Baltimore Ecosystem Study Institute of Ecosystem Studies

2016 BES Annual Meeting Presentation and Poster Abstracts

Temporal Resolution of Data Controls Variability in Nitrate Concentration-Discharge Relationships in an Urban Watershed
Duncan, Jon
Co-Authors: Jonathan M. Duncan1, Claire Welty2, John T. Kemper2, Erin Stapleton

Abstract: Concentration-discharge (c-Q) relations have been used to infer processes governing solute transport at watershed scales. Prior studies have documented inconsistent concentration-discharge patterns driven by changes in end-member concentrations.  Here we examine a novel data set consisting of three-years of high-frequency nitrate and discharge data for an urban stream in the Baltimore region to quantify temporal variability at storm-event, seasonal, and interannual time scales. On a storm-event scale, we observe a watershed-specific dQ/dt threshold when storms switch from counter-clockwise to clockwise c-Q behavior. On a composite scale, the c-Q data exhibit chemostasis for 14-years of weekly data (676 data points) but not for 3 years of high-frequency sensor data (52,560 data points). Furthermore, the slope of the c-Q high frequency data differs between dry and wet years.  We examine plausible hydrologic and metabolic controls on stream nitrate concentrations and fluxes. This work highlights the value of long-term, high-frequency c-Q data collection for resolving the transport of nitrate in an urban watershed.