Impact of Land Use and Land Cover Changes on the Stream Flow and Water Quality of Big Creek Lake Watershed South Alabama, USA

Abstract

Land use is one of the key factors affecting the stream flow of a watershed. This research aimed to evaluate the impact of changing land use and land cover (LULC) on stream flow and water quality by applying the Soil and Water Assessment Tool (SWAT) to the Big Creek Lake watershed located in Mobile County, South Alabama. Digital elevation model (DEM), LULC data, weather data, soil data, observed streamflow, nitrogen, and phosphors data were used as input files to calibrate and validate the SWAT model. The SWAT model was calibrated and validated using the Sequential Uncertainty Fitting (SUFI-2) algorithm in the SWAT Calibration Uncertainties Program (SWAT-CUP) software. Agricultural land increased by about 11,045 acres and urban area increased by 3350 acres, and forest area decreased by 11,482 acres, between 1991 and 2020. This changing scenario of LULC not only increased the streamflow but also the total nitrogen and phosphorus. The total streamflow was higher, at about 38 m3/s in the LU_2020 scenario, than in the LU_1990 scenario. Increases of about 1,136,919 kg of nitrogen and 324,467 kg of phosphorus were found from 1990 to 2020, and these increases can be explained by an increase in agricultural land of about 11,045 acres. The results obtained in this study are able to provide guidance to water resource management and planning for policymakers and water managers in Mobile County.