Water of Estuaries

The water of estuaries is turbid because of the great number of particulates in suspension in the water. The turbidity is minimum near the mouth and increases with distance inland. The major ecological effect of turbidity is a marked decrease in the penetration of light. This, in turn, decreases photosynthesis by phytoplankton and benthic plant, thereby reducing productivity. One of the most important factors in estuary water is oxygen. Since the solubility of oxygen in water decreases with increased temperature and salinity, the precise amount of oxygen in water varies with these parameters. Oxygen is severely depleted in the substrate.

The high organic content and high bacterial population of the sediments exert a large oxygen demand on water. Estuarine sediments are, therefore, anoxic below the first few centimetres unless they have large particle size and/or large number of burrowing animals such as ghost shrimp Callianassa and the hemichordate worm Balanoglossus which by their activities oxygenate lower sediment layers.