Baltimore Ecosystem Study Institute of Ecosystem Studies

2015 BES Annual Meeting Presentation and Poster Abstracts

Insights into urban watershed dynamics from long-term deployment of high-frequency water quality sensors
Welty, Claire
Co-Authors: Claire Welty, Jon Duncan, John T. Kemper, Joshua N. Cole

Abstract: Deployment of high-frequency sensors over long periods of time in urban streams is rare. We have intensively maintained of a suite of water quality sensors in Dead Run at 6 USGS gaging stations since 2012 that can now be used to evaluate interannual, seasonal, and event trends in water quality and solute loads in unprecedented detail. Here we focus on nitrate dynamics at Dead Run Franklintown, which drains an area of 14.1 sq km with 45% impervious surface cover. Discharge data are collected by USGS at 5-minute intervals; nitrate, temperature, specific conductance, turbidity, and dissolved oxygen data are collected by UMBC at 30-minute intervals. Preliminary findings include: (1) strong diel variability in nitrate concentration at baseflow conditions year-round is evident; (2) nitrate concentration is reduced dramatically during large storm events due to dilution; for small storms nitrate sometimes increases with discharge; (3) during dry periods, there is occasional pronounced nitrate concentration build-up (over days) followed by quick release that exceeds average diel variability; (4) peak nitrate concentrations reach an annual low around Julian Day 100 that coincides with a dramatic annual shift in dissolved oxygen variability; (5) inter-annual climate variability exhibits strong controls on nitrate concentrations. For example, concentration fluctuations at the storm-event scale are higher during wetter years when ambient base-flow concentrations are higher. (6) Median nitrate daily loads calculated using sensor data and instantaneous discharge values are about double the median values calculated using a grab sample with daily discharge values, when compared on a seasonal basis. Much of the nitrate load that passes at night and in storm events and is missed by sampling in daytime only and once a week.