IDENTIFYING GROUNDWATER DISCHARGE LOCATIONS IN TIDAL WETLANDS USING ENVIRONMENTAL THERMOGRAPHY IN PRIME HOOK NATIONAL WILDLIFE REFUGE, DELAWARE, USA

Environmental thermography is used to identify locations of groundwater discharge in the tidal wetlands in Prime Hook National Wildlife Refuge (PH). Large breaches in the estuarine barrier between PH and Delaware Bay initiated between 2008 and 2011 resulted in significant increases in salinity in large impoundments that were previously managed as fresh water ecosystems. The modern impoundments were created in the 1980s but landowners have been modifying the hydrology since the early 1900s. Updated plans are to manage the impoundments as salt-water ecosystems, but conserving freshwater and brackish habitat is also part of the plan to contribute to biological integrity. A large saltmarsh restoration is underway where they are cutting new channels and modifying existing channels to increase circulation and lower water levels in PH. The sediment from these operations will be spread onto the surrounding area to increase bed elevation conducive to growing saltmarsh vegetation. This study identifies locations where freshwater is entering channels and ponds in the marsh, where it may be upwelling onto the marsh platform and/or entering from the upland fringe boundary. Two aerial surveys were conducted in a 1946 Aeronca Champion fixed-wing aircraft in early April 2015. Groundwater is warmer than surface water at this time of year. A FLIR SC6000 long-wave thermal imager and a GoPro Hero visual camera were custom mounted to the rear window and were operated by the author from the rear seat. Thermal and visual data were collected at 4 and 60 Hz, respectively. Thermal data are fully radiometric allowing for data exploration during analysis. Most discharge areas appear to be located in ponds and channels that were parts of Open Marsh Water Management projects. These ponds and ditches were dug deep enough to create permanent habitat for fish that eat mosquito larvae. One discharge area is in an abandoned river channel adjacent to the estuarine barrier. Other discharge areas appear to be in ponds dug for watering cattle prior to 1963.