- On 18th October 2015
- In Dredging
- By William
Young CEDA are hosting a range of Pitch Talks on the 6th November during the CEDA Dredging Days, Rotterdam. Exo Environmental has been invited to hold a PechaKucha 20×20 style presentation on ‘The ecological potential of geosynthetic fabrics to provide novel habitat and trap sediment’. For the full programme of Pitch Talks, please follow the link.
The presentation will touch upon topics like ‘Climate Change, Coastal Squeeze, Bioengineering, Green Infrastructure, Working with Nature and Saltmarsh creation’.
Biofilm created by microscopic algae is important, as it improves stability of sediment against erosion on intertidal mudflats and salt marshes. This biostabilisation plays in important role in the accumulation of sediment and accretion of intertidal habitats, subsequently enabling a succession of higher plants to colonise intertidal sediments. Higher plants such as grasses and glassworts in turn form a natural barrier to the seas energy, dampening waves and reducing the amount of coastal erosion that occurs. Biofilm also appears on the surfaces of geosynthetic fabrics often used in soft and bio-engineering. Fabrics are generally grouped into three different types, woven, non-woven and hybrid. Within each group there is a large range of different types of fabrics. The fabrics are generally selected on their engineering quality; this is the primary function of the fabrics. Yet, through bio-engineering, green infrastructure and ‘working with nature’, the ecological characteristics of the fabrics are becoming a more important element. This study, carried out by Exo Environmental Ltd and the University of East Anglia investigated fabrics used in marine engineering supplied by Tencate Geosyntetics for their potential to trap sediment and provide habitat for microalgae. Eight different fabric types were mounted in a ladder arrangement at low, mid and high tidal heights to assess biofilm growth and accumulation of sediment on the fabric.
The surface of intertidal sediments often looks bare; but it is not, it is covered by thousands or millions of microscopic algae. These include diatoms and cyanobacteria, which secrete carbohydrate polymers (called Extracellular Polymeric Substance or EPS for short), which enable the microalgae to move through the mud. As the tide goes out, they migrate up through the mud to the surface where they can photosynthesise in the light. Then, before the tide comes back in, they migrate back down into the mud. The EPS they excrete into the mud is sticky and forms a surface layer called a biofilm, a matrix of cells, mud particles and the polymer.
When the tide comes back in, the matrix of the biofilm can better resist the hydrodynamic forces of the water and as a result the sediment below is less likely to be eroded. This process is called biostabilisation, and forms the basis of successional processes of mudflats towards higher plant species related to coastal saltmarshes.