Excavation of material from an aquatic environment is called dredging. Historically, dredging has been crucial for mining, maintaining the navigability of the waterways, and, recently, removing toxins and restoring natural habitat. Dredged material is the sediment that has been extracted from the channel.
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Importance of Ecological Restoration
An ecosystem is a community of interacting living things and their natural surroundings. Ecosystems have traditionally suffered from human disruptions that change their structure or function, leading to their degradation, damage, or destruction. Many formerly thriving species have been classified as at-risk because of the harm done to these ecosystems, which were once home to various plants and animals. These ecosystems are under heightened stress due to reduced, inadequate habitats.
The primary objective of ecological restoration is to reconstruct, promote, or accelerate the recovery of a disrupted ecosystem. Environmental changes affecting ecosystems' composition and functionality are known as disturbances. The scientific study of restoring degraded ecosystems via human intervention is called restoration ecology.
Key components of ecosystem restoration are specific to certain ecosystem types, disturbance regimes, environmental factors, and objectives. Various innovative techniques are required to implement various interventions at appropriate times in places with varying degrees of degradation. Environmental dredging, performed to remove polluted sediments to restore environmental risks, is one method for achieving this.
Dredging Techniques Used in Habitat Restoration and Conservation Projects
Over time, sustainable dredging techniques have been employed for habitat restoration and conservation initiatives.
Sediment dredging is an engineering technique that extracts sediments from aquatic systems. Around the world, shallow eutrophic lakes have been using sediment dredging as a technique to reduce sediment P release. Dredging is a management technique that recovers wetland habitat on former agricultural land and can improve the water quality downstream by reducing sediment P flow. In wetlands restored on former agricultural areas, sediment dredging is a helpful method for striking a balance between habitat restoration objectives and water quality improvements.
Remediation dredging is performed to remove or remediate underwater contaminants to enhance the quality of the water. Dredging for remediation can be used to clear up contaminated streams, settlement or sewage ponds, mining tailing ponds, and contaminated industrial zones so they can be restored.
Finally, precision dredging involves GPS-guided dredging, which accurately regulates the location of the dredge, making it more precise and less destructive. Another precise dredging technology is multi-beam sonar dredging, which employs multi-beam sonar to create a three-dimensional image of the waterway's bottom. Precision dredging is usually employed to dredge around delicate environments.
The Beneficial Role of Dredging in Ecosystem Restoration
Dredging can positively contribute to ecosystem restoration in the following ways:
Dredging can be used to construct, restore, or sustain wetland, upland, island, and aquatic regions to support species relocated or endangered due to habitat degradation. Dredging can create shoals, restore oyster reefs, create/restore intertidal marshes, and remediate/create highland ecosystems.
Dredged material from backwaters and side channels can be used to build new islands or expand existing ones. Constructed islands may need to be long and narrow to have the least influence on river flood heights. They can also be constructed high enough to provide habitat for riverbank hardwood trees and other native species that cannot adapt to the current changed hydrologic conditions. In addition to blocking wind fetch and wave movement, constructed islands provide secure nesting and resting locations for birds.
Agriculture: soil reconstruction/remediation
Dredging has been used in agriculture to produce soil products that offer farmers soil for restoration and remediation. For example, soil created from municipal tree debris, dredged material, backwater sediment, and agricultural by-products has been proposed to lower operating expenses for dredging material disposal while also increasing the economic advantages of dredging.
Beach nourishment is a beneficial and cost-effective way to address erosion of shorelines in the Great Lakes and along the coastlines. Borrow dredging, maintenance, and new-work dredging are the primary forms of beach nourishment activities.
Borrow dredging is often done by dredging sand from inshore or offshore locations and transferring it to an eroding beach via truck, split-hull hopper dredge, or hydraulic pipeline. Beach nourishment was carried out on the Great Lakes utilizing barriers to reduce coastal erosion caused by water waves and to replenish sand to the deteriorating beaches.
Case Study: Dredging for Ecosystem Restoration
The Woodland Islands site comprises several small islands and a sheltered side channel region near St. Helens, Oregon, between the FNC and the Washington side of the LCR coast. Considering its relatively large area available for installation, proximity to a dependable sediment supply, and scarcity of wetland and floodplain habitat in the LCR, the site was an excellent candidate for beneficially employing excavated sediment to rebuild river island habitat.
The project's goal was to restore shallow water and wetland habitats to sustain ducks, shorebirds, neotropical migratory songbirds, native animals, reptiles, amphibians, and non-listed aquatic species, as well as to assist in the rebuilding of federally listed salmon species populations. The placement of excavated material resulted in several direct environmental advantages. It supported the creation of new habitats and foraging sites for federally listed species. The restored shallow water habitat attracted a range of aquatic species.
Research and Innovations in Dredging to Minimize Ecological Impact
Improved technology and targeted dredging techniques have allowed for extracting essential sediments required for restoring natural habitats while minimizing distribution and lowering environmental adverse effects in recent decades. The EU-funded Toolbot project, for example, created a very accurate remote-operated vehicle (ROV) that allows for exceptionally selective and exact dredging, low turbidity, and optimum sediment transfer. This approach is beneficial when regular dredging is prohibited and in difficult sites like dams.
Challenges Associated with Dredging
Governments and private companies are unwilling to use dredging materials to restore natural habitats due to their inadequate awareness of their beneficial uses. Second, due to a lack of uniform regulation establishing the safety of dredging materials, bringing useful dredge materials products to market is challenging. Third, the expense of transporting dredged materials for beneficial use was identified as the most significant practical impediment to beneficial applications.
Local communities are critical to the success of any beneficial use dredging program because they indicate projects that could be suited for recycling dredge materials instead of source materials. As a result, citizen involvement in the positive reusing of dredged materials is crucial.
The beneﬁcial use of dredged material for habitat creation, enhancement, and restoration is an integral part of the DMMP for the Port of NY/NJ. Habitat creation,
restoration and enhancement projects are among the most environmentally sound and technically feasible options for dredged material placement in modern ports and harbors
Projects to restore and improve habitats are among the most environmentally sound and technically possible solutions for dredged material disposal in modern harbors and ports. Several actions must be taken before these beneficial use possibilities can be implemented. Before a full-scale implementation strategy could be devised, nearly all of these uses would require an experimental project, including post-construction environmental surveillance.
Continue Reading: Environmental Impact of Dredging: Balancing Progress and Conservation
References and Further Reading
Suedel, B. C., McQueen, A. D., Wilkens, J. L., Saltus, C. L., Bourne, S. G., Gailani, J. Z., ... & Corbino, J. M. (2022). Beneficial use of dredged sediment as a sustainable practice for restoring coastal marsh habitat. Integrated Environmental Assessment and Management, 18(5), 1162-1173. https://setac.onlinelibrary.wiley.com/doi/abs/10.1002/ieam.4501
Acevedo-Acevedo, D., & Suedel, B. C. (2023). Beneficial Use of Dredged Material to Mitigate for Erosion. In Soil Erosion Research Under a Changing Climate, January 8-13, 2023, Aguadilla, Puerto Rico, USA (p. 1). American Society of Agricultural and Biological Engineers. https://elibrary.asabe.org/abstract.asp?aid=53839
Russ, E. R., Yarnall, A. H., & Altman, S. (2023). Dredged Material Can Benefit Submerged Aquatic Vegetation (SAV) Habitats. [Online] Available at: https://apps.dtic.mil/sti/citations/trecms/AD1207835