Total phosphorus (TP) concentrations generally increased with depth. TP concentrations were elevated in the hypolimnion (lower layer of water in a stratified lake) from early spring through summer. Phosphorus increases in the hypolimnion can be caused by internal loading or result from the decomposition of algal cells and other organic matter settling from higher levels in the water column. Inflows of cold runoff water, which have a higher density than warmer, surface waters and sink to the bottom as they enter a lake, can also directly increase hypolimnetic nutrient concentrations, especially in Reservoirs.

During WY 2021, TP concentrations ranged between 69 and 115 μg/L with an annual mean of 97 μg/L. The seasonal TP mean (July- Sept) was 76.7 μg/L which is lower than the long-term average (1992-present) of 94.7 μg/L. In June and July, significantly elevated TP concentrations were seen at the bottom of the Reservoir.

TP is made up of both particulate and dissolved phosphorus. Particulate phosphorus includes both inorganic material, such as soil particles and clay minerals, and organic phosphorus, which includes particulate forms such as algal cells and plant fragments. Total dissolved phosphorus includes dissolved organic and inorganic material. Dissolved inorganic phosphorus is usually reported as soluble reactive phosphorus, which represents the bioavailable form of phosphorus. The reactive or bioavailable forms of nutrients are readily available for uptake by algae or cyanobacteria.

During WY 2021, TN concentrations ranged between 605 and 1,240 μg/L with an annual mean of 942 μg/L. The seasonal TN mean (July- Sept) was 861.1 μg/L which is lower than the long-term average (1992-present) of 896 μg/L.

Useful Links

• link Section 4.9 Total Phosphorus
• link Section 4.11 Total Nitrogen