Features of Estuaries
The physicochemical properties of the estuaries have large variation in several parameters and this often creates stressful environment for organisms. This is the one cause that large organisms are less in number in this area than smaller organisms.
The most dominant feature of the estuarine environment is the fluctuation in salinity. Though salinity gradient exists sometime in an estuary but the pattern of gradient varies seasonally with the topography, with the tides and with the amount of fresh water.
The estuaries are dominated by muddy substrates which are often very soft. The deposition of particles is also controlled by currents and size of particle. If the strong currents prevail, the substrate will be coarse (sand) whereas where waters are calm and the currents are weak only fine silt will settle out. These particles in the estuary are of much organic origin derived from both the terrestrial and marine movements. As a result, the accumulated substrate is very rich.