Predicting fish assemblage characteristics under shifting land cover and climate regimes using the Soil and Water Assessment Tool (SWAT)

SWAT is a watershed-scale hydrologic model that quantifies water, sediment, and nutrient yields to streams. Because hydrologic and sediment regimes are known to influence fish communities, SWAT has potential to target threats to fish communities associated with changes in land use/cover (LULC) and climate. We used SWAT to model impacts at sixteen Ohio stream reaches and identified key environment-fish relationships. Results suggest that fish assemblage diversity (1/D), abundance (#/m2), and biomass (g/m2) are linked to various watershed-scale factors (e.g., land-use class). The same assemblage characteristics were also correlated with local geomorphic variables, which are tightly coupled to hydrologic and sediment regimes. To assess the impacts of changes in LULC and climate on fish assemblages, we adjusted model inputs to reflect possible future scenarios based on likely trends. We then input predicted sediment and hydrological values into our fish-environment regressions to forecast impacts on fish assemblages under the different scenarios. By modeling shifts in sediment and water yields based on LULC and climate change we have established mechanistic links between watershed-scale LULC and precipitation patterns and fish assemblages. SWAT has not often been used in ecological studies and we anticipate that it will prove a useful conservation and management tool.