Impact of contaminated sediment elutriate on coastal phytoplankton community (Thau lagoon, Mediterranean Sea, France)

Abstract

Effects of sediment-released contaminants and nitrogen were assessed on phytoplankton communities sampled from Thau lagoon (France, Mediterranean Sea) and one close offshore marine station. Phytoplankton was exposed to sediment elutriate (seawater containing a mix of metals, organic chemicals, and nutrients) or to ammonium enrichment for four days using immersed microcosms exposed to natural conditions of light and temperature. Functional (production-respiration balance) and structural (taxonomy and cell densities) responses of the phytoplankton community were assessed. In the lagoon, both treatments stimulated phytoplankton growth, compare to controls. Conversely in the offshore station, the phytoplankton growth was stimulated only with the sediment elutriate addition. In offshore and lagoon stations, both treatments caused a shift in the taxonomic composition of the phytoplankton. Proliferation of potentially toxic diatoms and dinoflagellates resulted from the addition of elutriate. Correspondence analysis determined that phytoplankton from the offshore station was more sensitive to both treatments compared to the lagoon community. According to daily production and respiration balance, lagoon community metabolism remained heterotrophic (P < R) for all treatments, whereas only transient shifts to net autotrophy (P > R) were observed in the offshore community. Direct toxicity of contaminants released from sediment, if any, was therefore masked by nutrient enrichment effects, whereas indirect evidence of contaminant pressure was highlighted by changes in community composition and metabolism. Highlights ► Contaminated sediment elutriates trigger changes in phytoplankton dynamics. ► Phytoplankton community structure and metabolism are affected. ► Elutriates effects are not identical to those of nutrient addition alone. ► Elutriates effects differ depending on the initial community structure.

Influence of bacteria on the response of microalgae to contaminant mixtures

“…Therefore, the lack of effect, or the positive effect, of metal and pesticide mixtures on microalgal growth at concentrations found in elutriate (x1) may explain why microalgae growth was not affected when supplemented with filtered elutriate containing both contaminants. This is also consistent with the absence of any toxic effect observed during a previous experiment performed using a filtered sediment elutriate from Bizerte Lagoon and added to a natural phytoplankton community (Ben Othman et al, 2017).…”

Remobilization of polycyclic aromatic hydrocarbons and organic matter in seawater during sediment resuspension experiments from a polluted coastal environment: Insights from Toulon Bay (France)

“…2. This distribution reflected the dominance of Flt and Pyr, which has been observed in other coastal areas of the Mediterranean Sea (Ben Othman et al, 2017;Pérez-Fernández et al, 2015). The isomeric ratios were quite close from one depth to another, and showed that PAHs in the MIS sediment more probably originated from combustion processes, especially of grass/wood/coal, rather than from burned/unburned petroleum residues (Fig.…”

Impact of Contrasted Weather Conditions on CDOM Absorption/Fluorescence and Biogeochemistry in the Eastern Lagoon of New Caledonia

“…This biological stimulation would induce inputs of OM and nutrients by wind-driven resuspension of sediments and atmospheric inputs. Indeed, sediment resuspension in shallow waters is known to carry to the overlying water/water column particulate and dissolved OM, nutrients, and metals (Stahlberg et al, 2006;He et al, 2016) that may favor planktonic activity (Ben Othman et al, 2017). Resuspension would affect shallow areas (bays and reefs), and to a lesser extent the middle lagoon due to its depth (>60 m).…”