SEASONALLY HYPERSALINE ESTUARIES IN MEDITERRANEAN-CLIMATE REGIONS

Data collected in three Californian estuaries indicate that hypersalin e conditions exist during the dry summers typical of a Mediterranean c limate. The generalised seasonal and longitudinal hydrographic structu res are described and explained. It is argued that this seasonal hyper salinity is common and that it represents a major class of estuaries. The observed accumulation of salt indicates surprisingly long residenc e times in small basins which have free exchange with the ocean. This semi-isolation of the inner basin leads to a large build-up or severe depletion of nutrients, pollutants and plankton in these systems. Of c oncern are the trends to increase pollutant loading in the same system s that are experiencing an increase in residence times owing to freshw ater extraction in the watershed. (C) 1997 Academic Press Limited.