Mixing allows bottom waters to contact the atmosphere, raising the water's oxygen content. However, warming may occur too rapidly in the spring for mixing to be effective, especially in small sheltered kettle lakes. Soluble reactive phosphorus is the amount of phosphorus in solution that is available to plants. Photosynthesis is essential in producing a lake's food base, and is an important source of oxygen for many lakes. The average length of time water resides in a lake, ranging from several days in small impoundments to many years in large seepage lakes.
Retention time is important in determining the impact of nutrient inputs.
Long retention times result in recycling and greater nutrient retention in most lakes. Calculate retention time by dividing the volume of water passing through the lake per year by the lake volume. The process by which aquatic organisms convert organic material to energy. It is the reverse reaction of photosynthesis. It also takes place as organic matter decays.