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.2022 Jan 1:802:149585.
doi: 10.1016/j.scitotenv.2021.149585. Epub 2021 Aug 11.

COVID-19 lockdown improved river water quality in China

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COVID-19 lockdown improved river water quality in China

Dong Liu et al. Sci Total Environ..

Abstract

The impacts of COVID-19 lockdowns on air quality around the world have received wide attention. In comparison, assessments of the implications for water quality are relatively rare. As the first country impacted by COVID-19, China implemented local and national lockdowns that shut down industries and businesses between January and May 2020. Based on monthly field measurements (N = 1693) and daily automonitoring (N = 65), this study analyzed the influence of the COVID-19 lockdown on river water quality in China. The results showed significant improvements in river water quality during the lockdown period but out-of-step improvements for different indicators. Reductions in ammonia nitrogen (NH4+-N) began relatively soon after the lockdown; chemical oxygen demand (COD) and dissolved oxygen (DO) showed improvements beginning in late January/early February and mid-March, respectively, while increases in pH were more temporally concentrated in the period from mid-March to early May. Compared to April 2019, the Water Quality Index increased at 67.4% of the stations in April 2020, with 75.9% of increases being significant. Changes in water quality parameters also varied spatially for different sites and were mainly determined by the locations and levels of economic development. After the lifting of the lockdown in June, all water quality parameters returned to pre-COVID-19 lockdown conditions. Our results clearly demonstrate the impacts of human activities on water quality and the potential for reversing ecosystem degradation by better management of wastewater discharges to replicate the beneficial impacts of the COVID-19 lockdown. CAPSULE SUMMARY: River water quality improved during China's COVID-19 lockdown, but returned to normal conditions after the lockdown.

Keywords: COVID-19; China; Lockdown; Spatiotemporal variations; Water quality.

Copyright © 2021 Elsevier B.V. All rights reserved.

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Conflict of interest statement

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Unlabelled Image
Graphical abstract
Fig. 1
Fig. 1
The river water quality sampling sites. Region I is a relatively economically developed area in China. National and provincial boundaries were obtained from the National Geomatics Center of China (http://www.ngcc.cn/ngcc/). The inset global map was obtained from Google Earth. The Shuttle Radar Topography Mission digital elevation model (DEM) with a spatial resolution of 90 m was obtained from NASA (earthdata.nasa.gov). The H-T Line refers to a demarcation line of China's population density and economic development, with much higher values in the east (Hu, 1935).
Fig. 2
Fig. 2
Daily values of different indicators. (a) New confirmed COVID-19 cases and railway transport passenger numbers across China between 23 January and 22 June 2020. (b–e) Daily arithmetic mean values of pH, DO, NH4+-N, and COD derived from data for 65 monitoring sites (Fig. 1) over the same dates in 2018, 2019, and 2020. Based on the values in Table S2, the water quality standards are shown on the right axis.
Fig. 3
Fig. 3
Proportions of different water quality levels between January and June in 2018, 2019, and 2020.
Fig. 4
Fig. 4
Mean values of different water quality parameters in January–June 2018, 2019, and 2020: (a) pH; (b) DO; (c) NH4+-N; and (d) COD. The error bars indicate the standard deviations. Based on the values in Table S2, the water quality standards are shown on the right axis.
Fig. 5
Fig. 5
Mean percentage changes in the four water quality parameters across monitoring sites in eastern China during different periods of 2020 and the same months in 2018 and 2019, respectively: (a–b) are for H+ during March–April; (c–d) are for DO during March–May; (e–f) are for NH4+-N during February–April; (g–h) are for COD during February–May. Base maps show the province boundaries in China (Fig. 1).
Fig. 6
Fig. 6
Comparisons of monthly mean WQI in 2020 to those in 2018 and 2019. (a) Monthly mean WQI values across all stations. The water quality standards are shown on the right axis: WQI ≥ 80, excellent; 61–80, good; 30–60, acceptable; and WQI < 30, poor (Chang et al., 2020). (b–e) are the comparisons of values in March and April 2020 to the corresponding months in 2018 and 2019, respectively.
Fig. 7
Fig. 7
Statistical data from the National Bureau of Statistics. (a) The provincial population density in 2019; (b) urban population ratio in different provinces in 2019; (c–d) NH4+-N and COD discharges per square kilometre in different provinces in 2014.
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