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

verfasst von

Philipp Maurischat, Michael Seidel, Thorsten Dittmar, Georg Guggenberger

Abstract

The Tibetan Plateau (TP) is the world's largest and highest plateau, comprising the earth's biggest alpine pasture system. It is sensitive to the impacts of climate change and anthropogenic pressure. Carbon cycling on the TP is influenced by glaciation and degradation of the pasture ecosystem. Dissolved organic matter (DOM) connects carbon reservoirs, following the hydrological continuum from glaciers and headwaters to lakes. Due to its complexity, DOM cycling along the aquatic continuum and the impact of land use and climate change on DOM characteristics are still not 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 the endorheic Lake Nam Co. Our study revealed that the SPE-DOM composition was largely influenced by local sources of glaciers, wetlands, and groundwater springs as well as pasture degradation. Glacial meltwater SPE-DOM contained more saturated compounds suggesting microbial sources together with aromatic compounds probably derived from aeolian deposition. In comparison, wetland and stream SPE-DOM were characterised by a higher percentage of highly unsaturated and aromatic molecular formulae. These were likely derived from inputs of vascular plants and soils. Groundwater spring SPE-DOM from degraded pastures differed from intact pasture samples. In degraded systems a strongly oxidised signature with the lowest counts of P heteroatoms, a lower O/C ratio, and a higher aromaticity of SPE-DOM together with a high degradation index suggested a strong transformation of SPE-DOM. SPE-DOM of the endorheic lake was richer in unsaturated molecular formulae compared to the tributaries. This suggests algae and microbial sources and production in the lake. The SPE-DOM rich in aromatic and highly unsaturated formulae visible in the brackish zone of the lake shore contrasted sharply with that of the lake. Aromatic molecular formulae were strongly depleted in the lake deep water suggesting photooxidation of riverine SPE-DOM. This indicates that alpine SPE-DOM signatures are shaped by small-scale catchment properties, land degradation, and the influence of glaciers and wetlands. The close link of alpine SPE-DOM composition to landscape properties is indicative of a strong susceptibility of DOM characteristics to climatic and land use changes in High Asia.

Organisationseinheit(en)

Institut für Bodenkunde

Externe Organisation(en)

Carl von Ossietzky Universität Oldenburg

Typ

Artikel

Journal

BIOGEOSCIENCES

Band

20

Seiten

3011-3026

Anzahl der Seiten

16

ISSN

1726-4170

Publikationsdatum

27.07.2023

Publikationsstatus

Veröffentlicht

Peer-reviewed

Ja

ASJC Scopus Sachgebiete

Ökologie, Evolution, Verhaltenswissenschaften und Systematik, Erdoberflächenprozesse

Ziele für nachhaltige Entwicklung

SDG 13 – Klimaschutzmaßnahmen, SDG 15 – Lebensraum Land

Elektronische Version(en)

https://doi.org/10.5194/bg-20-3011-2023 (Zugang: Offen)