Atrium Lobby (Hyatt Regency Baltimore on the Inner Harbor)
Jason VerHoef, University of Maryland Baltimore County;
Claire Welty, University of Maryland Baltimore County;
Julia Miller, University of Maryland Baltimore County;
Melissa Grese, University of Maryland Baltimore County;
Sujay Kaushal, University of Maryland College Park;
Andrew J. Miller, University of Maryland Baltimore County;
Michael P. McGuire, University of Maryland Baltimore County;
Jonathan M. Duncan, University of North Carolina;
Lawrence E. Band, University of North Carolina;
Peter M. Groffman, Cary Institute of Ecosystem Studies;
Kenneth Belt, US Forest Service, Northern Research Station;
Reed M. Maxwell, Colorado School of Mines;
We are taking a number of approaches to understand how groundwater is connected to the surface water system as a function of land cover, land use, and landscape position in the Baltimore Ecosystem Study Long Term Ecological Research project. One recent endeavor involves deployment of high-frequency nitrate, temperature, and conductivity sensors at USGS stations already outfitted with pressure transducers, in nested design in a highly urbanized (41 percent impervious surface) watershed. This project expands on a 12-year program of weekly grab sampling and analysis of major anions at the 14.3 sq km scale.
We have deployed a Satlantic SUNA nitrate sensor and a YSI 660 LS temperature/ conductivity sensor at 6 USGS stream gaging stations beginning in October 2010. Nested watershed drainage areas range from 1.3 sq km to 14.3 sq km. Initial results illustrate example behavior of the spatial and temporally variability of the groundwater/surface water interactions. Strong nitrate and conductivity signals are present at base flow, with nitrate exhibiting an increasingly pronounced diurnal pattern at some stations as mean temperatures decrease in autumn and under drier (post-storm) conditions. Under storm conditions, both signals show a sharp drop in concentration with the onset of storm flow, with minimum values at peak storm flows, and gradual recovery to pre-storm conditions as storm flow recedes. Any observed base-flow diurnal nitrate pattern is washed out during storm flow, but gradually reappears as the system dries out.
We have used the conductivity signal in various mixing models to estimate the volume of groundwater contributing to storm flow. Initial results for the 14.3–km scale show that the volume of groundwater comprising storm flow is more sensitive to storm duration than intensity and ranges from 21- 46 % of storm flow.
