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Mangrove forests are considered to be the first line of defence against climate-change-induced impacts like coastal erosion and sea-level rise. In Tamil Nadu, however, they are under threat, making coastal communities more vulnerable to climate change.
Pichavaram mangrove forest, dubbed as the “second-largest in the world” after the Sunderbans in West Bengal, is located in the coastal district of Cuddalore in Tamil Nadu. Consisting of 51 small and large islands, the forest has a total area of nearly 1,350 hectares and was declared a Forest Reserve in 1987.
Pichavaram is home to 14 mangrove species. While locals in the area believe the forest will never decrease in size the mangroves face threats on multiple fronts. According to the SDG INDIA report released recently by the NITI Aayog, in 2019 the area under mangroves in Tamil Nadu increased by 4.26%, but in 2020 it has decreased drastically to 8.16%.
Recent studies conducted in the forests have found that the 2004-tsunami, decreasing freshwater and increasing pollutants inflow, have all resulted in the modification of the geochemistry of the region — all factors detrimental to the forests. They also indicate that even though the forest cover in Pichavaram is increasing, the average tree crown size has reduced, suggesting alterations in species succession and plant growth capability.
The prevalence of only salt-tolerant species of mangroves was also noted, which indicates a decrease in species richness. Frequent and intense cyclones, a consequence of climate change, are also a threat to the mangrove forest cover.
“Low reliability of monsoonal rainfall, unscientific agricultural practices, and intrusion of saline seawater in the coastal strips have adversely affected several areas along the Indian coastline including Pichavaram mangroves.
“Restriction of inland water input to the estuary by damming water for agriculture and various other purposes coupled with weak monsoonal pattern increases salinity,” says Dr Jyoti Srivastava, a Scientist at the Birbal Sahni Institute of Palaeosciences who has done extensive research on the Pichavaram mangrove forests
She says that the sustenance of these forests requires a mix of both freshwater and seawater influx into them.
“At present, most of the estuaries and nearshore wetlands along the South-east coast including the Pichavaram mangrove forest are covered by salinity tolerant mangroves species. A gradual increase in salt-tolerant plants such as Avicennia and Suaeda species is of great concern and needs investigation for the rapidly changing mangrove habitat,” she told Youth Ki Awaaz.
The Tamil Nadu Agricultural University (TNAU) also notes that many species of mangroves in the Pichavaram mangrove forests face the risk of extinction. The substantial reduction in the forest cover is due to frequent cyclones at least every alternate year which devastated several mangrove species and reduced the total area from 4,000 hectares at the beginning of the century to nearly 1,100 hectares at present, as per the university.
As a result, many plants previously recorded from the Pichavaram mangrove have completely vanished.
The population surrounding the mangrove forests has also increased drastically over the years which further stresses the sensitive mangrove ecosystem as it leads to overexploitation. According to a geospatial study of the Pichavaram mangrove region, the area under settlements was only 8.49 sq km in 1972 but in 2018 it increased to nearly 12.10 sq km.
Local communities use the mangrove forests for firewood, fodder, boat-building and tannin extraction. As the pandemic induced lockdown affected aquaculture — a major source of livelihood — the mangroves presently are at an even greater risk of overexploitation.
With fishing being one of the major sources of livelihood in this region, the degradation of the forests due to pollution, increasing salinity, changing mangrove habitat and overexploitation also threatens the reduction of fish catch in the region.
Seawater intrusion in coastal areas is also a rising threat to the area’s agricultural economy and likely to have an impact on local livelihoods. “As seawater is heavier in density it occupies the bottom level making its removal impossible. Therefore, it becomes easy for the seawater to percolate down to the depths through capillary action. Hence, the groundwater in these areas would also have higher salinity,” says Srivastava.
“During the past few decades, there has been a rapid increase in the number of aquaculture ponds as well as the cultivation pattern due to which the wastes are being transferred to the estuary through Vellar estuary, Uppanar estuary and Khan Saheb Canal,” says Srivastava.
Irrigation canals and aquaculture farms dumping their waste into the mangrove region is, therefore, also a threat to the forests. In addition, aquaculture in the area is highly unregulated with aqua farms also operating close to the mangroves without registration, making things even more dangerous.
Mangrove forests enable sediment deposition by slowing down water flows, thus, preventing seawater pollution and coastal erosion. But this ability to trap polluting effluents is harmful to the lush forest cover of the mangroves in the long run as pollution levels increase.
Effluents from motor-operated fishing boats, industrial waste and household wastes from surrounding villages also end up in the mangrove region through small water canals, polluting the brackish waters.
“During our studies, we found enhanced levels of various harmful heavy metals in the mangrove sediments. These heavy metal effluents are from urban and industrial development in the upstream areas of the mangrove forests.
“Cobalt and Copper sediments from antifouling boat paints, untreated domestic sewage and industrial effluent discharge, and also from agriculture and aquaculture practices, fungicides and algaecides from fish farming, Iron sediments from discarded rusty boats and dams, Nickel from effluent discharge from nearby chemical industries like paint industries, Lead from aquaculture effluents, thermal power plants, agricultural runoff and domestic sewage and also due to operation of a large number of mechanised fishing boats in the area,” says Srivastava.
“This enhanced metal content leads to degradation of the mangrove forest and triggers ecological imbalances. We also observed the high concentrations of Rubidium and Titanium in the mangrove sediments which is evidence of seawater ingression. Rubidium is easily ionised and the human body tends to concentrate rubidium ions which are radioactive. This can be dangerous if taken in excess,” she added.
The Pichavaram mangrove forest is rich in biodiversity and is home to a variety of fish, shrimp and crabs. Fishing is also one of the major sources of livelihood in this region. But the degradation of the mangrove forests due to pollution, increasing salinity, changing mangrove habitat and overexploitation threatens the reduction of fish catch in the region.
In addition to protecting coastal areas from sea-level rise and coastal erosion, mangrove forests also act as carbon sinks. A carbon sink has the capability to accumulate and store carbon and this ability is vital in the fight against climate change.
According to a recent study, Pichavaram mangrove forests are a moderate carbon sink but their capability is in danger of decline due to rising temperatures, salinity levels, decreasing rainfall and tidal inundations.
The fragile region — that is already overstressed — faces another potentially catastrophic threat. In 2019, the Central Government granted rights for exploratory drilling of hydrocarbons to Vedanta just 0.49 kms away from the ecologically sensitive Pichavaram mangrove forests, drawing widespread flak from environmentalists and local communities alike, who say the forests could face extinction if the project is implemented.
Instead of preserving this fragile ecosystem, it is a surprise that the government is planning to further distress the population by locating more polluting industries in the region.