NITROGEN FLUX IN WATERSHEDS: THE ROLE OF CRITICAL BUFFER ZONES IN RIVER NITRATE CONCENTRATION VARIATIONS

Abstract:

Quantifying the flux of nitrate from different landscape sources in watersheds is important to understand the increased flux of nitrogen to coastal ecosystems. We have used optical nitrate sensors to assess temporal and spatial river concentration variations in NC coastal plain rivers over the past decade on a 15 minute time scale. River nitrate concentrations exhibit large variations at one station on hourly to weekly time scales, indicating that flux estimates from weekly or monthly sampling can contain large errors. We also have mapped downstream nitrate concentration variations with optical sensors in boats and kayaks. Detailed spatial analysis indicates that nitrate, Chlorophyll a, and CDOM are not spatially coherent and one concentration cannot be used to predict the distribution of the other parameters as suggested by some regulatory agencies. Downstream nitrate concentration variations are not related specifically to buffer conditions adjacent only to the main stem river system, but to conditions of all the tributaries and main stem river buffers in the drainage. Hydric soil distributions are an excellent predictor of nutrient transport in watersheds, and are related to the distribution of biogeochemical “hotspots”. Changes in riverine nitrate concentrations on a fine scale are related to the % of cultivated or pastureland located within the 100 foot river buffer area that is underlain by partially hydric or non-hydric soils. These findings have important implications for water resource and drought management by public agencies and utility managers. Not all buffers are created equally in terms of nutrient transport, and resources to remediate and improve buffers should be concentrated in these “critical” buffer areas that are prone to “leak” contaminates into the river ecosystems. For more information see: Rivernet.ncsu.edu.