Phosphorus (P) is a labile naturally occurring element. It is one of a few essential elements required for the health and growth of many plants and animals; both terrestrial and aquatic. P comes in many forms, and is generally measured in the form of Total Phosphorus (TP) which includes all forms that P in in a given space. TP is broken down into multiple forms including Soluble Reactive Phosphorus (SRP), Particulate Phosphorus (PP), Inorganic Phosphorus, and Organic Phosphorus. The Environmental Protection Agency and other agencies typically measure P concentration of a space through TP in pounds of loading or in concentration of milligrams per liter.
The concentration of P will shift naturally based on a variety of factors. This can include precipitation patterns, agricultural land use practices, and the exposed bedrock of an area. One of the most influential factors is the agricultural land use. Many farms utilize fertilizer to grow healthy and profitable crops. This fertilizer provides extra nutrients to stimulate plant growth including P. Terrestrial plants on average need higher concentrations of P than aquatic plants. This is important in considering another important factor: precipitation patterns. The rainfall patterns over an agricultural area will result in run off to local tributaries within the watershed and the run off from fertilizer will wind up in those streams and creeks carrying high concentrations of P. Ultimately, within the Red Cedar Watershed, these P concentrations will wind up in the impoundment of Lake Menomin.

