Research in Hoogly estuary has discovered that the mangroves have started moving upstream, growing in less-saline regions.
Over the years due to gradual environmental changes and anthropogenic activities, mangroves have started to redistribute. Mangroves have reclaimed even the upper course of the river, which was completely devoid of mangroves before 1995.
Researchers spent years mapping the distribution of mangroves and associated species using ground surveys and satellite data. They also studied the sediments and water samples along the river banks.
With the rapid growth of Kolkata city, sewage disposal has increased the pollution load in the river waters. Globally, there is also rapid mean sea-level rise. All these factors might have played a role in this upstream migration.
The discovery directly indicates changes in the micro-environment. The rate of sedimentation, quality of the sediment, and biogeochemistry of the river has all been affected by elevated anthropogenic activities and global climate change events.
The team emphasised the fact that the construction of Farakka Barrage in 1975 has increased fresh water flow in River Hooghly, thereby causing change in ecology and chemistry of the river.
They also found high chemical oxygen demand in the river because of increased release of harmful chemicals from multiple point and non-point sources.
The decline in the mangrove area along with this migration may increase the amplitude of coastal hazards such as storm surges, erosion and flooding.