Implications of land-use and climate change for meeting environmental flows and water quality targets in a groundwater-dominated watershed

Study region This study was conducted in the Santa Fe River Basin (SFRB), a tributary basin of the Suwannee River in the Southeastern USA. The SFRB is an agriculturally important, groundwater-dominated watershed, which overlies the Upper Floridan Aquifer (UFA). Its mixed agricultural, forested and urban land uses, strong surface-groundwater interactions, and sensitive spring and river ecosystems make it ideal for understanding important water-resource responses across the broader region. Study focus This work addressed two specific research questions: How do climate and land-use change affect groundwater recharge, streamflow and nitrate loads in the SFRB; and under what future conditions can existing regulations for minimum streamflow and nitrate loading be achieved? We addressed these questions using SWAT-MODFLOW to simulate five land-use scenarios under historical climate and future climates representing extreme wet and dry projections. New hydrologic insights for the region Climate was the dominant driver of changes in groundwater recharge and streamflow, whereas land use had the greatest influence on nitrate loads. All land-use scenarios met minimum streamflow requirements under historical and wet future climates. However, no land-use scenarios met minimum flows for the RCP8.5 dry future, and only the pre-development scenario met minimum flows for the RCP4.5 dry future. The 65% nitrate load reduction required to meet current nutrient regulations was achieved only under the pre-development scenario and, even then, not under the RCP8.5 wet future.