夏季闽江CDOM的空间分布与降解特征

利用三维荧光光谱-平行因子分析技术(EEMs-PARAFAC)以及微生物和光降解实验等方法,分析夏季闽江下游-河口区有色溶解有机质(CDOM)的组成、分布及其降解特征.结果表明,闽江下游-河口区CDOM存在三类荧光组分:类腐殖质、类酪氨酸和类色氨酸;类腐殖质是河段CDOM的主要荧光组分,在河口区随着盐度增加主要的荧光组分逐渐变为类蛋白质.CDOM的丰度变化呈现出明显的空间分布格局:河段CDOM的吸收系数a(280)较低,进入市区后有所增加,到了郊区呈现下降的趋势,而在河口区迅速下降;保守估计福州市区对闽江CDOM的贡献为8%.河段a(280)易被微生物降解和光降解,降解率分别为(28±8)%和(44±7)%,其生物可利用性和光化学活性远高于受海源CDOM影响的河口区;类腐殖质、类酪氨酸和类色氨酸荧光组分在河段具有较高的光化学活性,降解率分别为(75±0.5)%、(58±21)%和(73±3)%,但不易被微生物降解,而且在28 d微生物培养后出现类腐殖质的累积.

Spatial Distribution and Degradation of CDOM in the Minjiang River in Summer

The composition, distribution, and degradation of chromophoric dissolved organic matter (CDOM) in the lower reach and estuary of the Minjiang River were analyzed using fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC) and microbial and photochemical degradation experiments. The results show that there are three types of fluorescence components in the study area:humic-like, tyrosine-like, and tryptophan-like. The humic-like components are the main components in the river zone, while the protein-like components become dominant with increasing salinity in the estuary. The change of the CDOM abundance shows a notable spatial distribution pattern. The absorption coefficient a(280) of CDOM is lower in the river, increases after entering the urban area, shows a decreasing trend in the suburbs, and rapidly declines in the estuary. A conservative estimate of the contribution of the Fuzhou urban area to the CDOM of the Minjiang River is 8%. The a(280) in the river is susceptible to microbial and photochemical degradation and the degradation percentages are (28±8)% and (44±7)%, respectively. The bioavailability and photochemical reactivity of a(280) are much higher in the river than in the estuary. The humic-like, tyrosine-like, and tryptophan-like components show a higher photochemical reactivity in the river, with degradation percentages of (75±0.5)%, (58±21)%, and (73±3)%, respectively. The fluorescent components are not labile with respect to microbial degradation and humic-like components are accumulated after 28 days of microbial culture.