Figure 1. Map of global distribution of wetlands. Adapted from Gore (1983).

Figure 2. (a) Relative importance of the water resource to major wetland types on the landscape. The proportion of the water contribution to a wetland from precipitation, groundwater or surface flow creates different types of wetlands. Ombrotrophic bogs lack groundwater contributions and upstream inflow. Minerotrophic wetlands, such as fens, receive water and minerals from groundwater. Fringe marshes include both lacustrine and estuarine marshes. Modified from Brinson (1993). (b) Model of the different types of wetlands found along a gradient of nutrient (x-axis) and water regimes (y-axis). The swamps are dominated by trees under both long and short hydroperiods. The changes of water level within wetland types vary from permanently flooded or long hydroperiods and small water-level changes (lacustrine marshes) to those with short hydroperiods and large water-level changes, such as tropical swamp forests. Modified from Gopal et al. (1990).

Figure 3. Oxidation–reduction sequence developed from soil-flooding research work by Gambrell and Patrick (1978). The major redox stability points in millivolts (mV) for soils are shown for each element or compound.

Figure 4. Nitrogen transformation in wetland soils under oxidized and reduced conditions.

Figure 5. Comparison of net annual above- and below-ground plant productivity for wetland and terrestrial ecosystems. All values are in grams dry weight per square metre per year. To convert to the carbon equivalent, multiply the values by a factor of 0.45. Adapted from Richardson (1995).

Figure 6. Annual water budgets for (a) prairie pothole marsh in North Dakota, (b) a pocosin bog in North Carolina, (c) an alluvial cypress swamp in southern Illinois, and (d) a rich fen in North Wales, UK. All water flow values are given in centimetres per year. General hydroperiod patterns are shown within each box by curved blue lines. Data from Mitsch and Gosselink (1993) and from Richardson (1994).