Lakes play a crucial role in the nitrogen (N) cycle, and eutrophication disrupts the balance of the nitrogen cycle within lakes, including both the N removal process and the N supplement process. However, the mechanisms by which different nutrient levels affect seasonal nitrogen variations in the water columns are not clear, especially for long-term and large- scale studies. In this study, we used 206 independent spatial samples from a total of 108 subtropical shallow lakes from four surveys in the middle and lower reaches of the Yangtze River, as well as time-case study data from Lake Taihu and Lake Donghu of up to 23 and 14 years, respectively, to analyze the changes in summer TN compared to spring (delta TN). Delta TN was significantly negatively correlated with initial spring TN concentrations, with similar trends observed in both space and time. Furthermore, the slopes of spring TN vs. delta TN varied little across lakes in both time and space, suggesting a consistent relationship between initial spring TN and summer TN changes. When initial TN or TN: TP ratio was low, N fixation by algae played a significant role in compensating for summer N removal, thus mitigating summer N reductions; when TN was high or TN: TP ratio was high, ammonia stress reduced the compensatory effect of algae and denitrification played a significant role in summer N removal, thus increasing summer N reductions. Our study suggested that no matter what the initial conditions are, lakes tend to evolve towards a common nutrient status through biological regulation.

中文翻译：

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亚热带浅水湖泊中氮的季节性变化导致的营养均匀性


湖泊在氮 （N） 循环中起着至关重要的作用，富营养化破坏了湖泊内氮循环的平衡，包括氮去除过程和氮补充过程。然而，不同营养水平影响水体中季节性氮变化的机制尚不清楚，特别是对于长期和大规模的研究。在这项研究中，我们使用了来自长江中下游 4 次调查的总共 108 个亚热带浅水湖的 206 个独立空间样本，以及分别长达 23 年和 14 年的太湖和东湖的时间案例研究数据，分析了夏季 TN 与春季 （delta TN） 相比的变化。Delta TN 与初始春季 TN 浓度呈显著负相关，在空间和时间上观察到类似的趋势。此外，春季 TN 与 delta TN 的坡度在时间和空间上随湖泊变化不大，表明初始春季 TN 和夏季 TN 变化之间存在一致的关系。当初始 TN 或 TN：TP 比值较低时，藻类的固氮在补偿夏季氮去除方面起着重要作用，从而减轻了夏季氮的减少;当 TN 高或 TN：TP 比高时，氨胁迫降低了藻类的补偿作用，反硝化作用在夏季氮去除中起了重要作用，从而提高了夏季氮的减少。我们的研究表明，无论初始条件如何，湖泊都倾向于通过生物调节进化为共同的营养状态。