渤海湾西南部典型站位营养盐限制特性的加富培养实验研究

摘要

In October 2010, nutrient enrichment experiments were conducted at a sampling station in the south-western Bohai Bay to determine the limiting nutrient and to investigate the ecological responses of the phytoplankton to the different N/P ratios and different ways of nitrate additions under controlled conditions. The initial concentrations of dissolved inorganic nitrogen (DIN), phosphate, silicate and chlorophyll a were 20.68μmol/L, 0.24μmol/L, 4.58 μmol/L, and 1.05 μg/L, respectively and the phytoplankton cell density was 1080 cells/L The results showed that among the groups of single nutrient addition, the phytoplankton in group 1-3 (group with P addition) showed the most significant growth. The maximum concentration of chlorophyll a of group 1-3 reached 2.48 times of that of group 1-1 (group without nutrient addition) and reached 48 % of that of group 1-5 (group with N,P,Si addition). The maximum cell density of phytoplankton of group 1-3 reached 1.66 times of that of group 1-1 and reached 72 % of that of group 1-5. These results indicated a possible P limitation. The experiment with different N/P ratios revealed an increased growth of phytoplankton under low N/P ratios with an optimum range of 5-15, which was less than the global level-the Redfield ratio of 16. The results also revealed an increased growth of phytoplankton under continuous addition conditions, which may imply the significant impact of low level continuous nitrogen pollution load and an underestimation of the growth potential using the ordinary method.%2010年10月,对渤海湾西南部海域典型站位表层水体进行了模拟现场的营养盐加富培养实验.初始状态下,培养水样中溶解无机氮浓度为20.68μmol/L,磷酸盐浓度0.24 μmol/L,硅酸盐浓度4.58 μmol/L,叶绿素a浓度为1.05 μg/L.浮游植物细胞密度为1 080 cells/L.通过改进实验设计,研究了该水样的营养盐限制类型、水样中浮游植物对不同氮磷比以及不同硝酸盐添加方式的生态响应.实验结果表明,在单一添加营养盐的各组中,添加磷酸盐的1-3组叶绿素a浓度和浮游植物细胞密度的增长状况最显著,1-3组叶绿素a浓度峰值为空白对照组1-1组的2.48倍,达到营养盐全加组1-5组同期浓度的48％,其细胞密度峰值为1-1组的1.66倍,达到1-5组间期密度的72％,该水样为磷限制.在实验条件下,浮游植物的增长在总体上随着氮磷比的降低而增大,最适宜的氮磷比为5-15左右.略低于Redfield比值16.硝酸盐的连续性添加比一次性添加更有利于浮游植物的生长,暗示了低浓度长期持续性氮污染可能会比高浓度冲击性氮污染更有效地刺激浮游植物的增长,从而造成更严重的生态问题,而此时用以往的一次性添加培养实验可能会低估浮游植物的增长潜力.