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
<p>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 pastu...
Main Authors: | , , , |
---|---|
Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2023-07-01
|
Series: | Biogeosciences |
Online Access: | https://bg.copernicus.org/articles/20/3011/2023/bg-20-3011-2023.pdf |
Summary: | <p>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
<span class="inline-formula">P</span> heteroatoms, a lower <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">O</mi><mo>/</mo><mi mathvariant="normal">C</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="aa3ee63d16a9544135a7a9f6ec90028c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-3011-2023-ie00001.svg" width="25pt" height="14pt" src="bg-20-3011-2023-ie00001.png"/></svg:svg></span></span> 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.</p> |
---|---|
ISSN: | 1726-4170 1726-4189 |