Spencer Robert G M, Bolton Lucy, Baker Andy
Ocean Research Group, School of Marine Science and Technology, University of Newcastle-upon-Tyne, The Ridley Building, NE1 7RU, UK.
Water Res. 2007 Jul;41(13):2941-50. doi: 10.1016/j.watres.2007.04.012. Epub 2007 May 30.
The UV-visible and fluorescence excitation-emission matrix spectrophotometric properties of dissolved organic matter (DOM) were compared for the effects of both pH and freeze/thaw on a wide range of freshwater DOM samples from the United Kingdom. It was observed that the spectrophotometric properties of our freshwater samples were sensitive to pH and that the recorded change varies with fluorescence and absorbance intensity, DOC concentration and the wavelength observed. Large and variable responses to pH were particularly severe at extremes of pH, but within the natural levels typically observed in freshwaters the response to pH was limited. For the same sample set large and variable responses were observed when subjected to freeze/thaw. From our data, knowledge of the original properties cannot be used to determine the amount of change that will occur with freezing and subsequent thawing. It is therefore recommended that in future research, to maintain the natural signal of the DOM, analysis is conducted at natural pH and without freezing to facilitate ease of comparison between studies. Our results also have implications for studies that utilise spectrophotometric techniques to investigate long-term trends in dissolved organic carbon in rivers. Spectrophotometric parameters from upland derived samples show varied responses of samples to pH and there is clear potential to complicate trends in the interpretation of long-term water colour data if pH is changing over time in a system or if samples are treated with different storage protocols with respect to acidification and freezing.
针对英国多种淡水溶解有机物（DOM）样品，比较了pH值和冻融对其紫外可见光谱和荧光激发-发射矩阵光谱特性的影响。研究发现，我们的淡水样品的光谱特性对pH值敏感，记录的变化随荧光和吸光度强度、溶解有机碳（DOC）浓度以及观测波长而变化。对pH值的大幅且多变的响应在极端pH值条件下尤为明显，但在淡水通常观测到的自然水平范围内，对pH值的响应有限。对于同一组样品，冻融处理时也观察到了大幅且多变的响应。根据我们的数据，无法依据原始特性来确定冷冻及随后解冻所导致的变化量。因此建议在未来研究中，为保持DOM的自然信号，应在自然pH值下且不进行冷冻处理时开展分析，以便于不同研究之间进行比较。我们的研究结果对于利用光谱技术研究河流中溶解有机碳长期趋势的研究也具有启示意义。来自高地的样品的光谱参数显示出样品对pH值的不同响应，如果系统中的pH值随时间变化，或者样品在酸化和冷冻方面采用不同的储存方案，那么在解释长期水色数据的趋势时，显然有可能使趋势变得复杂。
