Effect of riverine nutrients on coastal water ecosystems: A case study from the northeastern Mediterranean shelf

Hydro-chemical data were obtained from a shallow and deep water station in the Turkish shelf zone of the NE Mediterranean with approximately monthly intervals from January to December 2002. The shallow station (0.5 miles off the coast) is influenced directly by the small Lamas River having high nitrate (63-121 muM) and silicate (52-118 muM) values, but very low phosphate concentrations (30-760 nM). Thus, nitrate and silicate concentrations of the shallow station are extremely variable and much higher than those in the upper layer (0-50 m) of the deep station. Similarly, the phosphate concentrations, measured using the high-sensitivity magnesium-induced coprecipitation (MAGIC) method, fluctuate markedly between 20 and 180 nM in the shallow water, but vary little (15-30 nM) in the deep water samples. Particulate organic matter (POM) abundance increases markedly from the shallow to the deep station. However, chemical composition (C/N ratio) of bulk POM in the shelf waters ranges between 7 and 13, displaying small temporal fluctuations at the nutrient-depleted deep station.