From Fresh to Marine Waters: Characterization and Fate of Dissolved Organic Matter in the Lena River Delta Region, Siberia

Rafael Gonçalves-Araujo,Astrid Bracher,Ivan Dubinenkov,Birgit Heim,Alexandra Kraberg,Denis Moiseev,Colin A Stedmon

doi:10.3389/fmars.2015.00108

Abstract

Connectivity between the terrestrial and marine environment in the Artic is changing as a result of climate change, influencing both freshwater budgets and the supply of carbon to the sea. This study characterizes the optical properties of dissolved organic matter (DOM) within the Lena Delta region and evaluates the behavior of DOM across the fresh water-marine gradient. Six fluorescent components (four humic-like; one marine humic-like; one protein-like) were identified by Parallel Factor Analysis (PARAFAC) with a clear dominance of allochthonous humic-like signals. Colored DOM (CDOM) and dissolved organic carbon (DOC) were highly correlated and had their distribution coupled with hydrographical conditions. Higher DOM concentration and degree of humification were associated with the low salinity waters of the Lena River. Values decreased towards the higher salinity Laptev Sea shelf waters. Results demonstrate different responses of DOM mixing in relation to the vertical structure of the water column, as reflecting the hydrographical dynamics in the region. Two mixing curves for DOM were apparent. In surface waters above the pycnocline there was a sharper decrease in DOM concentration in relation to salinity indicating removal. In the bottom water layer the DOM decrease within salinity was less. We propose there is a removal of DOM occurring primarily at the surface layer, which is likely driven by photodegradation and flocculation.

Highlights

Colored or chromophoric dissolved organic matter (CDOM) is the fraction of DOM that absorbs light and it is one of the dominant components influencing the underwater light field in coastal and inner-shelf waters (Siegel et al, 2002; Nelson and Siegel, 2013)
Temperature ranged from -1.2 to 10.3◦C, with higher values related to the warmer and fresher Lena river plume and the lowest values attributed to the presence of the colder and saltier Laptev Sea shelf waters
Our results demonstrate that the Fluorescent DOM (FDOM) composition in the Lena Delta region was mainly characterized by the dominance of riverine humic-like compounds

Summary

Introduction

Colored or chromophoric dissolved organic matter (CDOM) is the fraction of DOM that absorbs light and it is one of the dominant components influencing the underwater light field in coastal and inner-shelf waters (Siegel et al, 2002; Nelson and Siegel, 2013). With the recent adaptation of the Parallel Factor Analysis (PARAFAC) for analysis of DOM, a more holistic analysis of excitation-emission matrices (EEMs) allows for the differentiation of wider range of underlying DOM components (Stedmon and Bro, 2008). A recent study showed significant associations between molecular groups and PARAFAC-derived DOM components (Stubbins et al, 2014). The humic-like fluorescent peak A (e.g., Coble, 2007) is associated with high molecular weight compounds with little nitrogen, whereas the humic-like peak C correlated to lignin-derived phenols and the amino acid-like peak T was associated to low molecular weight and aromatic content compounds, such as hydrolysable amino acids (Stubbins et al, 2014)

Methods

Results

Discussion

Conclusion