Effect of Irrigation and Climate Variability on Water Quality of Coastal Watersheds: Case Study in Alabama

Abstract

Agricultural activities are considered the leading cause of surface water quality degradation in the United States. While agricultural production in the state of Alabama is mainly rain-fed, irrigation is currently being promoted to reduce drought vulnerability associated with the El Niño Southern Oscillation (ENSO). It is not clear, however, how increased irrigation and ENSO-induced seasonal to interannual climate variability will affect the transport of pollutants [mainly nitrogen (N) and phosphorus (P)] to surface water bodies. The objective of this study was to quantify the effect of irrigation and ENSO on nutrient transport. A standard model to assess soil and water was applied in the Big Creek watershed of southwest Alabama to address this objective. The hydrologic and water quality parameters of the model were calibrated and validated by comparing model predictions with 15 years of observed data, and the effect of irrigation was evaluated. Model simulations were performed for 59 years (1950–2008) to quantify the effect of ENSO on nutrient transport. Results show that total nitrogen (TN) and total phosphorus (TP) loads increased by 4 and 3%, respectively, when irrigation was applied to cropland subwatersheds. The increase in TN load was significant at 90% confidence level (