Agricultural land use alters nitrate (NO₃^–) uptake dynamics in streams, but the specific mechanisms linking individual agricultural stressors to benthic and hyporheic uptake remain unclear. Using stream-side mesocosms and ¹⁵N-nitrate additions, we examined the individual and combined effects of fine sediment (FS) and augmented light and phosphorus levels (L&P) on benthic and hyporheic NO₃^– uptake rates. In absence of FS, L&P stimulated uptake of autotrophic and heterotrophic biofilms, leading to a 12- and 7-fold increase in the benthic and hyporheic compartments, respectively. Under ambient light and nutrient conditions, FS reduced by 3-fold benthic uptake, but effects were not significant. Conversely, in the hyporheic compartment, FS induced anoxic conditions, likely stimulating denitrification and causing a 14-fold increase in hyporheic uptake. When these stressors were combined, they did not interact in the benthic compartment. Conversely, in the hyporheic compartment they interacted antagonistically, with L&P diminishing the increase in uptake induced by FS. Our results indicate that the previously observed increase of whole-stream NO₃^– uptake in agricultural streams is attributable to nutrients and light stimulating benthic uptake, while fine sediment effects and the role of the hyporheic compartment to total uptake are modest. Moreover, the finding that stressor interactions vary with ecosystem compartments calls for a consideration of all compartments and their contribution to whole-system functioning in multiple stressor studies. We are beginning to understand how multiple interacting stressors affect stream functioning, but more mechanistic evidence is needed to disentangle whether additive or non-additive effects prevail in human-altered ecosystems.

农业用地改变了溪流中硝酸盐（NO ₃ ^-）的吸收动态，但将个体农业压力源与底栖和潜流吸收联系起来的具体机制仍不清楚。使用溪边中生态系统和^{15 N-硝酸盐添加物，我们研究了细沉积物 (FS) 和增强的光和磷水平 (L&P) 对底栖和潜流 NO} ₃^吸收率的单独和组合影响。在没有 FS 的情况下，L&P 刺激自养和异养生物膜的吸收，导致底栖和潜流区室分别增加 12 倍和 7 倍。在环境光和营养条件下，FS 减少了底栖生物吸收的 3 倍，但影响并不显着。相反，在潜流室中，FS 诱导缺氧条件，可能刺激反硝化作用并导致潜流吸收增加 14 倍。当这些压力源结合在一起时，它们在底栖隔间中不会相互作用。相反，在潜流室中，它们以拮抗的方式相互作用，L&P 减少了 FS 诱导的摄取增加。我们的结果表明，先前观察到的农业溪流中全流NO ₃ ^-吸收的增加可归因于营养物和光刺激底栖吸收，而细沉积物效应和潜流区对总吸收的作用是适度的。此外，压力源相互作用因生态系统分区而异的发现要求在多个压力源研究中考虑所有分区及其对整个系统功能的贡献。我们开始了解多种相互作用的压力源如何影响河流功能，但需要更多的机械证据来阐明在人类改变的生态系统中是否普遍存在加性效应或非加性效应。