三峡库区典型农业小流域土壤溶解性有机质的紫外-可见及荧光特征

Ultraviolet-Visible( UV-Vis) and Fluorescence Spectral Characteristics of Soil Dissolved Organic Matter( DOM) in Typical Agricultural Watershed of Three Gorges Reservoir Region

以三峡库区典型农业小流域土壤溶解性有机质(DOM)为研究对象,利用紫外-可见和荧光光谱,分析和讨论了不同土地利用类型(包括林地、田地、菜地和民用地)对土壤DOM地化特征的影响.结果表明,不同土地利用条件下DOM性质差异明显,以林地DOM的芳香性程度较高,腐殖化特征最强,其次为田地;尽管居民用地和菜地溶解性有机碳(DOC)含量高(均值分别为0.81 g·kg-1和0.89 g·kg-1),但是芳香化程度低,DOM中非生色组分对高DOC含量的贡献明显.所有样本荧光指数(FI)介于自生源特征(FI=1.9)和陆源特征(FI=1.4)之间,自生源(类蛋白组分)和异生源(类腐殖组分)对DOM均有贡献.大部分样本r(T/C)都大于2.0,说明该农业小流域土壤DOM受外来因素尤其是人类活动影响较大,尤以菜地为代表.另外,不同特征光谱参数对不同土地利用条件下DOM结构和性质差异性的灵敏程度不同,光谱斜率比值(SR)和腐殖化指数(HIX)不能反映DOM地化特征的差异性,因此单一光谱指标并不能全面提供DOM的特征信息,建议两种光谱分析方法联用.

As an important geo-factor to decide the environmental fate of pollutants in watershed,soil dissolved organic matter( DOM)sampled from a typical agricultural watershed in the Three Gorges Reservoir area was investigated using ultraviolet-visible( UV-Vis)and fluorescence spectroscopies,to analyze and discuss the effect of different land uses including forest,cropland,vegetable field and residence,on soil DOM geochemical characteristics. The results showed that significant differences in DOM samples amongst different land uses were observed,and DOM from forest had the highest aromaticity and humification degree,followed by DOM from cropland.Although DOM from vegetable field and residence showed the highest dissolved organic carbon( DOC) concentration( average values0. 81 g·kg- 1and 0. 89 g·kg- 1,respectively),but the aromaticity was lower indicating lower humification,which further suggested that the non-chromophoric component in these DOM samples contributed significantly to total DOM compositions. Additionally,in all DOM samples that were independent of land uses,fluorescence index( FI) values were between 1. 4( terrigenous) and 1. 9( authigenic),evidently indicating both the allochthonous and autochthonous sources contributed to DOM characteristics. Meanwhile,r( T/C)values in most of samples were higher than 2. 0,suggesting that soil DOM in this agricultural watershed was heavily affected by anthropogenic activities such as agricultural cultivation,especially,vegetable field was a good example. Additionally,sensitivities of different special spectral parameters for reflecting the differences of DOM characteristics amongst different land uses were not identical.For example, neither spectral slope ratio( SR) nor humification index( HIX) could clearly unveil the various geochemical characteristics of soil DOM from different sources. Thus,simple and single special spectral parameter cannot comprehensively provide the detailed information of DOM,and combined application of UV-Vis and fluorescence spectroscopies is highly recommended.