Proceedings of the 2019 Mississippi Water Resources Conference

Year: 2019 Authors: Yasarer L., Martin H., Locke M.A., Taylor J., Lizotte Jr. R.E., Stevens E.

Agricultural soils in the Mississippi Delta are notoriously rich in legacy phosphorus. Due to high erosion rates, nutrient-rich soil often ends up in Delta lakes and water bodies. However, few studies have been conducted to quantify the phosphorus stored in these sediments and to estimate potential fluxes in lake environments. This study represents a starting point for characterizing legacy phosphorus in aquatic environments in the Delta utilizing sediment and data collected from Beasley Lake, an oxbow lake in an agricultural watershed that has been studied by the USDA-ARS since 1995. Twelve sediment cores were collected from two locations: six from the littoral zone (depth = 1.5 m) and six from the limnetic zone (depth = 2.8 m). Cores were incubated for two weeks with either aerobic or anaerobic treatments. Sediment samples were also taken from each lake coring site and chemical and physical characterization, sequential phosphorus extractions, and phosphorus isotherm analyses were performed. Results from the experimental incubated cores demonstrated average phosphorus fluxes of 0.77 and 1.72 mg/m²/day under aerobic conditions and 15.26 and 22.33 mg/m²/day under anaerobic conditions from the littoral and limnetic zones, respectively. Results from the sediment characterization demonstrated that Beasley Lake sediments are indeed storing a large amount of phosphorus (P), up to 279 g-P per g dry sediment. Yet, results of the isotherm analysis suggest the sediments have the potential to adsorb up to 3200 g-P per g dry sediment under oxygenated conditions. These results suggest that Beasley Lake has a large pool of available phosphorus, but still has the potential to store more under oxygenated conditions. With anaerobic conditions this phosphorus may be released into the water column where it could stimulate algal growth. Dissolved oxygen (DO) conditions near the sediment interface in Beasley Lake have been measured since May 2018 and will be continuously measured to understand seasonal DO patterns. The combination of experimental analysis of phosphorus release and field observation of lake conditions will help provide a deeper understanding of aquatic nutrient cycling in Beasley Lake and potentially other Delta water bodies.