Other
Lenntech: The Phosphorus Cycle
A concise explanation of the phosphorus cycle. Also contains a flow diagram which illustrates the flow of phosphate through the cycle.
Geography 4 kids
Geography4 kids.com: Cycling Phosphorus
An essential element in the ecosystem is phosphorus. Discover the phosphorus cycle, what depends upon it, and how it works.
Other
Marietta College: Ecosystems
Complete illustrated discussion of energy flow within ecosystems, including discussions of trophic levels, ecological pyramids, food chains and webs, biological magnification, and cycles.
Ohio State University
Ohio State University: Concepts of Plant Ecology
An advanced discussion of plant interactions and relationships. Energy flow, nutrient cycling and succession are discussed. Try the quiz to check your understanding.
University of Illinois
University of Illinois Extension: Energy and Ecosystems Use Some Lose Some
Life on Earth is possible because energy flows one way through ecosystems, while matter cycles endlessly. Water and elements, such as carbon, nitrogen, phosphorous, and sulfur are examples of matter that cycles through ecosystems.