"The phenomena of the year take place every day in a pond on a small scale... The night is the winter, the morning and evening are the spring and fall, and the noon is the summer."
Recently, over the course of 7 years, I repeated many of Thoreau’ observations of water temperatures using a digital thermometer. Springs are still Concord’s coldest waters. For example, Thoreau measured Brister’s Spring at 49 degrees, and it varied from 48 to 52 degrees during my years of measurements.
Many of Concord’s brooks have distinctly warmed since Thoreau’s measurements. This is because a dam pond or beaver pond has slowed the water, giving it more time to be heated by the sun than in the past. The temperatures of the brooks are also affected by yearly variations; they are warmer in warm summers and colder in cool summers.
A longer version of this article was published in the Concord Journal.