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Optical signatures of dissolved organic matter in the watershed of a globally large river (Yangtze River, China)

机译：全球大型河流（中国长江）流域中溶解有机物的光学特征

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摘要

Parallel factor analysis of fluorescence excitation emission matrices of surface water samples of a globally large river (Yangtze River, China) watershed identified three classes of fluorescent dissolved organic matter (FDOM) that had ex/em=280/330nm, 305/385nm and 350/450nm respectively, resembling "peak T", "peak M" and "peak C" commonly identified in natural water, respectively. Peak T (a tyrosine/tryptophan-like FDOM) did not show correlations to peak M or C which were humic-like substances, while a positive correlation (r=0.935, p<0.001) was present between the natural log-transformed maximum fluorescence intensity (F_(max)) of peaks T and M indicating a tight link during their production and processing. F_(max) values (in Raman unitnm~(-1)) normalized to dissolved organic carbon (DOC) concentration were low, varying in ranges 15.93-85.95, 29.83-83.54 and 19.73-51.05×10~(-5)nm~(-1) (μmol/L)~(-1) for peaks T, M and C, respectively, in line with the history of strong photobleaching of the water samples as indicated by fairly high absorption spectral slope ratios (0.75-1.53 with a mean 1.03). Intermediate fluorescence index (FI) (1.46-1.83 with a mean 1.61) and small specific absorption at 254nm (0.64-1.93 with a mean 1.15m~(-1)mg~(-1)L) of the water samples, indicated the presence of both aquatic microbial DOM (e.g. peak T) and soil DOM (e.g. peak C). Peak C could be substantially removed by UV-A (320-400nm) irradiation, while peak M was slightly increased when a microbe-containing water was exposed to the same UV-A irradiation. Taken together, peak C was attributed to diffuse soil source while peak M was likely attributed to joint effects of microbial activities and solar irradiation on the chromophores in the sample.
机译：全球大河流域（中国长江流域）地表水样品的荧光激发发射矩阵的并行因子分析确定了三类荧光溶解有机物（FDOM），它们分别为ex / em = 280 / 330nm，305 / 385nm和350 / 450nm，分别类似于天然水中常见的“峰值T”，“峰值M”和“峰值C”。峰T（酪氨酸/色氨酸类FDOM）与腐殖质样物质的峰M或C没有相关性，而自然对数转换的最大荧光之间存在正相关性（r = 0.935，p <0.001）。 T和M峰的强度（F_（max））表示在生产和加工过程中存在紧密联系。归一化为溶解有机碳（DOC）浓度的F_（max）值（以拉曼单位nm〜（-1）为单位）较低，范围在15.93-85.95、29.83-83.54和19.73-51.05×10〜（-5）nm〜之间变化T，M和C峰分别为（-1）（μmol/ L）〜（-1），这与水样品强烈的光漂白历史一致，如较高的吸收光谱斜率比（0.75-1.53平均1.03）。样品的中间荧光指数（FI）（1.46-1.83，平均值为1.61），在254nm处的比吸收较小（0.64-1.93，平均值为1.15m〜（-1）mg〜（-1）L），表明同时存在水生微生物DOM（例如T峰）和土壤DOM（例如C峰）。峰C可以通过UV-A（320-400nm）辐照基本除去，而当含微生物的水暴露于相同的UV-A辐照时，峰M略有增加。两者合计，峰C归因于土壤来源的扩散，而峰M可能归因于微生物活动和太阳辐射对样品中发色团的共同作用。

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