Nitrogen cycle conceptual model

A conceptual model of sedimentary nitrogen cycling. Dashed arrows represent pore water diffusion and advection. Dotted arrows represent sedimentation. Source-. After Burdige, D.J. (2006). Geochemistry of Marine Sediments. Princeton University Press, p. 453. 

Numerical models of the global nitrogen cycle 4.4.2.1 Conceptual schemes of the nitrogen cycle in nature... 

From a conceptual standpoint, the phosphorus cycle would be relatively simple to understand and model if phosphorus sorption isotherms could simply be added to ecosystem models, parameterized using the abundance of phosphorus sorption data from the scientific literature, and allowed to run alongside the carbon and nitrogen submodels that are so familiar to the ecological community. Unfortunately, there are two central issues that make this approach untenable. First, phosphorus sorption dynamics are not straightforward, and simple representations fail to capture... 

---