Effect of river inputs on environmental status and potentially harmful phytoplankton in an eastern Mediterranean coastal area (Maliakos Gulf, Greece)

Abstract

This paper examines the response of phytoplankton and potentially harmful species to river inflows in an eastern Mediterranean coastal area, within the context of environmental status assessment suggested by the European Commission's Water Framework Directive (WFD, 2000/60/EC) and the Marine Strategy Framework Directive (MSFD, 2008/56/EC). The spatio-temporal distribution of phytoplankton communities and biomass (as chlorophyll a), potentially harmful species, nutrient levels, dissolved oxygen, salinity and temperature were studied. A marginal good to moderate physicochemical status was assigned to downstream of River Spercheios that flows into Maliakos Gulf. Silicates and nitrates were indicated as proxies of freshwater influence in Maliakos Gulf, whereas ammonium, nitrites and phosphates as proxies of pollutants from non-point sources. Phytoplankton biomass and abundances reached high levels throughout Maliakos Gulf inter-seasonally. High silicates favoured the dominance of Diatoms. The potentially harmful species bloomed frequently, with higher levels in the estuary, and they were associated with low salinity, thus demonstrating the riverine influence on them. Pseudo-nitzschia was the most frequent potentially harmful genus with an interesting strong linkage with low silicates and nitrates. Maliakos Gulf demonstrated an overall mesotrophic condition and failed to achieve good ecological status.