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首页> 外文期刊>Journal of great lakes research >Pelagic Nitrogen Fixation in Lake Victoria (East Africa)
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Pelagic Nitrogen Fixation in Lake Victoria (East Africa)

机译：维多利亚湖（东非）中上层固氮

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Between 1994 and 1998 biological nitrogen fixation was measured using the acetylene reduction method at inshore and offshore sites on northern Lake Victoria. Rates of biological N-fixation were high and often exceeded 0.5 μg N/L/h. Average rates of volumetric N-fixation at optimal irradiance were 8 times higher at inshore locations than in the offshore. Rates of annual areal N-fixation, modeled from the N-fixation light-response and light attenuation in the lake were moderate to high (1.8 to 23.1 g N/m~2/y) depending on location within the lake, and were, on average, only twice as high inshore as offshore. Variations in the light extinction coefficient explained a small but significant proportion of the variation in the optimal N-fixation in Lake Victoria. Algal biomass and N-fixation were lower in the more deeply mixing (> 20 m) offshore waters, because of the persistently low mean light intensities (108 +- 41μE/m~2/s) in the water column most of the year. N-fixation increased with increased light availability, and maximal rates occurred when the lake was shallowly mixing and thermally stratified. At both inshore and offshore stations, minima of algal biomass and N-fixation were consistent with low light availability in July when the lake was most deeply mixing. The ratio of the mean water column irradiance (I_(24)) to the irradiance at which N-fixation approaches saturation (I_k) was often < 1, and provides evidence that N-fixation was light-limited, chronically so in the offshore region. Light limitation of algal growth lessens the algal demand for N, and it constrains algal biomass development and N-fixation more in the offshore compared to the inshore surface waters of Lake Victoria. Biological N fixation is the largest input of fixed N to Lake Victoria, greatly exceeding estimates of atmospheric deposition and river inputs of N.
机译：在1994年至1998年之间，使用乙炔还原法在维多利亚湖北部的近岸和近海站点对生物固氮进行了测量。生物固氮率很高，经常超过0.5μgN / L / h。在近海位置，最佳辐照度下的固氮体积平均速率比近海高8倍。根据湖泊中N固定光响应和光衰减模拟的年面积N固定率取决于湖泊中的位置，为中等到较高（1.8至23.1 g N / m〜2 / y），分别为平均而言，近海的高度仅是近海的两倍。消光系数的变化解释了维多利亚湖最佳N固视变化的很小但很重要的一部分。由于一年中大部分时间水柱中的平均光照强度持续较低，因此在混合更深的海域（> 20 m）中藻类生物量和固氮能力较低（108 +-41μE/ m〜2 / s）。 N固定随着光的可用性增加而增加，并且当湖泊浅层混合并热分层时，发生最大速率。在近岸和近海站，藻类生物量和固氮量极小，与7月湖水最深混合时的可用光不足保持一致。平均水柱辐照度（I_（24））与N固色接近饱和度（I_k）的辐照度的比率通常<1，这提供了N固色长期受光限制的证据，因此在近海地区。藻类生长的光限制减少了藻类对氮的需求，并且与维多利亚湖的近岸地表水相比，其在近海处更多地限制了藻类生物量的发展和氮的固定。生物固氮是维多利亚湖中固定氮的最大输入量，大大超过了大气沉积和氮对河流输入的估计。

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