Lake
Ecology 101
Trophic state is a method to classify lakes and is an indicator of water quality. Common characteristics used are water clarity, chlorophyll (a measure of algae present), and total phosphorus concentration.
Oligotrophic lakes have low nutrient content, and thus are very clear, produce few weeds, and do not support large fish populations. Eutrophic lakes are rich in nutrients, are subject to frequent algae blooms, and support large plant and fish populations. Eutrophic lakes may be subject to oxygen depletion resulting in fish kills. Mesotrophic lakes lie between these two states. Lake Singletary is classified as mesotrophic.
The transition from oligotrophic to eutrophic is part of the natural aging process of a lake, but human activities accelerate this process. The introduction of nutrients from the watershed leads to algae blooms, oxygen depletion, and weed growth.
One nutrient that contributes to excessive weed and algae growth in lakes is phosphorus. Major sources include human and animal wastes, soil erosion, fertilizer runoff from farms and lawns, and detergents. Because phosphorus acts as a fertilizer, it is important to prevent its introduction into the lake. Nitrogen is second only to phosphorus as a nutrient for weeds and algae. Nitrogen may come from fertilizer, animal wastes, and septic systems.
The ratio between nitrogen and phosphorus determines which nutrient is the limiting factor for weed and algae growth. As with most lakes in this region, phosphorus is the limiting nutrient in Lake Singletary. This means that we can prevent, to some degree, excessive weed growth and algae blooms by reducing the flow of phosphorus into the lake.
Click here to see a graph of in-lake phosphorus levels for samples collected between 1994 and 2002. Association volunteers collected the samples as part of our monitoring program with Mass WWP.