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S. Kalita and H. Talukdar
been a key factor responsible for the sustenance of life and welfare of human beings.
However, the increasing human population coupled with pollution, destruction of
wetlands and forests, rapid urbanisation and industrialisation has altered hydrology
and hydroclimatology. A quarter of the world’s population is already affected by
water scarcity crisis; further, aggravation of the issue is predicted by experts [63].
‘Day Zero’ situation in places like Cape Town, South Africa and Chennai, India
are epiphany case studies regarding the indefinite withdrawal of water and poor
management of water sources. Today most of the Earth’s water sources are facing
the brunt of unchecked and escalated anthropogenic activities, and are being directly
or indirectly polluted, physically altered (induced stratification in water bodies or
acidification of ocean water) and destructed (by construction of dams). The World
Commission on Water states that in the twenty-first century, 50% of the world’s 500
rivers are heavily polluted [2]. Pollutants such as heavy metals, pesticides, chemicals
and by-products of industrial and mining activities, oil and oil by-products, organic
pollutants, and radioactive substances are known to cause changes in water chemistry.
Major anthropogenic sources of water pollution are improper disposal of solid-waste,
burning of fossil fuels for energy and transport, entry of municipal wastewater and
agricultural run-off, and discharge of industrial and domestic effluents. Industrial
wastes and sewage alone pollute more than 66% of India’s water resources and
54 of the 78 monitored rivers and streams of China. Marine environment is also
threatened due to large-scale dumping of untreated municipal (80–90%) sewage into
oceans by most coastal developing countries and some coastal developed countries
[64]. As such the quarantine lockdown provides a temporary relief to the aquatic
ecosystems due to restricted human mobility. Reduction in solid wastes and effluents
has caused rivers, lakes, and beaches to self-purify. Currently, literature regarding
the impact of quarantine lockdown on the quality of water is very limited. However,
those few studies have succinctly emphasised the positive impact of reduced human
activities on water quality status. We found that during the COVID-19 restricted
period, most of the research papers on improved water quality has been reported
from India. River Ganga and River Yamuna are severely polluted water bodies of
India. From late 1970s several research studies [65–70] have evaluated the water
chemistry and the effects of anthropogenic activities on the both rivers. Though
many initiatives in terms of policies and action plans have been taken up by the
government and non-governmental agencies; nevertheless, optimistic results in the
river water quality was not observed until now. Real-time water monitoring data
study on Ganga demonstrated positive changes such as an increased dissolved oxygen
(DO) and decreased biological oxygen demand (BOD), nitrate concentration, total
coliform and faecal coliform count [71]. In fact, the alterations in the water parameters
indicate the improved water quality of Ganga due to reduced industrial effluents and
solid wastes disposal under lockdown restrictions. Other reported improvements in
the water sources of India include Yamuna [72], Cauvery and its tributaries [73],
and groundwater samples of a costal industrial city of Tuticorin in Southern India
[74]. Apart from real-time monitoring, the remote sensing imaging techniques have
also been used for assessment of prevailing conditions of water bodies. Satellite
imagery revealed an improvement in surface water quality of Vembanad Lake [7] and
S. Kalita and H. Talukdar
been a key factor responsible for the sustenance of life and welfare of human beings.
However, the increasing human population coupled with pollution, destruction of
wetlands and forests, rapid urbanisation and industrialisation has altered hydrology
and hydroclimatology. A quarter of the world’s population is already affected by
water scarcity crisis; further, aggravation of the issue is predicted by experts [63].
‘Day Zero’ situation in places like Cape Town, South Africa and Chennai, India
are epiphany case studies regarding the indefinite withdrawal of water and poor
management of water sources. Today most of the Earth’s water sources are facing
the brunt of unchecked and escalated anthropogenic activities, and are being directly
or indirectly polluted, physically altered (induced stratification in water bodies or
acidification of ocean water) and destructed (by construction of dams). The World
Commission on Water states that in the twenty-first century, 50% of the world’s 500
rivers are heavily polluted [2]. Pollutants such as heavy metals, pesticides, chemicals
and by-products of industrial and mining activities, oil and oil by-products, organic
pollutants, and radioactive substances are known to cause changes in water chemistry.
Major anthropogenic sources of water pollution are improper disposal of solid-waste,
burning of fossil fuels for energy and transport, entry of municipal wastewater and
agricultural run-off, and discharge of industrial and domestic effluents. Industrial
wastes and sewage alone pollute more than 66% of India’s water resources and
54 of the 78 monitored rivers and streams of China. Marine environment is also
threatened due to large-scale dumping of untreated municipal (80–90%) sewage into
oceans by most coastal developing countries and some coastal developed countries
[64]. As such the quarantine lockdown provides a temporary relief to the aquatic
ecosystems due to restricted human mobility. Reduction in solid wastes and effluents
has caused rivers, lakes, and beaches to self-purify. Currently, literature regarding
the impact of quarantine lockdown on the quality of water is very limited. However,
those few studies have succinctly emphasised the positive impact of reduced human
activities on water quality status. We found that during the COVID-19 restricted
period, most of the research papers on improved water quality has been reported
from India. River Ganga and River Yamuna are severely polluted water bodies of
India. From late 1970s several research studies [65–70] have evaluated the water
chemistry and the effects of anthropogenic activities on the both rivers. Though
many initiatives in terms of policies and action plans have been taken up by the
government and non-governmental agencies; nevertheless, optimistic results in the
river water quality was not observed until now. Real-time water monitoring data
study on Ganga demonstrated positive changes such as an increased dissolved oxygen
(DO) and decreased biological oxygen demand (BOD), nitrate concentration, total
coliform and faecal coliform count [71]. In fact, the alterations in the water parameters
indicate the improved water quality of Ganga due to reduced industrial effluents and
solid wastes disposal under lockdown restrictions. Other reported improvements in
the water sources of India include Yamuna [72], Cauvery and its tributaries [73],
and groundwater samples of a costal industrial city of Tuticorin in Southern India
[74]. Apart from real-time monitoring, the remote sensing imaging techniques have
also been used for assessment of prevailing conditions of water bodies. Satellite
imagery revealed an improvement in surface water quality of Vembanad Lake [7] and