Kinetic and equilibrium studies of copper-dissolved organic matter complexation in water column of the stratified Krka River estuary (Croatia)

Abstract

To cite this version:Yoann Louis, Cédric Garnier, Véronique Lenoble, Stéphane Mounier, Neven Cukrov, et al.. Kinetic and equilibrium studies of copper-dissolved organic matter complexation in water column of the stratified Krka River estuary (Croatia). Marine Chemistry, Elsevier, 2009, 114, pp.An interaction of dissolved natural organic matter (DNOM) with copper ions in the water column of the stratified Krka River estuary (Croatia) was studied. The experimental methodology was based on the differential pulse anodic stripping voltammetric (DPASV) determination of labile copper species by titrating the sample using increments of copper additions uniformly distributed on the logarithmic scale. A classical at-equilibrium approach (determination of copper complexing capacity, CuCC) and a kinetic approach (tracing of equilibrium reconstitution) of copper complexation were considered and compared. A model of discrete distribution of organic ligands forming inert copper complexes was applied. For both approaches, a home-written fitting program was used for the determination of apparent stability constants (K i equ ), total ligands concentration (L iT ) and association/dissociation rate constants (k i 1 ,k i -1 ). A non-conservative behaviour of dissolved organic matter (DOC) and total copper concentration in a water column was registered. An enhanced biological activity at the freshwater-seawater interface (FSI) triggered an increase of total copper concentration and total ligand concentration in this water layer. The copper complexation in fresh water of Krka River was characterised by one type of binding ligands, while in most of the estuarine and marine samples two classes of ligands were identified. The distribution of apparent stability constants (log K 1 equ : 11.2-13.0, log K 2 equ :8.8-10.0) showed increasing trend towards higher salinities, indicating stronger copper complexation by autochthonous seawater organic matter. Copper complexation parameters (ligand concentrations and apparent stability constants) obtained by atequilibrium model are in very good accordance with those of kinetic model. Calculated association rate constants (k 1 1 :6.1-20 × 10 3 (M s) − 1 , k 2 1 : 1.3-6.3 × 10 3 (M s) − 1 ) indicate that copper complexation by DNOM takes place relatively slowly. The time needed to achieve a new pseudo-equilibrium induced by an increase of copper concentration (which is common for Krka River estuary during summer period due to the nautical traffic), is estimated to be from 2 to 4 h. It is found that in such oligotrophic environment (dissolved organic carbon content under 83 µM C , i.e. 1 mg C L − 1 ) an increase of the total copper concentration above 12 nM could enhance a free copper concentration exceeding the level considered as potentially toxic for microorganisms (10 pM).

Evidencing the natural and anthropogenic processes controlling trace metals dynamic in a highly stratified estuary: The Krka River estuary (Adriatic, Croatia)

“…In line with this, as the particulate fraction is low, the contribution of potentially released metals to the dissolved pool is also probably minor. The subsurface maximum within FSI layer previously reported to occur for organic matter and trace metals (Bilinski et al, 2000;Kniewald et al, 1987;Louis et al, 2009;Zutic and Legovic, 1987) was not registered in our study mainly due to insufficient number of points in the vertical profile (only three points, from which only one in FSI layer). In most cases, the concentrations in FSI layer for all metals were between those measured in two adjacent layers (Table 2).…”

“…First studies of trace metals , organic matter and SPM (Cauwet, 1991) and biological activities (Denant et al, 1991;Grzetic et al, 1991;Legovic et al, 1991a;Legovic et al, 1991b;Legovic et al, 1991c;Legovic et al, 1994) revealing the low pollution within the estuary were partially confirmed by more recent studies (Bilinski et al, 1992;Bilinski et al, 2000;Cetinic et al, 2006;Louis et al, 2009;Omanović et al, 2006;Supraha et al, 2014). An anthropogenic influence noticed in the estuary was mainly related to the increased nautical tourism in (Louis et al, 2009;Omanović et al, 2006).…”

“…Calibration was done with hydrogenophtalate (Shimadzu) and NaHCO3/Na2CO3 standard solutions, respectively, with an accuracy of 0.02 mg C L −1 (Louis et al, 2009;Oursel et al, 2013). A satisfactory accuracy of analyses was validated using certified reference material MISSIPPI-03 (Environment Canada).…”

“…microtidal estuaries) are especially vulnerable to those inputs. Aside of the hydrodynamic patterns, common processes for all estuaries which are considered in order to understand and explain the spatiotemporal distributions of trace metals primarily encompass adsorption/desorption, flocculation, biological uptake, sediment resuspension, as well as organic/inorganic complexation alongside with the competitive effects of major cations/anions (Abril et al, 2002;Dassenakis et al, 1995;Elbaz-Poulichet et al, 1996;Hatje et al, 2003b;Louis et al, 2009;Oursel et al, 2013;Rigaud et al, 2013;Waeles et al, 2009). …”

“…Cu in estuaries is well documented in the literature and generally exhibits contrasting behaviours, with no specific pattern. Formation of strong organic complexes is known to control Cu speciation and distribution in natural waters (Bruland and Lohan, 2004;Louis et al, 2009;Waeles et al, 2008b), and thus the concentration and the type of organic matter may be of great importance in the mixing zone in regulation of dissolved/particulate Cu fractionation.…”