What is trophic status?

Trophic status is the ability of a lake to sustain growth. While one might think more growth suggests a healthier lake, in fact, it’s the opposite. To support trout, bass and other species, organic matter needs to be kept in check. This is because an influx of organic matter or fertilizer will cause algae to grow, depriving the lake bottom of oxygen and light and stressing fish populations.

The trophic level of a lake can be determined by measuring clarity, chlorophyll-a, and phosphorous. The above graphs illustrate trends in these parameters for each of Kezar’s three bays over the last ten years. Each is explored in depth below.

Clarity

Water clarity is a measure of how deeply light can penetrate through the water. It is measured using a Secchi disk, which is a black and white disk that is lowered into the water. When the disk reaches a distance at which it is no longer visible, its depth is recorded. A high concentration of algae in the water reduces water clarity, resulting in a low Secchi disk reading.

The clarity of Maine lakes varies widely from 0.5 to 9.2 meters. Values less than two meters generally indicate a water quality problem. Kezar has consistently had very healthy clarity numbers. Measurements taken since 1970 show median visibility of 7.7 meters in Upper Bay, 7.2 meters in Middle bay. Lower bay measurements average 3.2 meters. However, this lower number is due to the fact that the disk typically hits bottom before it becomes invisible.

Chlorophyll-a

Chlorophyll-a is the green pigment found in all plants used for photosynthesis. High levels of chlorophyll in a water body reflect high levels of algae, which lead to reduced levels of dissolved oxygen at the bottom of the water body. This occurs because once algae dies, it falls to the bottom where it decomposes–a process that consumes dissolved oxygen. Since 1977, Kezar’s chlorophyll-a measurements have been healthy relative to the state average of 5.4 ppb. Upper Bay, Middle Bay, and Lower Bay have median chlorophyll-a levels of 2.1, 2.0, and 2.4 ppb, respectively. Chlorophyll-a trends over the past ten years are shown in yellow in the graphs at the top of this page.

Phosphorous

Phosphorous acts as a fuel that promotes the growth of algae in an aquatic environment. It occurs naturally in soil, but is also found in fertilizers and animal waste. Phosphorous is washed into lakes and streams by rainwater carrying eroded soil, plant residues, fertilizer, and/or animal waste. Since 1977, phosphorous measurements in Upper and Middle Bays have remained healthy with median values of 5.0 ppb and 4.5 ppb respectively. Lower Bay’s median value over this time has been 9.0 ppb. While this significantly higher than the deeper bays, it is still below the state median of 11.8 ppb. Fortunately, the high flush rate of water moving through the Lower Bay (fueled by the influx of Sucker Brook and flow from the Narrows) has enabled the trophic status of the Lower Bay to remain stable.

KLWA is concerned about climate change’s impact on our phosphorous levels. With an increased number of intense storm events, erosion from those heavy rains will wash more phosphorous-laden soils into our lake, ponds, and streams, creating conditions conducive to algal growth. Maintaining camp roads and septic systems, having adequately-sized culverts, and planting effective shoreline buffers all are critical actions to help diminish this impact. Please see our Lake Dwellers Handbook for more detail on information on how you can help.

 Trophic Status of Our Ponds

For the most part our waterbodies, while fragile, are in great shape. However, the trends in increasing levels of growth of several of our ponds gives reason for caution. 

While Horseshoe and Trout Ponds are in a stable trophic state; Bradley, Cushman, Heald and Farrington Ponds are showing trophic trends that appear less healthy.

For additional information about the water quality of each of our ponds, click here.

Next: Dissolved Oxygen–>