高原湖泊溶解有机质的三维荧光光谱特性初步研究

THREE-DIMENSIONAL EXCITATION EMISSION MATRIX FLUORESCENCE SPECTROSCOPY OF DISSOLVED ORGANIC MATTER FROM CHINESE HIGHLAND LAKES

提要近年来,荧光光谱技术被广泛应用于研究天然水体中溶解有机质(Dissolved Organic Matter,DOM)的物理化学特性。为了理解高原湖泊中DOM的组成、荧光光谱特性及其在湖泊水体中的垂直分布情况,作者利用荧光发射光谱、三维荧光光谱研究云贵高原湖泊红枫湖和百花湖中的DOM。结果显示,高原湖泊DOM主要表现为类富里酸荧光,包括可见区和紫外区两种类型的荧光峰,各种天然水体中都有报道的类蛋白荧光在红枫湖DOM中并不明显,而在百花湖DOM中则有较强的类蛋白荧光。溶解有机质所含三种类型荧光峰(PeakA:紫外区类富里酸荧光峰;PeakB:可见区类富里酸荧光峰;PeakC:类蛋白荧光峰)的荧光强度与溶解有机碳之间没有明显的线性相关关系,可能与高原湖泊水体pH值、DOM在湖泊不同深度由于受到光降解、微生物降解等作用存在差异等因素有关。与有机质结构和成熟度有关的荧光峰比值r(A,C)在1.40—2.09范围内,红枫湖南湖、百花湖DOM样品的r(A,C)值随着水体深度有下降的趋势,而红枫湖北湖DOM的r(A,C)值则随着水体深度有较大起伏,揭示了高原湖泊水体中DOM的结构以及分布情况存在差异。另外,r(A,C)值与pH之间具有良好的正相关关系,其相关系数红枫湖南湖DOM为0.95,百花湖两个采样点DOM分别为0.67、0.75,而红枫湖北湖DOM则显示出一定的负相关性(R2=0.45)。

Fluorescence spectroscopy has been widely used to elucidate the origin and structure of dissolved organic matter （DOM） since last decades. For better understanding the fluorescence of DOM in Chinese highland lakes, Lake Hongfeng and Lake Baihua in the southeastern China were chosen for research on fluorescence emission spectroscopy and three-dimensional excitation emission matrix fluorescence spectroscopy （3DEEM）. Results show that traditional fluorescence emission spectra could not determine the source of DOM in a lake. With 3DEEM technique, three fluorophores in lake DOM samples could be differentiated： Peak A and B are responsible for fulvic-like fluorescence, the former is by UV-excitation and the latter by visible excitation; and Peak C, the protein-like fluorescence. The fulvic-like fluorescence was found in all samples. Protein-like fluorescence was more obvious in samples from Lake Baihua than that from Lake Hongfeng. The correlation between fluorescence and DOC concentrations of the DOM samples shows that fluorescence could not indicate DOC concentration as fluorescence could vary with pH of lake waters, and the origins and the photodegradation of lake DOM. The fluorescence index r（A,C）, an indicator of structure and maturity of organic matter ranged from 1.40-2.09. Some r（A.C） values of the DOM decreased with the depth, while others fluctuated largely, indicating that the origin and chemistry of DOM changes with depth in the study lakes. In addition, some r（A.C） values show a linear positive relation with pH, while some others, a negative one, being the result of local argo-industrial pollution.