7077-R2_NewGloucester_2019_AnnualReport_Web

SABBATHDAY LAKE | 2018 Water Quality Report

t r

lity

rt

|

Though 2018 was not an abnormally dry year, many water quality parameters resembled a those of a very dry year on Sabbathday lake, such as 2016. Phosphorus had the best annual average of the entire historical record. • Water clarity, chlorophyll-a, and color annual averages were all close to the best values of the entire historical record. • pH was in line with the historical average for Sabbathday Lake. • Total alkalinity in 2018 was the highest since 2004. s t r l r r, t r lit r t rs r s l t s f r r r t l , s s . s r s t st l r f t tir ist ri l r r . t r l rit , l r l- , l r l r s r l l s t t st l s f t tir ist ri l r r . s i li it t ist ri l r f r t . t l l li it i s t i st si .

It is possible that runoff was limited by the timing or the intensity of rainfall events, thereby producing water quality characteristic of a dryer year. Further study would be necessary to determine if these or other factors were at play. DO depletion at the deep spot of Sabbathday Lake is a consistent issue, with less than 5 ppm as shallow as 9 meters in August September 2018. Desirable habitat of cool, oxygenated water for cold-water fish was restricted to between 6 and 9 meters below the water surface in 2018. This low DO may also be releasing biologically available phosphorus from bottom sediments, though phosphorus remains low overall in Sabbathday Lake. RECOMMENDATIONS • Continue the baseline annual water quality monitoring program at Sabbathday Lake. • Consider adding hypolimnion (bottom) grab samples for phosphorus to the three sampling events. • Consider collecting water quality data (especially DO and temperature profiles and epilimnion and/or hypolimnion grab samples for phosphorus and chlorophyll-a) immediately after spring and fall turnover to better characterize internal phosphorus cycling in Sabbathday Lake. Low oxygen in late summer when thermal stratification sets in (creating a barrier to lake mixing, so oxygen-rich surface waters cannot replenish bottom waters) causes a chemical reaction with iron-bound phosphorus in bottom sediments that can re- release phosphorus into the water column and fuel algal growth. It is ssi l t t r f s li it t ti i r t i t sit f r i f l ts, t r r i t r lit r t risti f r r r. rt r st l ss r t t r i if t s r t r f t rs r t l . l ti t t s t f t is sist t iss , it l ss t s s l s t rs i st t r . sir l it t f l, t t r f r l - t r fis s r stri t t t t rs l t t r s rf i . is l ls r l si i l i l il l s r s fr tt s i ts, t s r s r i s l r l i t . ti t s li l t r lit it ri r r t t . si r i li i ( tt ) r s l s f r s r s t t t r s li ts. si r l ti t r lit t ( s i l t r t r r fil s ili i / r li i r s l s f r s r s l r l- ) i i t l ft r s ri f l t r r t t r r t ri i t r l s r s li i t . i l t s r t r l str tifi ti s ts i ( r ti rri r t l i i , s -ri s rf t rs t r l is tt t rs) s s i l r ti it ir - s r s i tt s i ts t t r - r l s s r s i t t t r l f l l l r t .

• Consider adding a water quality monitoring buoy that continuously measures DO and temperature throughout the ice-free season (can also measure temperature during the winter months). This will help pinpoint spring and fall turnover and the extent and duration of low DO in Sabbathday Lake. WAYS TO PROTECT THE LAKE There are many ways that individual landowners can help reduce sediment and nutrient input to Sabbathday Lake to protect and even improve water quality, including: si r i t r lit it ri t t ti sl s r s t r t r t r t t i -fr s s ( ls s r t r t r ri t i t r t s). is i l l i i t s ri f l t r r t t t r ti f l i t . r r s t t i i i l l rs l r s i t tri t i t t t r t t i r t r lit , i l i : t

7

104