长江口盐度梯度下有色溶解有机物的分布、来源与季节变化

摘要

Absorption and fluorescence spectroscopies were used to examine the distribution,composition,sources and mixing behavior of colored dissolved organic matter (CDOM) in the Changiiang estuary in March and July 2015.The characteristics of fluorescent components of CDOM in the Changiiang Estuary were determined by fluorescence excitation emission matrix spectroscopy (EEMs) combined with parallel factor analysis (PARAFAC).Three humic-like components,i.e.,C1(260,375/490 nm),C2(365/440 nm) and C3(330/400 nm) and one protein-like component C4 (295/345 nm) were identified by EEMs-PARAFAC.The distribution and non-conservative mixing behavior of these four components were consistent with the total fluorescence intensity (TFI) both in March and July 2015,first increasing and then gradually decreasing from the inner estuary to outside the estuary,with the additional behavior and highest value observed at Turbidity Maximum Zone and removal process outside the estuary.Ranging from 1.12 to 7.19 in March and 0.87 to 6.71 in July,the humification index (HIX) values showed that CDOM in March had a higher degree of humification than that in July.The biological index (BIX) values ranged from 0.76 to 1.11 and 0.62 to 1.15 in March and July respectively,suggesting a greater contribution of biological activities to CDOM in July.In March,The average value of α(355) was 0.55 m-1,lower than that in July (0.61 m-1),reflecting higher content of CDOM in summer.The seasonal variation of SR was not obvious,increasing along the salinity in both seasons,which indicated that the average molecular weight of CDOM increased from the inside to the outside of the Changjiang Estuary.%通过测定有色溶解有机物(CDOM)的吸收光谱和荧光光谱研究了2015年3月和7月长江口盐度梯度下CDOM的分布、组成、来源及河口混合行为等.利用激发发射矩阵荧光光谱(EEMs)并结合平行因子分析(PARAFAC),研究了CDOM的荧光组分特征,共识别出两类4个荧光组分组成,即类腐殖质荧光组分C1 (260,375/490 nm)、C2 (365/440 nm)、C3 (330/400 nm)及类蛋白质荧光组分C4(295/345 nm).结果表明,3月和7月,4种荧光组分的分布模式与总荧光强度都基本一致:从口内到口外,先升高后降低,且4种组分都在河口呈现不保守混合行为,在最大浑浊带处存在添加过程,达到峰值,在口外有去除过程.3月腐殖化指数HIX范围在1.12～7.19,而7月HIX的范围在0.87～6.71;生物指数BIX在3月范围在0.76～1.11,7月为0.62～ 1.15,表明3月CDOM的腐殖化程度较7月高,而自生贡献比例较7月略低.3月吸收系数α(355)的平均值为0.55m-1,7月的略高,为0.61 m-1,表明7月长江口CDOM的含量略高.光谱斜率比值SR的季节性变化不大,都是近岸低,远岸高,表明CDOM的平均分子质量从口内到口外在逐渐增加.