Concrete ecological enhancement in the temperate marine environment
Authors: Bone, J.
Conference: Bournemouth University, Faculty of Science and Technology
Abstract:In the coming years, intertidal habitat loss is expected to increase as coastal development and sea level rise squeeze coastal ecosystems. Concrete coastal infrastructure is known to be a poor surrogate for natural intertidal reef habitats, but ecological enhancement can improve biodiversity and habitat availability on these structures. This thesis investigates one of the most commonly used interventions, the artificial rockpool, and how they affect biodiversity on urban coastlines in previously unquantified ways on the south coast of England. It will also examine how one of the most used engineering materials, concrete, may affect biological colonisation and the impacts colonisation may have on a concrete substrate in the marine environment. Firstly, the bioreceptivity of concrete in the coastal environment is reviewed, discussing the various methods by which bioreceptivity may be enhanced. The chemical bioreceptivity of concrete remains somewhat unclear, and emphasis should be placed on increasing the micro- and macro-scale superficial rugosity which is known to reliably increase colonisation. The impact of colonisation on concrete infrastructure is then reviewed, and it is suggested that bioprotective and biodeterioration of concrete substrates occur in tandem. Some species may offer more bioprotection than others, including calcareous encrusting species like oysters and barnacles. Finally, this section concludes with an experiment comparing the bioreceptivity of two low-carbon cement mixes with an ordinary Portland cement control. It is concluded after 1 year of subtidal immersion that bioreceptivity of the three mixes performs inconsistently between sites, with each mortar mix demonstrating some limited bioreceptivity. It is advised that local environmental conditions, seasonal timing of structure deployment and surface texture are prioritised when designing concrete-based ecological enhancements. The second section focuses on the use of retrofitted concrete artificial rockpools as ecological enhancements. Firstly, the behavioural interactions of fish and crabs with artificial rockpools and the adjacent seawall at high tide were monitored between April and October in a temperate harbour. Using video footage, it was possible to ascertain the length of time bass, shore crabs, and shanny spent in each habitat and what behaviours they engaged in. More time was generally spent sheltering within the seaweed-covered rockpools, whereas the barnacle-covered seawall also provided feeding opportunities. Conspecific behaviour, including pre-copulatory behaviour, was observed only in the rockpools. Further comparisons were made between the seawall and artificial rockpools at low tide in another urbanised harbour, at three tidal heights between mean tide level and high-water neaps. Although the middle and lower level rockpools contained more species, compared to the seawall the uppermost rockpools provided greater biodiversity benefits and elevated the presence of brown perennial seaweeds. Vertical arrays allow species to migrate up the tidal zone and find refugia in a warming climate. Finally, a vertical array of rockpools on sheet piling in another urbanised estuary retained a significant amount of sediment which was sampled to determine the presence of any infauna. This was compared to sediment cores taken from the local mudflats. Species typical of disturbed estuarine mudflats were identified in the retained rockpool mud, demonstrating an added benefit artificial rockpools can provide. As soft sediment habitats are often lost when coastal defences are constructed, sediment retaining interventions may provide some mitigation against this. It is evident that artificial rockpools can provide significant biodiversity benefits compared to an unenhanced seawall, through the provision of shelter for mobile fauna, provision of refugia at sensitive upper tidal levels and the retention of sediment for infaunal species. Through the use of artificial rockpools, combined with low-carbon, durable and rugose concretes, vertical intertidal infrastructure can be made to provide valuable habitat in a persistently threatened urban coastal environment.
Source: Manual