Innovative Cement Set to Save Coastline Ecosystems

In an effort to address the ongoing damage to coastal ecosystems, researchers in China have developed a new type of cement designed to improve the ecological compatibility of artificial coastlines.

Natural coastlines, including coral reefs, marshes, and mangroves, provide natural barriers against erosion, storms, and flooding, and support biodiversity. However, human interventions, such as overdevelopment, urbanisation, and pollution have made these valuable ecosystems vulnerable.

Artificial coastlines, such as human-made dikes, can prevent erosion, and provide protection from storms and flooding, but these existing methods to preserve these ecosystems still fall short.

In a journal published by AIP Publishing, researchers from Southeast University and the University of Chinese Academy of Science investigated the use of specialised types of cement for coastline ecological protection.

"New substrate materials need to be developed to reduce the biological toxicity effects on marine organisms," said author, Xiaolin Lu.

Artificial reef blocks and coastal structures are commonly built with cement that has a high alkaline pH of +12, which is harmful to biofilm on reef surfaces.

This biofilm, which is composed of microorganisms, such as bacteria, algae, and fungi, provides food for grazers, and promotes larval settlement. The cement used inhibits biofilm growth, in turn negatively affecting marine life, and the overall health of coastal ecosystems.

A research team developed an innovative cement made from limestone and clay, which hardens underwater. The cement is designed to be more environmentally-friendly, and biocompatible with its environment.

To enhance the ecological benefits of the cement, the research team added two key treatments: 

• Polyacrylamide (PAM), a synthetic resin commonly used in water treatment, which helps promote biofilm growth on the cement surface.
• Chitosan, a form of sugar made from the shells of shrimp and other crustaceans, is a natural biopolymer that enhances the cement’s ability to support coral settlement.

The research team conducted extensive tests of the new cement mixture to evaluate the performance. These two treatments were mixed into the cement to form the hardened substrate.

The bulk-treated, and surface-treated samples were tested for strength, biofilm, and coral growth. These samples were placed in a sea tank and treated with biofilm cultures and transplanted coral, along with a control of plain cement.

After two days, biofilm was found to be actively growing on the surface-treated samples. After thirty days, biofilm growth was greatest on the surface-treated samples, slightly less on the bulk-treated samples, and significantly less on the cement control.

The reduced growth on the cement control was attributed to its high alkalinity. Transplanted coral samples also survived, and grew better on the surface-treated samples.

"These new treatments showed the necessary biocompatibility in a simulated marine eco-environment, which can be used to promote biofilm growth without interfering in extended habitation of model coral samples," said Lu.

The research team will focus their efforts on long-term surface wear testing, and biocompatibility in real-life applications.

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