Biological control of avalanching and slope stability in the intertidal zone

Abstract

Abstract Sediment structure and stability are important features of soils and sedimentary environments, and are of great importance for the maintenance of estuarine, and intertidal banks and channels. Avalanching and slope stability are critical factors controlling the shape of intertidal dunes. The role of biological activity in these processes, either in the form of vegetation and roots, animal burrows, algal mats or microbial glues, is now a forefront area of research. The objective of our research has been to quantify the effects of biological activity on the avalanching of intertidal sediments. Natural microbial and meiofaunal communities and particularly burrowing infauna such as Corophium volutator and Nereis diversicolor dramatically increase angles of avalanche and factors of safety. They do not significantly alter angles of repose. Factors of safety, duration of avalanches, and percentage increase in sediment volume, all increase with increasing angles of avalanche. Video analysis of the avalanching process shows that different slope failure mechanisms are associated with the different types of biological activity, and probably reflect specific chemical and mechanical stabilizing effects produced by the different types of biological activity. These latter include tubes, extracellular polymeric materials, and a small element of compaction. These mechanisms include rotational failure, block and wedge failure and translational failure. The significance of our results for the stability of slopes under field conditions is discussed, and it is concluded that field seeding experiments in the intertidal zone with the species that we have used would be very productive.