Assessment of the provenance of organic matter discharged from a permafrost watershed (Lena River) using lignin phenols

Gesine.Mollenhauer [ at ]


The Lena River (central Siberia) is one of the substantial pathways shifting terrestrial organic matter from its catchment area to the coastal zone of the Laptev Sea and the Arctic Ocean. The permafrost soils, which store huge amounts of OM, will most likely respond differently to climate warming and remobilize previously frozen OM with distinct properties specific for the source vegetation and soil. Particulate organic matter (POM) discharged by rivers and deposited close to their mouth is commonly assumed to record an integrated signal from the watershed. Furthermore, the POM likely undergoes degradation during its transport from source to sink. Therefore, investigating the different organic matter (OM) sources within a watershed will improve our understanding of OM sources and transport in large river systems. The present study investigated the composition of organic matter (OM) along the land–ocean continuum by characterizing lignin phenol composition in different grain size fraction in soils from the different vegetation zones (the boreal and northern Taiga and the Tundra) and marine surface sediments collected in the south-east Laptev Sea. Lignin is the rigidifying component of terrestrial higher plants, and it consists of different phenolic units, which allow to distinguish different vegetation sources, such as woody and non-woody tissues as well as gymnosperm and angiosperm tissues. The end-member calibration with plant tissues show that the taiga soils are dominated by gymnosperms, what reflect the predominant vegetation in the southern watershed of the Lena river, and that the actual tundra soils show a maximum angiosperm percentage of 50 %. In this case, the high S/V values in the marine surface sediments provide a further angiosperm source beside the watershed. The analyzes of the grain size fractions show that the finer fraction is generally more degraded than the coarser fraction in the soils, as well as in the marine surface sediments, which could be assume that the finer grain size fraction is transported more likely, e.g. during the spring freshet. All in all, the study indicated that in the marine sediments angiosperm tissues are more important than assumed in previous studies, in particular in the coarse grain size fraction, and that the gymnosperm signal in the marine sediments could be a real gymnosperm vegetation signal and not a result of high degradation as presumed before.

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Thesis (Master)
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Not peer-reviewed
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Trojahn, S. (2016): Assessment of the provenance of organic matter discharged from a permafrost watershed (Lena River) using lignin phenols , Master thesis, Universität Bremen.


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