Estuarine modification of dissolved and particulate trace metals in major rivers of East-Hainan, China

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

“…release of Cd from the SPM into solution as a result of the formation of stable chloro-complexes (ElbazPoulichet et al, 1996;Elbaz-Poulichet et al, 1991;Kraepiel et al, 1997;Oursel et al, 2013;Waeles et al, 2005). Although such behaviour is consistent with other studies, in most of these studies which reported non-conservative Cd behaviour in an estuarine mixing, the concentration of SPM was much higher than in our case, and the distribution is characterised by the "concentration peak" appearing mainly at salinities between 10 and 20 (Dabrin et al, 2013;Elbaz-Poulichet et al, 1996;Elbaz-Poulichet et al, 1987;Fu et al, 2013;Hatje et al, 2003a;Kraepiel et al, 1997;Oursel et al, 2013;Oursel et al, 2014;Paucot and Wollast, 1997;Waeles et al, 2005;Waeles et al, 2004). As the particulate concentration of Cd measured in the freshwater end-member is very low (<10%), the release of Cd from SPM is excluded as a main contributor to the observed trends in the Krka River estuary (although it can contribute partly to the overall increase).…”

“…This is opposite to many other estuaries, characterized by high input of metals to the sea by the river (CobeloGarcia et al, 2004;Elbaz-Poulichet et al, 1984;Hatje et al, 2003a;Kraepiel et al, 1997;Oursel et al, 2013;Turner and Millward, 2002;Waeles et al, 2007;Waeles et al, 2008a). Due to the low SPM input, the impact of removal processes within estuarine mixing zone is diminished, making identification of this processes (by comparison of the theoretical dilution curve and the actual concentrations) much more complicated (Dorten et al, 1991;Elbaz-Poulichet et al, 1991;Fu et al, 2013). In line with this, as the particulate fraction is low, the contribution of potentially released metals to the dissolved pool is also probably minor.…”

“…Thus, the time of the filtration after the sample is taken, is found to be of great importance in interpretation of the dissolved/particulate partitioning of several trace metals (Oursel et al, 2013). Basically, conservative ElbazPoulichet et al, 1996) and non-conservative (Fu et al, 2013;Waeles et al, 2007) behaviour with declining trend was recorded for Pb in different estuaries. Behaviour of Cd in mixing zone is characterised by its release due to the competitive effect of chloride, i.e.…”

“…Behaviour of Cd in mixing zone is characterised by its release due to the competitive effect of chloride, i.e. formation of stable Cd chloro-complexes, causing consequently a non-conservative behaviour (Comans and Vandijk, 1988;Elbaz-Poulichet et al, 1996;Elbaz-Poulichet et al, 1987;Fu et al, 2013;Oursel et al, 2013;Waeles et al, 2009;Waeles et al, 2005). Cu in estuaries is well documented in the literature and generally exhibits contrasting behaviours, with no specific pattern.…”

“…solution and particle composition, speciation, dissolved organic carbon (DOC) and SPM concentration, pH, temperature, salinity), a large variation could be expected in systems which undergo different physico-chemical changes, implying that the justification of KD variation should be taken with caution (Bourg, 1987;Comans and Vandijk, 1988;Elbaz-Poulichet et al, 1996;Fu et al, 2013;Hatje et al, 2003b;Turner, 1996) and thus the direct comparison of results within different studies is not always straightforward.…”