摘要
三峡库区消落区作为水陆衔接的过渡地带,具有敏感而脆弱的生态系统,可能引起一系列生态环境问题。土壤溶解有机质(DOM)可与痕量重金属离子相互作用,影响其在水陆界面的迁移转化、毒性和生物可利用性等。因此,关于消落区土壤中DOM的物理化学特性研究是其生态环境问题防控和治理的重要环节。本文选取开县消落区,通过对土壤DOM荧光光谱特征进行分析,得到以下结论:
(1)土壤DOM的浸提采用冷冻干燥的土壤样品,浸提时间为16h, DOM样品采取4℃冷藏且避光的方法保存。
(2)消落区土壤DOM含有可见光区类腐殖质荧光峰A和紫外光区类腐殖质荧光峰C、长波处类色氨酸荧光峰B和短波处类色氨酸荧光峰D,仅在某些土壤中出现长波处类酪氨酸荧光峰E和短波处类酪氨酸荧光峰F。土壤DOM峰A、峰B、峰D、峰F位置变化范围较大,峰C、E位置无较大范围波动。对荧光峰强度分析发现,土壤腐殖质是消落区土壤DOM的主要来源,消落区土壤DOM中类腐殖质以大分子量的腐殖酸物质为主。
(3)对2009年1月~7月采集的消落区土样DOM分析发现,在研究时段内,DOM中类腐殖质荧光物质有所增加,类色氨酸和长波处类酪氨酸荧光物质有所减少,短波处类酪氨酸物质变化不大,这预示着消落区土壤被淹没后,对上覆水体释放类腐殖质物质的潜力较大。
(4)对沿小江流向的消落区土壤DOM的变化分析发现,峰A、峰C、峰D荧光强度变化趋势大致相同;峰B、峰E和峰F则无明显规律。对开县各镇消落区土壤DOM分析表明,各镇类腐殖质荧光强度变化趋势相同,荧光物质含量无明显差异;各镇类色氨酸、类酪氨酸荧光强度变化趋势不同,荧光物质含量存在明显的差异。对裸露区和淹没区土壤DOM荧光强度的比较发现,土壤周期性的淹没和裸露对DOM中的荧光峰C和峰D强度影响较大,裸露区土壤比淹没区含有更多DOM。
(5)荧光强度比值分析揭示消落区土壤污染尚不严重,且土壤DOM中至少含有两种类型的类腐殖质荧光基团和类蛋白荧光基团;类腐殖质荧光峰A与C之间具有较好的相关关系,类色氨酸荧光峰B与峰D之间的相关性较差,类酪氨酸荧光峰E与峰F存在一定的相关关系;而峰A与峰B、峰E之间均存在着一定的相关关系。各荧光峰与有机质之间存在着一定的相关关系。对DOM的HIX值分析发现,裸露区土壤DOM腐殖化程度较高、芳香性较大,土壤被周期性的淹没和裸露对DOM腐殖化程度有较大的影响。在研究时段内,消落区土壤DOM的腐殖化程度有所提高。
(6)消落区土壤中类腐殖质和类蛋白荧光物质是重金属Cd(Ⅱ)、Pb(Ⅱ)的强有机配位体,且Cd (Ⅱ)、Pb(Ⅱ)与DOM中的富里酸结合能力强于与腐殖酸的能力;紫色土DOM中类腐殖质荧光物质与Pb(Ⅱ)结合的荧光基团的比例均大于与Cd(Ⅱ)结合的比例,预示着在紫色土中Pb(Ⅱ)较易随DOM发生迁移和转化; Cd(Ⅱ)易与沙质土DOM中类腐殖质荧光物质结合,Pb(Ⅱ)易与类蛋白荧光物质结合,预示着在沙质土中两者均易随DOM迁移或扩散到水环境中去;Cd (Ⅱ)、Pb(Ⅱ)与消落区沙质土DOM中类蛋白荧光物质结合的能力比与类腐殖质荧光物质的能力强。
论文研究成果可为研究三峡库区消落区土壤DOM特征及其迁移转化规律提供基础数据,为治理消落区生态和环境问题提供基础数据与理论依据。
As the zone where the transition between land and water converges, the water-level-fluctuating zone (WLFZ) has a sensitive and fragile ecosystem. This could result in a series of ecological and environmental problems in the WLFZ as well as the Three Gorges Reservoir (TGR). Dissolved organic matter (DOM) plays an important role in the migration and transformation of pollutants. DOM may interact with trace heavy metal ions, influencing their migration and transformation at the land and water interface, their toxicity and their bio-availability. Therefore, the study on physical and chemical characteristics of DOM in the WLFZ soil is the important part of prevention and control of ecological environmental problems in the WLFZ, TGR. So in this paper, the author selects soil samples in the WLFZ of Kai County, from the analysis of Three-dimensional fluorescence spectral of soil DOM, making conclusions as follows:
(1) Extraction of soil DOM used freeze-drying soil samples, and samples were shaken for 16 h. Samples were kept in a refrigerator at 4°C.
