PREDICTING FLOW AND TEMPERATURE REGIMES AT THREE ALASMIDONTA HETERODON LOCATIONS
IN THE DELAWARE RIVER

Technical Report NPS/NER/NRTR—2008/109

Jeffrey C. Cole^1,2, Philip A. Townsend³,
and Keith N. Eshleman<sup>2

1</sup>Frostburg State University
Department of Biology
201 Compton Science Center
101 Braddock Road,
Frostburg, MD 21532-2303

²UMCES Appalachian Laboratory
301 Braddock Road
Frostburg, MD 21532

³University of Wisconsin
Department of Forest Ecology and Management
1630 Linden Drive
Madison, WI 53706

July 2008

U.S. Department of the Interior
National Park Service
Northeast Region
Philadelphia, Pennsylvania

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Executive Summary

The federally endangered dwarf wedgemussel, Alasmidonta heterodon, requires certain habitat conditions for survival, which may include specific temperature and flow regimes. Dewatering caused by chronic drought and increased water demands of the New York City metropolitan area may threaten A. heterodon populations in the National Park Service Upper Delaware Scenic and Recreational River (UPDE) by reducing flow levels and increasing water temperatures, particularly during summer months.

In this study, we evaluate discharge and temperature relationships between mainstem Delaware River USGS gages and three known A. heterodon locations in order to develop models that will assist managers in preventing detrimental impacts to mussels. We developed discharge and temperature prediction models and depth profiles for each of the three A. heterodon sites using established USGS gage and thermal stations. Bathymetry and wetted perimeter data indicate standing water is present at each mussel site during periods of zero within-site discharge. In all three sites it was found that significant benthic habitat would likely be available even under low discharge rates if minimal wetted perimeter (P_min) values were maintained. Both discharge prediction and water depth profile models indicate that Site 3 is the most vulnerable of the three sites, as it requires the highest discharge rate (26.3 cms [928.8 cfs]) at the USGS Callicoon gage to maintain both the fully wetted perimeter (P_full) and minimal wetted perimeter as well as to prevent occlusion of areas within each site that contain A. heterodon. We also developed temperature prediction models for all three sites. Temperature models which included the Kellams Bridge thermal station were most predictive for Sites 1 and 2, while the USGS Callicoon gage was most predictive for Site 3. We observed temperatures at Site 1 to be cooler during periods of extremely warm mainstem temperatures and warmer during periods of extremely cold mainstem temperatures, indicating this site may serve as a thermal refuge for mussels. Simple linear temperature prediction models using established mainstem thermal stations were successful in predicting the site temperatures in Site 2 and 3. As the Site 1 temperature regime did not follow a simple linear trend, a more complex relationship was used for predicting site temperature conditions.

Data from this study indicate that Site 3 is the most vulnerable of the three sites based upon USGS Callicoon gage discharge levels required to: 1) maintain flow into the site, 2) maintain the minimal wetted perimeter, as well as 3) maintain the fully wetted perimeter. The study also showed that if Site 3 is protected then the other two sites would remain protected as indicated by the lower USGS Callicoon gage discharge levels required to maintain similar conditions in Site 1 and Site 2. Depending upon how management objectives relate to A. heterodon in the Delaware River, different flow targets would be justified.

This study showed that occlusions occur when discharge at the USGS Callicoon gage is at 12.8 cms (451 cfs). A discharge of 15.8 cms (557 cfs) at the USGS Callicoon gage is required to maintain minimal wetted perimeter (P_min) which provides a water refuge within the site in areas where the A. heterodon were originally found. The stressed condition of A. heterodon within Site 3 during 2002 under low flow conditions (20.8 cms [734.5 cfs]) and warm water temperatures (27.5°C [81.5°F]) at the USGS Callicoon gage, suggests that this P_min flow target may not be sufficient to protect the A. heterodon when flow levels are low and water temperatures are high. A discharge of 26.3 cms (928 cfs) at the USGS Callicoon gage is required to maintain the fully wetted perimeter (P_full) which allows for any shifting in mussel locations within the site that may have occurred since the 2002 Lellis survey. A discharge above 30 cms (1059 cfs) for Site 2 and 27.6 cms (974 cfs) for Site 3 is required to maintain site temperatures within two degrees of mainstem temperatures. However, it is currently unknown whether this temperature difference is physiologically significant to A. heterodon under high temperature, low flow conditions. Further physiological and hydrological studies are likely needed to better assess an optimal flow rate to maintain site thermal conditions.

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