Acidity
Lake acidity is of critical importance, and has been an area of recent concern. Most aquatic species require a pH between 6.5 and 8.0 (7.0 is neutral, with lower numbers reflecting an increase in acidity.) pH is influenced by many factors, including bedrock, acid rain or snow deposition, wastewater discharge, and natural carbon dioxide fluctuations.
Beginning in 2014, we experienced a pH drop (increased acidity) in all water bodies within the watershed from near 7.0 to nearly 6.0. As can be seen below, all ponds and lake basins were simultaneously affected.
Experts whom we contacted to explain the reduction in pH presumed a connection to several winters with inadequate snow cover, and recovery did, coincide with several snowy winters. This reason for this phenomenon is that in light snowfall years with frequent rain and mild temperatures, soil respiration (which in a cold, snowy year would slow with falling temperatures) produces carbonic acid. Because this additional carbonic acid is left unbuffered due to the low alkalinity conditions present in our region, the overall water pH becomes more acidic. In snow rich winters, this respiration is diminished and pH stays closer to neutral. During snow melt, as during a heavy rainstorm, there is a temporary increase in acid run-off which may lead to episodic, but not chronic acidification of streams and lakes, usually not exceeding 24 hrs.
Buffering and Alkalinity
The acid neutralizing capacity of a water body refers to the presence of buffering substances such as carbonate, bicarbonate and hydroxides that enable the water to resist swings towards acidity. These alkaline substances are valuable in neutralizing acidity caused by heavy rainfalls, sudden snow melt or soil disturbance. The presence of such buffers is largely determined by the geology of the soil and bedrock. In our watershed, total alkalinity is uniformly low (3-5 mEq/l) as granite is abundant and limestone, non-existent. This relatively low ability to buffer acid leaves the watershed vulnerable to pH change.