8984-R2_NewGloucester_2023-2024_AnnualReport_Web

2024 Sabbathday Lake Water Quality Report

and years with more precipitation may result in higher phosphorus levels and poorer water quality. The highest precipitation in the region over the past 10 years occurred in 2023, with 32 inches of rain from May-September. In 2024, precipitation in the region was just under the 10-year average (17.2 inches compared to 18.1 inches). In 2024, precipitation was highest in August (5 inches) and lowest in September (2 inches). Due to climate change, the overall trend of bigger and more frequent storms is expected to continue and could lead to an increase in the amount of phosphorus getting to the lake via increased erosion and polluted runoff.

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May June July August September Summer total

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Precipitation (inches)

2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024

TROPHIC STATE INDICATORS Trophic state indicators (SDT, Chl-a, and TP) and are key parameters for measuring how productive a lake is and can be used to calculate a Trophic State Index (TSI) which can be compared to other lakes across the state. In Maine lakes, TSI ranges from 8-136 with a mean of 45. The last TSI index calculated for Sabbathday Lake is from 2016 with a value of 29.9. Lakes with TSI values <30.68 are categorized as unproductive, so Sabbathday Lake is on the high end of this range, moving toward the moderately productive category (TSI 30.68 – 60.93). Ongoing data collection will allow this value to be updated. Water Clarity Measuring water clarity (a.k.a. transparency) is one of the most useful ways to show whether a lake is changing from year to year. Changes in transparency may be due to increased or decreased algal growth, or the amount of dissolved or particulate materials in a lake, resulting from human disturbance or other impacts to the lake watershed area. Factors that affect transparency include algae, water color, and sediment. Since algal density is usually the most common factor affecting transparency in Maine lakes, transparency is an indirect measure of algal abundance. Water clarity is measured using a Secchi disk, obtained by lowering a black and white disk into the water until it is no longer visible. Figure 2. Total and monthly precipitation for Sabbathday Lake from May-September, 2014-2024. (Data source: NOAA NCDC, station GHCND: US1MECM0003 - New Gloucester 3.0, SE, ME, US (2023) and station GHCND:USC00173295 – Gray, ME, US)

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