千岛湖有色可溶性有机物光谱学特征及环境指示意义

有色可溶性有机物的光谱学特征能在一定程度上揭示湖泊溶解性有机物来源及其迁移转化规律,探究其光谱学特征对水质保护具有重要的现实意义.本文基于2018年10月在国家级水源供给水库千岛湖布设的60个采样点进行样品采集,运用光谱吸收及三维荧光,结合平行因子分析等方法揭示该湖有色可溶性有机物的光谱特征及其在空间上的变化,进而揭示有机物来源和迁移转化规律,探讨荧光光谱在水质监测应用等方面的指示意义.三维荧光矩阵经平行因子分析解析获得4种荧光组分包括陆源类腐殖酸C1、类酪氨酸C2、类色氨酸C3及微生物作用的类腐殖质C4.类腐殖质组分C1和C4与溶解性有机碳、有色可溶性有机物特征波长吸收系数a(350)均呈现出由西北入湖河口至其它湖区递减的分布趋势,并且C1和C4与溶解性有机碳、a(350)具有很好的相关性与之印证,说明上游新安江输入是千岛湖有机物的主要来源,类腐殖酸是主要的荧光组分.两种类蛋白组分包括类酪氨酸C2和类色氨酸C3分布均具有高度的空间异质性,高值均集中分布在靠近淳安县的湖心区及大坝附近的东南湖区,且该两个组分与叶绿素a浓度无显著相关性.从上游新安江河口至下游大坝出水口方向类腐殖酸组分所占比重逐步减小,而类蛋白组分所占比重增大.结合对该湖周边城镇居民用地分析表明湖心区及东南湖区类蛋白组分一定程度上可能来源于淳安县居民区生活污水的排放;同时,来自上游的类腐殖酸不断稀释及光降解转化为类蛋白组分可能是荧光光谱组成空间变化的又一个原因.C1为主要的荧光信号并与溶解性有机碳、a(350)及叶绿素a浓度具有更好的线性拟合优度,说明陆源类腐殖酸C1相比于其他荧光组分对有机物反演更为准确灵敏.由此表明,千岛湖有色可溶性有机物荧光光谱对有机物来源和迁移转化规律及水质监测等方面具有重要的环境指示意义.

Spectral characteristics and environmental significance of chromophoric dissolved organic matter in Lake Qiandao, a large drinking water reservoir

The optical characteristics can be used to trace the sources and transformation processes of chromophoric dissolved organic matter (CDOM). Lake Qiandao is an important drinking water reservoir, and it is of great significance to explore the optical characteristics of CDOM in the lake for its water quality protection. In October 2018, CDOM variability in the lake was investigated using CDOM absorption and excitation-emission matrices (EEMs) based on the collection of 60 surface water samples (0.5 m). Four fluorescent components were obtained using EEMs coupled with parallel factor analysis (PARAFAC), including a terrestrial humic-like component C1, a tyrosine-like component C2, a tryptophan-like component C3, and a microbial humic-like component C4. C1 and C3 contributed primarily to the CDOM fluorescence pool in Lake Qiandao. The two humic-like components C1 and C4 share similar spatial distribution patterns with dissolved organic carbon (DOC) concentration and CDOM absorption coefficient at 350 nm a(350) with high values found in the northwestern inflowing river mouths and decreased gradually to the eastern downstream lake regions. This result indicated that CDOM associated with upstream terrestrial soil organic-rich substances may be the main source of the organic matter pool in Lake Qiandao. There was no significant correlation between chlorophyll a (Chla) and tyrosine-like C2 or tryptophan-like C3. Both C2 and C3 shared high spatial heterogeneity with high values recorded in the lake center surrounding the city of Chun''an. The contribution of protein-like components (%protein) increased from northwestern inflowing river mouth to the downstream eastern lake regions, which might be explained by the release of domestic sewage from the surrounding residential areas, and the dilution and photochemical degradation of terrestrial humic-like components. Terrestrial humic-like component C1 was closely correlated to DOC, a(350), and Chla than the remaining three components, indicating that C1 (Ex/Em=255 (315)/428 nm) might be a useful indicator tracing the input of organic matter from upstream rivers. In conclusion, the optical characteristics of CDOM in Lake Qiandao can be used as important environmental indicators tracing the sources of organic matter and were helpful for water quality monitoring in the lake.