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A Secchi disk is a tool used to measure water turbidity and clarity. It is a round disk which is divided into four alternating quadrants, two of which are white and two of which are black. The measurements in this document were taken as the disk was submerged deeper and deeper beneath Lake Wissota and Little Lake Wissota’s surface and once the Secchi disk was no longer visible, the depth was taken. The higher the value for Secchi disk depth, the clearer the water.
Total Phosphorus is the combination of both particulate, and dissolved phosphorus. Dissolved phosphorus is that which can taken up and utilized by plants. Levels of dissolved phosphorus vary significantly on a daily basis as plants continually remove it from the water system and utilize it for growth. Particulate phosphorus is the phosphorus which has already been taken up by either a plant or animal and can be found suspended in the water in the form of some organic matter. Using Total Phosphorus rather than particulate or dissolved phosphorus gives us a better idea as to exactly how much phosphorus is already in Little Lake Wissota and Lake Wissota.
Trophic State Index (TSI)
The Trophic State Index (TSI) is a means of measuring the biological productivity of a given body of water. The nutrient content of the water is, generally, a good determinant of TSI. So, for the graphs below, Total Phosphorus (TP) was one of the factors used to calculate the TSI of Lake Wissota and Little Lake Wissota. Additionally, Secchi disk depth and chlorophyll were also used to calculate the Trophic State Index and the three values were averaged.
By Burak Öterler
Water bodies with a TSI of 0-29 are minimally productive and are ideal for drinking water and water sports. A TSI of 30-45 is indicative of a moderately productive body of water. These lakes, ponds, streams, etc. generally support a good amount of biodiversity. On few occasions, did Little Lake and Lake Wissota test this low. The vast majority of data collected points to Little Lake Wissota and Lake Wissota having a TSI of 46-70. The average for all the sampled data was a TSI of 59.26. Water bodies with a TSI of 46-70 can support significant biodiversity and are sufficiently productive. A TSI of 71-100 indicates an overabundance of nutrients and will support the highest level of biodiversity.
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