8646-R1_NewGloucester_2022-2023_AnnualReport_Web

2023 Sabbathday Lake Water Quality Report

In 2023, alkalinity ranged from 11 – 12 ppm with an average of 11.7. This is slightly higher than the historical average (11 ppm), and similar to the 10-year average (11.8 ppm) (Table 5). Average annual alkalinity in Sabbathday Lake is similar to the statewide average of 11.1 ppm. Lakes with total alkalinity values >20 ppm, are considered well buffered against changes in pH, whereas lakes like Sabbathday Lake, with alkalinity between 10 and 20 ppm fall within the USEPA’s “sensitive” category. pH pH is the standard measure of the acidity or alkalinity of a solution on a scale of 0-14. Most aquatic species require a pH between 6.5 and 8. As the pH of a lake declines, particularly below 6, the reproductive capacity of fish populations can be greatly impacted as the availability of nutrients and metals changes. pH is influenced by bedrock, acid rain deposition, wastewater discharge, and natural carbon dioxide fluctuations.

pH in Sabbathday Lake has ranged from 6.5 (2022) to 7.5 (2013). In 2023, average pH was 7.0, with a maximum pH of 7.1 (September) and a minimum pH of 6.9 (July). The pH in Sabbathday Lake in 2023 was similar to the historical average and the 10 year average for the lake (Table 6). A statistical analysis of pH at Sabbathday Lake in 2022 showed a decrease in pH between 2012-2018 based on 7 years of data, however, at least 10 years of data is needed to determine the significance of this trend. Compared to the statewide average, Sabbathday Lake has slightly lower pH. SUMMARY

Table 6. Average annual pH for Sabbathday Lake, Station 1 (1982-2023).

pH

Years Table 12. Summary of 2023 data and historical averages for water clarity, total phosphorus (TP), chlorophyll a (Chl-a), color, alkalinity, and pH at Sabbathday Lake. Average Maine lake values were obtained online from Maine DEP/Lake Stewards of Maine. Table 13. Average annual pH for Sabbathday Lake, Station 1 (1982-2023). Annual pH Mean Min Max 7.1 2023 Sabbathday Lake 7.0 6.9 6.6 Historical Average (1982-2023) 10-Year Average (2014-2023) Avg. Maine Lakes 7.1 7.5 7.0 7.2 6.6 3.1 7.4 9.9

Sabbathday Lake has above average water quality compared to the average for Maine Lakes (Table 7). 2023 monitoring results for some parameters indicate that water quality in 2023 was worse than it has been in recent years, with the following observations: • Summer (May-September) precipitation totals were high compared to rainfall records from the past 10 years (9 to 20 inches more than previous years). Both May and August monthly rainfall totals were the highest of the last 10 years. • Average annual water clarity was low (less clear) compared to the historical and 10-year averages, and the lowest since 2009. • Total phosphorus was also somewhat elevated (more nutrients in the lake) compared to overall and 10-year averages, and the highest since 2007.

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