Magnitude of External Phosphorus Loading Likely Reduces Effectiveness of Aluminum Sulfate Treatments for Management of Sediment Phosphorus Flux

Highlights Phosphorus fluxes were quantified before and after alum treatments five times between 2014 and 2019. Phosphorus fluxes were not significantly different from baseline after five treatments spread over six years. Long-term effectiveness of alum treatments was reduced due to large external phosphorus loads. Abstract. This study quantified sediment P fluxes under aerobic and anaerobic conditions at Quarry Island Cove at Lake Wister, Oklahoma, before and after alum treatments, which occurred five times between 2014 and 2019. Sediment-water cores were collected from the cove and incubated for 10 days at room temperature under aerobic and anaerobic conditions, and P fluxes were estimated as the slope of the increase in P mass over time divided by the area of the core. Aerobic P fluxes were not significantly different before or after alum treatments. Under anaerobic conditions, P fluxes significantly decreased one week after alum treatments compared to a week before treatment. However, after five treatments across six years, sediment P fluxes under anaerobic conditions were not significantly different than prior to any alum treatments in 2010 and 2014 (3 to 4 mg m-2 day-1). The lack of overall improvement in anaerobic P fluxes over time is likely due to the magnitude of P and sediment loads entering Lake Wister from the watershed, where 92% of the total P load to Lake Wister from 2010 to 2020 was from external sources. Therefore, while alum treatments provide short-term reductions in P fluxes, external P sources must be addressed. Keywords: Aluminum sulfate, Lake management, Nutrient loads, Phosphorus.