Northeastern Section - 53rd Annual Meeting - 2018

Paper No. 48-3
Presentation Time: 8:45 AM


MCDOWELL, William H.1, KOENIG, Lauren E.2, SNYDER, Lisle E.1 and POTTER, Jody D.1, (1)Department of Natural Resources and the Environment, University of New Hampshire, 114 James Hall, 56 College Road, Durham, NH 03824, (2)Department of Natural Resources and the Environment, University of Connecticut, 1376 Storrs Road, Storrs, CT 06268

Stream chemistry integrates plant, soil, and aquatic biogeochemical cycling at the catchment scale, and therefore, understanding the drivers of its temporal and spatial variability is a fundamental challenge for watershed biogeochemistry and water resources management. Seasonal patterns in stream nitrogen chemistry have commonly been attributed to terrestrial vegetative nitrogen demand as well as nitrogen saturation status. Therefore, because climatic conditions and atmospheric nitrogen deposition tend to vary across broad regional extents, regional coherence in seasonal nitrate (NO3) export might be expected in watersheds that share similar land use features. Here we use a network of 11 stream and river sites instrumented with an in situ NO3 sensor for 2-5 years to test the extent to which there is regional coherence in the seasonality and overall temporal variation in stream NO3 concentrations across gradients of stream size, watershed topography, and land use in New England. We found that across sites, there is little regional coherence in the overall seasonal variation in stream NO3 concentrations, although multiple watersheds displayed similar NO3 responses to particular annual events including autumn leaf fall. Diel NO3 variability is surprisingly common, even in heavily-shaded streams, and the magnitude of diel variation increases with NO3 concentration across sites. These results suggest that our conceptual models of drivers of seasonal NO3 export may not adequately account for the complex suite of catchment factors affecting stream nitrogen availability across a range of temporal scales.