INTERNAL PHOSPHORUS LOADING AND CYANOBACTERIA POPULATIONS OF LAKE KANASATKA: MONITORING BEFORE AND AFTER ALUMINUM SULFATE TREATMENT

Despite extensive implementation of best management practices to mitigate external nutrient runoff, numerous New Hampshire lakes are continuing to experience adverse impacts from internal phosphorus loading (IPL). This remobilization of legacy nutrients can lead to more frequent and prolonged cyanobacteria blooms and exacerbate the process of eutrophication. This is the case for Lake Kanasatka, Moultonborough, NH, where IPL contributes to nearly 25% of its total phosphorus budget, with that percentage increasing towards the end of summer. As the hypolimnion reaches anoxia from lake stratification, phosphate is released through reductive dissolution. Cyanobacteria blooms at Lake Kanasatka have become more prevalent in recent years, heightened around fall turnover when bioavailable phosphate is upwelled into the epilimnion following dissolutive release. Alum treatment, in which aluminum sulfate precipitates phosphate out of the water column through adsorption, has become a popular method to treat IPL. Phosphate-bound flocculent becomes dormant in the sediment, with that burial lasting up to decades under the right biogeochemical conditions at the surface-water interface (SWI). With the proposal to perform an alum treatment on Lake Kanasatka in early 2024, we present historical total phosphorus trends and its correlation to seasonal stratification. Water column profiles from 2021 to 2023 show a significant increase in total phosphorus over three field seasons, with a peak in concentration towards the end of summer. Sediment cores will be taken before and after the proposed alum treatment to determine the percentage of phosphate reduction at the SWI, and how phosphorus fractionates with sediment depth. Combined with extensive water quality sampling, we will compile a comprehensive biogeochemical profile of the benthic environment to better understand its influence on IPL and the efficacy of alum treatment. With only two other lakes in the state receiving an alum treatment since 1984, it is important to analyze historical trends in phosphorus loading along with consistent hypolimnetic monitoring to better understand the longevity of treatment.