Figure 1. Many processes affect phosphorus levels in a shallow lake. (1) Phosphorus enters the lake from the surrounding watershed. (2) When living organisms in the lake die, they sink to the bottom, transporting phosphorus to the sediments and building up an internal phosphorus reserve. (3) Certain algae can regulate their buoyancy in the water column and travel down to the sediments to obtain phosphorus and then back up into the lighted area of the upper waters to grow and form blooms. (4) Bottom-dwelling worms and certain fish feed in the sediments and excrete phosphorus back into the water, where it can be used by algae. (5) Healthy, submerged plants perform a variety of functions that reduce amounts of phosphorus in the water. [click on photo to enlarge]
Credit: Illustration by Chris Jones, Florida Sea Grant.