Concentrations of phosphorus and nitrogen (a) as well as chlorophyll a (b) in the Nanliu River (left panels) and Lianzhou Bay including the outer estuary (right panels) in comparison to literature values reflecting trophic states of freshwater streams and coastal waters, respectively (Smith et al., 1999). (a) also includes data from the Huangzhu River and estuary (spring 2010). Phosphorus refers to total phosphorus in reference values but shows only PO 4 for the data points, nitrogen is total nitrogen for both reference values and data. Notice the logarithmic scale of the right panel in (a). Primary production in Nanliu River and Lianzhou Bay is not limited by nutrient availability. Although nutrient concentrations decrease along the salinity gradient (Chapter 1), minima in Lianzhou Bay are above half saturation constants for phytoplankton growth (Eppley et al., 1969; İzgören-Sunlu and Büyükışık, 2006) and are sufficient to sustain high primary production (Chapter 2). Consequently, indicators for productivity do not correlate well with any dissolved nutrient concentration (Tab. 2). Uptake of riverine nutrients by marine