And it’s not good news. We’ve received the results back on our first Total Phosphorus (TP) sample for 2016, taken last month on May 20th. At 22 μg/L (micrograms per liter), TP is up at levels typically not seen until mid to late summer. The chart at left has been updated to include this latest data point, you can see where it plots up: it’s the first (only) dot in 2016, furthest to the right. We usually take 3 [the_tooltip text=”core” tooltip=”a sample of the whole water column from the surface down to 7 meters” url=”” background=”” color=””] samples of lake water each season for Phosphorus testing, and send them off to the State Lab for analysis. In the early spring, TP values on the order of 14 to 18 μg/L are more “normal” (for some value of the term “normal”) though in recent years they have been trending higher. Last spring on April 30th TP was 14 μg/L and 17 μg/L on April 25th the year before that. TP values above 18 μg/L typically mean an algae bloom is on the way. This does not bode well for water quality this coming summer.
Phosphorus is the primary nutrient responsible for algae growth in lakes. It comes from various sources including runoff containing eroded soil and sediments. Under conditions of low dissolved oxygen it can be released from bottom sediments in the lake. Wave action on exposed bottom sediments can also result in Phosphorus being released into the lake. Low water conditions resulting in exposed bottom sediments and reduced lake volume certainly contribute to higher Phosphorus concentrations.
David Hodsdon, Jack Holland and I went out yesterday morning for our regular biweekly water quality monitoring session. The transparency of the lake water has already dropped from 4.1 meters to 3.65 meters since May 20th . Data collected back through 2012 is available on the Clary Lake Water Quality Data page. Data back to 1975 is available upon request.