EGU2020-9015
https://doi.org/10.5194/egusphere-egu2020-9015
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Influence of organic matter quality on organic matter degradability in river sediments

Florian Zander1, Julia Gebert1, Rob N. J. Comans2, Alexander Groengroeft3, Timo J. Heimovaara1, and Annette Eschenbach3
Florian Zander et al.
  • 1TU Delft, Civil Engineering and Geosciences, Geoscience & Engineering, Den Haag, The Netherlands (f.zander@tudelft.nl)
  • 2Wageningen University and Research, Environmental Sciences, Wageningen, The Netherlands (rob.comans@wur.nl)
  • 3University of Hamburg, Earth Sciences, Hamburg, Germany (annette.Eschenbach@uni-hamburg.de)

The project BIOMUD, part of the scientific network MUDNET (www.tudelft.nl/mudnet), investigates the decomposition of sediment organic matter (SOM) in the Port of Hamburg. The microbial turnover of sediment organic matter under reducing conditions leads to the formation of methane, carbon dioxide and others gases causing a change in the sediment rheological parameters. BIOMUD is aiming to explain the effect of organic matter lability on the rheological properties impacting the navigable depth of the harbour.

Samples of freshly deposited material were taken in 2018 and 2019 at nine locations in a transect of 30 km through the Port of Hamburg. Analyses included abiotic parameters (among others grain size distribution, standard pore water properties, standard solid properties, stable isotopes, mineral composition) and biotic parameters (among others anaerobic and aerobic organic matter degradation, DNA, protein and lipid content, microbial population). At four locations, physical density fractions and chemical organic matter fractions were analysed.

The quality of organic matter was described by normalising carbon released from microbial degradation under both aerobic and anaerobic conditions to the share of total organic carbon (mg C/g TOC). Organic matter pools with different degradation rates were used to quantify the lability of organic matter. The share of faster degradable (more labile) pools correlated strongly with the size of the hydrophilic DOC fraction, confirming results of Straathof et al. (2014) who investigated dissolved organic carbon pools in compost. The hydrophilic DOC fraction was closely correlated to the polysaccharide concentration, explaining the input of easily degradable organic matter. Moreover, the amount of organic carbon present in the sediment’s light density fraction < 1.4 g/cm3 strongly correlated with the hydrophilic DOC fraction and, less strongly, with organic matter lability. High organic matter quality, i.e. the labile, easily degradable fraction, was further related to the chlorophyll concentration in the water column but also the ammonium concentration in the sediment’s pore water.

It was hypothesised that the observed toposequence of decreasing organic matter quality from upstream to downstream could be explained by a chronosequence of increasing degradation and therefore ageing of organic matter as the sediment passes through the harbour area. Further, it was hypothesized that the harbour received organic matter of higher degradability, originating from phytoplankton biomass, from the upstream part of the Elbe river, whereas the input from the tidal downstream area provided organic matter of lower quality (degradability).

This study was funded by Hamburg Port Authority.

How to cite: Zander, F., Gebert, J., Comans, R. N. J., Groengroeft, A., Heimovaara, T. J., and Eschenbach, A.: Influence of organic matter quality on organic matter degradability in river sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9015, https://doi.org/10.5194/egusphere-egu2020-9015, 2020

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Presentation version 2 – uploaded on 04 May 2020
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  • CC1: Comment on EGU2020-9015, Damien Cardinal, 04 May 2020

    Dear Florian

    Thx for this nice presentation and exhaustive data. I'm interested in silicon cycle and I'd like to have more information on the data displayed slide 17. This data is from porewater after degradation experiments presented before? Then on which sediment depth layer? Why algae would produce silicic acid? You mean dissolution from opal?

    Best

    Damien

  • AC1: Comment on EGU2020-9015, Florian Zander, 04 May 2020

    Dear Damien,

    Thank you for your questions.

    The data are from pore water before degradation happened, basically directly after sampling. These data are from the pre-consolidated layer (PS), i.e. the (freshly) consolidated layer. Algae like diatoms are meant as silicon producer – more diatoms at areas with higher silicic acid concentration.

    Best,
    Florian

Presentation version 1 – uploaded on 04 May 2020 , no comments