Department or Program

Environmental Studies

Abstract

Extreme precipitation events are becoming more frequent in Maine as a result of climate change, and these events may be responsible for a large proportion of the total annual nutrient and sediment load to lakes. Identifying and quantifying these inputs is important for those managing lakes to preserve water quality, particularly lakes used for drinking water. However, routine manual sampling typically occurs in good-weather conditions and fails to quantify these events. To build a more detailed understanding of the impact of these events on Lake Auburn, the unfiltered drinking water supply for Lewiston and Auburn, Maine, we use in situ, high-frequency data to complement manual samples collected through a routine monitoring program. High-frequency data show changes in temperature, oxygen, conductivity, and water level over the course of precipitation events, revealing that the largest tributary to the lake (Basin Stream), has a larger impact on in-lake conductivity values than the second-largest (Townsend Brook). In addition to having substantial material influx from Basin Brook, the northwest arm of the lake is shallow and sheltered from the wider lake, so inputs from the watershed are hypothesized to have a large impact on productivity. The diurnal differences in dissolved oxygen were larger here than near the inlet of Townsend Brook, suggesting that this part of the lake had both more photosynthesis occurring during the day and more respiration and decomposition overnight. Lake transparency was inversely correlated with chlorophyll a, illustrating more broadly that biological activity is influencing lake transparency, and both these factors changed following large external inputs from precipitation events following a dry period in 2022. However, this relationship between precipitation and water transparency was only discernable with higher frequency data across the course of the year, as there was no relationship between total annual precipitation and in-lake transparency over the years between 2014 and 2023. While water transparency decreased rapidly in 2022 following a large storm that occurred following regional drought, in 2023, spring and early summer water clarity was worse, which was similarly attributed to material suspended from winter and spring precipitation events. The additional understanding of both spatial and temporal heterogeneity in inputs and in-lake responses that the high-frequency data provide underscores their importance as compliments to traditional monitoring programs.

Level of Access

Restricted: Campus/Bates Community Only Access

First Advisor

Holly Ewing

Date of Graduation

5-2024

Degree Name

Bachelor of Arts

Number of Pages

74

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Available to Bates community via local IP address or Bates login.

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