加拿大海盆北部营养盐限制作用研究

Nutrient limitation in the northern Canada Basin

利用2008年夏季中国第三次北极科学考察获得的营养盐、叶绿素a、温度和盐度等数据资料,结合现场营养盐添加实验的结果讨论西北冰洋加拿大海盆北部营养盐对浮游植物生长的限制作用。结果表明:由于融冰水稀释作用,加拿大海盆B80站约20m深度存在较强的盐跃层,阻碍了水体上下混合。较低浓度的溶解无机氮(DIN)和硅酸盐(分别为0.31μmol/L和0.94μmol/L)以及严重偏离Redfield比值的N/P、N/Si比值(分别为0.42和0.32)表明加拿大海盆表层水体存在N和Si限制。根据现场营养盐加富实验各培养组叶绿素a浓度变化、营养盐吸收总量差异和浮游植物种群结构,进一步表明氮是北冰洋海盆首要限制营养盐,而Si则抑制了硅质生物的生长。同时,较小的硝酸盐半饱和常数(Ks)证明即使在营养盐充足的情况下北冰洋海盆浮游植物生长速率也处于较低水平。计算得到各培养组营养盐吸收比例(N/P比值)均大于Redfield比值,可能是培养实验过程中以微型、微微型浮游植物为主,硅藻等小型浮游植物为辅造成的。

The concentrations of nitrate, phosphate, silicate, Chl a were analyzed and in situ nutrients enrichment ex periment was conducted in the summer of 2008 to discuss the impact of macronutrient limitation on phytoplankton biomass and community structure in the western Arctic Canada Basin. The results showed that there was a strong stratification in the upper 20 m at B80 station. Lower concentrations of dissolved inorganic nitrogen （DIN） and sili- cate （0.31 and 0.94 μmol/L,respectively） and serious deviation from the Redfield ratio of the N/P,N/Si （0.42 and 0. 32,respectively） indicated N and Si limited in the upper layer of the Canada Basin. According to the trend of Chl a,nutrients uptake and phytoplankton community structure during the experiment deduced that nitrogen was the primary limited nutrient,while silicate inhibited the growth of siliceous phytoplankton in the upper layer of the Canada Basin. Meanwhile,the smaller half saturation constant （Ks） of nitrate can also prove that the phytoplank- ton growth rates were at a low level even the absence of nutrient limitation in the Arctic Basin. The phytoplankton species were dominated by nano-or pico-phytoplankton rather than diatom, which would be responsible for the higher nutrient assimilation ratios of N/P compared to the Redfield ratio.