Seasonal significance of N2 fixation in coastal and offshore waters of the northwestern Baltic Sea
Seasonal significance of N2 fixation in coastal and offshore waters of the northwestern Baltic Sea
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DOI：
10.3354/meps07379
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发表时间：
2008-01-01
影响因子：
2.5
通讯作者：
Soderback, Erik
中科院分区：
文献类型：
--
作者：
Degerholm, Jenny;Gundersen, Kjell;Soderback, Erik
在波罗的海的一个开放水域站（BY31）和2个沿海站（H4和X1），测量了3年（1998 - 2000年）的N-2固定年速率。这是第一份关于波罗的海一个以上完整生长季节N-2固定深度综合率的报告。在波罗的海地区，每年固定的N-2估计值为56 000至125 000吨N，在近海站（希默夫雅顿）为18 000至162 000吨N。使用N-15示踪技术，在0至25 m之间的4个深度处原位测量了大于和小于20 pm的大小分级生物体的N-2固定率。N2固定率最高的发现在表面沃茨（0至4米深），这一活动的主要部分（80%在沿海和89%在近海沃茨）发生在白天。在> 20 μ m的细胞中，N-2固定的综合速率遵循丝状蓝藻（主要是束丝藻属）的平均丰度。在水柱里。在大于20 μ m的颗粒中，即丝状蓝藻中的C：N摩尔质量比表明，该尺寸部分在夏季是N充足的，而C：P摩尔质量比表明在此期间P限制。在研究期间，污水排放到希默夫雅顿海湾地区的减少似乎没有得到补偿的N-2固定率的增加。蓝藻的斑块状分布和高季节性变化的N-2固定率强调需要适当的空间和时间采样策略在波罗的海的沿海和开放沃茨的N-2固定的研究。
Annual rates of N-2 fixation were measured over 3 yr (1998-2000) at an open water station (BY31) and 2 coastal stations (H4 and X1) in the Baltic Sea. This is the first report on depth-integrated rates of N-2 fixation from more than one complete growth season in the Baltic Sea. Annual estimates of N-2 fixation ranged from 56 000 to 125 000 t N in the Baltic Proper, and 18 000 to 162 000 t N at the inshore stations (Himmerfjarden). Rates of N-2 fixation were measured in situ at 4 depths between 0 and 25 m using the N-15 tracer technique for size fractionated organisms larger and smaller than 20 pm. Maximum rates of N2 fixation were found in surface waters (0 to 4 m depth), and a major part of this activity (80% in coastal and 89% in offshore waters) took place during daylight hours. Integrated rates of N-2 fixation in cells >20 mu m followed the average abundance of filamentous cyanobacteria (primarily Aphanizomenon sp.) in the water column. Molar C:N mass ratios in particles >20 mu m, i.e. filamentous cyanobacteria, suggest that this size fraction was N-sufficient during summer, whereas the molar C:P mass ratios indicated P-limitation during this period. A reduction in sewage discharge to the Himmerfjarden bay area during the study period appears not to have been compensated for by increased rates of N-2 fixation. The patchy distribution of cyanobacteria and the high seasonal variability in N-2 fixation rates emphasize the need for adequate spatial and temporal sampling strategies in studies of N-2 fixation in coastal and open waters of the Baltic Sea.