Dredging - Environmental Impacts

Environmental Impacts

Dredging can create disturbance to aquatic ecosystems, often with adverse impacts. In addition, dredge spoils may contain toxic chemicals that may have an adverse effect on the disposal area; furthermore, the process of dredging often dislodges chemicals residing in benthic substrates and injects them into the water column.

The activity of dredging can create the following principal impacts to the environment:

• Release of toxic chemicals (including heavy metals and PCB) from bottom sediments into the water column.
• Short term increases in turbidity, which can affect aquatic species metabolism and interfere with spawning.
• Secondary effects from water column contamination of uptake of heavy metals, DDT and other persistent organic toxins, via food chain uptake and subsequent concentrations of these toxins in higher organisms including humans.
• Secondary impacts to marsh productivity from sedimentation
• Tertiary impacts to avifauna which may prey upon contaminated aquatic organisms
• Secondary impacts to aquatic and benthic organisms' metabolism and mortality
• Possible contamination of dredge spoils sites

The nature of dredging operations and possible environmental impacts cause the industry to be closely regulated and a requirement for comprehensive regional environmental impact assessments with continuous monitoring. The U.S. Clean Water Act requires that any discharge of dredged or fill materials into "waters of the United States," including wetlands, is forbidden unless authorized by a permit issued by the Army Corps of Engineers. As a result of the potential impacts to the environment, dredging is restricted to licenced areas only with vessel activity monitored closely using automatic GPS systems.