| Summary: | 碩士 === 國立中興大學 === 土壤環境科學系 === 92 === Abstract
Water is an important resource to human being and life on the globe. Understanding every material in the water helps to prevent from water pollution. The major ion resources of water are contributed from atmosphere, weathering process and human being activities. In this study, we collect surface waters in Nantou area to analyze the major ion composition to know the meaning and hydrochemical characteristics from regional water. We can use the chemical compositions in rain and ground water as a reference for interpretation. Nitrogen isotope composition (δ15N value) of fertilization and surface waters were also measured in this study. Beside the δ15N value , we can evaluate the possible nitrate resource from river water.
In hydrochemical characteristics, whether is rain, surface or ground water, the main compositions are HCO3- and SO42- in anions ,Ca2+ and Mg2+ in cations. In ground water, it contains more Na+ than rain and surface waters because silicate weathering process is more obviously . From various ion ratios in the rain water, we assumed that all Na+ contributed from sea-salt, then, beside Cl- of rain water in Chuanghsing University obviously contributed by sea-salt contribution. There is no significant sea-salt contribution for the other ion of the rain water in Chuanghsing University and the whole ion of the rain water in Wuxi bridge.
As the result of hydrochemical characteristics of rain water, and sea-salt contribution in the surface water, we can conclude that atmosphere contribution doesn’t effect too much to the major ion of suface water. The resource of major ion in the surface water related to weathering process. According to the hydrochemical characteristics, the major ion resource in the suface water producted from the weathering process of carbonate. However, not only weather process caused by carbonate acid in the surface water, but also weather process caused by sulfuric acid that producted by human being activities. In Maoluo river drainage basin, beside carbonate weathering process that we described above, silicate weathering process is also significantly. As the hydrochemical characteristic of ground water is similar to that of surface water, it makes even more clear to identify that the importance of carbonate weathering and silicate weathering to major ion in the surface water .
In nitrogen isotope sdudy, comparing the composition of nitrogen isotope in fertilization with records value, we find the d15N of chemical fertilizations (-1.1~6.20/00) is similar to the record value. The d15N of organic fertilizations and non-leguminous plants (1.2~6.20/00) is corresponded with soil organic matter. Due to the biological fixation then the d15N of leguminous plants (-3.7~0.30/00) is lower than it of the non-leguminous plants.
Ten surface water sample in this study, the d15N from each sample shows nitrate in the surface water is from nature soil in Meixi river drainage basin, Moaluo river and Chuoshui river drainage basin expect Guanyin bridge of Meixi river. The possible resource of nitrate is nitrogen from forest soil in Qilin bridge and soil organic nitrogen in the other samples. The d15N of Guanyin bridge suggested that it is associate with fresh animal manure. The difference of NO3- concentration and d15N in dry and rainy season suggests that while in the rainy seasons, the nitrate is possible effected by mineralization, nitrification and chemical fertilization. It increases the NO3- concentration and decreases d15N value. The relationship between d15N and pH shows the nitrogen cycle of surface water could possible effected by assimilation.
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