Hurricane Isaiah on Candlewood Lake

August 4 - 5, 2020

This summer I’ve been doing bi-weekly water quality monitoring in the middle of the lake off my dock on Candlewood Lake in SW Connecticut. As Hurricane Isaiah approached, I thought it would be interesting to measure the lake immediately before and after to see how the storm affected the it.  To that end, I sampled at 8 AM Tuesday as the storm approached, and again at 9 AM on Wednesday after the storm had passed, and compiled the results on this chart.

Not surprisingly, the high, sustained winds mixed up the surface waters.  What was surprising to me was the depth to which that mixing occurred. Surface water temps decreased by almost 2° F, while water deeper down warmed slightly indicating a downward transfer of heat.  Notice also that dissolved oxygen (HDO) shows similar mixing - compare the amount of O2 in the water at 6,7, and 8m before and after the storm - it’s pretty clear that the storm mixing reached a depth of at least 7m (23 feet!!).  Since the storm, BTW, O2 levels in the top 6 meters are back at saturation.
The “bg ppb” column is a measure of blue green algae (cyanobacteria) abundance, and it’s interesting to note how they like to hang out in the colder water this time of year - on 8.14 there were even fewer at the surface, and they were again hanging out in the colder water.  “Sp. cond” stands for specific conductivity, which is a proxy for the salinity of the water, and the numbers we’re recording are at the high end of what we’d like to see. It’s of concern because blue green algae tolerate it better than other plants and animals that normally keep them in check. All fresh water has some salinity, but a likely source of increased salinity in Candlewood are ice melting salts and inorganic fertilizers. Anyway, the influx of fresh rainwater apparently made the lake a tiny bit "fresher".