A significant decrease in navigational and industrial activities along the river bank brought down the level of coloured dissolved organic matter (CDOM) and nutrients in the Mandovi estuary during the lockdown last year.
A study by Albertina Dias and other scientists of the National Institute of Oceanography (NIO), which involved sampling of water in the estuary during May 2020, showed that CDOM was low at two stations between the Mandovi bridge and Ribander as compared to the previous five years’ average, from 2014 to 2018.
With restrictions in place during the Covid-19 pandemic, operation of pleasure cruises, water transport systems such as barges and shipbuilding activities came to a standstill.
Relieved of anthropogenic stressors, the water quality improved due to penetration of more light in the water column and aquatic biota in the estuary benefitted from it.
“When CDOM is more in the water column, it will not allow light to penetrate through and growth of phytoplankton, which is the basis of food chain, will be hampered,” Siby Kurian, co-author of the paper related to the study, and NIO scientist, said.
The study was recent published in the journal Frontiers in Marine Science.
Sunlight facilitates production of phytoplankton, the algae which are fed on by zooplankton, which in turn are consumed by small fishes in the food chain.
But, if the CDOM is too low, it allows penetration of ultra violet light to greater depth and can affect the marine biota adversely. On the other hand, CDOM occurs not only due to anthropogenic factors, but also natural ones, like decay of phytoplankton also releases CDOM into the system.