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. 2022 Feb 21;12:2870. doi: 10.1038/s41598-022-06900-6

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(a) Yearly variation of COD from 2009 to 2019. The red line shows a linear trend of COD. (b) Monthly distribution of COD saturation at Palla station from 2009 to 2019. (c) Monthly mean variation of COD from 2009 to 2019.