地下水中地源铵(NH4)的过量存在引起了全球环境关注,通常与含氮溶解有机物(DOM)的降解有关。然而,关于沉积物中可溶性有机物(SOM)和地下水中DOM的组合的系统研究存在差距,很少有室内孵化实验来验证它们的降解途径。本研究利用超高分辨率傅里叶变换离子回旋共振质谱分析了受地质NH4影响的含水层系统中DOM和SOM的分子特征。随后,进行了长达140d的室内孵育实验,以验证降解途径。实验结果揭示了DOM和SOM的两阶段降解过程。初始阶段的特征在于脂肪族化合物(ALC)的降解,产生多酚(PPE)和高度不饱和化合物(HUC)。第二阶段主要是PPE和HUC的降解,伴随着一些ALC的重新消费,而更顽固的HUC持续存在。值得注意的是,SOM退化的第一阶段超过了DOM退化的第一阶段,表明SOM表现出更大的耐老化性。这种现象可能归因于沉积物中更广泛的活性酶,沉积物中有机物对SOM的快速补充,或者DOM的加速退化。实验结果与实际含水层系统中DOM和SOM的分子表征一致。假设通过SOM的直接矿化产生的NH4可能比通过DOM的矿化产生的NH4对地下水中NH4的富集贡献更大。本研究首次在含水层系统中一起分析DOM和SOM,并通过孵化实验验证其降解途径,从而为地下水中地质NH4+的富集提供了新的见解。
The excessive presence of geogenic ammonium (NH4+) in groundwater poses a global environmental concern, commonly linked to the degradation of nitrogen-containing dissolved organic matter (DOM). However, there is a gap in systematic studies on the combination of soluble organic matter (
SOM) in sediments and DOM in groundwater, with few indoor incubation experiments to validate their degradation pathways. This study utilized ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry to analyze the molecular characteristics of DOM and SOM in aquifer systems affected by geogenic NH4+. Subsequently, indoor incubation experiments spanning up to 140 d were conducted to verify the degradation pathways. The experimental results revealed a two-phase degradation process for both the DOM and
SOM. The initial stage was characterized by the degradation of aliphatic compounds (ALC) with the production of polyphenols (PPE) and highly unsaturated compounds (HUC). The second stage was dominated by the degradation of PPE and HUC, accompanied by the re-consumption of some ALC, while more recalcitrant HUC persisted. Notably, the first stage of
SOM degradation exceeded that of DOM degradation, indicating that
SOM exhibited greater resistance to aging. This phenomenon may be attributed to a wider range of active enzymes in sediments, the rapid replenishment of SOM by organic matter in sediments, or the accelerated degradation of DOM. The experimental results aligned with the molecular characterization of DOM and
SOM in actual aquifer systems. It is hypothesized that NH4+ produced through the direct mineralization of
SOM may contribute more to the enrichment of NH4+ in groundwater than that produced through the mineralization of DOM. This study is the first to analyze DOM and SOM together in aquifer systems and validate their degradation pathways through incubation experiments, thereby providing novel insights into the enrichment of geogenic NH4+ in groundwater.