Seasonal changes of chemical contamination in coastal waters during sediment resuspension

Abstract

The potential of remobilization of pollutants is a major problem for anthropogenic ecosystems, because even when the anthropogenic source of pollution is identified and removed, pollutants stored in sediments can be released into the water column and impact pelagic communities during sediment resuspension provoked by dredging, storms or bottom trawling. The objectives of the present study were to assess the changes observed in the chemical composition of the water column following resuspension of a polluted marine sediment and the consequences for the chemical composition of adjacent marine waters according to season. For that purpose, an experimental sediment resuspension protocol was performed on four distinct occasions, spring, summer, fall and winter, and the changes in nutrients, organic contaminants and inorganic contaminants were measured after mixing sediment elutriate with lagoon waters and offshore waters sampled nearby. Significant seasonal variations in the chemical composition of the contaminated sediments were observed, with a strong accumulation of PAHs in fall, whereas minimum PAH concentrations were observed during winter. In all seasons, sediment resuspension provoked a significant enrichment in nutrients, dissolved organic carbon, and trace metal elements like Ni, Cu, and Zn in offshore waters and lagoon waters, with enrichment factors that were season and site dependent. The most pronounced changes were observed for offshore waters, especially in spring and winter, whereas the chemical composition of lagoon waters was weakly impacted by the compounds supplied by sediment resuspension.

Impacts of chemical contamination on bacterio-phytoplankton coupling

“…The third series of three microcosms (artificial contaminated water microcosms; ACW) was filled with 6 L (L and O stations) and spiked an artificial solution of pesticides and some metabolites (acetochlore, alachlore, DCPU 1- (3,4-dichlorophenyl)urea, DIA deisopropylatrazine, diuron, linuron and simazine) and metals (Ni, Cu, Zn, Cd, As, Pb). Final concentration of pesticides and metals were adjusted to mimic the concentrations observed in elutriate as wall as possible (Table S1, supplementary materials) (see Bancon-Montigny et al, 2019, for more details). All microcosms, performed in triplicate, were incubated outside under natural sunlight in a 3 m 3 pool where seawater was circulating (open system) to maintain in situ water temperature.…”

“…Chemical analysis of the nutrients, Chlorophyll a (Chla) dissolved organic carbon (DOC), organic contaminants (pesticides and polycyclic aromatic hydrocarbons) and metal trace elements (MTE) were performed using the analytical protocols described in Bancon-Montigny et al (2019) and Pringault et al (2016).…”

“…This long period can promote the development of a community resistant to chemical pollution according to the concept of pollution induced community tolerance (Blanck, 2002) and observed for meiobentic communities (Boufahja and Semprucci, 2015). Furthermore, the accumulation of pollutants and nutrients in lagoon waters results in weak enrichment when exposed to the artificial cocktail of contaminants (Bancon-Montigny et al, 2019), reducing the potential toxicity of the added contaminants for the microbial lagoon communities.…”

“…This mixing resulted in important enrichment in nutrients (especially in dissolved ammonium and silicates), dissolved organic matter, metal trace elements (Mn, Fe, Mo, Zn and Ni) and pesticides (simazine, alachlor, deisopropylatrazine and 1- (3,4-dichlorophenyl)urea) (Bancon-Montigny et al, 2019) and exogenous bacteria by sediment resuspension (Goni-Urriza et al, 2018). Enrichments in nutrients, DOM and chemical contaminants were more pronounced in offshore waters relative to lagoon waters, explained by higher initial concentrations of compounds in the lagoon; thus the addition of sediment elutriate with their compounds does not change the chemical status of the lagoon significantly (Bancon-Montigny et al, 2019). For offshore waters, the metabolic and biomass changes upon elutriate were more pronounced during spring and fall with Chla concentration and primary production up to five times more than observed in the control.…”

“…For that purpose, water incubations in 9L microcosms were performed in different seasons, with additions of a sediment elutriate or an artificial mixture of contaminants mimicking the main contaminants present in sediment elutriate (pesticides and metal trace elements). The chemical changes, along with the experiments with both contaminant exposures, were previously analyzed (Bancon-Montigny et al, 2019), and the present study focused on the changes observed for phytoplankton and bacterioplankton activities and the consequences for the coupling between both compartments.…”