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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Nitrogen and carbon uptake dynamics in Lake Superior
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Nitrogen and carbon uptake dynamics in Lake Superior

机译：苏必利尔湖的氮和碳吸收动态

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Despite a fivefold rise in nitrate concentration over the last century, many fundamental aspects of Lake Superior's N and C cycles are still very poorly understood. We present here the first measurements of inorganic N uptake and in situ C uptake rates in Lake Superior, one of the largest lakes in the world. A profile of C uptake suggests that more than 95% of production occurs in the top 30 m with highest productivity to biomass ratio in the epilimnion. High C uptake: N uptake and particulate C: N ratio compared to the Redfield ratio (6.6) in the epilimnion suggests higher turnover rate of C compared to N in epilimnetic particles. Experiments performed over a range of typical environmental conditions suggest a strong temperature dependence of N uptake with maximum rates observed during the warmest stratified period. Lakewide N uptake estimates derived from a temperature-based model suggest that on an annual basis, uptake is considerably higher than total N inputs from outside the lake. This difference indicates that the lake is recycling N rapidly, leading to a shorter turnover time in the water column than previously assumed. The long-term buildup of nitrate in the lake has been hypothesized to arise from limited assimilation of nitrate entering the lake. In contrast, our results suggest that nitrate accumulating in the lake is a result of internal N cycling, a finding consistent with recent studies based on a nitrogen budget and NO3- stable isotope analyses.
机译：尽管上个世纪硝酸盐浓度增加了五倍，但苏必利尔湖的氮和碳循环的许多基本方面仍知之甚少。我们在这里展示了世界上最大的湖泊之一苏必利尔湖中无机氮吸收和原位C吸收率的首次测量。 C吸收曲线表明，超过95％的生产发生在前30 m处，而上层生境中的生产率与生物量之比最高。与上表层中的Redfield比率（6.6）相比，较高的C吸收：N吸收和颗粒C：N比率表明，与上表层颗粒中的N相比，C的转换率更高。在一系列典型环境条件下进行的实验表明，在最温暖的分层期间，对氮素吸收具有强烈的温度依赖性，且观察到的速率最大。基于基于温度的模型得出的全湖N吸收量估算值表明，每年的吸收量都大大高于湖外N的总输入量。这种差异表明湖泊正在快速循环利用N，这导致水柱中的周转时间比先前假定的要短。据推测，湖中硝酸盐的长期积累是由于进入湖中的硝酸盐的同化作用有限。相反，我们的结果表明，湖中硝酸盐的积累是内部氮循环的结果，这一发现与基于氮预算和NO3稳定同位素分析的最新研究一致。

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