Signatures of Molecular Unification and Progressive Oxidation Unfold in Dissolved Organic Matter of the Ob-Irtysh River System along Its Path to the Arctic Ocean

I V Perminova,A S Grigoryev,E N Nikolaev,O V Dudarev,N Shakhova,A Zherebker,I I Pipko,I P Semiletov,S P Pugach,E A Shirshin

doi:10.1038/s41598-019-55662-1

Abstract

The Ob-Irtysh River system is the seventh-longest one in the world. Unlike the other Great Siberian rivers, it is only slightly impacted by the continuous permafrost in its low flow. Instead, it drains the Great Vasyugan mire, which is the world largest swamp, and receives huge load of the Irtysh waters which drain the populated lowlands of the East Siberian Plain. The central challenge of this paper is to understand the processes responsible for molecular transformations of natural organic matter (NOM) in the Ob-Irtysh river system along the South-North transect. For solving this task, the NOM was isolated from the water samples collected along the 3,000 km transect using solid-phase extraction. The NOM samples were further analyzed using high resolution mass spectrometry and optical spectroscopy. The obtained results have shown a distinct trend both in molecular composition and diversity of the NOM along the South-North transect: the largest diversity was observed in the Southern “swamp-wetland” stations. The samples were dominated with humic and lignin-like components, and enriched with aminosugars. After the Irtysh confluence, the molecular nature of NOM has changed drastically: it became much more oxidized and enriched with heterocyclic N-containing compounds. These molecular features are very different from the aliphatics-rich permafrost NOM. They witnesses much more conservative nature of the NOM discharged into the Arctic by the Ob-Irtysh river system. In general, drastic reduction in molecular diversity was observed in the northern stations located in the lower Ob flow.

Highlights

Arctic ecosystems are most vulnerable both to global climate change and to its consequences
Each tributary had its specific biogeochemical features associated with the landscape-geochemical characteristics of the drained areas; the signal of these waters could be traced in the mainstream of the Ob River
Application of FTICR MS and optical spectroscopy for molecular analysis of DOM sampled along the South-North transect of the Ob-Irtysh river system showed qualitative and quantitative trends in its molecular composition

Summary

Introduction

Arctic ecosystems are most vulnerable both to global climate change and to its consequences. Due to the size and length of the Irtysh river, its confluence transforms the Ob river into the Ob-Irtysh river system This makes the study of molecular components of the NOM in the Ob – Irtysh river system of particular importance for understanding evolution of the Arctic ecosystems under conditions of global climate change. We believe that this study might fill in this gap and provide the missing data on molecular fingerprints of the Ob – Irtysh river basin, which drains the largest swamp in the world - the Great Vasyugan Mire, and stretches over the multiple climatic zones. The main objective of this study was to assess transformation of molecular composition of NOM along the 3,000 km transect of the Ob-Irtysh river system from the Ob Bay (Kara Sea) up to its confluence with the Tom’. All three features are important for understanding the transformation pattern of NOM in the fluvial system of the Ob-Irtysh

Objectives

Results

Conclusion