我国南方桉树人工林区水体泛黑物质分子组成及形成机理

我国南方桉树人工林区水库在秋冬季频繁出现黑水现象。现有研究指出,桉树叶中单宁酸等物质与金属离子(如铁离子)反应产生的金属-有机质络合物是导致这一现象的主要原因。然而,目前对于桉树叶中能形成金属-有机质络合物的潜在有机质前体物认识仍然有限,基于分子组成层面的桉树人工林区水库水体泛黑形成机理也尚不清楚。为此,本研究利用傅立叶变换离子回旋共振质谱(FT-ICR MS)等手段,对桉树叶浸泡液与典型桉树林区水库(金窝水库和天雹水库)水体中可溶性有机物进行了分子组成的分析。研究结果显示,桉树叶浸泡液主要由以苯三酚、没食子酸为母体的多酚类化合物及其多聚衍生物构成,其中最典型的化合物是鞣花酸(C₁₄H₆O₈)。冬季水库水中鞣花酸强度远高于夏季,且表层水体高于底层水体,这表明秋冬季大量凋落的桉树叶释放出的这些芳香多酚类物质会显著促进水库黑水的形成。进一步的实验证明,鞣花酸、苯三酚和没食子酸都会与铁离子发生络合反应,生成黑色沉淀。这些结果均表明,桉树叶溶解出的芳香多酚类物质是导致水库变黑的核心因素。本研究基于分子组成层面提出了桉树人工林区水库水体泛黑形成机理,对于桉树人工林区的黑水治理和保障水库饮用水安全具有十分重要的意义。

Molecular composition and formation mechanism of black matter in water body of Eucalyptus artificial forest area in southern China

Black water frequently occurs in reservoirs within Eucalyptus artificial forest regions of southern China during the autumn and winter seasons. Previous studies have identified the primary cause as the complex formed by the reaction between substances like tannic acid in Eucalyptus leaves and metal ions, particularly iron ions. However, potential organic matter precursors forming these complexes in Eucalyptus leaves remains unclear. The molecular composition-based mechanism behind water blackening in Eucalyptus artificial forest reservoirs is not yet clear. This study employed Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to analyze the molecular composition of soluble organic compounds in Eucalyptus leaf soaking solutions and reservoirs in typical Eucalyptus forest areas (Jinwo and Tianbao Reservoirs). The results revealed that the Eucalyptus leaf soaking solution predominantly comprised polyphenolic compounds and their polymeric derivatives, primarily based on phenolic and gallic acids, with ellagic acid (C₁₄H₆O₈) being the most prevalent compound. Tannic acid concentration in winter reservoir water was higher than that in summer, with higher concentration observed in surface water compared to bottom water. This suggested that the substantial release of aromatic polyphenols from fallen Eucalyptus leaves during autumn and winter had a large contribution to black water. Subsequent experiments demonstrated that ellagic acid, pyrogallol, and gallic acid undergo complex reactions with iron ions, resulting in black precipitates. These outcomes collectively highlighted that aromatic polyphenols dissolved from Eucalyptus leaves were the primary factor causing black water. The study proposed a molecular composition-based mechanism for the formation of black water in Eucalyptus artificial forest area reservoirs, and offered crucial insights for effective management and ensuring the safety of drinking water in such reservoirs.