Item Details

Insights into Nitrogen Fluxes: Quantifying Variations in Groundwater-Steam Hydrologic Connectivity

Cosans, Cassandra L.
Format
Thesis/Dissertation; Online
Author
Cosans, Cassandra L.
Advisor
Mills, Aaron
Herman, Janet
Abstract
Significant nutrient nitrogen (N) that degrades coastal waters comes from groundwater that discharges through base flow in streams; thus, understanding the movement of N from groundwater to streams is essential. Nitrate in the groundwater and streamwater was studied at four low-relief, gaining coastal streams on the Delmarva Peninsula of Virginia with the goal of identifying factors important in controlling N flux. Saturated hydraulic conductivity (Ks) was measured by rising and falling head tests in piezometers installed at depths of 60, 100, and 150 cm below the sediment surface and in 70-cm-long sediment cores taken at each stream. Percent organic matter was determined along the sediment cores through weight-loss on ignition. Percent organic matter was inversely related to Ks, but both were extremely variable among the different samples at each stream, differing as much within a single stream as among streams. Ks was between <0.006 and 0.24 cm/sec, while organic matter content ranged from 0.3 to 42%. Nitrate concentrations in the streamwater were fairly similar among the streams and were always less than 8 mg NO3--N L-1, although Tommy’s Ditch consistently had the highest concentrations. Tommy’s Ditch also had the lowest groundwater NO3- concentrations. Cobb Mill Creek had groundwater NO3- concentrations that ranged from 8.5 to 13.3 mg NO3--N L-1, which were dramatically larger than the groundwater at the other streams (range of <0.1 to 3 mg NO3--N L-1). The notable differences in the N content of water at Cobb Mill Creek compared to the other streams is likely a direct result of their respective hydrologic settings. The relatively great topographic relief at Cobb Mill Creek favors deep groundwater circulation, and such a flowpath results large hydraulic gradients and higher N concentrations persisting at very shallow depths under the stream channel.
Language
English
Published
University of Virginia, Department of Environmental Sciences, BS (Bachelor of Science), 2015
Published Date
2015
Degree
BS (Bachelor of Science)
Collection
Libra ETD Repository
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