Water Quality Enhancement Projects
Acquiring tracts of land that are located on the banks of surface water segments provides an opportunity to reduce sediment and pollutant delivery to the coastal ecosystem by maintaining the natural landscape. Further restoring or enhancing the wetlands on these properties also aid in the treatment of polluted stormwater runoff.
What is runoff?
Stormwater runoff is defined as water that flows overland during a rain event. This runoff can contain a number of pollutants such as nitrogen, phosphorus, sediment, and fecal coliform bacteria.
How does development affect runoff?
New housing and business developments along with the associated transportation infrastructure increase the amount of impervious surface within the watershed.
This increase generates 9 times more runoff than a woodland area of the same size (US EPA, 2002). As more runoff is generated, the amount of stormwater delivered to local streams and creeks also increases which erodes stream banks and degrades water quality. Pollution from these waters also contributes to the closure of local oyster beds, due to contamination from fecal coliform bacteria.
Erosion of stream banks and increases flow velocity are also detrimental to the biodiversity of streams. Healthy aquatic communities rely on riffle pool sequences to provide spawning habitat for fish species and the invertebrates which provide food for juveniles. Loss of tree cover, due to development, increases water temperature within the streams, exerting additional stress on the populations. Over time, competition within the biologic community replaces the original inhabitants with new, pollution tolerant species.
How do wetlands aid in pollution removal?
Wetlands in both natural and urban settings provide an area for the retention of sediment and nutrient pollutants. Sediments are removed as a result of the decrease in flow velocity that occurs as stormwater flow spreads across the area. Retention of stormwater also allows for removal of nutrients through a series of biological interactions between the soil and plant communities. Large populations of microbes that inhabit the leaf litter and other debris in the area thrive under the anaerobic conditions that accompany the retention of stormwater, providing an additional mechanism for removal of pollutants.
Wetlands are also able to transform nutrients. In impacted watersheds, delivery of inorganic nutrients often occurs at high levels. Chemical reactions within wetlands alter to the composition of these inorganic nutrients and release them in an organic form. This release is significant as organic nutrients are not readily available for use by plants and algae. By reducing the availability of nutrients, algal blooms and the detrimental water quality aspects that accompany them are avoided.
Does wetland restoration work?
When implemented correctly, restored and created wetlands have been found to improve water quality. Research has shown removal rates of >80% for sediment and bacteria. Removal of total phosphorus and nitrogen ranged from 40 to 90% (Center for Watershed Protection, 2000).
Are there any completed projects in New Hanover County?
Yes, a .8 acre site located on S. Kerr Avenue was one of the first projects completed within the state. This site, located in the Burnt Mill Creek watershed, was designed to filter stormwater runoff and has already produced encouraging results.
A second project was completed at the Pine Valley Golf Course. The project involved the stabilization of a badly eroded drainage feature which empties into the headwaters of Hewletts Creek. With assistance provided by the City of Wilmington Stormwater Services Division, Cape Fear Resource Conservation and Development, and North Carolina Sea Grant, the drainage area was widened to create a more natural floodplain and the stream was altered so that its course now mimics a more natural free flowing stream. Vegetation native to such streams has also been planted.