Algal blooms have increased in frequency, intensity, and duration in response to nitrogen (N) cycling in freshwater ecosystems. We conducted a high-resolution sedimentary study of N transformation and its associated microbial activity in Lake Taihu to assess the accumulation rates of the different N fractions in response to algal blooms, aiming to understand the mechanisms of N cycling in lacustrine environments. Downcore nitrification and denitrification processes were measured simultaneously in situ via diffusive gradients in thin-films technique, peeper, and microelectrode devices in a region of intensified algal blooms of shallow lake. The decomposition of different biomasses of algal blooms did not change the main controlling factor on different N fractions in profundal sediment. However, the decomposition of different algal biomasses led to significant differences in the nitrification and denitrification processes at the sediment–water interface (SWI). Low algal biomasses facilitated the classic process of N cycling, with the balanced interaction between nitrification and denitrification. However, the extreme hypoxia under high algal biomasses significantly limited nitrification at the SWI, which in turn, restricted denitrification due to the lack of available substrates. Our high-resolution results combined with estimates of apparent diffusion fluxes of the different N fractions inferred that the lack of substrates for denitrification was the main factor influencing the positive feedback loop between N and eutrophication in freshwater ecosystems. Moreover, this positive feedback can become irreversible without technological intervention.

中文翻译：

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确定浅水富营养化湖泊中氮循环与藻华之间正反馈回路的机理

响应于淡水生态系统中的氮（N）循环，藻华的频率，强度和持续时间都有所增加。我们对太湖中的氮转化及其相关的微生物活性进行了高分辨率的沉积研究，以评估不同的氮组分对藻华的响应，从而了解湖泊环境中氮循环的机理。下游的硝化和反硝化过程通过薄膜技术，窥视器和微电极装置中的扩散梯度在浅湖藻类密集区的区域同时进行原位测量。藻华的不同生物量的分解并没有改变深部沉积物中不同氮组分的主要控制因素。然而，不同藻类生物质的分解导致沉积物-水界面（SWI）的硝化和反硝化过程出现显着差异。低藻类生物量促进了氮循环的经典过程，同时硝化和反硝化之间具有平衡的相互作用。然而，高藻生物量下的极端缺氧严重限制了SWI的硝化作用，由于缺乏可用的底物，反过来又限制了反硝化作用。我们的高分辨率结果与不同N分数的表观扩散通量的估计值相结合，推断出反硝化基质的缺乏是影响淡水生态系统中N与富营养化之间正反馈回路的主要因素。而且，