Rivers, lakes and other fresh water bodies need some aquatic vegetation to support fish and other aquatic life.  Excessive growth of aquatic vegetation, however, is harmful to aquatic life because it leads to depletion of oxygen, reduction of light transmission and water clarity, and increased production of algal toxins. The progressive deterioration of water quality through over-stimulation of aquatic vegetation is called eutrophication. Phosphorus (P) is often the most limiting nutrient to the growth of vegetation in freshwater bodies; therefore, an increase in P levels can cause excessive growth of aquatic vegetation, leading to eutrophication.

This lesson addresses agricultural P management, P dynamics in water bodies, and how these interact.  The lesson focuses on the process of eutrophication, the relationship of land application of manure and soil P dynamics on P delivery to surface waters, and on the P dynamics in water bodies that result in increased P available to aquatic vegetation. It is written to target the educational needs of upper-level undergraduate students and graduate students, and the continuing education of professionals in advising, planning and regulating for improved land resource management.


Upon completing this lesson, a student should have gained an understanding of this subject to the level that he/she will be able to understand and explain to others, in concise terms, the following concepts:

1. The forms of P available to plants.

2. The process of eutrophication of surface waters.

3. The role of P in eutrophication of surface waters.

4. The value and problems of manure P applied to agricultural land.

5. The basic relationships between soil P and the delivery of P to surface waters.

6. The four forms of P in surface waters and the basic dynamics of each form.

JNRLSE Approved, 2006

Copyright 2005

Development of this lesson was supported, in part, by a University of Nebraska Cooperative Extension grant. A contribution of the University of Nebraska Cooperative Extension, Journal Series 1047. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s).