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242 Flooding and Aquatic Ecosystems Table 9.2. Wetland functions in a river-floodplain ecosystem Hydrology Source of water supply Groundwater recharge Flood storage Reduction of water velocities Sediment deposition Water quality Erosion control Nutrient retention and transformation Contaminant retention and transformation Fish and wildlife habitat Habitat diversity Diverse types of shallow wetlands Open water wetlands Riparian zone Connectivity of lotic to lentic ecosystems Transition zone from lotic to lentic environments Biological diversity Invertebrates Reptiles Amphibians Fish Birds Mammals Ecosystem processes Provides diverse habitats for flora and fauna Maintains natural biological diversity Maintains natural food chain and food web Allows for habitat protection Provides for streamflow mediation Human benefits Flood control Water supply Recreation Education Research Linkage of Nutrient and Energy Transfer from Floodplains to River Ecosystems Primary production by phytoplankton and periphyton provides the basis for development of a food web (Allee et aI., 1949; Odum and Odurn, 1959). Phytoplankton and periphyton production and standing crops increase in concert with increases in annual input of nutrients regardless of latitude. Cycling and spiraling of carbon, nitrogen, and phosphorus - key elements for phytoplankton production - are described in detail by Newbold (1992). Nitrogen is the most abundant element in the atmosphere and is generally not limiting. Also, abundant carbon dioxide in the atmosphere provides the necessary carbon. Phosphorus is the most limiting element in north temperate and subarctic waters (Schindler, 1978). Therefore, phytoplank- ton production and standing crop in north temperate fresh waters are gener- ally proportional to the phosphorus input. Particulate phosphorus, either