Phytoplankton standing crop and sewage nutrient enrichment along the central coast of Lebanon

Abstract

Surface nearshore water samples from seven stations along the central coast of Lebanon were analysed at different seasons for concentrations of nitrate, nitrite, ammonia, phosphate and chlorophyll- a standing crop. Concentrations of nutrients and chlorophyll- a are higher within a 10 km long coastal zone south of Beirut and increase with decreasing distance from two major untreated sewage outfalls. In some cases, chlorophyll- a standing crops near outfalls ( e.g. 2·18 mg m −3) are about 10 times greater than unenriched stations further south or than values reported from elsewhere in the eastern Mediterranean. Near outfalls, concentrations of phosphate, ammonia and chlorophyll- a tend to be greatest in summer, while nitrate is greatest in winter. Preliminary measurements by carbon-14 assimilation indicate that the enriched coastal region has a higher rate of primary production than the unenriched area more than 10 km south of Beirut.