Silica (Si), nitrogen (N) and phosphorus (P) loads and stoichiometry are key factors controlling the trophic status of lakes and coastal seas. In the hydrographic network, lakes also act as biogeochemical reactors, controlling both nutrient retention and fluxes. This work aimed to examine the coupling of Si, N and P cycling, together with their stoichiometry in a deep meromictic subalpine lake (Lake Iseo, Northern Italy). Si, N and P mass budgets were calculated by quantifying loads in the inlets and in the outlet over a period of 30 months (May 2016−October 2018), in-lake sedimentation rates and net nutrients accumulation in the water body. Lake Iseo acts as a biogeochemical filter, which differentially retains the external Si, N and P loads. Retention of Si and P was similar (75–79%), but considerably higher than N (45%), evidencing a decoupling of their fate due to in-lake processes. This differential retention is likely to be exacerbated by meromixis which enhances Si and P accumulation in the monimolimnion, while impairing denitrification, thus limiting N removal. Such decoupling resulted in an increase of the N:Si and N:P ratios in both the epilimnion and in the outlet compared to the inlets, whereas the ratios decreased in the monimolimnion. As a result, there may be a stronger Si and P limitation of the photic zone, leading to a shift towards more oligotrophic conditions. This transient equilibrium could be impaired in the case of water overturn produced by extreme climate events—a highly relevant issue, considering that a growing number of deep lakes are turning from holo-oligomictic to meromictic as a result of combined eutrophication and climate change.

二氧化硅 (Si)、氮 (N) 和磷 (P) 负荷和化学计量是控制湖泊和沿海海洋营养状况的关键因素。在水文网络中，湖泊还充当生物地球化学反应器，控制养分保留和通量。这项工作旨在研究 Si、N 和 P 循环的耦合，以及它们在深亚高山湖泊（意大利北部伊塞奥湖）中的化学计量。通过量化 30 个月（2016 年 5 月至 2018 年 10 月）期间入口和出口的负荷、湖内沉降率和水体中的净养分积累来计算 Si、N 和 P 质量预算。伊塞奥湖充当生物地球化学过滤器，不同地保留外部硅、氮和磷负荷。Si 和 P 的保留率相似（75-79%），但远高于 N（45%），证明由于湖内过程而导致它们的命运脱钩。这种差异保留可能会因meromimixis而加剧，这会增强monimolimnion中的Si和P积累，同时削弱反硝化作用，从而限制N的去除。与入口相比，这种解耦导致外壁和出口中的 N:Si 和 N:P 比率增加，而在monimolimnion 中的比率降低。因此，光区可能存在更强的 Si 和 P 限制，导致向更贫营养条件的转变。在极端气候事件导致水体倾覆的情况下，这种短暂的平衡可能会受到损害——这是一个高度相关的问题，考虑到由于富营养化和气候变化的共同作用，越来越多的深湖正从全寡聚变为聚聚。