17 Aug 2023
 | 17 Aug 2023
Status: this preprint is currently under review for the journal BG.

Quantification of allochthonous and autochthonous organic carbon in large and shallow Lake Wuliangsu based on distribution patterns and δ13C signatures of n-alkanes

Qingfeng Zhao, Aifeng Zhou, and Yuxin He

Abstract. Identification and quantification of allochthonous and autochthonous organic carbon (OC) are crucial for the interpretation of burial behaviors of sedimentary OC of shallow lakes under anthropogenic interferences. In this study, we analyzed distribution patterns and δ13C signatures of mid- and long-chain n-alkanes on various types of surface samples from a typically large and shallow Lake Wuliangsu in the Hetao Irrigation District. The results indicate that n-alkanes among submerged macrophytes, emergent plants, and riverine soil show unique distribution patterns and δ13C signatures, supporting the practicability of quantification on OC of these sources by end-member mixing models. Introducing the δ13C values of n-alkanes into the end-member mixing models could effectively reduce the potential error derived from end-member determination on n-alkane distribution patterns and OC degradation. The model results suggest that the riverine sourced OC from the main channel to Lake Wuliangsu has settled down during the southward migration process. Therefore, Lake Wuliangsu serves as an important trap and sink for the allochthonous OC from the Upper Yellow River Reaches. The model results also show a predominate contribution from the autochthonous OC to Lake Wuliangsu (mostly >85 %), with open-water areas dominated by submerged macrophytes and the rest of areas by emergent plants, largely modulated by water transparency, water depth, and nutrient concentrations. Together with previously published tetraether results, we further proposed that areas dominated by submerged macrophytes might be more favorable for heterotrophic anaerobic bacteria and methanogenic archaea, largely due to active recycling processes for the labile OC derived from submerged macrophytes.

Qingfeng Zhao et al.

Status: open (until 04 Oct 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2023-134', Anonymous Referee #1, 23 Aug 2023 reply
    • AC1: 'Reply on RC1', Yuxin He, 02 Sep 2023 reply
  • RC2: 'Comment on bg-2023-134', Anonymous Referee #1, 04 Sep 2023 reply
  • RC3: 'Comment on bg-2023-134', Anonymous Referee #2, 07 Sep 2023 reply

Qingfeng Zhao et al.

Qingfeng Zhao et al.


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Short summary
We presented a quantitative method to calculate the contributions of different OC sources to a shallow lake by combining distribution pattern and δ13C values of n-alkanes. This method could be more accurate than the one from bulk organic proxies, and effectively reduce the potential impacts from OC degradation. The results indicate that submerged macrophytes mainly situated in open water zone could play a more important role inducing stronger both OC accumulation and CH4 production.