Sources of Pollution
As land-use change alters habitats and contributes pollution to downstream waterways, Edisto Island and the Town of Edisto Beach are on the downstream receiving end of the effects of upstream (and local) activities. The primary pollutant of concern across these sub-watersheds is bacteria (measured by the levels of enterococcus and fecal coliform), that can result from both natural (e.g. wildlife) and human-influenced (e.g., pets and septic systems) sources. High levels of bacteria in local waterways has resulted in the closure of shellfish beds, which is a major impediment to local traditions and way of life. Recreational and commercial harvest of shellfish and other seafood is a cultural tradition in the watershed practiced by long-term residents, as well as by visitors to the area. High levels of bacteria can also make it unsafe to swim, particularly following heavy rains.
Sediment, generally derived from upland or stream bank erosion, is the other key pollution of concern across the area. Sediment in the water column increases turbidity, or cloudiness, of the water. This turbidity can smother shellfish beds, increase siltation in navigable waterways, and is often associated with additional pollutants such as chemicals and heavy metals which stick to soil particles. When sediment clouds the water, less light can penetrate, which can affect aquatic plants and animals that live in the water. Edisto’s tourism-based economy is dependent on clean water. Activities like swimming, kayaking, charter fishing, and eating local seafood are primary draws for visitors, and these activities support the livelihood for many area residents. All of these can be affected by water quality pollution, and excess sediment deposition in waterways used for navigation can be a costly fix for local communities.
Stormwater runoff often serves as the conduit to transport pollution from land to the water. During dry periods, pollution builds up on hard surfaces, such as roofs, driveways, roads, sidewalks, and even turfgrass lawns. When it rains, stormwater runoff flowing across the land sweeps up pollution and carries it downstream. Stormwater infrastructure, such as ditches, pipes, and storm drains are designed to move water off the landscape as quickly as possible, which limits opportunities to treat water quality onsite and to reduce both runoff volume and velocity.