Indus Delta, PakistanThe Indus Delta is considered one of the world’s most threatenedlarge deltas due to upstream freshwater extraction which irrigates180,000 square kilometer of agriculture area (Spalding et al.,2010). A severe reduction in fresh water flow from 93 to 48 millionacre feet (maf) was observed during a 80 years period spanningfrom 1922 to 2002 http://cms.waterinfo.net.pk/pdf/indusbasin.PDF.The impact of the reduction in freshwater flow to mangroves in theIndus Delta is not fully understood because of conflicting figuresfrom various stakeholders including the Sindh Forest Department,Sindh Coastal Development Authority, the International Union forConservation of nature (IUCN) and World Wide Fund for Nature ePakistan (WWF e Pakistan). Previous estimates of mangrove coverchange in Indus Delta were based on comparison between the resultsof different one-time-assessments done by numerous institutionsover a period of time.We assessed the mangrove cover change during the last fourdecades using multi-temporal Landsat MSS and TM satellite imagesacquired during 1973e2010 (Fig. 2). The results show currentmangrove cover on the Indus Delta is 98,014 ha including 26,555 haof dense mangrove forest (>50% canopy cover) and 71,459 ha ofsparse mangrove (<50% canopy cover) forest (Table 3).Our multi-temporal change analysis from 1973 to 2010 revealedthat the delta is highly dynamic and there is simultaneous processof erosion and accretion occurring in the area. In terms of mangrove
cover a total net increase of 1530 ha (1.5%) has been observed.
Considering the highly dynamic ecosystem and image interpretation
inaccuracies, this total change is insignificant. However, cumulative
forest gain and losswas 45,126 ha and 43,596 respectively.
We found extensive degradation of mangrove forest in the upper
tidal zone of the western end and intertidal zone of eastern part
along the country boundary line with India. The degradation in the
upper tidal zone can be seen in context of decreasing fresh water
discharges from the Indus River. Over the past sixty years the
quantity water flow reaching the delta has been reduced significantly,
which has created two environmental problems. First, the
salinity of water within the mangroves has increased to 50 parts
per thousand (ppt) Aziz and Khan (2001), which is detrimental to
mangrove growth. Second, the flow of alluviumethe fine gained
nutrient-rich soil brought by the rivers during their course through
the fertile plains has declined from 400 million to 100 million tons
per year. This decline has prevented transport and uniform
dispersal of suspended sediments over mangrove areas. As a result
of these two factors, the surviving Indus Delta mangroves are
sparse and stunted.
On the eastern side of the Indus Delta, the Left Bank Outfall
Drain (LBOD) was constructed during late 1980’s to dispose the
saltwater of Indus Plans in the Arabian Sea to reduce the water
logging and salinity from the productive agriculture lands. As a
consequence, higher quantities of saline water and salt load added
to the delta degraded the mangrove cover as well as impacted other
marine habitat.
The other major causes of mangrove deforestation and degradation
in Indus Delta include over harvesting for fuel wood, camel grazing and fodder use, meandering and erosion of creeks, and sea
water intrusion.
Most of the regeneration has been observed in the intertidal
zone. The gain in mangroves forest cover has been attributed to
conservation efforts in the area including intensive mangrove
plantation and raising awareness of the importance of mangroves
in the local communities. IUCN began its efforts to restore
degraded mangroves forests in Pakistan in the early nineties and
over 30,000 ha have been restored and restocked, mainly in the
Indus Delta. During this time fast growing and salt tolerant
mangrove species, Rhizophora mucronata (Kumri), and Avicennia
marina (Teemer) were planted in the inter-tidal zones of the Indus
Delta. The other possible causes of mangrove cover increase may
include changes in local morphology driven by changes in stream
flows and an increase in atmospheric CO2 concentrations suggested
by several studies (Archer et al., 1995; Eamus and Palmer,
2008; McKEE and ROOTH, 2008), which require further investigations
in context of Indus Delta.
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