Gu Yufei, Lensu Anssi, Perämäki Siiri, Ojala Anne, Vähätalo Anssi V
Department of Biological and Environmental Science and Department of Chemistry, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland.
Department of Forest Sciences, University of Helsinki, P.O. Box 27, FI-00014 Helsinki, Finland.
ACS Omega. 2017 May 9;2(5):1905-1914. doi: 10.1021/acsomega.7b00453. eCollection 2017 May 31.
Solar radiation mineralizes dissolved organic matter (DOM) to dissolved inorganic carbon through photochemical reactions (DIC photoproduction) that are influenced by iron (Fe) and pH. This study addressed as to what extent Fe contributes to the optical properties of the chromophoric DOM (CDOM) and DIC photoproduction at different pH values. We created the associations of Fe and DOM (Fe-DOM) that cover the range of loadings of Fe on DOM and pH values found in freshwaters. The introduced Fe enhanced the light absorption by CDOM independent of pH. Simulated solar irradiation decreased the light absorption by CDOM (i.e., caused photobleaching). Fe raised the rate of photobleaching and steepened the spectral slopes of CDOM in low pH but resisted the slope steepening in neutral to alkaline pH. The combination of a low pH (down to pH 4) and high Fe loading on DOM (up to 3.5 μmol mg DOM) increased the DIC photoproduction rate and the apparent quantum yields for DIC photoproduction up to 7-fold compared to the corresponding experiments at pH >6 or without Fe. The action spectrum for DIC photoproduction shifted toward the visible spectrum range at low pH in the presence of Fe. Our results demonstrated that Fe can contribute to DIC photoproduction by up to 86% and produce DIC even at the visible spectrum range in acidic waters. However, the stimulatory effect of Fe is negligible at pH >7.
太阳辐射通过受铁（Fe）和pH值影响的光化学反应（溶解无机碳光生成，DIC光生成）将溶解有机物（DOM）矿化为溶解无机碳。本研究探讨了在不同pH值下，铁对发色溶解有机物（CDOM）光学性质和DIC光生成的贡献程度。我们创建了铁与溶解有机物的结合物（Fe-DOM），其涵盖了淡水中铁在溶解有机物上的负载范围和pH值范围。引入的铁增强了CDOM的光吸收，且与pH值无关。模拟太阳辐射降低了CDOM的光吸收（即导致光漂白）。铁提高了低pH值下CDOM的光漂白速率并使光谱斜率变陡，但在中性至碱性pH值下抑制了斜率变陡。与pH>6或无铁的相应实验相比，低pH值（低至pH 4）和高铁负载（高达3.5 μmol Fe/mg DOM）的组合使DIC光生成速率和DIC光生成的表观量子产率提高了7倍。在铁存在的情况下，低pH值下DIC光生成的作用光谱向可见光谱范围移动。我们的结果表明，铁对DIC光生成的贡献可达86%，甚至在酸性水体的可见光谱范围内也能产生DIC。然而，在pH>7时，铁的刺激作用可忽略不计。
