Baltimore Ecosystem Study Institute of Ecosystem Studies

2016 BES Annual Meeting Presentation and Poster Abstracts

Spatial and temporal variability of nitrate loads from groundwater using baseflow separation and high-frequency nitrate data in Dead Run
Stapleton, Erin
Co-Authors: Erin Stapleton and Claire Welty

Abstract: Understanding the extent to which various sources contribute to nutrient loads that are delivered to the Chesapeake Bay can help better focus remediation efforts in the overall goal of meeting EPA TMDL regulations. Nitrate loads for groundwater and surface runoff were estimated for 6 gaged subwatersheds within Dead Run using the method of M.P. Miller et al. (2016), which requires use of stream hydrograph baseflow separation and high-frequency stream nitrate data. Partitioning of stream observed nitrate loads into surface runoff and groundwater loads was carried out spatially across gaged subwatersheds within Dead Run as well as temporally from December 2012 to December 2015. The calculated fraction of groundwater contribution to the total stream nitrate load ranged from 13% to 54%, varied across subwatersheds, and was generally greatest in the wet year of 2014 at all stations, when baseflow was higher than normal. Annual first-order watershed-scale reaction rate constants for nitrate loss were determined for each site for each of the three years of data evaluated. Reaction rates generally ranged from about 0.10 to 0.60 d^-1, and varied spatially across subwatersheds and temporally across seasons. At some sites, this reaction rate was found to be negative, implying net export of nitrate. Known anthropogenic perturbations to the stream network from potable water leaks and sewer leaks complicate interpretation of the results.