旱雨季岩溶地表河不同河段正构烷烃相态组成变化和来源解析

岩溶作用产生的无机碳可以在水生植物、微生物等作用下形成有机质,转化为较稳定的内源有机碳,这为寻找全球遗漏碳汇提供了新的突破口,而加强对岩溶区有机质的溯源研究是重要手段.为探究金佛山岩溶地表河溶解态、颗粒态和沉积物正构烷烃的含量、组分及来源,于2017年3月20日、9月26日分别在石钟溪上、中、下游进行采样,并利用气相色谱-质谱联用仪(GC-MS)对三相态正构烷烃的组分进行定量分析.结果显示,旱季溶解态、颗粒态和沉积物正构烷烃的平均含量分别为737 ng·L~(-1)、6108 ng·L~(-1)和7149 ng·g~(-1),雨季三者的平均含量分别为7129 ng·L~(-1)、8146 ng·L~(-1)和6213 ng·g~(-1).正构烷烃的含量整体表现为雨季高于旱季,以溶解态正构烷烃表现得最为显著,这主要由外源高等植物输入增多所致.旱季上、下游正构烷烃含量差异明显,以沉积物正构烷烃表现得最为显著,自上而下整体保持微升态势;雨季外源输入量较大,差异性减弱,整体变幅较小.不同季节降雨和气温的变化导致水动力条件、浊度及水温的不同,深刻地影响着不同相态和不同河段正构烷烃的来源和迁移.整体上,随着海拔降低,高等植物贡献度降低,水生植物和低等生物贡献度增高.当水动力条件较弱和浊度较低时,造成内源溶解有机质增多,同时会出现溶解态至颗粒态乃至沉积物的缓慢沉降迁移.

Phase composition changes and sources of n-alkanes in the upper and lower reaches of Karst surface river during dry & rainy season

The inorganic carbon produced by Karstification can form the organic matter under the action of aquatic plants and microbes, and then transform into a stable endogenous organic carbon, which provides a new breakthrough for finding the global leakage of carbon sequestration. It provides an important means for strengthening the research on the source of organic matter components in the Karst area. To explore the composition, migration and sources of dissolved n-alkanes, particulate n-alkanes, and sedimentary n-alkanes of the Karst surface waters in Jinfo Mountain, water samples were collected in the upper reaches, middle reaches and lower reaches of Shizhong stream in March 20th, 2017 and September 26th respectively. The composition of n-alkanes was quantitatively analyzed using the gas chromatography-mass spectrometry (GC-MS). The results showed that the average content of dissolved, particles and sediment normal alkanes in the dry season were 737 ng·L^-1, 6108 ng·L^-1and 7149 ng·g^-1. These three in the rainy season were 7129 ng·L^-1, 8146 ng·L^-1 and 6213 ng·g^-1. The content of n-alkanes is generally higher in the rainy season than it is in the dry season. And the dissolved n-alkanes is most significant, which is mainly caused by the input of higher plants. The difference in n-alkane content between the upper and lower reaches of the dry season is obvious, and the overall remains elevated slightly. And the external input during the rainy season is relatively large, the difference is weaken, and the overall changes are little. The changes in rainfall and temperature in different seasons lead to the differences in hydrodynamic conditions, turbidity, and water temperature. And it profoundly affects the source and migration of n-alkanes in different phases and different reaches. When the hydrodynamic condition is weak and the turbidity is low, the input ratio of dissolved organic matter is increasing and the slow rate sedimentation and migration from the water phase to the granular phase and sediments will occur.