Abstract
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.
Highlights
The residence time is a fundamental descriptor in hydrology that provides information on the timescales of a molecule of water spend in a specific system
To validate our hypothesis and to understand the effect of lockdown on primary productivity in aquatic systems, this study explores to quantify the level of Chl-a before and during the lockdown period using remote sensing techniques
The hydrological residence time in our study area was expected to the lockdown period owing to following reasons: (i) sewage disposal to the lakes has completely increase during the lockdown period owing to following reasons: (i) sewage disposal to the lakes has stopped, causing reduced discharge via inlets, and (ii) all anthropogenic activities, including boating completely stopped, causing reduced discharge via inlets, and (ii) all anthropogenic activities, has stopped during the lockdown period, causing still waters
Summary
The residence time is a fundamental descriptor in hydrology that provides information on the timescales of a molecule of water spend in a specific system. Hein et al [5] and others noticed that a prolonged residence time increases the primary productivity in aquatic systems. We hypothesize that the hydrological residence time in closed or semi-enclosed lakes has increased, which may, in turn, increase the primary productivity. The hydrological residence time is not the only factor that influence the primary productivity, other factors such as temperature, increased light exposure, oxygen level, initial nutrients levels, etc., could cause an increase or decrease in the level of Chl-a concentration in the aquatic environments [12,13,14]. We assume in this study that the boundary conditions remain unchanged during the observation period for both the study areas and, examined the effect of HRT on water quality
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