A flooded future for River Chub? Future impacts of climate change and urbanization on reproduction of a keystone native fish species

Abstract

AbstractObjectivePredicted impacts of climate change in the eastern United States are pervasive and complex, including increased precipitation, increased frequency of heavy precipitation events, and altered seasonality of rainfall. This will potentially lead to increased flooding frequency and severity. The River Chub Nocomis micropogon is an important keystone and engineer species in the eastern United States, primarily through its construction of nesting habitat, which is shared with other species (“nest associates”) in a mutualistic relationship. River Chub nests are vulnerable to high flows caused by excessive precipitation and by urbanization of watersheds. Using predictions of climate change models, we examined the potential for increased River Chub nest disruption under two climate change scenarios.MethodsPublished thresholds linking River Chub nest disruption with stream discharge were used to interpret fine‐scale predictions of a downscaled climate prediction model (HadGEM2‐ES) using a stochastic weather generator (LARS‐WG6) calibrated to two climate change scenarios. This was examined for a case study watershed (Big Elk Creek, Maryland). The amount of River Chub nest disruption was compared between present‐day stream discharge observations (1995–2021) and simulated data for 2061–2080 under the “worst case” (RCP85) and “probable‐case” (RCP45) scenarios. Potential nest disruption in an urbanized stream that lost its River Chub (Gwynns Falls, Maryland) was also evaluated for comparison with Big Elk Creek scenarios.ResultSignificantly elevated nest disruption under both RCP45 and RCP85 relative to observed current conditions was found under status quo watershed characteristics in the form of more disruptive events, more disrupted days, and shorter periods of disruption‐free days during the River Chub nesting season. Potential nest disruption in the urbanized case study stream was far greater than that observed for any scenario.ConclusionIncreased nest disruption projected by the downscaled HadGEM2‐ES climate prediction model was moderate and far below the level of nest disruption observed in flashy urbanized streams that have lost or may have lost River Chub populations in the region. The moderate impacts of increased flooding from climate change will interact with projected population growth and urbanization for the Big Elk Creek watershed. Mechanistic modeling of fine‐scale processes by using stochastic weather generators shows promise for modeling the responses of ecosystems to changing conditions.