conceptual diagram of Dredging threat

  1. Dredging results in the short term degradation of animals, vegetation and microbial communities that live in the dredged sediment. This reduces the estuary’s capacity for nutrient cycling, primary production and habitat provision and can have flow on effects up the food web. Though these effects tend to be short lived, in some cases they may trigger long-term changes. (Larkum and West, 1990; Lewis et al, 2001; Thrush and Dayton, 2002; Lohrer and Wertz, 2003; da Silva et al, 2004; Waycott et al, 2004; Ohimain et al; 2005)
  2. Changes in channel profile caused by dredging can increase tidal area, wave height and water velocity, resulting in bank erosion. Eroding banks threaten mangroves and other mudbank communitites and can lead to increased turbidity. Suspended sediment in the water column blocks light, reducing benthic primary productivity and inhibits the ability of benthic plants to recover from impacts of dredging. (Pringle, 1989; Larkum and West, 1990; Lewis et al, 2001; Rasheed and Balchand; 2001; Lohrer and Wertz, 2003; Sampson et al, 2005)
  3. Dredging exposes anaerobic layers of sediment, potentially disturbing and remobilising toxic sediments, releasing contaminants. This has implications for water quality. (Linkov et al, 2001; Thibodeaux and Duckworth, 2001; Van Den Berg, 2001; Nayar et al, 2004)
  4. Dredge spoil needs to be deposited somewhere, though this could be deemed habitat creation, it can smother existing habitats and frequently contains contaminants which often move and bioaccumulate through the food web. The impacts of dredge spoil disposal can range from short term to long term (Linkov et al, 2001; Smith and Rule, 2001; National Ocean Disposal Guidelines for Dredged Material, 2002; Fredette and French, 2004)
  5. Changes to tidal range and wave action can result in mangrove encroachment into saltmarsh areas (Saintilin and Williams, 1999)


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  2. Larkum, A.W.D., West, R.J. 1990 Long-term Changes of Seagrass Meadows in Botany Bay, Australia Aquatic Botany, 37 (1): 55-70.
  3. Lewis, M.A., Weber, D.E., Stanley, R.S. & Moore, J.C. 2001 Dredging impact on an urbanized Florida bayou: effects on benthos and algal-periphyton, Environmental Pollution, vol. 115, no. 2, pp. 161-171.
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  15. Waycott, M., Longstaff, B.J. & Mellors, J. 2005, “Seagrass population dynamics and water quality in the Great Barrier Reef region: A review and future research directions”, Marine Pollution Bulletin, vol. 51, no. 1-4, pp. 343-350.