Dissolved organic matter dynamics in the pristine Krka River estuary (Croatia)

Marcinek, Saša; Santinelli, Chiara; Cindrić, Ana-Marija; Evangelista, Valtere; Gonnelli, Margherita; Layglon, Nicolas; Mounier, Stéphane; Lenoble, Véronique; Omanović, Dario (2020) Dissolved organic matter dynamics in the pristine Krka River estuary (Croatia). Marine Chemistry, 225 . ISSN 0304-4203

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Abstract

The karstic Krka River is characterized by having lower dissolved organic carbon (DOC) concentrations (~30 μM) than coastal seawater (~60 μM). This peculiarity, together with the pristine nature of this area, makes the Krka River estuary a natural laboratory where it is possible to discriminate among the different dissolved organic matter (DOM) sources (riverine, marine and produced in-situ) and to study the main processes of DOM production and removal. The hypothesis behind this work is that in winter, due to the high discharge of the river, most of the DOM has a terrestrial signature, whereas in summer autochthonous DOM compose the main fraction of the DOM pool because of the reduced discharge, the high temperature and primary production. Our data shows that DOM in the river mainly consists of terrestrial molecules, as suggested by the high chromophoric content and low spectral slope (S275–295) values, as well by the predominance of humic-like substances. DOM in the seawater features the concentration and optical properties of the “typical” marine DOM from open sea waters. In summer, low riverine discharge and high temperature promote the intense biological activity, with an increase in DOC concentrations of up to 148 μM, resulting in a non-conservative behavior of DOM in the estuary. The high stratification combined with a decoupling between production and removal processes can explain the observed DOM accumulation. In the bottom layer DOM was released and quickly removed when oxygen was available, whereas in hypoxic waters the production of DOC, chromophoric DOM (CDOM) and fluorescent DOM (FDOM) was linearly related to oxygen consumption. Our work highlights the need of further studies combining chemical and biological information in order to gain new insights into the main processes responsible for DOM dynamics in this system.

Item Type:	Article
Uncontrolled Keywords:	chromophoric dissolved organic matter (CDOM); dissolved organic carbon (DOC); excitation-emission matrices (EEMs); PARAFAC; Krka River estuary; stratified estuary; in-situ production; terrestrial DOM
Subjects:	NATURAL SCIENCES > Interdisciplinary Natural Sciences NATURAL SCIENCES > Interdisciplinary Natural Sciences > Marine Science
Divisions:	Division for Marine and Enviromental Research
Projects:	Project title Project leader Project code Project type Novi metodološki pristup biogeokemijskim istraživanjima specijacije metala u tragovima u obalnim vodenim ekosustavima-MEBTRACE Dario Omanović IP-2014-09-7530 HRZZ
Depositing User:	Dario Omanović
Date Deposited:	12 Nov 2021 14:24
URI:	http://fulir.irb.hr/id/eprint/6629
DOI:	10.1016/j.marchem.2020.103848

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