Human and natural activities regulate organic matter transport in Chinese rivers

Dong Liu; Xintong Jiang; Mengwei Duan; Shujie Yu; Yan Bai

doi:10.1016/j.watres.2023.120622

Human and natural activities regulate organic matter transport in Chinese rivers

Water Res. 2023 Oct 15:245:120622. doi: 10.1016/j.watres.2023.120622. Epub 2023 Sep 11.

Authors

Dong Liu¹, Xintong Jiang², Mengwei Duan³, Shujie Yu⁴, Yan Bai⁵

Affiliations

¹ Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China; Faculty of Natural Sciences, University of Stirling, Stirling FK9 4LA, UK.
² Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China.
³ School of Transportation and Geomatics Engineering, Shenyang Jianzhu University, Shenyang 110168, China.
⁴ State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China. Electronic address: yushujie@sio.org.cn.
⁵ State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China. Electronic address: baiyan@sio.org.cn.

PMID: 37716299
DOI: 10.1016/j.watres.2023.120622

Abstract

Rivers connect terrestrial and aquatic ecosystems and export approximately 55.47 % of the net terrestrial carbon fixation. However, due to unavailable high-frequency monitoring data, litter is known about diurnal variation in riverine carbon transport on a national scale. Based on daily measurements between March 2021 and February 2022 at 1491 stations across China, this study clarified the spatiotemporal variations in riverine organic matter indicated by chemical oxygen demand (COD). Spatially, COD content showed a spatial pattern with high values in the northwest (p < 0.05), and COD flux was determined by water discharge (84.01 %). Human activities explained 73.20 % of the spatial variations in riverine COD content; in particular, agricultural planting significantly elevated riverine COD (r = 0.73, p < 0.01). Seasonally, 95.53 % of stations showed significant seasonal variations in COD contents (p < 0.05); 69.72 % (25.81 %) were identified as Type II (III) typically had the maximum (minimum) COD in summer (autumn). Moreover, except for human activities (41.08 ± 22.94 %), natural factors also contributed 47.41 ± 24.04 % to the seasonal variations. In summer, high temperatures increased COD by promoting algal proliferation at Type II stations; however, heavy precipitation diluted COD contents at Type III stations. In these cases, seasonal measurements were essential for estimating riverine organic matter transport, especially the values measured in spring and winter. This study has significant implications for managing the aquatic environment, estimating riverine organic matter transport, and balancing the global carbon budget.

Keywords: Chemical oxygen demand; Chinese rivers; Driving factors; Human activities; Spatiotemporal variations.