浙皖丘陵区饮用水水库夏季有色可溶性有机物光谱特征及环境指示意义

Characterizing optical characteristics of chromophoric dissolved organic matter in drinking water reservoirs in Zhejiang and Anhui Provinces in summer and the corresponding environmental significance

大型水库是我国特大、大中型城市集中式饮用水供水源地且兼具调蓄洪峰、农田灌溉、旅游观光等多种功能.浙皖丘陵地区饮用水水库分布广泛,夏季因藻类增殖而面临一定的水质风险.本研究借助总氮(TN)、总磷(TP)、叶绿素(Chl a)、透明度(SDD)等水质参数,以及基于以上参数所构建的综合富营养指数(TLI),结合有色可溶性有机物(CDOM)吸收光谱、三维荧光光谱(EEMs)及平行因子分析法(PARAFAC),试图揭示浙皖丘陵地区共计12个饮用水库夏季营养水平、CDOM光谱特征及环境指示意义.结果表明,本研究调查水库的TLI处于25.0~48.8范围内,属中营养水平,对应a_(254)为7.0~10.2 m^(-1).TP与Chl a、TLI、a_(254)、陆源类腐殖酸C2均具有显著的相关性(p<0.01),表明TP是饮用水水库藻类增殖的主要制约因子,且与TLI关联密切.水库中Chl a浓度普遍较低,平均值为(8.4±5.7)μg·L^(-1),且与类酪氨酸C1、类色氨酸C3不存在显著相关性(p>0.05),说明藻源CDOM在水库中迅速降解且不是饮用水水库监测到的CDOM的主要来源.在坝前敞水区陆源类腐殖酸C2与a_(254)(r=0.81,p<0.01)、Chl a(r=0.37,p<0.05)呈显著正相关,并且腐殖化指数(HIX)、光谱斜率S_(275~295)与TLI亦具有显著的相关性,说明饮用水水库营养水平受陆源有机质输入的影响较大.然而,坝前S_(275~295)平均值为(23.2±2.8)μm^(-1),HIX平均值为1.56±0.62,表明CDOM腐殖化程度较低;这可能是由于饮用水水库受强烈光降解的影响,因而CDOM表现出“表观”陆源信号弱的特征.坝前a_(254)、陆源类腐殖酸C2与TLI的回归系数较低,说明陆源类腐殖酸在应用于大型水库坝前敞水区营养水平估测时应当更加谨慎.

Large reservoirs supply drinking water to metropolitans and large cities,and serve as flood regulator and provide water for farmland irrigation,tourism,and entertainment.Drinking water reservoirs are widely distributed in the hilly areas of Anhui and Zhejiang Provinces,and these waters encounter certain water quality risks in the summer with the proliferation of algae cells and release of algal-derived chromophoric dissolved organic matter(CDOM).We used total nitrogen(TN),total phosphorus(TP),chlorophylla(Chl a),Secchi disk depth(SDD),and calculated trophic level index(TLI)based on these four indices,together with CDOM absorption and fluorescence spectroscopy to unravel the sources and optical composition of CDOM in a total of 12 drinking water reservoirs in Zhejiang and Anhui Provinces.Our results showed that the drinking water reservoirs were mostly mesotrophic with TLI ranged from 25.0 to 48.8 and a_(254) ranged from 7.0 to 10.2 m^(-1).we found Chl a,TLI,a_(254),and terrestrial humic-like C2 increased with increasing concentration of TP(p<0.01),indicating that TP was a major influencing factor controlling algal growth in drinking water reservoirs and TP was closely associated with TLI.The average concentration of Chl a was(8.4±5.7)μg·L^(-1),and we found no significant correlation between Chl a and tyrosine-like C1 or tryptophan-like C3(p>0.05),indicating that rapid algal degradation contributed insignificantly to the CDOM pool in those reservoirs.Terrestrial humic-like C2 showed a significant positive correlation with a_(254)(r=0.81,p<0.01)and Chl a(r=0.37,p<0.05),and TLI increased with increasing humification index(HIX)and with decreasing spectral slope S_(275~295)in the open water region,indicating that terrestrial input of organic substances contributed importantly to nutrient levels in the open waters of the studied reservoirs.The mean of S_(275~295) was(23.2±2.8)μm^(-1),corresponding to a mean HIX of 1.56±0.62,indicating a relatively low aromaticity of CDOM in the drinking water reservoirs,likely due to a high SDD and enhanced photodegradation of CDOM,and thereby a low apparent terrestrial signal of CDOM in those waters.The regression coefficient of a_(254),terrestrial humic-like C2 and TLI were low,suggesting that we should be more cautious when terrestrial humic-like components were applied to the estimation of nutrient levels in open water areas of large reservoirs.