Date of Award

Spring 2025

Project Type

Thesis

Program or Major

Earth Sciences

Degree Name

Master of Science

First Advisor

Ruth Varner

Second Advisor

M. Florencia Fahnestock

Third Advisor

Laura Diemer

Abstract

Even with extensive implementation of best management practices to mitigate external nutrient loading, numerous New Hampshire lakes are experiencing diminished water quality due to internal phosphorus loading (IPL). Remobilization of legacy nutrients like phosphorus can lead to more frequent and prolonged cyanobacteria blooms and exacerbate the process of eutrophication. This is the case for Lake Kanasatka, located in Moultonborough, New Hampshire, where IPL contributes to nearly 25% of its total phosphorus budget, with that percentage increasing towards 50% by the end of summer, as the hypolimnion becomes anoxic. After years of monitoring and watershed management, Lake Kanasatka received an aluminum sulfate treatment in May of 2024. Residing in the same watershed as Lake Kanasatka and recently exhibiting similar seasonal patterns in water quality and cyanobacteria diversity, Wakondah Pond was established as a reference site to compare to Lake Kanasatka, before and after treatment, to understand the effectiveness of treatment as well as the trends in water quality within the watershed as a whole.In this study, both lakes were monitored monthly from April to October 2024 to understand changes in phosphorus loading and ecological dynamics following this chemical treatment. Full water column profiles were collected for phosphorus fractionation, photosynthetic pigments, and plankton identification to establish seasonal trends and elucidate the relationship between IPL and cyanobacteria in this watershed. After treatment, Lake Kanasatka had a significantly smaller fraction of soluble reactive phosphorus (SRP), the crucial bioavailable form of phosphorus utilized by cyanobacteria and other phytoplankton. Towards the end of the season in October, over 60% of the total phosphorus concentration was SRP in Wakondah Pond, compared to Lake Kanasatka that was estimated to be only 6%. Wakondah Pond was dominated by diverse populations of cyanobacteria and frequently experienced blooms, whereas Lake Kanasatka shifted to a dominance in diatoms and golden-brown algae. With IPL effectively suppressed in Lake Kanasatka, there was much less SRP available to promote the growth of cyanobacteria to the extent it had in previous years. With only two other lakes in New Hampshire receiving an aluminum sulfate treatment since 1984, it is important to analyze seasonal trends in nutrient loading along with consistent monitoring to better understand the longevity of treatment and its impact on water quality in New Hampshire lakes. Understanding the role of Wakondah Pond in the Lake Kanasatka watershed will allow us to determine future management and monitoring techniques. Long-term monitoring can determine the geochemical and biological effects of lake treatment, especially when compared to a reference site, to better manage freshwater resources and assist in future preservation.

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