Hydrodynamics, organisms and pollution of coastal sands

Abstract

This account concerns the movement of water in sublittoral sands, the exchange of air and water in littoral sands, the role of organisms in these ecosystems and the modifications caused by pollution. The patchy distribution of sand organisms, and the capacity of coastal sands for the degradation of organic debris, are considered. Porosity, permeability and the related concepts of specific permeability, capillary and cavity space, generated by fluid-flow and recognised by amphioxus acting as an environmental probe, are discussed. The importance of the organic component, consisting of bacterial films on sand-grains above and below the redox potential discontinuity as a modifier of sand properties, is emphasised. In sublittoral sands, where air is absent, the mechanisms causing irrigation are outlined. The effects of pollution by fine mineral particles, sewage and heated effluents are considered. In littoral sands, where both water and air are present, the relative movement and distribution of water and air, due to irrigation by tidal fluctuation, water inputs from the land and capillarity, are considered. The effects of pollution by low concentrations of detergents on the permeability of beaches are discussed.