Assessing the impacts of agricultural conservation practices on freshwater biodiversity under changing climate

Freshwater systems are some of the most threatened ecosystems in the world. Factors contributing to their degradation can be associated with the expansion and intensification of agriculture in the 20th century, which has led to habitat degradation and water pollution. To mitigate the impacts of agricultural activities and improve stream ecosystem quality, government-funded conservation programs have promoted the implementation of best management practices (BMPs) during the last three to four decades. However, these conservation programs have been implemented within agricultural landscapes without evaluating exhaustively their potential side effects on freshwater species at the watershed scale. This study aimed to assess the changes in freshwater biodiversity in terms of fish species richness under future climate and potential conservation land-management schemes in the Kaskaskia River Watershed, Illinois, USA. Fish regression models were integrated to the Soil and Water Assessment Tool (SWAT) to simulate the responses of total- and game-fish species richness to four major management practices (crop rotation, cover cropping, reduced tillage, modified fertilizer application) identified as the most feasible in terms of stakeholder acceptability and environmental soundness, under 32 distinct climate projections. Results showed that fish species in the KRW are more sensitive to changes in the climate regime than to changes in the land-management practices. Specifically, the most likely percentage changes in fish species revealed a potential decline in richness in all stream orders over time with the worst impacts in the first and second order streams (-5%--10% decade(-1)) due to the progressive increase in the temperatures (0.61 degrees C -0.92 degrees C decade(-1)) expected in the watershed. The long-term impacts on fish species richness may be inevitable if the proposed land-management alternatives were not accompanied by additional measures specifically design to protect aquatic life.