溶解性有机质在盐田中的光谱学变化特征

Spectroscopic Characterization of Dissolved Organic Matter Isolated From Solar Pond

二维相关光谱技术(2D-COS)、三维荧光光谱技术结合平行因子分析(EEM-PARAFAC)具有扩展识别重叠峰,判断不同组分动态变化规律的技术特点。因此,2D-COS和EEM-PARAFAC分析技术可以用来分析溶解性有机质(DOM)结构组成和光谱变化特征。采用溶解性有机碳(DOC)、紫外-可见吸收光谱(UV)和EEM分析技术,借助2D-COS和PARAFAC分析模型,对青藏高原具有代表性的察尔汗盐湖、西台吉乃尔盐湖和马海盐湖中DOM在盐田摊晒过程中的结构组成和光谱学变化特征进行了研究。结果表明,随着日照时间延长,盐田中DOM和有色DOM(CDOM)含量逐渐升高,且DOM的增长倍数明显高于CDOM。在整个盐田摊晒阶段,察尔汗、西台吉乃尔和马海盐田中DOM和CDOM分别增长了1.5 vs.1.0、8.2 vs.5.3和15.7 vs.11.0倍。此外,SUVA254、HIX值在盐田中总体上呈现出逐渐减小的变化趋势。2D UV-COS分析结果表明,在察尔汗、西台吉乃尔和马海盐田中,吸收峰分别在230、217和235 nm处的DOM变动较大,变化顺序分别为228>229>230>231>232 nm&235>234>233>232 nm、200>216>300 nm和201>203>231>232>237>238>281>217 nm。EEM-PARAFAC分析结果表明,盐湖卤水中有5种荧光组分,包括4种类腐殖质荧光组分,分别是类海洋腐殖质C1(Ex/Em:320/400 nm)、类腐殖酸C2(Ex/Em:250/400 nm)和C3(Ex/Em:260/400 nm)、疏水性腐殖酸C5(Ex/Em:280,360/430 nm)和1种类蛋白质组分C4(Ex/Em:280/350 nm)。其中,尤以类腐殖质为主,分别占总荧光组分的84.0%(察尔汗)、87.2%(西台吉乃尔)和93.1%(马海)。随着盐田日晒时间的延长,C1、C2和C5在盐田中逐渐减少直至稳定不变。其中,C2组分在盐田的尾卤阶段基本消失,表明C2组分更加容易降解。C3和C4在察尔汗和马海盐田的前期逐渐减少,后期却略有升高。相对来说,C3和C4性质相对顽固,在盐田中降解程度远小于其他三个组分:6.7%<C3/C4<75.2%vs.52.8%<C1/C2/C5<100%。

Two-dimensional correlation spectroscopy(2D-COS)and three-dimensional excitation-emission matrix fluorescence technologies coupled with parallel factor analysis(EEM-PARAFAC)are characterized by separating overlapping peaks and insight into different component variations.Therefore,the 2D-COS and EEM-PARAFAC technologies can be used to probe into the compositions and spectral changes of dissolved organic matter(DOM).Here,the compositions and variations of DOM in solar ponds isolated from three representative salt lakes,i.e,Qarham Xitaijinaier and Mahai salt lake,were investigated using dissolved organic carbon UV-Visible absorption spectrum(UV)and EEM coupling with 2D-COS and PARAFAC.The results indicated that the contents of DOM and color DOM(CDOM)increased with the prolongation of sunshine times,and they increased 1.5 vs.1.0,8.2 us.5.3 and 15.7 us.11.0 times for DOM and CDOM they originated from Qarham Xitaijinaier and Mahai,respectively.Moreover,the values of SUVA254 and HIX decline in solar ponds suggested that the relative contents of aromatic compounds were decreased.The 2D UV-COS results indicated that the DOM with absorption peaks at 230,217 and 235 nm were susceptibility in solar ponds,and following the sequence:228>229>230>231>232 nm&235>234>233>232 nm,200>216>300 nm and 201>203>231>232>237>238>281>217 nm for Qarham Xitaijinaier and Mahai,respectively.The EEM-PARAFAC results revealed that the salt lake DOM is mainly composed of four humic-like substances,i.e.marine humic-like component C1(Ex/Em:320/400 nm),humic-like acids C2(Ex/Em:250/400 nm)and C3(Ex/Em:260/400 nm),hydrophobic humic acid C5(Ex/Em:280,360/430 nm)and one protein-like substance C4(Ex/Em:280/350).The percentages of humic-like substances were 84.0%,87.2%and 93.1%in total fluorescent contents in Qarham,Xitaijinaier and Mahai,respectively.Along with the sunshine extent,the relative contents of Ci,C2 and C3 exhibited an initial decrease followed by a gradual decline or stabilization,especially C2 absence from the tail brine,indicating its lability.C3 and C4 exhibited an initially decrease,followed by the gradual increase in the solar ponds of Qarham and Mahai.Compared to other components,C3 and C4 were more refractory to degrade,i.e.,6.7%<C3/C4<75.2%us.52.8%<C1/C2/C5<100%.