Reducing the ecosystem-based carbon footprint of coastal engineering

Greenhouse gas emissions from coastal engineering do not only involve emissions from (dredging) vessels, but also from impacting sediments and coastal ecosystems.

A new report by Wetlands International, developed with Witteveen+Bos and Deltares, outlines a simplified methodology for quantifying the ecosystem-based carbon footprint of coastal engineering projects.

The developers also present potential options to reduce the carbon footprint, including through Nature-based Solutions.

With the report ‘‘Reducing the ecosystem based carbon footprint of coastal engineering’, the authors aim to facilitate discussions among those that commission, finance, design or implement projects towards more climate and ecosystem friendly coastal engineering.

Coastal ecosystems such as mangroves, sea grass meadows, salt marshes and unvegetated intertidal wetlands contain sediments that are often rich in organic carbon. Mangroves for example, typically hold five times as much carbon as a similar area of rainforest, with most of the carbon stored within the sediment.

Coastal engineering projects like land reclamation, port development and coastal protection involve activities that interfere with the carbon cycle of sediments and coastal ecosystems, which can result in significant emissions, both on or off-site.

This includes dredging and displacement of sediment, or activities that change the hydrological or sedimentation dynamics. Under some circumstances such disturbance causes previously sequestered carbon to be emitted as greenhouse gases.

The new methodology presented in the report simplifies the complexity of organic carbon cycling in coastal systems. It distils the most relevant information that needs to be assessed in the form of a ‘sediment passport’, based on which one can zoom in on those engineering activities that influence key carbon stocks and processes. This in turn helps to identify potential ways to reduce emissions or sequester carbon.

The ecosystem-based footprint of coastal engineering projects can be reduced with the right adjustments. These include, among others the more carbon-benign handling of sediments during dredging, the beneficial use of dredging sludge; for instance for wetland creation and restoration, or land reclamation, and the careful release of dredged materials into the seascape.

Moreover, there are also opportunities to enhance blue carbon sequestration by applying the so-called Building with Nature approach that integrates Nature Based Solutions into water and marine engineering practice.

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