Rapid soil organic carbon decomposition in river systems: effects of the aquatic microbial community and hydrodynamical disturbance
<p>Different erosion processes deliver large amounts of terrestrial soil organic carbon (SOC) to rivers. Mounting evidence indicates that a significant fraction of this SOC, which displays a wide range of ages, is rapidly decomposed after entering the river system. The mechanisms explaining th...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-03-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/18/1511/2021/bg-18-1511-2021.pdf |
| Summary: | <p>Different erosion processes deliver large amounts of terrestrial
soil organic carbon (SOC) to rivers. Mounting evidence indicates that a
significant fraction of this SOC, which displays a wide range of ages, is
rapidly decomposed after entering the river system. The mechanisms
explaining this rapid decomposition of previously stable SOC still remain
unclear. In this study, we investigated the relative importance of two
mechanisms that possibly control SOC decomposition rates in aquatic systems:
(i) in the river water SOC is exposed to the aquatic microbial community
which is able to metabolize SOC much more quickly than the soil microbial
community and (ii) SOC decomposition in rivers is facilitated due to the
hydrodynamic disturbance of suspended sediment particles. We performed
different series of short-term (168 h) incubations quantifying the rates of
SOC decomposition in an aquatic system under controlled conditions. Organic
carbon decomposition was measured continuously through monitoring dissolved
O<span class="inline-formula"><sub>2</sub></span> (DO) concentration using a fiber-optic sensor (FireStingO<span class="inline-formula"><sub>2</sub></span>,
PyroScience). Under both shaking and standing conditions, we found a
significant difference in decomposition rate between SOC with aquatic
microbial organisms added (SOC <span class="inline-formula">+</span> AMO) and without aquatic microbial
organisms (SOC <span class="inline-formula">−</span> AMO). The presence of an aquatic microbial community enhanced
the SOC decomposition process by 70 %–128 % depending on the soil type and
shaking–standing conditions. While some recent studies suggested that
aquatic respiration rates may have been substantially underestimated by
performing measurement under stationary conditions, our results indicate
that the effect of hydrodynamic disturbance is relatively minor, under the
temperature conditions, for the soil type, and for the suspended matter
concentration range used in our experiments. We propose a simple conceptual
model explaining these contrasting results.</p> |
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| ISSN: | 1726-4170 1726-4189 |