8984-R2_NewGloucester_2023-2024_AnnualReport_Web

2024 Sabbathday Lake Water Quality Report

18°C (64°F) but can tolerate temperatures up to 24°C (75°F). In the summer, the sun warms the surface water, forcing coldwater fish to retreat to deeper, cooler, and more oxygenated water. In lakes with elevated phosphorus levels due to inputs from the watershed, cycles of de-oxygenation can form in deep water when the lake is stratified in the summer, reducing the amount of coldwater habitat available to fish. Decreased DO levels can also cause internal release of phosphorus from the sediments, contributing to elevated TP levels and increasing the likelihood of nuisance algae blooms. Sabbathday Lake has a history of DO depletion below 8 m developing annually in late summer. Dissolved Oxygen The 2024 DO profiles in Sabbathday Lake indicate that the lake is well oxygenated through the epilimnion (0 4 m), but that dissolved oxygen levels began to drop around 8 m in the hypolimnion (bottom layer of cold water). The dissolved oxygen peak is in the metalimnion (transition area between the warm surface water and cold deep waters. The metalimnetic maximum or “oxygen bubble” is typical for the area of the lake where algae are most productive, taking up carbon dioxide, and giving off oxygen. Below this depth light becomes limited which in turn limits algal growth. DO was 2 ppm or less (upper threshold for anoxia) at the bottom of the hypolimnion in August and September. In July, DO dropped to a minimum of 3.8 ppm at 17.5 m. In August and September, DO at 18 m dropped to 0.1 and 0, respectively. Low levels of dissolved oxygen at the bottom of the lake can result in the release of phosphorus from bottom sediments. Collection of TP (bottom grab) can be used to help determine the influence of anoxia on internal

2024 Temperature Profiles Sabbathday Lake, Station 1

Temperature (°C)

0

10

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30

0 2 4 6 8

Depth (m)

10 12 14 16 18

7/10/2024 8/14/2024 9/11/2024

Figure 5. 2024 temperature profiles for Sabbathday Lake, Station 1.

2024 Dissolved Oxygen Profiles Sabbathday Lake, Station 1

Dissolved Oxygen (ppm)

0

5

10

15

0 2 4 6 8

Depth (m)

10 12 14 16 18

7/10/2024 8/14/2024 9/11/2024 Stress Fish Anoxic

Figure 6 . 2024 dissolved oxygen profiles for Sabbathday Lake, Station 1.

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