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Communication Dans Un Congrès Année : 2021

Modification of the composition of dissolved organic matter during rain events; in search of genericity.

Résumé

The biogeochemistry of dissolved organic matter (DOM) is of main importance towards major societal issues such as biodiversity, climate change and water quality. Throughout surface hydrosystems, headwater catchments are the main contributors of the export of DOM with a specific emphasis on rain events that represent up to 80% of the annual export of DOM. This high proportion is not only due to the increase in discharge but also to an increase in dissolved organic carbon (DOC) concentrations. In the same time the composition of DOM has been shown to change during rain events with an increase in the aromaticity and also a modification of the composition of lignins, with the export of less biodegraded lignins with implications on the biodegradability of DOM. However this modification of the composition of lignins has been observed in only three catchments, which ask the question of its genericity? In order to answer this question, river waters were sampled in five French catchments from the OZCAR research infrastructure in base flow conditions and during rain events (Naizin, Strengbach, Roujan, Montoussé and Capesterre catchments). These catchments cover a range of climates: temperate oceanic, temperate continental, mediterranean and tropical. The concentrations of DOC were quantified and river waters were freeze-dried in order to isolate colloidal and dissolved substances (< 0.7 μm). The molecular composition of DOM was investigated by thermochemolysis coupled to gas chromatography and mass spectrometry that allows the simultaneous investigation of different classes of organic biomolecules such as carbohydrates, lignins, phospholipid fatty acids, cutin and suberin. These analyses were performed with an internal standard to make them semi- quantitative. First the sum of the concentrations of target compounds was correlated to the concentration of DOC, which highlights the fact that this set of molecules, although it is not exhaustive, is representative of the DOM compartment and can be used to investigate the fate of DOM at the soil-stream interface during rain events. Then the distribution of target compounds can differentiate aromatic compounds. Their proportion increased in the five catchments for all rain events, which is in line with the increase of aromaticity that is observed in other catchments throughout the worlds. This combination of previous and present observations seems to indicate that the increase in the aromaticity of DOM during rain events is generic. Moreover the magnitude of the increase and the absolute final values were catchment and event dependants. Finally the composition of lignins was modified in all catchments during rain events with the exception of the tropical catchment (Capesterre) and the snow event at the Strengbach catchment. Similarly to the proportion of the proportion of aromatic compounds the magnitude of the increase and the extreme values were catchment and event dependants. Rain events represent an hot moment for the export of less biodegraded lignins at the soil-stream interface, which may impact its fate in the hydrosystems and the export of micropollutants.
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Dates et versions

hal-03369834 , version 1 (07-10-2021)

Identifiants

  • HAL Id : hal-03369834 , version 1

Citer

Laurent Jeanneau, Ophélie Fovet, Mikael Faucheux, Gerard Gruau, Marie-Claire Pierret, et al.. Modification of the composition of dissolved organic matter during rain events; in search of genericity.. Advancing Critical Zone science. First OZCAR TERENO International Conference, Oct 2021, Strasbourg, France. ⟨hal-03369834⟩
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