太湖有色可溶性有机物(CDOM)对COD及BOD5的指示意义

化学需氧量(COD)、五日生化需氧量(BOD_5)及溶解性有机碳(DOC)是指示湖泊水质的重要指标,然而上述指标测定通常耗费大量时间、试剂及人力物力且排放大量有害废液.有色可溶性有机物(CDOM)是溶解性有机物(DOM)中可以强烈吸收光谱中的紫外光和可见光的部分,数据测定耗时短、方便快捷,且样品处理过程环境友好,能在很大程度上反映湖泊水质.本研究基于2016年2、5和8月在太湖均匀布设的32个采样点进行样品采集,运用光谱吸收与三维荧光-平行因子分析(EEMs-PARAFAC)探究太湖CDOM的光谱吸收和荧光组分,探讨CDOM光谱指标对湖泊BOD_5、COD及DOC浓度等湖泊环境质量指标的可替代性.结果表明:(1)运用EEMs-PARAFAC方法解析出3种荧光组分:类腐殖酸C1、类酪氨酸C2和类色氨酸C3.(2) COD和BOD_5和DOC在空间上呈现出相似的分布趋势,不同水期的最高值均出现在竺山湾和梅梁湾,由西北湖区至中部敞水区、东南湖湾递减.(3)在不同水期,COD、BOD_5、DOC浓度和C1组分均表现为丰水期极显著大于枯水期和平水期,a_(254)在丰、平、枯水期间无显著性差异,最大值出现在丰水期;C2与C3组分均在枯水期和平水期极显著大于丰水期.(4)在不同水文时期,COD、BOD_5和DOC浓度均与a_(254)、类腐殖酸C1呈显著正相关,丰水期太湖COD、BOD_5和DOC浓度与CDOM光谱指标的线性相关性要优于枯水期和平水期.(5) CDOM光谱指标在不同水文时期均能很好地替代COD、BOD_5和DOC等作为反映太湖水体中有机物污染程度及湖泊水质的指标.

Optical indices of chromophoric dissolved organic matter (CDOM) as potential indicators tracing the variability of chemical oxygen demand (COD) and biochemical oxygen demand (BOD5) in Lake Taihu*

Chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), and dissolved organic carbon (DOC) are important indicators tracing lake water quality, but their measurement processes are time-consuming and require a large amount of reagent, manpower and material resources, and discharges harmful waste during measurements. Chromophoric dissolved organic matter (CDOM) is the fraction of dissolved organic matter (DOM) that can strongly absorb light at the ultraviolet region. The CDOM measurement is time-saving and convenient, and environmentally friendly, and the optical indices of CDOM can be used to trace lake water quality. We collected samples from 32 sampling sites in Lake Taihu for three occasions in February, May and August of 2016, using spectral absorption and the combination of excitation-emission matrices and parallel factor analysis (EEMs-PARAFAC) to explore the optical variability of CDOM in Lake Taihu and the applicability of using CDOM indices to trace the variability of BOD₅, COD, and DOC concentrations. Three fluorescent components were identified using EEMs-PARAFAC, including a humic-like C1, a tyrosine-like C2, and a tryptophan-like C3. COD, BOD₅, DOC and the optical indices of CDOM all showed similar spatial distribution trends with the highest values of these indices in different hydrological scenarios being found in Zhushan Bay and Meiliang Bay in the inflowing regions of the lake. The means of COD, BOD₅, DOC, and humic-like C1 in the rainy season were all significantly higher than those in the dry season and the wet-to-dry transition season. We found no significant difference between the mean of a₂₅₄ during the rainy, dry season, and the wet-to-dry transition season. The means of protein-like C2 and C3 were significantly higher in the dry season and wet-to-dry transition season than those in the rainy season. In different hydrological scenarios, COD, BOD₅, and DOC are all significantly positively correlated with a₂₅₄ and humic-like C1, and the linear correlation between COD, BOD₅, DOC and CDOM indices in Lake Taihu in the rainy season is better than that in the dry season and wet-to-dry transition season. CDOM optical indices including a₂₅₄, C1, C2, C3 are potential indices tracing the variability of COD, BOD₅ and DOC and are useful indicators tracing water quality in Lake Taihu and potentially a wider aquatic environment in different hydrological scenarios.