Impact of oil spills on mangroves off Mumbai and Raigad coast


The Bombay Natural History Society (BNHS) in a project funded by the MOEF carried out a study on the impact of oil spills on mangroves off Mumbai and Raigad coast during the period August 2010-October 2011. On August 9th 2010 two ships collided off shore near Uran resulting in a spill estimated at 400-500 tons of fuel oil.

With a view to access the oil spill pollution and its effect on mangrove cover a comprehensive assessment survey was undertaken in Mumbai and its adjacent coastal areas. During numerous visits soil samples were collected and analyzed for oil and grease content, along with phonological observations, and studies to access the seedling survival rate. The report details the effect of the oil spill on the fragile ecosystem, estimating the total area affected by the oil spill to be 1273.24ha. The oil spill caused by the MSC Chitra and the MV Khalija was supplemented by two subsequent incidents, the sinking of the MV RAC on 4th August 2011 and rapture of the Uran crude oil pipeline in January 2011, resulting in a significant hike in the oil content during these periods.

Following the oil spill In August it was observed that dwarf mangroves and saplings which were totally drenched in oil slicks had shed their leaves and eventually died. At Vashi 5 places out of 11 showed disappearances of seedlings, on the other hand Shewri showed no establishment of seedlings for which a high level of pollution can be accounted for. At Navi Nagar, Gharapuri and Uran these spills caused death of young patches of ‘Avicennia Marina’, the mature ones however suffered minimal damage.
The assessment thus infers that repetitive oil spills directly hamper the recruitment of seedlings which may endanger the entire mangrove population on affected coasts. It is highly unfortunate that the Mumbai coast is exposed to various anthropogenic perturbations including oil spills, the effects visible in the form of tar balls especially in the pre monsoon season. A number of previous studies surrounding Bombay and Thane creek record a substantial amount of petroleum hydrocarbon from the water and sediment samples along with bioaccumulation in some creatures.(Nikam et al 2008, Kadam 2009)

The observations made show symptoms of partial recovery of ecological functioning although anthropogenic interference is persistent in various ways. The report concludes calling for an additional 5years of robust monitoring which is essential to predict the ecological consequences of oil spills. The base data has unambiguously  concluded that mangrove regeneration has been severly affected due to oil spills caused by Khalija, and Chitra as well as the RAC and pipeline leakages at most of the sites under study.

Reference: Study of impact of oil spills on Mangroves off Mumbai and Raigad coast by the Bombay Natural History Society.




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