河口接收大量的陆地溶解有机氮(tDON),它将通过有力的交换过程从淡水运输到海洋终点。然而,在这种运输过程中TDON的复杂迁移和转化动力学,特别是在分子水平上,保持约束。为了解决这个知识差距,采用傅里叶变换离子回旋共振质谱(FT-ICRMS)分析珠江口DON的分子组成,受中国南方人为活动加剧的影响,以河流为主的河口系统。结果表明,研究区域DON浓度存在明显的时空变化。在分子水平上,tDON表现出降低的不饱和度和芳香性,再加上含有一个氮原子的DON化合物(1N-DON,53.17%)和含碳的化合物,氢气,氧气,氮,和硫(CHONS)(27.46%)。很明显,木质素被耗尽,而淡水-海水混合区中产生了更多的含氧单宁化合物。这种转变归因于生物活动的增强,可能受陆地养分投入的启动效应影响。在夏天,强混合区和外河口的盛行羽流与生物活动相结合,增加了3N-DON分子的丰度,同时增加了仅含碳的DON化合物的丰度,氢气,氧气,和氮气(CHON),含有碳的DON化合物,氢气,氧气,氮,硫磺,和磷(CHONSP),和CHONS。这一趋势也突显了海洋浮游生物和微生物在利用含碳的DON化合物中的作用日益扩大。氢气,氧气,氮,和磷(CHONP)。这些发现提供了以河流为主的河口在分子水平上的tDON转化过程的详细信息,并强调了河口内运输和改变DON所涉及的河口流体动力学。
Estuaries receive substantial amounts of terrestrial dissolved organic nitrogen (tDON), which will be transported from the freshwater to the oceanic terminus through vigorous exchange processes. However, the intricate migration and transformation dynamics of tDON during this transportation, particularly at a molecular level, remain constrained. To address this knowledge gap, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used for the analysis of DON molecular composition in the Pearl River Estuary (PRE), a river-dominated estuarine system influenced by intensified anthropogenic activities in southern China. The results showed a pronounced spatial-temporal variation in DON concentration in the study area. At the molecular level, tDON exhibited reduced unsaturation and aromaticity, coupled with an elevated abundance of DON compounds containing one‑nitrogen atom (1 N-DON, 53.17 %) and compounds containing carbon, hydrogen, oxygen, nitrogen, and sulfur (CHONS) (27.46 %). It was evident that lignin was depleted while more oxygenated tannin compounds were generated in the freshwater-seawater mixing zone. This transformation is attributed to heightened biological activities, likely influenced by the priming effect of terrestrial nutrient inputs. In summer, the prevailing
plume combined with biological activities in the strong mixing area and outer estuary increased the abundance of 3 N-DON molecules and a concurrent rise in the abundance of DON compounds containing only carbon, hydrogen, oxygen, and nitrogen (CHON), DON compounds containing carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus (CHONSP), and CHONS. This trend also underscores the expanding role of marine plankton and microbes in the utilization of DON compounds containing carbon, hydrogen, oxygen, nitrogen, and phosphorus (CHONP). These findings provide details of tDON transformation processes at the molecular level in a river-dominated estuary and underline the estuarine hydrodynamics involved in transporting and altering DON within the estuary.