Santos L, Santos E B H, Dias J M, Cunha A, Almeida A
Department of Biology & CESAM, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal.
Photochem Photobiol Sci. 2014 Aug;13(8):1146-59. doi: 10.1039/c4pp00005f.
The influence of photochemical transformations of chromophoric dissolved organic matter (CDOM) on microbial communities was evaluated in the estuarine system Ria de Aveiro. Two sites, representative of the marine and brackish water zones of the estuary, were surveyed regularly in order to determine seasonal and vertical profiles of variation of CDOM properties. Optical parameters of CDOM indicative of aromaticity and molecular weight were used to establish CDOM sources, and microbial abundance and activity was characterized. Additionally, microcosm experiments were performed in order to simulate photochemical reactions of CDOM and to evaluate microbial responses to light-induced changes in CDOM composition. The CDOM of the two estuarine zones showed different spectral characteristics, with significantly higher values of the specific ultra-violet absorbance at 254 nm (SUVA254) (5.5 times) and of the absorption coefficient at 350 nm (a350) (12 times) and lower SR (S275-295/S350-400) ratio at brackish water compared with the marine zone, reflecting the different amounts and prevailing sources of organic matter, as well as distinct riverine and oceanic influences. At the marine zone, the abundance of bacteria and the activity of Leu-AMPase correlated with a350 and a254, suggesting a microbial contribution to the HMW CDOM pool. The irradiation of DOM resulted in a decrease of the values of a254 and a350 and an increase of the slope S275-295 and of the ratios E2 : E3 (a250/a365) and SR, which in turn increase its bioavailability. However, the extent of photoinduced transformations and microbial responses was dependent on the initial optical characteristics of CDOM. In Ria de Aveiro both photochemical and microbial processes yielded optical changes in CDOM and the overall results of these combined processes determine the fate of CDOM in the estuarine system and have an influence on local productivity and in adjacent coastal areas.
在阿威罗里亚河口系统中评估了发色溶解有机物（CDOM）的光化学转化对微生物群落的影响。对河口的海洋和咸水区域具有代表性的两个地点进行了定期调查，以确定CDOM特性的季节性和垂直变化特征。利用指示芳香性和分子量的CDOM光学参数来确定CDOM来源，并对微生物丰度和活性进行了表征。此外，进行了微观实验以模拟CDOM的光化学反应，并评估微生物对光诱导的CDOM组成变化的反应。两个河口区域的CDOM显示出不同的光谱特征，与海洋区域相比，咸水区域在254 nm处的特定紫外吸光度（SUVA254）（高5.5倍）和350 nm处的吸收系数（a350）（高12倍）显著更高，而SR（S275 - 295/S350 - 400）比值更低，这反映了有机物质的不同数量和主要来源，以及不同的河流和海洋影响。在海洋区域，细菌丰度和亮氨酸氨肽酶活性与a350和a254相关，表明微生物对高分子量CDOM库有贡献。DOM的辐照导致a254和a350值降低，以及斜率S275 - 295和比值E2∶E3（a250/a365）和SR增加，这反过来又增加了其生物利用度。然而，光诱导转化和微生物反应的程度取决于CDOM的初始光学特征。在阿威罗里亚河口，光化学和微生物过程都导致了CDOM的光学变化，这些综合过程的总体结果决定了CDOM在河口系统中的命运，并对当地生产力和邻近沿海地区产生影响。
