Editing Dredging (section)

==Environmental impacts==
{{Globalize section|date=January 2023}}
Dredging can disturb [[aquatic ecosystem]]s, often with adverse impacts.<ref name="Brodie">{{Cite web|url=http://theconversation.com/dredging-set-to-swamp-decades-of-great-barrier-reef-protection-20442|title=Dredging set to swamp decades of Great Barrier Reef protection|last=Brodie|first=Jon|website=The Conversation|date=2 December 2013 |language=en|access-date=2019-09-21}}</ref><ref>{{cite journal | last1 = Newell | first1 = R.C. | last2 = Seiderer | first2 = L.J. | last3 = Hitchcock | first3 = D.R. | year = 1998 | title = The impact of dredging works in coastal waters: A review of the sensitivity to disturbance and subsequent recovery of biological resources on the sea bed | url =http://www.sussex.ac.uk/geography/researchprojects/coastview/dredging/Impact_of_Dredging_Oc_Bio.Ann_Rev.pdf | journal = Oceanography and Marine Biology: An Annual Review | volume = 36 | pages = 127–178 }}</ref> 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]], where they become toxic [[Dredge plume|dredge plumes]].{{Citation needed|date=September 2017}}

Dredging can have numerous significant impacts on the environment, including the following:
* Release of toxic chemicals (including [[heavy metal (chemistry)|heavy metals]] and [[Polychlorinated biphenyls|PCB]]) from bottom [[sediment]]s into the [[water column]].<ref name="Bridges, T S. 2010">Bridges, T S., Gustavson, K. E., Schroeder, P., Ells, S. J., & Hayes, D. (2010). Dredging processes and remedy effectiveness: Relationship to the 4 Rs of environmental dredging. Integrated Environmental Assessment and Management, 6 (4), 619–630.</ref>
* Short term increases in [[turbidity]], which can affect aquatic [[species]] [[metabolism]] and interfere with [[spawn (biology)|spawning]].<ref name="Brodie"/> Suction dredging activity is allowed only during non-spawning time frames set by fish and game (in-water work periods).<ref>{{Cite web|url=http://www.ukmarinesac.org.uk/activities/ports/ph5_3_2.htm|archive-url=https://web.archive.org/web/20020220120046/http://www.ukmarinesac.org.uk/activities/ports/ph5_3_2.htm|url-status=dead|archive-date=20 February 2002|title=Timing of dredging and disposal as a means of minimising maintenance dredging impacts|website=www.ukmarinesac.org.uk|access-date=2019-09-22}}</ref>
* Secondary impacts to [[marsh]] productivity from [[sedimentation]]<ref name="fondriest.com">{{Cite web|url=https://www.fondriest.com/environmental-measurements/environmental-monitoring-applications/monitoring-turbidity-at-dredging-sites/|title=Monitoring Turbidity at Dredging Sites|website=Environmental Measurement Systems|language=en-US|access-date=2019-09-22}}</ref> and general [[Chemistry of wetland dredging|changes in wetland chemistry after dredging]].
* Tertiary impacts to [[bird|avifauna]] which may [[prey]] upon contaminated aquatic organisms.<ref name="fondriest.com"/>
* Secondary impacts to aquatic and benthic organisms' [[metabolism]] and mortality.<ref>{{Cite news|url=https://www.theguardian.com/environment/2013/dec/11/the-facts-about-dredging|title=The facts about dredging|last=Milman|first=Oliver|date=11 December 2013|work=The Guardian|access-date=2019-09-21|language=en-GB|issn=0261-3077}}</ref>
* Possible contamination of dredge spoils sites.<ref name="Bridges, T S. 2010"/><ref>{{Cite web|url=https://www.brisbanetimes.com.au/national/queensland/inquiry-to-probe-gladstone-harbours-leaking-bund-wall-20140107-30fnp.html|title=Inquiry to probe Gladstone Harbour's leaking bund wall|last=Moore|first=Tony|date=7 January 2014|website=Brisbane Times|language=en|access-date=2019-09-22}}</ref>
* Changes to the topography by creating "spoil islands" from the accumulated spoil.<ref>{{Cite web|url=https://spoilislandproject.org/spoil-island-project/|title=About the Spoil Island Project|website=Spoil Island Project|language=en-US|access-date=2019-09-22|archive-date=20 December 2019|archive-url=https://web.archive.org/web/20191220175716/https://spoilislandproject.org/spoil-island-project/|url-status=dead}}</ref>
* Releases toxic compound [[Tributyltin]], a [[biocide]] often used in [[anti-fouling paint]] banned in 2008, into the water.<ref>{{Cite web|url=https://www.epa.gov/enforcement/case-summary-cleanup-settlement-addresses-contaminated-sediment-removal-blair-waterway|title=Case Summary: Cleanup Settlement Addresses Contaminated Sediment Removal in Blair Waterway, Washington State|last=US EPA|first=OECA|date=15 December 2015|website=US EPA|language=en|access-date=2019-09-22}}</ref>

The nature of dredging operations and possible environmental impacts requires that the activity often be closely regulated and requires comprehensive regional environmental impact assessments alongside continuous monitoring.<ref name="fondriest.com"/> For example, in the U.S., the [[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 [[United States Army Corps of Engineers|Army Corps of Engineers]].<ref>[[Clean Water Act]], {{USC|33|1311}}, {{USC|33|1362}}, {{USC|33|1344}}{{Citation needed|date=September 2017}}</ref> 
Due to potential environmental impacts, dredging is often restricted to licensed areas, with vessel activity monitored closely using automatic GPS systems.<ref name="fondriest.com"/>
Town Of Oyster Bay v. Commander Oil Corporation, Court of Appeals of New York (2001) , showed a case in which the dredger had received a permit from the Army Corps of Engineers preventing the nearby city (Town Of Oyster Bay) to stop the dredging.