Hyporheic Invertebrate Community Composition as a Function of Flow Regime in the Colorado River Basin, TX

Date

2023-08

Authors

Austin-Bingamon, Eryl

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Abstract

Climate change and an increase in groundwater extraction have contributed to longer and more frequent periods of stream intermittency in Texas rivers. This has ecological implications for all riverine habitats, including the hyporheic zone; an ecotone between surface water and groundwater in a river channel. The hyporheic zone is an often-overlooked habitat in river ecology, and little is known about how stream intermittency affects hyporheic invertebrate communities. This study examined hyporheic community composition and abundance as a function of flow regime at 34 hyporheic sample sites along 4 rivers in Central Texas. Flow regime was classified based on 10 selected hydrological indices calculated from the Indicators of Hydrological Alteration software. At sites without time-series gage data, multiple linear regression was used to create predictive models based on shared environmental characteristics between gaged and non-gaged sites. Cluster analysis was then used to group sampled sites into distinct flow regimes by their predicted index values, resulting in clusters of ‘wet’ and ‘dry’ sites, with ‘dry’ sites representing sites that are experiencing systematic declines in discharge or complete desiccation because of anthropogenic effects such as river withdrawals and groundwater extraction. A significant difference in invertebrate abundance was found between comparatively “wet” and “dry” sites, with a lower average total abundance at drier sites. Differences in community composition were also found between sites, driven mainly by the presence/abundance of Copepoda, Ostracoda, and Insecta taxa groups. Multiple linear regression was used to identify influential predictors of abundance, finding that more than 50% of variation in total invertebrate abundance between sites could be explained by mean annual flow and hydraulic conductivity. This study found a connection between flow regime and hyporheic invertebrate communities, confirming that low flow conditions result in lower abundance and a change in community composition. Better understanding of environmental controls on hyporheic communities will enable more effective prediction and mitigation of future damage to riverine ecosystems.

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Texas, hyporheic zone, Colorado River basin, intermittency, community composition, Llano, Pedernales, San Saba, concho, flow, Biology

Citation

Austin-Bingamon, E. (2023). Hyporheic invertebrate community composition as a function of flow regime in the Colorado River Basin, TX (Unpublished thesis). Texas State University, San Marcos, Texas.

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