(Table 2) Rates of nitrate and ammonium uptake, concentrations of particulate organic nitrogen and carbon, and dissolved nitrate and ammonium in waters of the Black Sea August-September 1990 and November 1991

To study inorganic nitrogen uptake rates by microplankton in the Black Sea the first 15N-experiments were carried out in August-September 1990 and in November 1991. In surface waters nitrate uptake rates varied from 5.7 to 28.5 nM/l/h in summer and from 1.9 to 7.8 nM/l/h in autumn. In both seasons maximal and minimal rates were observed in frontal zones of shelf/slope areas and in open waters, respectively. In summer average nitrate uptake rate per unit of particulate organic nitrogen was 0.0037 1/h for all stations. In autumn it varied from 0.0007 1/h in the central part of the sea to 0.0033 1/h in the slope near the southeastern Crimean coast. In autumn ammonium uptake rate varied from 7.1 to 22.2 nM/l/h and from 0.0025 to 0.00094 1/h. Ammonium uptake correlated linearly with nitrate uptake, with new production being 22-36% of total summary nitrate and ammonium uptake. There was a linear correlation between nitrogen uptake and chlorophyll a concentrations in the Black Sea. In the water column in autumn both nitrate and ammonium uptake decreased as chlorophyll a concentration diminishes with depth.为研究黑海微型浮游生物对无机氮的摄取速率，课题组于1990年8—9月及1991年11月开展了首批¹⁵N标记实验。表层水体中，夏季硝酸盐摄取速率介于5.7~28.5纳摩尔每升每小时，秋季则为1.9~7.8纳摩尔每升每小时。两个季节中，最高摄取速率均出现在陆架/陆坡锋面区域，最低摄取速率则均见于开阔水域。夏季所有站位的单位颗粒有机氮平均硝酸盐摄取速率为0.0037 h⁻¹。秋季该值在黑海中部海域为0.0007 h⁻¹，在克里米亚东南沿岸附近的陆坡区域可达0.0033 h⁻¹。秋季铵盐摄取速率介于7.1~22.2纳摩尔每升每小时，对应单位颗粒有机氮的摄取速率范围为0.0025~0.00094 h⁻¹。铵盐摄取与硝酸盐摄取呈线性相关，新生氮生产占硝酸盐与铵盐总摄取量的22%~36%。黑海海域的氮摄取速率与叶绿素a浓度存在线性相关关系。秋季水柱中，随着叶绿素a浓度随深度降低，硝酸盐与铵盐的摄取速率均随之下降。