Maurischat, Philipp;
Seidel, Michael;
Dittmar, Thorsten;
Guggenberger, Georg
Complex dissolved organic matter (DOM) on the roof of the world – Tibetan DOM molecular characteristics indicate sources, land use effects, and processing along the fluvial–limnic continuum
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Media type:
E-Article
Title:
Complex dissolved organic matter (DOM) on the roof of the world – Tibetan DOM molecular characteristics indicate sources, land use effects, and processing along the fluvial–limnic continuum
Contributor:
Maurischat, Philipp;
Seidel, Michael;
Dittmar, Thorsten;
Guggenberger, Georg
Published:
Copernicus GmbH, 2023
Published in:
Biogeosciences, 20 (2023) 14, Seite 3011-3026
Language:
English
DOI:
10.5194/bg-20-3011-2023
ISSN:
1726-4189
Origination:
Footnote:
Description:
Abstract. The Tibetan Plateau (TP) is the world's largest and highest plateau, comprising the earth's biggest alpine pasture system. It is sensitive tothe impacts of climate change and anthropogenic pressure. Carbon cycling on the TP is influenced by glaciation and degradation of the pastureecosystem. Dissolved organic matter (DOM) connects carbon reservoirs, following the hydrological continuum from glaciers and headwaters tolakes. Due to its complexity, DOM cycling along the aquatic continuum and the impact of land use and climate change on DOM characteristics are stillnot well understood. Here, we study solid phase extracted (SPE) DOM molecular characteristics using ultrahigh-resolution mass spectrometry(FT-ICR-MS) along the TP hydrological continuum from glaciers, groundwater springs, and wetlands, including pastures and alpine steppes, to theendorheic Lake Nam Co. Our study revealed that the SPE-DOM composition was largely influenced by local sources of glaciers, wetlands, andgroundwater springs as well as pasture degradation. Glacial meltwater SPE-DOM contained more saturated compounds suggesting microbial sourcestogether with aromatic compounds probably derived from aeolian deposition. In comparison, wetland and stream SPE-DOM were characterised by a higherpercentage of highly unsaturated and aromatic molecular formulae. These were likely derived from inputs of vascular plants and soils. Groundwaterspring SPE-DOM from degraded pastures differed from intact pasture samples. In degraded systems a strongly oxidised signature with the lowest counts ofP heteroatoms, a lower O/C ratio, and a higher aromaticity of SPE-DOM together with a high degradation index suggested a strongtransformation of SPE-DOM. SPE-DOM of the endorheic lake was richer in unsaturated molecular formulae compared to the tributaries. This suggestsalgae and microbial sources and production in the lake. The SPE-DOM rich in aromatic and highly unsaturated formulae visible in the brackish zone ofthe lake shore contrasted sharply with that of the lake. Aromatic molecular formulae were strongly depleted in the lake deep watersuggesting photooxidation of riverine SPE-DOM. This indicates that alpine SPE-DOM signatures are shaped by small-scale catchment properties, landdegradation, and the influence of glaciers and wetlands. The close link of alpine SPE-DOM composition to landscape properties is indicative of astrong susceptibility of DOM characteristics to climatic and land use changes in High Asia.