Immediate effect of sewerage improvement on the phytoplankton and physicochemical conditions in the Urdaibai estuary (southeastern Bay of Biscay)

Anthropic nutrient enrichment has become a major environmental issue in estuaries around the world, being effluents of wastewater treatment plants (WWTPs) one main causes. Phytoplankton is, together with nutrients, useful indicator for ecological status assessment due to its basal position food chain. The present study aims evaluate immediate effect cessation discharges on conditions and phytoplankton community along eutrophicated Urdaibai estuary (southeastern Bay Biscay). Thus, short-term comparison physicochemical abundance composition (by pigment analysis microscopy) was carried out before after sewerage works. Results confirmed that had an estuary, mainly noticed inner part. abrupt decrease ammonium (from 72.3 18.2?mol/L) phosphate 3.5 2?mol/L) concentrations led improvement water status, reaching values lower than “good” threshold whole estuary. also showed reaction surroundings WWTP, chlorophyll b becoming dominant secondary area diversion rapid increase Eutreptiella sp. However, since sampling-period this did not exceed month cessation, longer study-period is necessary, including interannual studies, test real sanitation works