Global distribution of dissolved organic matter along the aquatic continuum: Across rivers, lakes and oceans

Philippe Massicotte; Eero Asmala; Colin Stedmon; Stiig Markager

doi:10.1016/j.scitotenv.2017.07.076

Global distribution of dissolved organic matter along the aquatic continuum: Across rivers, lakes and oceans

Sci Total Environ. 2017 Dec 31:609:180-191. doi: 10.1016/j.scitotenv.2017.07.076. Epub 2017 Jul 26.

Authors

Philippe Massicotte¹, Eero Asmala², Colin Stedmon³, Stiig Markager²

Affiliations

¹ Aarhus University, Department of Bioscience, Frederiksborgvej 399, DK-4000 Roskilde, Denmark. Electronic address: philippe.massicotte@takuvik.ulaval.ca.
² Aarhus University, Department of Bioscience, Frederiksborgvej 399, DK-4000 Roskilde, Denmark.
³ Technical University of Denmark, National Institute for Aquatic Resources, Section for Marine Ecology and Oceanography, Kavalergården 6, 2920 Charlottenlund, Denmark.

PMID: 28738200
DOI: 10.1016/j.scitotenv.2017.07.076

Abstract

Based on an extensive literature survey containing more than 12,000 paired measurements of dissolved organic carbon (DOC) concentrations and absorption of chromophoric dissolved organic matter (CDOM) distributed over four continents and seven oceans, we described the global distribution and transformation of dissolved organic matter (DOM) along the aquatic continuum across rivers and lakes to oceans. A strong log-linear relationship (R²=0.92) between DOC concentration and CDOM absorption at 350nm was observed at a global scale, but was found to be ecosystem-dependent at local and regional scales. Our results reveal that as DOM is transported towards the oceans, the robustness of the observed relation decreases rapidly (R² from 0.94 to 0.44) indicating a gradual decoupling between DOC and CDOM. This likely reflects the decreased connectivity between the landscape and DOM along the aquatic continuum. To support this hypothesis, we used the DOC-specific UV absorbance (SUVA) to characterize the reactivity of the DOM pool which decreased from 4.9 to 1.7m² × gC^-1 along the aquatic continuum. Across the continuum, a piecewise linear regression showed that the observed decrease of SUVA occurred more rapidly in freshwater ecosystems compared to marine water ecosystems, suggesting that the different degradation processes act preferentially on CDOM rather than carbon content. The observed change in the DOM characteristics along the aquatic continuum also suggests that the terrestrial DOM pool is gradually becoming less reactive, which has profound consequences on cycling of organic carbon in aquatic ecosystems.

Keywords: Absorption; Biogeochemistry; Carbon cycling; Chromophoric dissolved organic matter (CDOM); Dissolved organic carbon (DOC); Specific UV absorbance (SUVA).