Is phytoplankton affected by sediment disposal at sea? The case of Kifissos river dredging in Saronikos Gulf (Eastern Mediterranean)

Dredging and dumping of sediments is a very common practice in estuarine and coastal waters, despite the potential environmental impact, mainly because of the low cost. However, some effects of dredged sediments disposal are not fully studied yet, such as the impact on phytoplankton. During 2010-2011, the urban river Kifissos in Athens, Greece, was dredged and the sediments were disposed at the coastal area of Saronikos Gulf on a daily basis. HCMR conducted a monitoring project at the disposal site and the adjacent area in order to assess the environmental impact and suggest management practices. The phytoplankton abundance and biomass and the presence of potentially toxic microalgal species demonstrated an increasing trend during one year of sediment disposal at sea. Similarly the ecological quality status demonstrated a decreasing trend. However, the phytoplankton abundance, biomass and diversity were found to be affected rather by seasonality than their vicinity to the dump site and consequently the impact of the dredged sediment disposal. Our findings indicate a deterioration of the marine environment but more research in the area is needed to support this.