Speciation of Ca in terrestrial water and its role in element cycle in forested ecosystem

点击翻译按钮获取中文摘要

In our previous study, we found that acidic deposition in Japan has already resulted in elevated concentrations of NO3- + SO42- in stream waters, and a high level of Ca (instead of Al) is serving as a major counterion for NO3- + SO42-. However, an additional loading of acidic deposition may result in shortage of Ca (essential element for plants) and mobilization of Al (toxic element for plants and fishes). We also found that reactive Al increased in proportion to the DOC/Ca ratio in Japanese stream waters, which imply the higher ratio of (organic ligand concentration)/(competitive cation concentration) in solution enhancing formation of soluble organic aluminum complexes. In this study, we tried to determine concentrations of soluble organic calcium complexes in stream waters in order to evaluate the influence of calcium complex on behavior of aluminum. We determined calcium ion concentration (CaI) using calcium ion selective electrode, reactive calcium concentration (CaR) using ion chromatography, and organic calcium complex concentration as a difference between CaR and CaI. However, we unexpectedly found the tendency of calcium ion selective electrode to overestimate CaI under dilute sample such as stream waters. It was found that more selective method is necessary to determine soluble organic calcium complexes in stream waters