Godavari river intensifies dead zone in Bay of Bengal: Study

According to the study, as Godavari sees peak discharge during the monsoon season, large amounts of organic matter from dead trees/plants or soil are carried into the BoB

Hyderabad: The Godavari river is intensifying the dead zone or oxygen-depleted zones (ODZ) near its river mouth in the Bay of Bengal (BoB). The dead zone refers to low oxygen levels in the water, affecting marine life.

This has been revealed in a study titled ‘Sub-seasonal through Interannual Variability of river discharge and its Impact on phytoplankton biomass in the Bay of Bengal’ carried out by researchers of University of Hyderabad, CSIR-NIO, Vizag and King Abdullah University of Science and Technology, Saudi Arabia.

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According to the study, as Godavari sees peak discharge during the monsoon season, large amounts of organic matter from dead trees/plants or soil are carried into the BoB. In addition, river water also carries significant amounts of nutrients to the coast, enhancing phytoplankton production.

Both organic matter brought by the river and that forms locally through phytoplankton production sink to a depth where they are decomposed. In this process, the dissolved oxygen in the water between 40 and 200 m depths is microbially consumed, leading to severe depletion in oxygen levels (referred to as hypoxia) in the BoB, the researchers said.

“This has potential implications for the fish catching several 10s of kilometres from the coast where the spread of river discharge from Godavari was observed, and intensive fishing is normally carried out,” the researchers said.

Since Godavari is rainfed, any decrease in monsoonal rainfall due to interannual climate drivers such as the ENSO, Indian Ocean Dipole, etc. will decrease river runoff, which in turn may improve the oxygen levels in the dead zones leading to improved fishery catch, they said.

The study involved an analysis of river discharge data at the Dowleswaram barrage, World Ocean Atlas 2018 data, and high-resolution biogeochemistry recorded Array for Real-Time Geostrophic Oceanography (ARGO) buoys in the Bay of Bengal off Godavari river mouth region.

The ARGO buoys are state-of-the-art buoys that collect vertical profiles of various oceanic parameters from the surface through 2000 m deep by slowly sinking and resurfacing over 10 days.

However, the researchers cautioned that the results need further reconfirmation through dedicated data campaigns as the ARGO buoys were about 50-100 km away from the river discharge recording point.

Dr. Sreejith, now a scientist at CSIR-NIO Goa, largely carried out the study at the Centre for Earth, Ocean and Atmospheric Sciences, UoH during his tenure as a research associate under the mentorship of Prof. K. Ashok and Prof. Sreenivas P.

The research findings appeared in the Frontiers in Marine Science, section Marine Biogeochemistry on November 4, 2024.