Zonation

Zonation

	Zonation On the basis of salinity, five zones of mangrove distribution are considered. These are the euhaline, polyhaline, mesohaline, oligohaline and limnetic zones. In India, the west coast is characterised by the rocky substratum and hence absence of mangroves in the mouth region. On the other hand, the same euhaline zone along the estuaries of the east coast, which is a delta region, shows the presence of luxuriant mangrove forests as observed in the Gangetic, Mahanadi and Godavari deltas.
In the euhaline zone, the salinity ranges from 30 ppt to 40 ppt. Wave action is maximum and the gradient is not steep; thus sediment deposition will take place in the region of confluence which is known as delta. Otherwise, the entire sediment load will be washed into the sea. The polyhaline region, characterised by salinity range of 18 ppt to 30 ppt, has a low wave action and substratum is sandy clay. The mesohaline region, with 5 ppt and 18 ppt salinity, has silty clay bottom and feeble wave action.
In the oligohaline zone, the salinity is reduced further to 0.5 ppt to 5ppt as a result of more freshwater influx. Its substratum is silty. The limnetic zone is almost freshwater with occasional intrusion of brackish water at the highest high tides. The salinity in this area is less than 0.5 ppt and the substratum is full of gravel and coarse grains of sand. Different mangrove species, according to their salt tolerant ability and substratum preference occupy different zones along the estuaries. The deposition of sediment at the mouth of the major estuaries like Ganga, Mahanadi, Godavari, etc. is quite common.
During this process, the fine alluvial silt is deposited in the form of shallow islands in the mouth region. Slowly the new mangrove formation develops following a typical succession pattern. After the growth of pioneer species, the dominant or climax vegetation of mangrove species takes over and flourishes. These new mangrove formations are very sensitive to the flood waters during rainy season. Depending upon the flood, the rate of erosion in the mangrove soil varies. During heavy to very heavy floods, these new mangrove formation may be completely washed out. During the rainy season, the rate of erosion is higher while during the non-monsoon season the accretion is higher. The effect of accretion and erosion seem to be more prominent along the east coast than on the west coast of India.

	Back to Home
Marine Ecosystem Downwelling General Characteristics of Sea Biota Marine Microbes Bacterial Flora of the Sea Functions of Marine Flora Estuarine Ecosystem Biota of Estuaries Mangrove Ecosystem Characteristic Features of Mangroves Zonation Biota of Mangrove Other Interrelated Ecosystems

Home | Site map | Submit Article | Directory | Search