Preprints
https://doi.org/10.5194/egusphere-2022-1375
https://doi.org/10.5194/egusphere-2022-1375
 
13 Dec 2022
13 Dec 2022
Status: this preprint is open for discussion.

A DOM continuum from the roof of the world – Tibetan molecular dissolved organic matter characteristics track sources, land use effects, and processing along the fluvial-limnic pathway

Philipp Maurischat1,2, Michael Seidel3, Thorsten Dittmar3,4, and Georg Guggenberger1 Philipp Maurischat et al.
  • 1Leibniz University Hannover, Institute of Soil Science, 30419 Hannover, Germany
  • 2Institute of Biology and Environmental Sciences (IBU), Carl von Ossietzky University of Oldenburg, 26129 Oldenburg, Germany
  • 3Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, 26129 Oldenburg, Germany
  • 4Helmholtz Institute for Functional Marine Biodiversity at the University of Oldenburg (HIFMB), 26129 Oldenburg, Germany

Abstract. The Tibetan Plateau (TP) is the world largest and highest plateau, also comprising the biggest connected alpine pasture system of the world. Like other alpine systems, it is sensitive to impacts by climate change and increasing anthropogenic pressure. Carbon cycling at the TP is complex, including sources such as primary production in lakes, glaciers, and terrestrial plants, agricultural land use but also organic matter (OM) from aeolian deposition. Dissolved organic matter (DOM) connects these carbon reservoirs in the network, following the hydrological cycle from precipitation, glaciers, and headwaters to lakes. DOM is highly complex, its molecular composition holds information from its diverse sources and transformations during transport. However, due to its complexity, DOM cycling along the headwater-fluvial-limnic pathway and how terrestrial change can impact carbon cycling in the diverse water bodies is still not well understood. Here, we study DOM molecular transformations using ultrahigh-resolution mass spectrometry (FT-ICR-MS) along the TP alpine continuum from glacial, groundwater springs, and wetland biomes including pastures and alpine steppe, to the large saline endorheic Lake Nam Co. DOM molecular composition differed with respect to allochthonous sources between endmembers, as well as between stream samples, the brackish mixing zone, and the lake. Glacial meltwater DOM contained autochthonous signatures of low-oxidised, unsaturated molecular formulae together with terrestrial-like, dust-borne DOM sources. Glacial-fed streams were characterised by fresh autochthonous, probably algal DOM, and aromatic compounds likely originating from pastoral land sources. DOM from a groundwater spring had a highly degraded, strongly oxidised signature, probably related to the shallow upper aquifer, and degraded pastoral land sources. Wetland and stream DOM were characterised by less oxidised and less degraded inputs from vascular plants and soils. At the brackish zone of the lake shore, DOM contained a mixture of lake- and terrestrial DOM inherited from the streams. At Lake Nam Co, depletion of aromatic terrestrial molecular formulae suggested photooxidation at the surface, and relative enrichment of potentially recalcitrant DOM within the lake. Additionally, a relative enrichment of more aliphatic, nitrogen-containing DOM suggests autochthonous algal and microbial DOM sources in the lake. Our study revealed that DOM composition was largely influenced by local sources and transformations in glaciers, wetlands, and groundwater springs, also incorporating molecular signatures of pasture degradation. Streams with less glacial influence had plant- and soil borne aromatic-rich DOM sources, while the endorheic Lake Nam Co had a recalcitrant DOM composition comparable to millennial-scale stable marine DOM. This suggests that there is no typical high-alpine DOM signature, but that complex processes form DOM characteristics in the fluvial-limnic continuum. Small-scale catchment properties, land degradation and aquatic domains shape the differences. Alpine DOM compositions hence appear to be closely linked to landscape properties suggesting their susceptibility to changes in water quality and OM cycling in sensitive High Asian ecosystems.

Philipp Maurischat et al.

Status: open (until 07 Feb 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1375', Anonymous Referee #1, 22 Dec 2022 reply
  • RC2: 'Comment on egusphere-2022-1375', Anonymous Referee #2, 19 Jan 2023 reply

Philipp Maurischat et al.

Philipp Maurischat et al.

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Short summary
Production and consumption of organic matter (OM) on the Tibetan Plateau are important for the this sensitive ecosystem. We investigated the chemical composition of dissolved organic matter, the most mobile fraction of OM in glaciers, wetlands and groundwater as well as in the rivers and a large terminal lake. Our data show that the sources differ in the molecular composition of OM, that the stream is influenced by agriculture and that the lake strongly changes the inflowing organic matter.