Preprints
https://doi.org/10.5194/egusphere-2022-30
https://doi.org/10.5194/egusphere-2022-30
 
15 Mar 2022
15 Mar 2022

Variations in dissolved and particulate organic carbon dynamics in the lower Changjiang River on time scales from seasonal to decades

Yue Ming1, Lei Gao1, and Laodong Guo2 Yue Ming et al.
  • 1State Key Laboratory of Estuarine and Coastal Research, East China Normal University, 3663 North Zhongshan Road, Shanghai 200241, China
  • 2University of Wisconsin-Milwaukee, School of Freshwater Sciences, 600 E Greenfield Ave., Milwaukee, WI 53204, USA

Abstract. Time series water samples were collected monthly between November 2016 and June 2019 from the Lower Changjiang (Yangtze) River at the Xuliujing station, representing the end-member freshwater exported to the ocean, in addition to monthly samples from November 2019 to January 2020 during an extreme drought event. Concentrations of dissolved (DOC) and particulate organic carbon (POC) as well as the stable isotopic composition of POC and PN (particulate nitrogen) were measured to elucidate their seasonal variations. Ultrafiltration was also conducted for selected samples to separate the bulk DOC into four different size-fractions to further examine changes in the molecular weight distribution of DOC. The seasonal variations of POC were characterized with higher proportions of autochthonous components in summer and lower proportions in winter on the basis of POC contents (% of total suspended particulate matter), δ13C, δ15N, and POC/PN values. The size spectra of DOC also illustrated a distinct seasonal variation pattern, although the different responses to different seasons were also shown between HMW- (high-molecular-weight) and LMW- (low-molecular-weight) DOC compounds. The strong correlation of δ13C values between HMW-DOC and POC suggested their close relationships in terms of origin and composition. Together with available literature data, DOC concentrations, POC (%), δ13C, and δ15N all showed a significant increase over the past decades, likely resulting from increase in the proportion of autochthonous organic components owing to intensified human activities and global warming in the river basin.

Yue Ming et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-30', Xuchen Wang, 24 Mar 2022
    • AC1: 'Reply on RC1', Yue Ming, 17 May 2022
  • RC2: 'Comment on egusphere-2022-30', Anonymous Referee #2, 03 Apr 2022
    • AC2: 'Reply on RC2', Yue Ming, 17 May 2022
  • RC3: 'Comment on egusphere-2022-30', Anonymous Referee #3, 06 Apr 2022
    • AC3: 'Reply on RC3', Yue Ming, 17 May 2022

Yue Ming et al.

Yue Ming et al.

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Short summary
According to our results, we found that the variations of POC were characterized with higher proportions of autochthonous components in summer and the size spectra of DOC illustrated a distinct seasonal variation pattern. Moreover, the strong correlation of δ13C values between HMW-DOC and POC suggested their relationships in origin and composition. Together with available literature data, DOC concentrations, POC (%), δ13C, and δ15N all showed a significant increase over the past decades.