Effects of Hydroclimate on In-ditch Water Quality: Case Study of Two Tailwater Recovery Ditches in Mississippi

Abstract. Nutrient loss via soil erosion caused by surface and irrigation runoff is of great concern for agricultural producers and the scientific community. Nutrients reach water bodies and in many instances exceed acceptable levels, which can adversely impact aquatic ecosystems. While best management practices (BMPs) are implemented with the goal of controlling nutrient pollution in agricultural landscapes, their efficiencies are highly sensitive to local changes in hydroclimate and irrigation schemes. This paper analyzes the impact of rainfall characteristics on water quality in two tailwater recovery (TWR) ditches implemented at two farms in the Porter Bayou watershed, Mississippi. Forty-seven rainfall events were selected to match water quality monitoring of the ditches conducted from March 2012 to March 2016. These events were classified according to their intensities and durations into five classes and then correlated with in-ditch nitrate nitrogen (NO₃ – N) concentrations. Rainfall frequency ranked from highest to lowest was class II > class III > class I = class V > class IV. In terms of total rainfall depth, the following order was class V > class III > class II > class IV > class I. NO₃ – N concentration correlated negatively with time between previous rainfall and sampling events and time before next-to-last rainfall event, and positively with depth of next-to-last rainfall event, which suggests that the possible nutrient reduction ability of the TWR ditches could be overwhelmed by high-magnitude intensity and recurrent rainfall events. According to our study, rainfall events classified as II and III were the most frequent and also the most occurred to trigger higher concentrations of NO₃ – N in the investigated ditches. Preliminary results of the present study will contribute to the improvement of nutrient loss management in agricultural landscapes in Mississippi and enhance understanding of the BMP‘s responses to agro-hydrologic variability.