8984-R2_NewGloucester_2023-2024_AnnualReport_Web

2024 Sabbathday Lake Water Quality Report

2024, a small number of Gloeotrichia were observed in September, but no Gloeotrichia was documented in July or August. SUMMARY Sabbathday Lake has above average water quality compared to the average for Maine Lakes (Table 7). 2024 monitoring results for some parameters indicate that water quality in 2024 is similar to or slightly better than what has been observed in recent years, with the following observations: • Summer (May-September) precipitation totals were similar to the 10 year average. • Average annual water clarity was higher (clearer) compared to the historical average, and just slightly clearer than the 10-year average. • Total phosphorus was reduced (less nutrients in the lake) compared to overall and 10-year averages and was consistent throughout the season. • Average annual Chl-a was low, 1 ppb or more below both the historical and 10-year averages. • True color was also low compared the annual average. Sabbathday Lake experienced relatively little agal growth in 2024 based on measures of water clarity and Chl-a. However, DO dropped to less than 2 ppm at the bottom of the lake in both August and September 2024, allowing phosphorus to be released from bottom sediments. Bottom grab TP in September was the second highest on record. The particularly early ice-out in Sabbathday Lake in 2024 likely contributed to a longer period of summer stratification, thereby increasing the amount of time the sediments were exposed to anoxia. Phosphorus release from the bottom of the lake should be monitored in years with early ice-out and longer periods of stratification.

Table 7. Summary of 2024 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.

Water Clarity (m)

TP (ppb)

Chl-a (ppb)

Color (PCU)

Alkalinity (ppm)

Date

pH

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

6.7 7.6 7.8 7.3 6.7 5.3

5.0 5.0 5.0 5.0 6.3

2.9 2.5 2.0 2.5 3.8 5.7

12.0 10.0 10.3 11.9 20.1 9.0

12.0 12.0 12.0 12.0 11.0 11.1

7.0 7.0 6.9 7.0 7.0 7.2

2024 Average

Historical Average Average (Maine Lakes)

11.2

12

98