How does sprawl affect wetlands?

By Riverkeeper.org: “Sprawl is a significant factor contributing to the rapid loss of critical wetland areas. Wetlands often are ditched and drained in order to accommodate new building, agricultural uses, or to provide alleged mosquito control. Additional pollutants are introduced from vehicles, house and lawn chemicals, factories and power plants. Native wetland vegetation can be replaced by nonnative, invasive plant species that are aesthetically pleasing, but do not provide equivalent wetland functions for water quality. Construction activities significantly increase sedimentation in waterbodies – a construction site can lose up to 1,000 tons of sediment per acre, per year. EPA states that “sediment runoff rates from construction sites are typically 10 to 20 times greater than those of agricultural lands, and 1,000 to 2,000 times greater than those of forest lands. During a short period of time, construction sites can contribute more sediment to streams than can be deposited naturally during several decades.” And, creation of more impervious surfaces – such as parking lots, rooftops, and semi-pervious areas like lawns – allows more pollutants to be more quickly carried into wetlands and other waterbodies at volumes and velocities that can rip important vegetation from, and thus destroy, protective wetlands that buffer our drinking water supplies. 

Loss of even small wetlands can have irreversible environmental impacts. Sprawling development patterns place wildlife species, particularly amphibians, at risk of extinction. Study of a sample area in South Carolina has shown that eliminating natural wetlands of less than 10 acres would increase the nearest-wetland distance from 1,570 feet to 5,443 feet. This distance would take most amphibian species several generations to travel, and thus increases the probability of extinction of local populations. 

Wetland degradation can be as devastating as complete wetland loss because degraded wetlands lose their ability to perform their valuable functions. When development projects disturb wetland areas, they often are required to mitigate losses by creating artificial wetlands in another location. However, successful creation of equivalent wetland functions is rarely accomplished. Wetland vegetation is important to the function of water quality, and hydrology affects the way in which seeds disperse and germinate. Many seeds cannot germinate in standing water and therefore flow is essential. Vegetation, in turn, influences flow rates and thus reciprocally affects hydrology. And wetland plantings require considerable monitoring for several years to insure they establish. A typical proposed self-monitoring period for wetland plantings in a development project is three to five years, but some wetland vegetation may not mature for many years afterward. Other disturbances occurring after monitoring periods may require plant replacement to ensure successful functioning of wetlands.”