Did the COVID-19 Lockdown-Induced Hydrological Residence Time Intensify the Primary Productivity in Lakes? Observational Results Based on Satellite Remote Sensing

The novel coronavirus pandemic (COVID-19) has brought countries around the world
to a standstill in the early part of 2020. Several nations and territories around the world insisted
their population stay indoors for practicing social distance in order to avoid infecting the disease.
Consequently, industrial activities, businesses, and all modes of traveling have halted. On the other
hand, the pollution level decreased ‘temporarily’ in our living environment. As fewer pollutants are
supplied in to the hydrosphere, and human recreational activities are stopped completely during
the lockdown period, we hypothesize that the hydrological residence time (HRT) has increased
in the semi-enclosed or closed lake bodies, which can in turn increase the primary productivity.
To validate our hypothesis, and to understand the effect of lockdown on primary productivity in
aquatic systems, we quantitatively estimated the chlorophyll-a (Chl-a) concentrations in different
lake bodies using established Chl-a retrieval algorithm. The Chl-a monitored using Landsat-8 and
Sentinel-2 sensor in the lake bodies of Wuhan, China, showed an elevated concentration of Chl-a.
In contrast, no significant changes in Chl-a are observed for Vembanad Lake in India. Further analysis
of different geo-environments is necessary to validate the hypothesis.