Land use and surface water withdrawal effects on fish and macroinvertebrate assemblages in the Susquehanna River basin, USA

Water withdrawals in the Susquehanna River basin, USA, are increasing due to burgeoning shale gas extraction activities. In order to determine if flow alteration resulting from shale gas industry surface water withdrawals impacts fish and macroinvertebrate assemblages in lotic habitats, data were collected upstream and downstream of 12 withdrawal and three reference sites in headwater, cold water, and large warm water streams. Watershed size ranged from 4 to 517 km² and average daily withdrawals ranged from 0.05 to 1.4 million liters. Analysis of withdrawal data indicated that approved withdrawals far exceeded actual withdrawals across all stream types. The largest withdrawals relative to stream size were from headwater streams, where on average 6.8% of average daily flow was withdrawn daily. Fish and macroinvertebrate assemblage similarity at study sites depended largely on stream sampled, rather than position upstream or downstream of withdrawals. Regression techniques were employed to determine if catchment-level variables or withdrawal metrics best described variation in fish and macroinvertebrate metrics shown to be sensitive to flow alteration. The catchment-level variables were responsible for the majority of observed variation in fish metrics. Macroinvertebrate models performed poorly, indicating that the stream sampled or variables not included in the analyses were responsible for the majority of variation. Overall, evidence suggests impacts of shale gas withdrawals within the Susquehanna basin are limited at the present state of flow alteration. Potential reasons include protective measures such as pass-by flow restrictions, which require withdrawals to cease when flows drop below a predetermined low flow threshold, maximum instantaneous and daily withdrawal limits, and recent initiation of withdrawals (1-3 years of operation).