Impact of contaminated-sediment resuspension on phytoplankton in the Biguglia lagoon (Corsica, Mediterranean Sea)

In shallow human-impacted systems, sediment resuspension events can result in pulsed exposures of pelagic organisms to multiple contaminants. Here, we examined the impact of the resuspension of contaminated sediment on phytoplankton in the Biguglia lagoon (Corsica, Mediterranean Sea), by conducting an in situ microcosm experiment over a 96-hour period. Natural phytoplankton was exposed to elutriates prepared from a contaminated sediment resuspension simulating process, and its functional and structural responses were compared with those of non-exposed phytoplankton. The elutriates displayed moderate multiple contamination by trace metals and PAHs. Our results show that elutriate exposure induced both functional and structural phytoplankton changes. Elutriates strongly stimulated phytoplankton growth after 24 h of exposure. They also enhanced phytoplankton photosynthetic performance during the first hours of exposure (up to 48 h), before reducing it towards the end of the experiment. Elutriates were also found to slightly stimulate Bacillariophyceae, and conversely to slightly inhibit Dinophyceae in the short term. Additionally, they stimulated phycocyanin-rich picocyanobacteria in the short term (8-48 h) before inhibiting it in the longer term (72-96 h), and to inhibit eukaryotic nanophytoplankton at short term (8-48 h) before stimulating it in the longer term (72-96 h). Sediment resuspension is thus likely to have a significant effect on the global dynamics of phytoplankton in contaminated coastal environments.