Department of Environment & Energy, Sejong University, Seoul 143-747, South Korea.
Department of Environment & Energy, Sejong University, Seoul 143-747, South Korea.
Water Res. 2014 Aug 1;59:80-9. doi: 10.1016/j.watres.2014.04.018. Epub 2014 Apr 18.
Despite the wide use of absorption and fluorescence spectroscopy for tracking the sources of dissolved organic matter (DOM), there are limited studies on evaluating their source discrimination capabilities at variable solution chemistry (pH, NaCl, Ca(2+), and DOM concentration). For this study, we compared the applicability of several well-known spectroscopic indices via end member mixing analysis based on two contrasting DOM sources (Suwannee River fulvic acid and an algal DOM). The absorption coefficients and the intensities of fluorescent components from parallel factor analysis (PARAFAC) showed linear relationships with increasing algal carbon fraction in the mixture of the two DOMs. In contrast, although they still behaved conservatively, spectral ratio indices such as spectral slopes, ratios of PARAFAC components, humification index, and fluorescence index changed in nonlinear patterns with the mixing ratios. The indices based on PARAFAC results exhibited strong discrimination capabilities, as indicated by high susceptibility to the changes in DOM sources relative to the analytical precision. While variable NaCl concentrations had limited effects, most fluorescence indices were considerably affected by other solution chemistry such as pH, Ca(2+), and DOM level. Our study demonstrated that the applicability of the source discrimination indices should be critically examined especially in the environments with notable changes in the solution chemistry. The solution chemistry effects could be minimized by adjusting samples to a constant condition prior to the measurements or otherwise the effects should be fully taken into account in interpreting the field observations.
尽管吸收和荧光光谱学被广泛用于追踪溶解有机物（DOM）的来源，但在评估其在可变溶液化学（pH、NaCl、Ca(2+)和 DOM 浓度）下的源区分能力方面的研究有限。在这项研究中，我们通过基于两种对比 DOM 源（苏万尼河富里酸和藻类 DOM）的端元混合分析比较了几种知名光谱指数的适用性。吸收系数和荧光成分的平行因子分析（PARAFAC）强度与混合物中藻类碳分数的增加呈线性关系。相比之下，尽管它们仍然表现出保守性，但光谱比指数（如光谱斜率、PARAFAC 成分比、腐殖化指数和荧光指数）的比值随着混合比的变化呈非线性模式变化。基于 PARAFAC 结果的指数表现出较强的区分能力，因为它们相对于分析精度对 DOM 来源的变化更为敏感。虽然可变 NaCl 浓度的影响有限，但大多数荧光指数受其他溶液化学（如 pH、Ca(2+)和 DOM 水平）的影响相当大。我们的研究表明，源区分指数的适用性应特别在溶液化学有显著变化的环境中进行严格检查。可以通过在测量前将样品调整到恒定条件来最小化溶液化学的影响，或者在解释现场观测结果时应充分考虑这些影响。
