太湖北部湖区春、冬季节天然有机质的荧光特征及环境意义

Fluorescence Characteristics and Environmental Significance of Organic Matter in the Northern Part of Lake Taihu in Spring and Winter

天然有机质(OM)广泛存在于各类水体,含有丰富的碳、氮、磷等生源要素,其形成、转化、归宿及其相伴随的营养盐再生过程是水生态系统营养盐生物地球化学循环的重要环节,在湖泊蓝藻水华暴发过程中势必也扮演着非常重要的营养盐供给者的角色.本研究于2015年2月和5月分别在太湖北部湖区采集了17个样品,利用POM-DOM PARAFAC三维荧光模型解析春、冬季节颗粒态有机质(POM)和溶解态有机质(DOM)的荧光特征及来源,并探讨POM和DOM各荧光组分之间及其与叶绿素a(Chla)的关系.结果表明,春、冬季节太湖北部湖区POM和DOM的荧光峰、荧光中心位置和荧光强度均存在明显的差别;POM有着比DOM更复杂的组分构成.综合POM和DOM的荧光强度和荧光指数可知,春、冬季节太湖北部湖区POM和DOM均以自生源为主,河口区受陆源贡献较大.POM(C1p^C5p)和DOM(C1d^C5d)有5种荧光组分,分别是类色氨酸(C1和C2)、类腐殖质(C3和C4)及类酪氨酸(C5).POM和DOM的荧光组分特征存在明显的差别;春、冬季节POM均以类腐殖质荧光C3为主,荧光组分高值区分别集中在梅梁湾区域和湖心区;而DOM均以类蛋白组分C2、C1和C5为主,荧光组分高值区均分布在竺山湾区域.相关分析结果显示,春季C1d与C2d(P<0.01)、C3d与C4d(P<0.01)、C1p与C4p(P<0.05)、C2p与C5p(P<0.01)均具有较强的相关性.值得注意的是,C3d(P<0.01)、C4d(P<0.05)与C3p均具有较好的相关关系,表明POM与DOM在组分、来源上具有某种联系.与春季类似,冬季荧光组分C1d与C2d、C3d与C4d、C1p与C2p、C1d与C2p亦具有极好的相关性(P<0.01).春季C5d与Chla之间存在正相关关系(P<0.01),而C2d(P<0.05)、C3p(P<0.01)与Chla之间具有负相关关系;冬季C4d与Chla之间也存在负相关关系(P<0.05).

Organic matter （OM） , rich in carbon, nitrogen, phosphorus and other biogenic elements, has numerous geochemical and ecological functions in all kinds of water bodies, and is highly valued in ecological studies of both marine and inland environments. The formation, transformation, and fate of OM, and its accompanying nutrient regeneration process are key links in the biogeochemical cycling of nutrients in aquatic ecosystems. Furthermore OM, as a provider of nutrients, also plays a very significant role during the outbreak of algal blooms in inland lakes. Two extensive sampling campaigns were conducted at the same site （n = 17） in Lake Taihu in February and May of 2015, and 34 （17 X 2） samples were collected. Excitation-emission matrix （EEM） fluorescence was combined with parallel factor analysis （PARAFAC） to characterize the spatial-temporal variations in the components and sources of particulate （POM） and dissolved （DOM） organic matter. Moreover, the correlations between fluorescence intensity and Chla were studied. Significant differences between the fluorescence peaks, fluorescence positions, and fluorescence intensities of POM and DOM indicated that the components of POM were more complex than those of DOM. Fluorescence intensities and fluorescence indices indicated that POM and DOM possessed endogenous characteristics and that estuaries possessed obvious exogenous characteristics. Five types of fluorophores were present in POM （Clp-C5p） and DOM （Cld-C5d） ： tyrosine-like fluorophores （ C1 and C2）, humic-like fluorophores （C3 and C4 ）, and tryptophan-like fluorophores （C5）. The fluorescent components of POM and DOM differed significantly. C3p was the dominant fluorophore in POM during spring and winter, and fluorescence intensities of C1 p-C5p were higher in the Meiliang Bay and the central part of thelake than in other areas. C2d, Cld, and C5d were the dominant fluorophores in DOM during spring and winter, and fluorescence intensities of Cld-C5d were higher in the Zhushan Bay than in other areas. In spring, positive correlations were observed between Cld and C2d （ P 〈 0.01 ） , C3d and C4d （ P 〈 O. 01 ） , Clp and C4p （ P 〈 0.05 ） , and C2p and CSp （P 〈0. O1 ）. Remarkably, C3p and C3d （P 〈 0.01 ） and C3p and C4d （P 〈 0.05 ） were positively correlated, suggesting that these two forms of OM were correlated. Similarly, highly significant, positive correlations were observed between Cld and C2d （P 〈0.01）, C3dandC4d （P〈0.01）, ClpandC2p （P〈0.01）, andCldandC2p （P〈0.01） during winter. Furthermore, Chlaand C5d were significantly and positively correlated （P 〈 0. 01 ）. However, both Chla/C2d and Chla/C3p were negatively correlated in spring. Furthermore, Chla and C4d were negatively correlated in winter.