Sediment Phosphorus Release at Lake Fayetteville, Summer 2020

The purpose of this project was to evaluate the release of dissolved phosphorus (P) from bottom sediment at Lake Fayetteville, and the potential use of aluminum sulfate (Al2(SO4)3) to remediate the P stored and released by bottom sediments. Intact sediment cores (n=18) were taken at three locations, named inlet, mid and dam sites at Lake Fayetteville. The cores were incubated with 1 L of overlying water with light excluded and bubbled with air (half, aerobic treatment) and N2 (other half, anaerobic). Water samples were pulled and analyzed for soluble reactive P (SRP), and that water was replaced with filtered lake water with SRP less than the lab’s method detection limit (MDL, ≤0.005 mg L‐1). The SRP mass accumulating in the overlying water was used to estimate SRP release rates from the sediment, and mean rates were compared by treatments, sites and before and after alum dosing. Sediment SRP release rates were significantly greater under anaerobic conditions (mean=7.22 mg m‐2 d‐1) than aerobic (mean=0.85 mg m‐2 d‐1), and within those conditions rates were not different between sites. The addition of alum to the overlying water reduced SRP concentrations near the MDL in most cores, and sediment SRP release rates were significantly less after alum dosing, except for the cores from the mid lake site under aerobic conditions. Overall, it likely that this internal SRP source is an important factor in the development and occurrence of harmful algal blooms (and likely microcystin production) at Lake Fayetteville. Alum might be a means to successfully reduce this internal SRP source