A team of researchers at CSIR-National Institute of Oceanography (CSIR-NIO), Goa, studied the variations of Coloured Dissolved Organic Matter (CDOM) in the Mandovi Estuary, Goa — “During Spring Inter-Monsoon: A Comparison with COVID-19 Outbreak Imposed Lockdown Period”.
One of the chemical parameters of importance is the Dissolved Organic Matter (DOM) in the water, which is the largest reservoir of organic carbon in the aquatic environment. A fraction of this organic carbon absorbs light and imparts colour to the water and hence is known as Coloured Dissolved Organic Matter. The origin of CDOM can be either natural or anthropogenic.
CDOM absorbs light highly in the UV and blue regions of the solar spectrum and hence can have a positive or negative impact on the ecosystem. If a high amount of CDOM is present in the water it will not allow light to penetrate the water column and hence primary production will be hampered. While low levels of CDOM allow penetration of UV light to greater depths affecting the marine biota.
Mandovi and Zuari are the two main estuaries of Goa and have been exploited in recent years for various anthropogenic activities. The CDOM in the Mandovi Estuary was monitored since 2014, wherein high CDOM absorption was observed in the summer (especially in the midstream region) due to anthropogenic activities.
In 2020, following the Government of India imposed COVID-19 lockdown (24 March-8 June), a significant decrease of CDOM by almost two folds was observed in the midstream region. The Sentinel-2 satellite data also showed similar variations of CDOM absorption with low values during 2020. Apart from this, the concentration of dissolved nutrients in 2020 was also low compared to the previous reports.
There was a complete standstill of anthropogenic activities such as operating pleasure cruises, water transport systems like barges, shipbuilding activities, and commercial establishments following the government-imposed lockdown, which might have reduced the CDOM and nutrients in the estuary.