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Groundwater Flowpath Controls on Seepage Temperature and Future Cold Water Stream Habitat
Citation:
Briggs, M., J. Lane, F. Day-Lewis, C. Snyder, S. Hurley, N. Hitt, E. White, Z. Johnson, D. Nelms, D Werkema, AND A. Bagtzoglou. Groundwater Flowpath Controls on Seepage Temperature and Future Cold Water Stream Habitat. 2016 Geological Society of America Fall Meeting, Denver, CO, September 25 - 28, 2016.
Impact/Purpose:
Presentation at the 2016 GSA Annual Meeting in Denver, CO
Description:
As surface-water temperatures increase, climate refugia driven by groundwater connectivity are expected to enable cold-water fish species to survive. Hydrogeophysical methods, including heat tracing, are enhancing understanding of coupled stream ecology and groundwater hydrology throughout the river corridor. We present two case studies regarding native brook trout (Salvelinus fontinalis), a vital cold-water fish that is challenged by poor water quality and rising temperatures. First, we demonstrate the utility of passive seismic measurements to evaluate bedrock depth along a headwater stream in Shenandoah National Park, VA, USA. Bedrock depth defines the vertical boundaries of shallow groundwater aquifers and should be related to groundwater influence potential. The bedrock contact adjacent to zones of known brook trout habitat was found to average 2.6 m beneath the streambed, and numerical models predicted strong sensitivity of shallow groundwater temperature to the downward conduction of surface heat. Annual stream temperature dynamics were observed to lag local air temperature by ~ 25-40 d, similar to predicted groundwater at 2.6 m, suggesting strong thermal exchange with shallow alluvial groundwater, for which the thermal buffering capacity will be reduced over time in a warming climate. Next we explore the interplay between subsurface geology, groundwater discharge, and preferential fish habitat, along a 2-km reach of the Quashnet River, Cape Cod, Massachusetts, USA. This stream represents a clear example of the role of groundwater discharge for native brook trout life processes, with zones of focused groundwater discharge groundwater discharge through the sandy streambed contributing to an approximate 110 L/s gain in streamflow over 1 km. Novel actively-heated high spatial resolution fiber-optic distributed temperature sensors installed within a zone of strong groundwater seepage indicate true vertical flow to at least the 0.6 m streambed depth, indicative of regional groundwater flowpath discharge. The active-heating approach allows quantitative evaluation of streambed water fluxes well below the depth of ambient surface signal extinction. Deeper regional groundwater flowpaths are predicted to show less near-term sensitivity to climate warming, therefore the Quashnet River may provide long-term thermal refuge for native brook trout.
URLs/Downloads:
https://community.geosociety.org/gsa2016/search?executeSearch=true&SearchTerm=werkema&l=1