoirs than in the Mohawk River watershed. Regardless of hydrologic management, discharge events consistently enhanced aromatic DOM export in the Hudson River and its subbasins, which suggests climate change and increased rainfall will enhance the delivery of humic-like DOM to the estuary and coastal margins.