Quantifying Effects of Flow Variability on Riverine Biota

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Stream and river biota around the world are imperiled by alterations to stream flow regimes that result from dams, land-use changes, water diversions and changing climate patterns. To manage and conserve stream-dependent species threatened by flow alterations, natural resource managers need quantitative information relating multiple aspects of ecological response to changes in a stream’s flow regime.  This research contributes flow-ecology relations for streams in the southeast US, where managers are concerned about effects of flow alteration on the ability of systems to support species-rich assemblages of fishes and invertebrates, including imperiled taxa.

The Challenge: Ecologists have shown that many ecological processes in rivers, including organism growth, reproduction, survival and dispersal, are attuned to natural patterns of streamflow variability.  However, to predict how riverine biota will respond to flow alteration caused by, for example, water diversions and dam operations, ecologists need to understand the mechanisms through which changes in streamflow affect plant and animal populations.  Therefore, we are conducting field studies and analyses to test hypothesized effects of streamflow variability on population (survival, reproduction, extirpation, colonization) and trophic (primary production and consumption) dynamics.

The Science: We are quantifying spatial and temporal variation in multiple biological responses in relation to streamflow dynamics and across gradients of streamflow variability. Our studies include: mark-recapture to estimate fish survival and production of juveniles in relation to river flow patterns; comparison of fish communities between flow-regulated rivers with differing dam operations; monthly sampling to track persistence of small-bodied fishes in perennial streams affected by groundwater pumping; analyses of long-term (20-yr) monitoring data to assess high- and low-flow effects on fish community dynamics; and experimental manipulation to measure effects of variation in hydraulic conditions on biomass accrual by a submerged macrophtye.

The Future: Our studies are providing data and insights on how aquatic biota – especially fishes, invertebrates and macrophytes – may respond to changes in patterns of streamflow variability in southeastern U.S. rivers and streams, with potential relevance to other ecological systems that have strong effects of abiotic drivers.  One of our goals is to use quantitative relationships between streamflow variability and biological processes to develop tools that allow stakeholders to forecast changes in riverine communities and productivity given shifts in streamflow regimes resulting from changes in climate, land use, and water management.