Freshwater lakes are essential hotspots for the removal of excessive anthropogenic nitrogen (N) loads transported from the land to coastal oceans. The biogeochemical processes responsible for N removal, the corresponding transformation rates and overall removal efficiencies differ between lakes, however, it is unclear what the main controlling factors are. Here, we investigated the factors that moderate the rates of N removal under contrasting trophic states in two lakes located in central Switzerland. In the eutrophic Lake Baldegg and the oligotrophic Lake Sarnen, we specifically examined seasonal sediment porewater chemistry, organic matter sedimentation rates, as well as 33-year of historic water column data. We find that the eutrophic Lake Baldegg, which contributed to the removal of 20 ± 6.6 gN m⁻² year⁻¹, effectively removed two-thirds of the total areal N load. In stark contrast, the more oligotrophic Lake Sarnen contributed to 3.2 ± 4.2 gN m⁻² year⁻¹, and had removed only one-third of the areal N load. The historic dataset of the eutrophic lake revealed a close linkage between annual loads of dissolved N (DN) and removal rates (NRR = 0.63 × DN load) and a significant correlation of the concentration of bottom water nitrate and removal rates. We further show that the seasonal increase in N removal rates of the eutrophic lake correlated significantly with seasonal oxygen fluxes measured across the water–sediment interface (R² = 0.75). We suggest that increasing oxygen enhances sediment mineralization and stimulates nitrification, indirectly enhancing denitrification activity.

淡水湖泊是清除从陆地运输到沿海海洋的过量人为氮 (N) 负荷的重要热点。负责氮去除的生物地球化学过程、相应的转化率和总体去除效率在湖泊之间存在差异，但尚不清楚主要控制因素是什么。在这里，我们调查了在位于瑞士中部的两个湖泊中，在不同的营养状态下调节 N 去除率的因素。在富营养化的巴尔德格湖和贫营养化的萨尔嫩湖中，我们专门研究了季节性沉积物孔隙水化学、有机物沉降速率以及 33 年的历史水柱数据。我们发现富营养化的 Baldegg 湖有助于去除 20 ± 6.6 gN m ^-2 年^-1，有效地去除了总面积 N 负载的三分之二。与此形成鲜明对比的是，贫营养化的萨尔嫩湖贡献了 3.2 ± 4.2 gN m ^-2 年^-1，并且仅去除了面积 N 负荷的三分之一。富营养化湖泊的历史数据显示，溶解氮（DN）的年负荷与去除率（NRR = 0.63 × DN 负荷）之间存在密切联系，底水硝酸盐浓度与去除率之间存在显着相关性。我们进一步表明，富营养化湖泊 N 去除率的季节性增加与通过水-沉积物界面测量的季节性氧通量显着相关（R ² = 0.75)。我们建议增加氧气会增强沉积物矿化并刺激硝化作用，从而间接增强反硝化作用。