ABSTRACT
Salinity variations and salinity gradients therefore are common features in estuaries with a varying degree depending upon the tide and the freshwater volume that enters the estuary. The patterns of dilution of the seawater entering the estuary varies from estuary to estuary: they depend on the tidal amplitude, the extent of evaporation of the water, the volume of freshwater, and the number of tributaries that contribute to the estuary. The tide is the most important factor that controls the basic environmental characteristics of estuaries and coastal lagoons. In some estuaries and shallow coastal lagoons, wave action may be an important factor stirring up sediment, changing and altering the morphometry of the ecosystem. The composition of the estuarine or coastal lagoon water can differ from the seawater to the freshwater entering their ecosystems. The oxygen content, the carbon dioxide and pH are dependent upon the characteristics of the freshwaters and the seawaters entering the estuary.
