17:15 〜 19:15
[HTT16-P04] 明確な人為負荷源の見られない河川水中の硫酸・硝酸の起源：多元素同位体を用いた解析
キーワード：予防原則に基づく水質評価、硝酸態窒素同位体、硝酸態酸素同位体、硫酸態硫黄同位体、硫酸態酸素同位体
The source of stream water pollution is a matter of concern for the residents. While non-point source solutes significantly affect river water quality and sometimes behave as pollutants, quantitative evaluation of the source was harder than point source loading. To elucidate factors influencing the spatial distribution of nitrate and sulfate in stream water and comparing the two, we assessed the impact of land use and geological property of a catchment on the isotope values of the solutes, as far as their concentrations.
Water sampling was conducted at the Chikusa River basin in Hyogo, Japan, from 2015 to 2019, where notable point sources were not identified. Generalized Linear Mixed-effects Models (GLMMs) were applied to test if proportional area of human-modified land (exploited lands) and geological rock type in a catchment area for sampling points, and season affected discharges of loading materials, taking the sulfate concentration, nitrate concentration, and those isotope ratios (δ15N-NO3-, δ18O-NO3-, δ34S-SO42-, δ18O-SO42- values) as the response variables.
Sulfate concentration increased with the area of exploited lands, i.e. aggregated area of fertilized land, residence, barren, or other type of highly exploited areas, irrespective of season. δ34S-SO42-, δ18O-SO42- values indicate that sulfate primarily leached from soil, consistent with solute levels increasing with larger exploited land areas. Based on GLMMs, δ34S-SO42- increased with proportional area of plutonic rock, which suggest soil sulfate is originated from local rock weathering. Contrasting to the little seasonal variation in sulfate concentration, nitrate concentration was lower in summer than in winter and δ15N-NO3- value was higher in summer than in winter, which might be explained by active photosynthesis or denitrification in summer than in winter. The δ15N-NO3- value ranged 0 to 5‰ at the sites of northern upstream, where little anthropogenic influence is expected and increased with the extent of fertilized land use. δ15N-NO3- value suggested that a dominant nitrate source is fertilizer, in particular manure for agriculture in the stream system. The combined analyses of isotopic signatures and solute concentrations provide important information to identify potential sources that were not revealed by measuring concentration alone.
Water sampling was conducted at the Chikusa River basin in Hyogo, Japan, from 2015 to 2019, where notable point sources were not identified. Generalized Linear Mixed-effects Models (GLMMs) were applied to test if proportional area of human-modified land (exploited lands) and geological rock type in a catchment area for sampling points, and season affected discharges of loading materials, taking the sulfate concentration, nitrate concentration, and those isotope ratios (δ15N-NO3-, δ18O-NO3-, δ34S-SO42-, δ18O-SO42- values) as the response variables.
Sulfate concentration increased with the area of exploited lands, i.e. aggregated area of fertilized land, residence, barren, or other type of highly exploited areas, irrespective of season. δ34S-SO42-, δ18O-SO42- values indicate that sulfate primarily leached from soil, consistent with solute levels increasing with larger exploited land areas. Based on GLMMs, δ34S-SO42- increased with proportional area of plutonic rock, which suggest soil sulfate is originated from local rock weathering. Contrasting to the little seasonal variation in sulfate concentration, nitrate concentration was lower in summer than in winter and δ15N-NO3- value was higher in summer than in winter, which might be explained by active photosynthesis or denitrification in summer than in winter. The δ15N-NO3- value ranged 0 to 5‰ at the sites of northern upstream, where little anthropogenic influence is expected and increased with the extent of fertilized land use. δ15N-NO3- value suggested that a dominant nitrate source is fertilizer, in particular manure for agriculture in the stream system. The combined analyses of isotopic signatures and solute concentrations provide important information to identify potential sources that were not revealed by measuring concentration alone.