Global warming, sea level change and the impact on estuaries

Abstract

Scientists and the general public alike recognize that the oceans are in a state of constant change. The twice daily tidal movements provide evidence of the inherent mobility of the oceans, this image being reinforced by the occurrence of freak storms which pound coastlines, destroying beaches and sea walls and endangering human life on land and at sea aboard shipping and oil rigs. The concept that the volume of water in the oceans also changes altering the height of the surface of the oceans relative to the land is more difficult to establish and for many years was discounted. Estuaries provide an exception to the generally correct assumption that water-based environments provide a more amenable medium for life forms than terrestrial-based environments (Clarke, 1957). The twice daily innundation of salt water interspersed by brackish or fresh water provide extreme biochemical variability to which resident life forms must adapt. Biophysical conditions will also be extreme, with the speed of water movement, its temperature and turbidity all showing variation depending on the state of the tide. In addition, the utilization of estuaries by humans over many centuries has caused substantial modifications. Construction of dredged channels for use by shipping combined with flood defence walls has often resulted in a canalization of flow. Industrialization of land adjacent to estuaries has often led to discharge of large volumes of polluted water to the estuary. Changes to the overland flow from within a catchment area that may have been deforested, ploughed and built over results in an increased river flow regime. Whereas a rise in sea level in the open ocean would be of negligible significance, along the sea/land interface, the impact would be pronounced. As the sea level rises, so estuaries will become wider and deeper (Bird, 1993). Tidal penetration will extend further upstream and tidal ranges may become altered. Sedimentation Dr. Jones is Senior Lecturer in Geography at Strathclyde University. He is a member of the Institute of Environmental Science and of the Institute of Ecology and Environmental Management. His area of research interest includes the effect of sea level change on land uses adjacent to coastal regions and on the computer mapping of the effects of flood potential in estuaries.