Hudy, Morgan, Department of Biology, Bucknell University, 1 Dent Drive, Lewisburg, PA, 17837 mth016@bucknell.edu; McTammany, Matthew, Department of Biology, Bucknell University, 1 Dent Drive, Lewisburg, PA, 17837, mmctamma@bucknell.edu.
Aquatic populations vary amongst valley floor ecosystems due to the presence of multiple aquatic habitats. Populations within off-channel aquatic habitats are valuable as they contribute to biodiversity across valley-floor ecosystems. Groundwater within the valley-floor environment typically connects active stream channels to other aquatic habitats, such as pools and side channels, which form when groundwater intersects with depressions on the valley floor. Groundwater connections benefit biota in off-channel pools by providing a reliable source of water during periods of drought and cool water during warm periods of the summer. As a result, groundwater supplied pools could provide stable habitats for populations of cold-water invertebrates and amphibians as climate warms. Historically, logging affected stream environments by incising stream channels, which concentrated flows and lowered groundwater levels across valley floors resulting in loss of off-channel aquatic habitats and associated biodiversity. Logging has affected groundwater flow to these off-channel habitats within the Allegheny National Forest, but addition of large woody debris (LWD) could restore valley floor hydrology by causing aggradation of bed material in streams and subsequent raising of water table elevation. If this increase in the water table is high enough, groundwater might reconnect to depressions across the valley floor and provide more persistent aquatic habitats. LWD has been added to 750m of Little Arnot Run in Allegheny National Forest as part of a project to restore a stream in a historically logged watershed. Benthic invertebrates have been collected from riffle and pool habitats in Little Arnot Run and from pools and side channels across the valley floor. Water temperature has been monitored in off-channel pools since 22 October 2022 using HOBO pendant temperature loggers mounted at two heights on stakes placed in the center of the pools. Data from these loggers were used to indicate water source (i.e. groundwater or surface runoff). If pools are fed by groundwater, water temperatures should be lower than in pools sustained by rain water, which might allow populations of cold-water species to survive in these pools and resist warming due to climate change. Additionally, temperature patterns will enable us to determine water depth and inundation period, as many of these pools potentially dry up or become extremely shallow seasonally. Size and depth of pools located off of Little Arnot Run were also measured on sample dates to determine potential habitat area. Variability in aquatic invertebrate communities among pools of varying sizes and water sources could illustrate the importance of groundwater connections across the valley floor to biodiversity. Any ecological changes to existing pools in response to LWD restoration might affect regional biodiversity of aquatic biota by altering the number and quality of aquatic habitats present.