What do Trophic Status, 20-Year Average, or Prior Year mean?
There are three benchmarks against which we compare the results of our water quality monitoring. These benchmarks provide us with some context to which we can compare the current measurements of Secchi Depth, Chlorophyll-a concentration, or Phosphorous concentration. When we select Trophic Status as our benchmark, we are comparing our current measurements against a scale that represents the range of what is generally considered to indicate the overall age and health of a lake. When we use 20-Year Average as our benchmark, we are comparing our current measurements against the average over the past 20 years to determine if the long-term trend is improving or deteriorating. When we choose Prior Year as our benchmark, we are comparing our current measurements against those that were done in the prior year to see if the short-term trend is improving or deteriorating.
What do the colors mean?
Depending on the benchmark you have selected (e.g. Trophic Status, 20-Year Average, or Prior Year), the colors represent the range of values that would generally be considered favorable (green) or unfavorable (red) compared to the specifc benchmark. The black needle points to the actual values that have been measured on the lake over the past 12 months. When the black needle is pointing to the green zone on the gauge, we consider that to be a favorable result relative to the benchmark. When the black needle is pointing to the red zone of the gauge, we consider that to be unfavorable relative to the benchmark.
What does Water Clarity mean?
Water Claity is an indication of how clear the water is. Measured in meters (m), the higher the number the better. It is important because it tells us the extent to which the water may be getting clouded by sediment stirred up by boating activities or runoff from the surrounding shoreline caused by rain. It also may be affected by the amount of algae gowing in the water, which would be a sign of excessive nutrient pollution washing into the lake from the surrounding watershed. We measure water clarity by lowering a Secchi disk into the water and noting the depth at which we can no longer see the black and white markings on the disk. A value of 2.0 means that we can see the Secchi disk up to 2 meters below the surface but no further.
Why is Chlorophyll-a important?
Chlorophyll-a is a specific form of chlorophyll that is used in photosynthesis. It Its presence in the water is an indication of the presence of algae. Measured in parts per billion (ppb), the higher the concentration of chlorophyll-a we see, the more algae are present. While algae are an important part of the food chain and a certain amount is considered to be a sign of a healthy lake, in excess amounts it can cloud the water and actually deplete the oxygen in the water as dying algae decompose. Certain species can produce toxins that are harmful to humans, pets, and native animals. These are usually referred to as blue-green algae, or cyanobacteria, although strictly speaking these are not considered to be included in the scientific definition of algae.
Why is Phosphorous important?
Phosphorous is an essential nutrient for all living things, including plants, animals, and algae. It is considered a limiting nutrient in fresh water systems, meaning that the rate of growth of aquatic plants and algae is limited by the amount of phosphorous available in the water. Measured in parts per billion (ppb), higher concentrations of phosphorous in the water can stimulate excessive growth of algae and can contribute to harmful algal blooms. While it is one of the most common naturally occurring elements on the planet, it can reach undesireable levels if it flows into the lake from the use of lawn fertilizer and agricultural activity.