Because of the unique ecology of wetlands, they provide habitat for numerous plant and animal species, including some of which can only survive in wetlands. Wetlands are aesthetically pleasing to many people and provide recreational activities like bird watching, ice-skating, fishing, and canoeing. In general ,water moves through a wetland slower than a river channel, allowing the soil and vegetation to interact with and remove pollutants. It controls how quickly water and contaminants pass through the soil. Sandy soil has large spaces between soil particles that allow water to move rapidly through the soil.
Clay soil slows movement of water because pore spaces are very small.
This means that sandy soil has less surface water runoff, while soil with a high clay content has more surface water runoff. The ability soil has to break down many pollutants is dependent on how fine the soil is and how long it takes water to pass through the soil before reaching the water table. The less vertical separation between the water table and a pollution source, the greater the risk to groundwater contamination. Let us take septic systems as an example. Septic systems function better in soils that have at least a 3 foot vertical separation distance between the bottom of the septic system drainfield and the seasonal high water table.