New studies reveal ecological importance of fine-scale groundwater connectivity for streams during drought
Stream ecosystems support vital resources that may be jeopardized by climate change and climate stressors such as drought.
Issue
Stream ecosystems support vital resources that may be jeopardized by climate change and climate stressors such as drought. In the headwaters of the Chesapeake Bay, native brook trout (Salvelinus fontinalis) are recognized as a high priority for conservation and restoration by Chesapeake Bay Program partners, and USGS research efforts are underway to provide science to address these needs. Prior research has demonstrated the importance of stream-groundwater connectivity in promoting thermal resiliency to air temperature in streams. However, the role of role of groundwater for stream ecosystems during drought is poorly understood, yet the frequency and magnitude of drought events are expected to increase due to climate change, and this necessitates new hydroecological research.
USGS Studies
Recent USGS studies provide new insights on the geophysical basis of stream dewatering during drought and the ecological consequences for brook trout populations in Shenandoah National Park, Virginia. The first study used passive seismic instrumentation to evaluate the depth to bedrock along eight mountain stream corridors, and differences in bedrock depth were associated with the onset of dewatering in streams and fine scale patterns of wet and dry patches in less resilient subcatchments (Briggs et al. 2022). The second study evaluated brook trout abundance data collected in the same study area over a 10-year period (2012-2021) and found evidence for population fragmentation associated with periodic dewatering that was not well informed by downstream streamflow records (Hitt et al. 2024).
Major Findings
- Stream sections draining thicker stream valley aquifers (i.e., deeper depth to bedrock) lacked the dewatering trends observed in shallow stream sections due to increased baseflow supply (figure 1). Local bedrock depth dynamics measured with geophysical methods for the study were not well predicted by large scale, gridded depth to bedrock or soils maps.
- In subcatchments with average shallow bedrock (i.e. <2m from land surface), subtle increases in sediment thickness created patchy dewatered sections during dry periods where the entirety of low streamflow could be transmitted through the porous, rocky colluvium (figure 2).
- Dewatering did not reduce total brook trout abundance but did fragment the population into fewer areas which increases competition pressures and risks for local extirpation (figure 3).
- In combination, these studies highlight the importance of hydrological analysis within headwater streams because downstream river gages could not explain the observed patterns of stream dewatering or fish distribution.
Management Applications
Management of brook trout fisheries requires monitoring within headwater streams, and this could benefit from geophysical analysis of groundwater dynamics within small catchments. Monitoring for the onset of dewatering could be accomplished through imagery analysis such as the Flow Photo Explorer, and locations with shallow depth to bedrock could serve as an early-warning system for deeper aquifers elsewhere.
For More Information
Contact Dr. Martin A. Briggs, mbriggs@usgs.gov
- Briggs, M. A., Goodling, P., Johnson, Z. C., Rogers, K. M., Hitt, N. P., Fair, J. B., and Snyder, C. D.: Bedrock depth influences spatial patterns of summer baseflow, temperature and flow disconnection for mountainous headwater streams, Hydrol. Earth Syst. Sci., 26, 3989–4011, https://doi.org/10.5194/hess-26-3989-2022, 2022.
Contact Dr. Nathaniel “Than” Hitt, nhitt@usgs.gov
- Hitt, N.P., K.M. Rogers, K.G. Kessler, M.A. Briggs, J.H. Fair, and C.A. Dolloff. 2024. Effects of episodic dewatering on brook trout spatial population structure. Freshwater Biology, DOI:10.1111/fwb.14287.
Stream ecosystems support vital resources that may be jeopardized by climate change and climate stressors such as drought.
Issue
Stream ecosystems support vital resources that may be jeopardized by climate change and climate stressors such as drought. In the headwaters of the Chesapeake Bay, native brook trout (Salvelinus fontinalis) are recognized as a high priority for conservation and restoration by Chesapeake Bay Program partners, and USGS research efforts are underway to provide science to address these needs. Prior research has demonstrated the importance of stream-groundwater connectivity in promoting thermal resiliency to air temperature in streams. However, the role of role of groundwater for stream ecosystems during drought is poorly understood, yet the frequency and magnitude of drought events are expected to increase due to climate change, and this necessitates new hydroecological research.
USGS Studies
Recent USGS studies provide new insights on the geophysical basis of stream dewatering during drought and the ecological consequences for brook trout populations in Shenandoah National Park, Virginia. The first study used passive seismic instrumentation to evaluate the depth to bedrock along eight mountain stream corridors, and differences in bedrock depth were associated with the onset of dewatering in streams and fine scale patterns of wet and dry patches in less resilient subcatchments (Briggs et al. 2022). The second study evaluated brook trout abundance data collected in the same study area over a 10-year period (2012-2021) and found evidence for population fragmentation associated with periodic dewatering that was not well informed by downstream streamflow records (Hitt et al. 2024).
Major Findings
- Stream sections draining thicker stream valley aquifers (i.e., deeper depth to bedrock) lacked the dewatering trends observed in shallow stream sections due to increased baseflow supply (figure 1). Local bedrock depth dynamics measured with geophysical methods for the study were not well predicted by large scale, gridded depth to bedrock or soils maps.
- In subcatchments with average shallow bedrock (i.e. <2m from land surface), subtle increases in sediment thickness created patchy dewatered sections during dry periods where the entirety of low streamflow could be transmitted through the porous, rocky colluvium (figure 2).
- Dewatering did not reduce total brook trout abundance but did fragment the population into fewer areas which increases competition pressures and risks for local extirpation (figure 3).
- In combination, these studies highlight the importance of hydrological analysis within headwater streams because downstream river gages could not explain the observed patterns of stream dewatering or fish distribution.
Management Applications
Management of brook trout fisheries requires monitoring within headwater streams, and this could benefit from geophysical analysis of groundwater dynamics within small catchments. Monitoring for the onset of dewatering could be accomplished through imagery analysis such as the Flow Photo Explorer, and locations with shallow depth to bedrock could serve as an early-warning system for deeper aquifers elsewhere.
For More Information
Contact Dr. Martin A. Briggs, mbriggs@usgs.gov
- Briggs, M. A., Goodling, P., Johnson, Z. C., Rogers, K. M., Hitt, N. P., Fair, J. B., and Snyder, C. D.: Bedrock depth influences spatial patterns of summer baseflow, temperature and flow disconnection for mountainous headwater streams, Hydrol. Earth Syst. Sci., 26, 3989–4011, https://doi.org/10.5194/hess-26-3989-2022, 2022.
Contact Dr. Nathaniel “Than” Hitt, nhitt@usgs.gov
- Hitt, N.P., K.M. Rogers, K.G. Kessler, M.A. Briggs, J.H. Fair, and C.A. Dolloff. 2024. Effects of episodic dewatering on brook trout spatial population structure. Freshwater Biology, DOI:10.1111/fwb.14287.