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Creators/Authors contains: "Brooks, Alexander C."

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  1. Abstract

    Water‐mediated linkages that connect landscape components are collectively referred to as hydrologic connectivity. In river‐floodplain systems, quantifying hydrologic connectivity is challenging yet enables descriptions of hydrologic function that emerge from complex, heterogeneous interactions of underlying geomorphic, climatic and biologic controls. Here, we quantify surface water hydrologic connectivity using field indicators and develop a connectivity strength metric across a river‐floodplain system. To measure connectivity strength, we analyzed hydrometric data, conservative tracers, and natural occurring geochemical and microbial tracers across streamflows. We developed empirical models of hydrologic connectivity and predicted daily connectivity strength values across sites and assessed the sensitivity of connectivity to streamflow variability. Some floodplain areas were consistently connected or disconnected to the river, while other floodplain areas exhibited variable connectivity strength through the season. Of the locations with intermittent connectivity, some disconnected quickly and others had a prolonged disconnection phase. At the river‐floodplain system scale, we found hydrologic connectivity always increased with streamflow while across‐system variance in connectivity peaked at intermediate streamflow. Floodplain locations with intermittent surface connectivity demonstrated inter‐annual variability in hydrologic connectivity as a function of climate variability. Our results suggest that intermediate flows are critical periods for seasonal connectivity regimes and understanding the influence of changing climate on full flow durations will be required to predict impacts on river‐floodplain connectivity.

     
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  2. Abstract

    The rivers of Appalachia (United States) are among the most biologically diverse freshwater ecosystems in the temperate zone and are home to numerous endemic aquatic organisms. Throughout the Central Appalachian ecoregion, extensive surface coal mines generate alkaline mine drainage that raises the pH, salinity, and trace element concentrations in downstream waters. Previous regional assessments have found significant declines in stream macroinvertebrate and fish communities after draining these mined areas. Here, we expand these assessments with a more comprehensive evaluation across a broad range of organisms (bacteria, algae, macroinvertebrates, all eukaryotes, and fish) using high‐throughput amplicon sequencing of environmental DNA (eDNA). We collected water samples from 93 streams in Central Appalachia (West Virginia, United States) spanning a gradient of mountaintop coal mining intensity and legacy to assess how this land use alters downstream water chemistry and affects aquatic biodiversity. For each group of organisms, we identified the sensitive and tolerant taxa along the gradient and calculated stream specific conductivity thresholds in which large synchronous declines in diversity were observed. Streams below mining operations had steep declines in diversity (−18 to −41%) and substantial shifts in community composition that were consistent across multiple taxonomic groups. Overall, large synchronous declines in bacterial, algal, and macroinvertebrate communities occurred even at low levels of mining impact at stream specific conductivity thresholds of 150–200 µS/cm that are substantially below the current U.S. Environmental Protection Agency aquatic life benchmark of 300 µS/cm for Central Appalachian streams. We show that extensive coal surface mining activities led to the extirpation of 40% of biodiversity from impacted rivers throughout the region and that current water quality criteria are likely not protective for many groups of aquatic organisms.

     
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