WaterSMART: Improving Tools for Assessing and Forecasting Ecological Responses to Hydrologic Alteration

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WaterSMART (Sustain and Manage America’s Resources for Tomorrow) is a program of the Department of the Interior that focuses on improving water conservation and helping water-resource managers make sound decisions about water use.

Research team seine sampling

Research team seine sampling

The Science Issue and Relevance: WaterSMART (Sustain and Manage America’s Resources for Tomorrow) is a program of the Department of the Interior that focuses on improving water conservation and helping water-resource managers make sound decisions about water use. The overarching purpose is to develop data and tools needed by water resource managers to meet challenges imposed by aging infrastructure, population growth, groundwater depletion, impaired water quality, water needs for human and environmental uses, and climate variability and change. Being able to assess and forecast ecological responses to changes in streamflow regimes forms a key component of sustainable water management. Whether streamflow regimes change as a result of management actions (such as allocations of water to offstream uses) or because of climatically driven shifts in amounts and timing of precipitation, the ecological responses may involve an array of interconnected processes (e.g., nutrient uptake and transport, sediment erosion and deposition, production and decomposition). Net effects often include changes in the ability of freshwater-associated ecosystems (streams and rivers, and downstream lakes, wetlands, estuaries and bays) to support fish and wildlife populations. Among drainages in the southeastern U.S. in which water allocation issues are paramount and where sound science is needed for management and policy is the Apalachicola-Chattahoochee-Flint (ACF), in the states of Florida, Georgia, and Alabama.

The ecology teams quantitatively sample fish and mussels semiannually in the spring and fall

The ecology teams quantitatively sample fish and mussels semi-annually in the spring and fall

Methodology for Addressing the Issue: Specifying the water needs of freshwater ecosystems is a task complicated by the natural temporal and spatial variability of hydrologic regimes. In recognizing the need for identifying environmental flows across large spatial extents where limited resources preclude evaluation of individual river systems, ecologists recently outlined an approach called the Ecological Limits of Hydrologic Alteration (ELOHA). ELOHA is a systematic and flexible approach for assessing and managing environmental flows, and is intended to accelerate the integration of environmental flows into regional water-resource planning, management, and decision-making (see http://conserveonline.org/workspaces/eloha). The SESC Ecology Team is working with other USGS investigators to apply the ELOHA approach in wadeable streams of the ACF basin. Focus is on headwater tributaries extending upstream (Chattahoochee River and Chestatee River) to downstream (Chipola River and Spring Creek), that are areas susceptible to dewatering from withdrawals, consumptive use, and drought. The ecology teams quantitatively sample fish and mussels semiannually in the spring and fall, while simultaneously collecting flow and water-quality parameters. The goal is to eventually associate ecological transistional stages (recruitment, colonization, extirpation), based on spatially replicated occupancy models, with hydrologic flows under different conditions and in different physiographic regions or across a geographical gradient. Concurrent with the ecological study, USGS hydrologists are developing surface-water and ground-water models to assess flows throughout the basin. These hydrologic models will interface with the ecological models to explicitly examine hydrologic-environmental flows relationships.

Future Steps: Analysis of ecological data will require updating existing models that relate population responses to streamflow metrics. Data analysis will entail using hierarchical regression to relate changes in species abundances or occurrences at sampled locations, to seasonal flow metrics for each interval between samples. Covariates in candidate models will include stream classes, water quality variables, and species traits. Streamflow simulations will eventually be used to forecast changes in the status of fishes and mussels under different management or climate scenarios. Results of simulations may be summarized as changes in species occupancy rates, changes in species richness, relative abundances, or in the case in population models, changes in probability of extinction over the simulated time period. The final step will be to develop flow-ecological response curves for different species or different physiographic regions, and to compare simulations for streams with differing characteristics (e.g., small vs. large, confined vs. unconfined, water-quality classes).