| Ammonium and nitrate uptake was measured in 6 European tidal estuaries (Ems, Rhine, Scheldt, Loire, Gironde and Douro) using <sup>15</sup>N-tracer techniques. Uptake rates of ammonium and nitrate ranged from 0.005 to 1.56 µmol N l<sup>-1</sup>h<sup>-1</sup> and 0.00025 to 0.25 µmol N l<sup>-1</sup> h<sup>-1</sup>, respectively, and differed significantly between and within estuaries. Analysis of nitrogen uptake using the relative preferential index (RPI) indicated ammonium to be the preferred substrate. The turnover times of particulate nitrogen (0.7 to 31 d) and dissolved ammonium (0.1 to 27 d) were similar to or shorter than estuarine-water residence times, whereas turnover times of dissolved... |
