Impact of reduced fresh water on Indus Mangrove ecosystem

By: Shahid Amjad

  River Indus is the sixth largest river in the world and the mangroves plantation (approx: 250,000 hac:) of the Indus delta are largest in the arid zone . The Indus delta is the most prominent feature of Sindh coastline is about 346 Km. The land forms are remarkably uniform and the region consists of a net work of seventeen small and large tidle creeks/channel that meander up to 10-15 Km towards and land from the open sea. The Indus delta continues to shrink due to non-availability of fresh wate downstream. Many of the tidle creeks are remnant courses of the Indus river with extensive mud flaks in between; sediments that make up the delta consist of fine silt and clay with high percentage of micaceous sand. Fine materials are carried off shore from the coast and coarser sand is left behind to form a series of barrier bars. The sand tracks on the bars are almost devoid of vegetation. The sand bars change continuously are a result of tidal currents and wave flats extend to the coast and the sand bars become fewer. The Indus delta has traditionally supported the mangroves forest, the mangrove themselves support the coastal fisheries by acting a breeding and spawning ground of economically important fish & shrimps. The leaves and seeds of mangrove are used as fodder for domestic animals; the wood is used as firewood and as building materials by the coastal communities. The mangroves of the Indus delta are largely depend upon the fresh water discharges from the river Indus.

 Significance of Mangroves .   

                            The mangrove ecosystem plays an important role in the production of living resources that supports the livelihood of an estimated 300,000 people. They provide shelter and protect the nursery and breeding grounds of fish and shell fish and sanctuaries to a variety of commercial species, industrial products such as tannin, pharmaceuticals, medical plants etc. The Indus delta mangroves provides fodder for domestic animals about (19.5 million Kg of grasses and 67 million Kg of leaves through browsing by about 6,000 camels, 32,000 buffaloes, 8,000 goats, sheep & cows) and wood harvesting (18,000 tons/year) by the coastal population of about 135,000 and there an estimated 20,654 families in 162 coastal villages, particularly oily wastes deteriorates the water quality of mangroves located in areas close to Karachi.

                           According to an estimate 1 hacter of mangroves produces, 100Kg of fish, 25 Kg of crab meat and 200 Kg of mollusk per annum beside it also supports the near shore and offshore fishery.Reduced availability of fresh water puts a physiological stress on the mangrove plant and growth the becomes stunted. The estimated fresh water requirements for the mangrove is more than 10 million-acre feet (MAF). Similarly lack of sediment process there by increasing the sediment erosion process as result of tidal currents.  Most important cause of environmental degradation of Indus delta is the reduction in volume of Indus water discharge due to construction of dams and barrages up country. The fresh water discharge has been reduced from 150 MAF (before 1947) to 35 MAF (1992-98) (Keerio & Bhatti 1999). Similarly deposition of slit decreased from 400 million tons to 100 million tons in 1992 and to35 million tons during 1992-98.

                           The negative impact has been the reduction of mangrove cover in Indus delta that has reduced from an estimated 43.3 % to 23.8 % during span of 32 years from 1966 to 1998.

Causes of Negative impacts .

• Rapid increase in coastal population and expansion in socio-economic activities, particularly along the coast near Karachi.

• Non-sustainable use of natural resource with time, resulting in loss of mangrove and with that the loss of biological diversity, threatening the breeding grounds of a variety of commercial species that necessarily require spending part of their life cycle.
• Indiscriminate and uncontrolled discharge of effluent from domestic, agricultural and industrial resources, exceeding the assimilation capacity of the natural system resulting in decline of fisheries.
• The sea encroachment due to the reduction of Indus discharge as well as gradual increase in sea level rise (estimated at 1.1 mm/year) and associated increase in the coastal erosion are major factors degradation of the Indus delta mangrove forest.
• Coastal erosion resulting from increasing action of high energy waves resulting from negative mass balance stemming from reduced flow of fresh water downstream.

Recommendations for conversation of Mangrove.

                           In order to conserve and manage the mangrove forests on sustainable basis, so that their economic, social and ecological benefits are optimized it is suggested that The required quantity of river discharge (freshwater & sediments) of water balance (10 MAF) allotted downstream Kotri barrage is maintained throughout the year that should reach the mangrove forests in the Indus deltic region for their sustained growth and survival.

• Introduce community participation and integrated approach for management and conversation measures of mangroves.
• Ensure that ecological functions of mangroves are not hampered.
• Reduce population stress on the coastline and aggressive coastal developments on land, adjacent to mangroves.
• Minimize non-sustainable use of mangroves so that they continue to contribute towards fishery development and coastal economy.
• Foster and encourage the restoration of degraded mangrove areas through natural or artificial regeneration (a forestation).
• Establish and enforce construction setback limits and unnecessary cutting of mangroves for the sake of development along the coastal areas.

                           For development of mangrove eco-system to be sustainable, it must meet objectives i.e economic, environmental and social, which require well co-ordinated  and integrated approach at all levels