(2) Soil DOM from the WLFZ of Kai County was found to contain four fluorescence peaks: peaks A and C, which represent humus-like fluorescence, and peaks B and D, which represent tryptophan-like fluorescence. Two additional peaks, E and F, which represent tyrosine-like fluorescence, were only present in certain soils. Analysis of location of the soil DOM fluorescence peaks showed that the fluctuations of the position of peak A, B, D, F varied greatly, and that of peak C, E was not large. Analysis of soil DOM fluorescence intensities showed that soil humus was the main source of soil DOM, and the humus-like material in the soil DOM from the WLFZ was mainly humic substances of large molecular weight.
(3) Analysis of soil DOM collected from January to July, 2009 showed that the humic-like substances increased, tryptophan-like and high-wavelength tyrosine-like substances reduced in the studing period, and low-wavelength tyrosine-like substances had no change. This indicated the potential ability of release in to the overlying water of humic-like substances were stronger.
(4) Analysis of soil DOM from the WLFZ along the flow of XiaoJiang showed the changing trend of Peak A, C, D fluorescence was similar; Peak B, E and F had no obvious rule. Analysis of soil DOM from the six towns showed that the changing trends of fluorescence intensity of humic-like in the six towns were the same, and there was no obvious difference between the content of humic-like in the six towns; The changing trends of fluorescence intensity of tryptophan-like and tyrosine-like in the six towns were different, and there was significantly difference between the content of that in the six towns. The comparison of the fluorescence intensities of soil DOM in submerged soil and in exposed soil showed that the fluorescence intensities of peaks C and D were greatly influenced by the water level fluctuations, and there was more DOM in the exposed soil than the submerged soil of the WLFZ. Analysis of the HIX values in submerged and exposed soil DOM indicated that the soil DOM in exposed areas had a higher degree of humification and aromaticity, and periodic submerging and exposure of soil had an impact on the humification of DOM.
(5) The fluorescence intensity ratios of soil DOM in the WLFZ showed that WLFZ soil was not polluted badly, and the soil DOM contained at least two types of humus-like fluorescence groups and two types of protein-like fluorescence groups. Analysis of the correlations between the fluorescence intensities of the different peaks showed that the fluorescence intensities of peaks A and C had a good correlation, the tryptophan-like fluorescence peaks B and D had a poor correlation and tyrosine-like fluorescence peaks E and F had some correlation. A good correlation between the humic-like fluorescence peak A and the protein-like fluorescence peaks E and F. The intensities of fluorescence peaks of soil DOM and SOM had some correlation.
(6) The humic-like and protein-like fluorescence matter of soil DOM were strong organic ligands of Cd (Ⅱ), Pb (Ⅱ) in the WLFZ, and the ability that Cd(Ⅱ) and Pb(Ⅱ) combined with fulvic acid (small molecular weight) was stronger than that of humic acid (large molecular weight). The combined ratio of fluorophores between Pb(Ⅱ) and soil DOM was larger than that of Cd(Ⅱ) in Zhenan town, indicating that Pb(Ⅱ) could easily migrate and convert with the purple soil DOM. Cd(Ⅱ) could easily combine with humic-like fluorescence matter of sandy soil DOM, and Pb(Ⅱ) could easily combine with protein-like fluorescence matter. In the sandy soil of the WLFZ, Cd(Ⅱ) and Pb(Ⅱ) could easily migrate or proliferate to the water environment. The ability that Cd(Ⅱ) and Pb(Ⅱ) combined with protein-like fluorescence matter was stronger than that of humic-like fluorescence matter in the sandy soil of the WLFZ.
The research results of the paper can provide the basic data and theoretical basis for the study of the characteristics and the migration and transformation of the DOM in the WLFZ of the TGR. It can also provide a theoretical basis for control ecological and environmental problems in the WLFZ.
引文
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