STRONTIUM ISOTOPES AND TRACE METALS IN THE DELINEATION OF FLOW PATHS IN THE LAMPREY RIVER WATERSHED

The combined use of trace elements and radiogenic isotopes, such as ⁸⁷Sr/⁸⁶Sr, is a useful technique in delineating groundwater flow paths at the watershed scale. The successful application of this technique requires the juxtaposition of a strong isotopic and trace element contrast within the watershed. This scenario exists in the Lamprey River watershed located in southern New Hampshire. The bedrock hosts include the White Mountain Magmatic Series of Mt. Pawtuckaway and the Massabesic Gneiss Complex. Bedrock leachate solutions from these two rock types show distinct signatures in the alkali and high field strength elements. Surface water samples collected from ponds underlain by the differing hosts also reflect the bedrock signals with ⁸⁷Sr/⁸⁶Sr ranging from 0.706861 +/- 0.000015 in the White Mountain Magmatic Series to 0.714434 +/- 0.000012 in the Massabesic Gneiss Complex. These two end members are located adjacent to one another within the Lamprey River watershed, and it is therefore anticipated that isotopic and trace elemental measurements along the Lamprey River will reflect the mixing of water from these bedrock aquifers. Surface water samples collected along the Lamprey River during Summer 2006 show an increase in concentrations of major ions (Si, Ca) and trace elements in the downstream direction as the water generally flows from the magmatic series to the gneiss complex. These geochemical signatures can be useful in delineating groundwater flow paths and providing information for managing water resources.