Abstract
An estuary is defined as that part of a river system in which the level or salinity of the water may be affected by that of the sea. Drawing largely on information for barrier estuaries from south-western Australia, it is emphasized that the productive fringing marshes may contain much of the plant biomass and nutrients. Submerged angiosperms and macroalgae are very productive in the shallows, and phytoplankton, of trivial biomass, are relatively highly productive. Benthic microalgae may make up a large proportion of the biomass of microscopic plants.
Light is of critical importance in controlling growth rates of submerged plants, but elevated nutrient levels allow marked increases in plant biomass. Mild nutrient enrichment may increase the growth of aquatics, but further eutrophication may lead to high macroalgal biomass and the loss of seagrasses. High levels of enrichment may lead to cyanobacterial blooms. The sediments play an important role in the transfer of nutrients from water column to plant biomass.
Emphasis is placed on the adverse effects of phosphorus loading into estuaries from cleared catchments on sandy soils on which phosphorus fertilizers are used; reduced loading is important in management strategies for preventing or ameliorating the consequences of estuarine eutrophication.