Biogeochemical Cycles
   A brief look at the major nutrient cycles, including pictures.
   http://www.colorado.edu/GeolSci/courses/GEOL1070/chap04/chapter4.html

Olympic Hands on the Land - Cycles
   From the National Park Service, animated diagrams of the water, nitrogen, and carbon cycles. Includes explanations.
   http://www.nps.gov/olym/hand/nutrition1.htm

Water What Ifs - Water Quality and Nitrates and Phosphates
   Shows the inter-relationship of these surface water parameters.
   http://www.ncsu.edu/sciencejunction/depot/experiments/water/lessons/np/