ABSTRACT
The primary productivity of many wetlands is quite high especially when compared to other natural communities or even to highly managed agricultural croplands (Table 6.1). A high value for the aboveground primary productivity of swamps and marshes in temperate zones is about 3500 grams dry weight per square meter per year (g m-2 yr-1). In cold wetlands and peat bogs an upper limit of about 1000 g m-2 yr-1 is typical (Bradbury and Grace 1993). Wetlands with emergent herbaceous vegetation are often more productive than other wetland types, although high values are found in some mangrove swamps as well (Table 6.2). Wetland primary productivity depends upon the type of wetland and the vegetation found there as well as on hydrology, climate, and environmental variables such as soil type and nutrient availability. Wetlands that receive nutrient subsidies either naturally from flooding or from farm runoff tend to be more productive than those that receive nutrients only from rainwater, such as scrub cypress swamps or ombrotrophic bogs (Brown 1981). In a highly productive freshwater marsh in Wisconsin (from 2800 to 3800 g m-2 yr-1), the soil nutrients were found in higher concentrations than in upland soils and in excess of what is needed for agricultural crops (Klopatek and Stearns 1978).
