Figure 2. Reprinted from Fitz, H. C. 2008. Ecological models: Wetlands. In: S. V. Jorgensen and B. D. Fath (Eds.), Encyclopedia of Ecology Vol. 5. Elsevier, Oxford, UK. pp. 3780-3790, with permission from Elsevier. Spatial discretization of the hydrologic component of wetland models largely determines the questions that can be addressed. a) Simplest case, with ponded surface water depths of a single unit area; b) Horizontal extension of surface water across multiple spatial units; c) Vertical stratification of surface and ground water storages; d) Complex case of both vertical and horizontal spatial discretization, which is implemented in the model(s) discussed here.