the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Dec 2025
Microbial role in CO2 fluxes along the river-estuary continuum in a rapidly uplifting catchment of eastern Taiwan
Abstract. The contribution of river metabolisms to carbon cycling is an essential issue, but not well examined in the catchment susceptible to the modulation of active tectonics. This study aims to quantify the rates of autotrophy and heterotrophy, and to identify the community compositions and potential members involved in these microbial processes in the Beinan River in eastern Taiwan. To address this, river water samples were collected in both the wet and dry seasons for incubations amended with 13C-labeled dissolved carbon dioxide and amino acids. The analyses revealed a general pattern pointing to the higher rates in the wet season than in the dry season, and for heterotrophy than for autotrophy. The obtained rates were further scaled up, resulting in the catchment-scale CO2 evasion of ~ 107 mole yr-1, a range constituting several percent of the CO2 flux derived from pyrite-induced weathering, oxidation of petrogenic carbon, and the river-air exchange. The community compositions generally varied with season for most upstream sites and with more abundant sulfur or nitrogen metabolizers in the wet season, as opposed to more abundant phototrophs or heterotrophs in the dry season. This study highlights the complex and dynamic nature of river metabolisms that contribute to carbon evasion in oligotrophic mountainous systems prone to the impacts of rapid uplift and erosion.
- Preprint
(6364 KB) - Metadata XML
-
Supplement
(6178 KB) - BibTeX
- EndNote
Status: open (extended)
- RC1: 'Comment on egusphere-2025-5904', Anonymous Referee #1, 20 Feb 2026 reply
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 195 | 145 | 28 | 368 | 30 | 21 | 24 |
- HTML: 195
- PDF: 145
- XML: 28
- Total: 368
- Supplement: 30
- BibTeX: 21
- EndNote: 24
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
Review Biogeosciences 2025-5904
Microbial role in CO2 fluxes along the river-estuary continuum in a rapidly uplifting catchment of eastern Taiwan.
Chen et al.
This manuscript describes the role of microbial CO2 fluxes along a river-estuary continuum in Taiwan. The specific situation with an uplifting catchment because of active tectonics is identified as a unique feature of this catchment study.
This study can reduce the bias towards river continuum studies in low altitude; temperate catchment as opposed to mountainous catchments. However, apart from better data coverage of CO2 exchange from mountainous catchments it is important to stress that insights this study, performed in a unique tectonic situation and related dynamic turbid river systems can bring new insights to the current field of river metabolism studies.
The study aims to disentangle assimilation rates and respiration rates of different metabolisms with 13C labelling techniques using DIC and amino acids. Furthermore, microbial community compositions were determined based on 16S rRNA gene tags. Sampling took place at different sampling sites in the Beinan river system. Specific metabolic rates were measured during four of seven field campaigns.
The results of this study give an indication of the size of the yearly CO2 evasion of the whole catchment and show seasonal shifts in the dominant metabolism in upstream systems waters between the wet and dry season.
General comments
This is a nice and thorough study on metabolic rates in dynamic turbid river systems in a tectonic active area. The use of isotopic labelling of DIC and amino acids in combination with environmental parameter measured in field campaigns and characterisation of the microbial community composition is an impressive achievement. Although at some point it is questionable if all this information in one paper is contributing to the communication of the main message and findings (e.g. are alpha diversity, Shannon index beta diversity needed?). The storyline can be strengthened in the intro and discussion if more focussed hypothesis are formulated.
The objective of this study was to get insights in the role of microbial CO2 fluxes at catchment scale and disentangling the metabolic processes of autotrophic and heterotrophic CO2 exchange in these understudied dynamic mountainous river systems in contrast to the more stable low-land catchments. The sampling strategy and major findings reported (seasonal shifts in metabolic wet-vs dry), although nice, do not seem to fully comply with my view of a study major strength to determine the effect of event-based flushes of groundwater and sediments on CO2 fluxes.
Furthermore, while Wang et al 2024 identified the effects of hot springs on the enrichment of waters with bicarbonate in the same sample locations in the tectonic active Beinan catchment this is not mentioned in this study. Is this not relevant in the total CO2 flux or is it included?
What about redox situation in the streams influenced by tectonics? Is CH4 exchange not relevant?
Specific comments
Abstract line 18 “several percent” please be more specific here. 107mol yr-1 from microbial origin vs annual total emission across the catchment 2,6 .109 ? (Line 295)
Line 38 landscape controlled or is it more topographically controlled?
Line 68 term “individual metabolisms” needs more clarification.
Lines 59-61 The information in this sentence is essential why this study in a rapid uplifting area is so different from the dominant body of literature in this field which is performed on the cratonic continent. While this relation between tectonics and torrential precipitation is a probably obvious for the authors this is not evident for everyone. It would help the storyline if this is relation between tectonics and dynamic, turbid high energy river systems is more explicit.
The expected deviations from the general bentic and hyporheic processes due to the turbid and dynamic river systems can be formulated more explicitely in hypothesis which will give ther reader more guidelines for interpretation in the result section.
Line 107-108, The selection of the 5 sample locations along the Beinan rver and tributaries is not explained. Which criteria were used to determine these sample sites? Likewise no argumentation is provided for the selection of sample moments/ timing. As the dynamic nature of the Beinan river is a part of the research objective the regular bi-monthly sampling scheme is surprising. One would expect a focus on events ( hot moments) and baseline moments.
Line 115. The use of cellulose membranes is not common practice and strongly discouraged in research on carbon dynamics due to the risks of contamination. Especially for DOC determination. The same is true for the use of polypropylene sample containers (risk of DOC contamination).
Line 386: is this influenced or correlation based?
Technical corrections
Figure 3 needs a more elaborate figure caption.