Gradual drop in fresh water flow sets alarm bells ringing
BHUBANESWAR: Composition of plant species in the mangrove forest of Bhitarkanika, one of the richest assemblages of mangroves in India, is undergoing slow change due to slight change in salinity over the last few decades.
Scientists and environmentalists have expressed concerns that if fresh water flows are severely restricted to the Bhitarkanika, the mangrove forest, which is a vital barrier to sea incursion, could get wiped out.
A study jointly taken up by Institute of Minerals and Materials Technology (IMMT) and Spatial Planning and Analysis Research Centre Private Limited (SPARC) on ‘effect of reduced water flow through Brahmani-Baitarani river system on the mangrove population of Bhitarkanika estuary,’ called for early estimation of minimum volume of water needed for sustenance of this crucial ecological barrier.
Experts especially assessed the impact due to change water flow regime into the region before and after the construction of the Rengali dam in 1985.
According to study, during the pre-Rengali dam period, the flow at delta head was 19,514 million cubic metres while the current flow has come down to 17,380 million cubic metres without any irrigation diversion in the Rengali command area.
However, the flow is likely to reduce to 14,000 million cubic metres by 2025 when full irrigation potential of Rengali would be utilised.
Mangrove species are sustained by a suitable combination of fresh and saline water while the desirable salinity requirement for the most species is 10 to 20 parts per thousand (PPT) for sustenance and healthy growth. However, increase in salinity had been noticed above the desirable level at some places.
If salinity grows, many plant species would suffer from delayed germination and stunted growth, sometimes leading to morbidity and mortality even at less than 20 ppt.
“The outer estuarine zone in Habelikati and Gahirmatha had 20-30 ppt salinity favouring species such as Avicenia marina and Sonnerata alaba. The coastal region with very high salinity has salt bushes,” the study found out.
“The situation Dangamal or further downstream is changing slowly towards higher salinity,” it said.
According to approximate estimation, the Rengali dam needs to release at least 500 million cubic metres of fresh water exclusively for sustaining mangrove forests even in non-monsoon during worst drought years
Speaking at a stakeholders’ meeting in wake of the study here on Tuesday, V. P Upadhaya from the Ministry of Environment and Forest said Bhitarkanika, which boasted of treasuring 65 plant species, would face further problems due to restricted flow of water to the estuary.
Of total species, 40 were endangered, five endemic and one was nearly extinct, he said. Scientists and researchers called for formulation of mangrove plan for Bhitarkanika.