In some areas, upstream use of river water for municipal and agricultural use can reduce the magnitude of river flooding to adjacent marshes and lead to reduction of marshland. Salt marshes are large ecosystems alongside oceans. Changing the hydrology of salt marshes can severely reduce the diversity of wildlife at a marsh. For example, salt marshes near the Kennedy Space center were impounded by dikes and flooded during mosquito season. As a result, plants in the marsh died.
Prairie potholes are common in the Midwest.
The landscape is a series of potholes with poorly drained soils in the bottom of potholes and well drained soils along the high areas. Drainage of potholes in Iowa began approximately 100 years ago and very few undrained potholes remain today in Iowa. Vernal pools are in potholes or depressional storage areas that are only submerged during part of the year. The Fish and Wildlife Service has an extensive classification system for wetlands. As we discussed before, wetlands are somewhat opposite from drainage systems because drainage removes water from the soil and wetlands contain water in the soil and above the soil surface.