Thermal Refugia Assessment for Endangered Dwarf Wedgemussel with DTS on the upper Deleware River

The upper Delaware River, a dam-regulated river forming the boundary between New York and Pennsylvania, is home to numerous native species of mussels, including the endangered dwarf wedgemussel, a species that is susceptible to temperature changes more so than other native species. Due to the nature of human water management practices, low flow events can be accentuated, resulting in increased stream temperature [Galbraith et al., 2012; Maloney et al., 2012]. Thermal refugia for aquatic species is vital for survival during these highly variable or extreme temperature conditions [Boulton et al., 1998]. Groundwater-surface water interactions at both diffuse and discrete locations can provide areas in which these endangered mussels can not only survive but also thrive. As part of an ongoing USGS project, four unique high-resolution temperature data collection techniques have been deployed at three locations. These techniques include fiber-optic distributed temperature sensing (FO-DTS), drone-mounted thermal imaging, boat-mounted real-time thermal mapping, and individual thermistors. All of these techniques are being used in a qualitative way with the goal to identify locations of groundwater discharge that provide aquatic species refuge during extreme temperature events as well as to build temperature models that will be incorporated into a larger riverine decision support system to help resource managers. While this ongoing study incorporates FO-DTS in an established manner, there is a unique opportunity to deploy a physical, vertically paired fiber-optic cable at one of the three sites. Located in Equinunk, PA, this well-characterized field site has been instrumented with vertical high-resolution temperature sensors (FO-DTS wrapped around a post) and hand-held
thermal imaging, providing point measurements of flux [Briggs et al., 2013]. Ecological surveys have also identified dwarf wedgemussles along the bank of this stream reach in locations of groundwater upwelling. Although numerous studies have deployed paired fiber-optic cable, both in physical laboratory experiments [Mamer and Lowry, 2013] and in field settings [Becker et al., 2013; Mawer et al., 2016], these deployments bury the cables vertically one over the other, resulting in differential spacing both horizontally and vertically, leading to erroneous results. By physically pairing two fiber-optic cables, FO-DTS transitions to a quantitative tool capable of providing thousands of flux measurements at a fine spatial and temporal scale. The act of physically connecting the cables removes this uncertainty.

Raw project data is available by contacting [e-mail]