Clay, sand, and silt left behind from dredging are repurposed as marshes and wildlife habitats. Benefits to local wildlife and the environment include the removal of contaminated sediments and their relocation to safe, contained areas, and the improvement of water quality through the restoration of water depth and flow.
There are significant beneficial improvements from the use of clean maintenance dredgings to enhance mudflat and saltmarsh habitats and to mitigate losses of intertidal land through sea level rise and capital dredging operations.
A few ways dredging helps the environment are:
- Removal of subtidal benthic species and communities.
- Short-term increases in the level of suspended sediment can give rise to changes in water quality which can favorably affect marine life.
- After the suspended sediments settle, the result is the smothering or blanketing of subtidal communities and/or adjacent intertidal communities, which is used beneficially to raise the level of selected areas to offset sea level rise and erosion.
- In soft sediment environments, recovery of animal communities occurs relatively quickly, and a more rapid recovery of communities has been observed in areas exposed to periodic disturbances, such as maintained channels.
- In general, recovery times increase in stable gravel and sand habitats dominated by long-lived components with complex biological interactions controlling community structure.
These findings are supported by studies of the Georgia Estuary system, USA, which suggest that maintenance dredging has only a short term effect on the animal communities of the silt and clay sediments. Although almost complete removal of organisms occurs during dredging, recovery begins within one month, and within two months the communities were reported to be similar to pre-dredge conditions.