HR: 14:10h
AN: H13M-02    [Abstracts]
TI: Coupling Strontium Isotope and Trace Metal Geochemistry With a Watershed Flow Path Model in the Lamprey River Watershed, New Hampshire
AU: * Smith, M A
EM: Melissa.Smith@unh.edu
AF: Dept. of Earth Sciences, University of New Hampshire, 121 James Hall, Durham, NH 03824, United States
AU: Bryce, J
EM: Julie.bryce@unh.edu
AF: Dept. of Earth Sciences, University of New Hampshire, 121 James Hall, Durham, NH 03824, United States
AU: Davis, J
EM: Matt.Davis@unh.edu
AF: Dept. of Earth Sciences, University of New Hampshire, 121 James Hall, Durham, NH 03824, United States
AB: One significant challenge in watershed characterization is accounting for the groundwater flow system. In temperate climates, the hydrologic cycle is dominated by surface processes such as precipitation, evapotranspiration, and shallow groundwater flow. While, volumetrically, groundwater flow is less significant, it remains critically important for maintaining instream flow and closing the water budget within the watershed. The objective of the current study is to assess the adequacy of a simple groundwater flow conceptual model to describe groundwater flow in a mesoscale (50 km²), fractured bedrock, watershed. We hypothesize that groundwater flowpaths and seasonal flowrates at the scale of kilometers can be adequately described by a highly-resolved (30 meter grid), topographically dominated, homogeneous isotropic system. To test this hypothesis, we utilize the distinct and traceable chemical and isotopic signatures of the host bedrock. The combined use of trace elements and radiogenic isotopes (e.g., ⁸⁷Sr/⁸⁶Sr) provides great promise for the delineation of groundwater flow paths at the watershed scale, especially when bedrock hosts have distinctive compositions. The Lamprey River, located in Southern New Hampshire, is an especially promising watershed to carry out these types of analyses because groundwater within the watershed is stored primarily in bedrock aquifers with two geochemically contrasting bedrock hosts lying adjacent to each other. The bedrock aquifers include the White Mountain Magmatic Series of Mt. Pawtuckaway, a local topographic feature, and the Massabesic Gneiss Complex. Bedrock measurements, as well as rock leachate solutions, show distinct signatures. Surface water samples collected from ponds underlain by the differing hosts also reflect the bedrock signals with ⁸⁷Sr/⁸⁶Sr ranging from 0.70686 in the White Mountain Magmatic Series to 0.71443 in the Massabesic Gneiss Complex. Surface water samples collected along the Lamprey River during Summer 2006 show a decrease in ⁸⁷Sr/⁸⁶Sr in the downstream direction as the water generally flows from the magmatic series to the gneiss complex, indicating that low ⁸⁷Sr/⁸⁶Sr groundwater is infiltrating the river. These results also indicate groundwater inputs from extrabasinal flow. Further refinements of the model, coupled with forthcoming trace element analyses, will provide a stronger means to quantify these contributions along the gradient of the river.
DE: 1847 Modeling
DE: 1858 Rocks: chemical properties
SC: Hydrology [H]
MN: 2007 Fall Meeting