17:15 〜 18:45
[AHW25-P03] Properties of SO42- and δ34S in spring waters in the western margin of the Kanto Plain
キーワード：都市域、湧水、汚染、マルチトレーサー
The Arakawa Fan (including the Kushibiki Plateau), Higashimatsuyama Hills, Iruma Upland, and Musashino Upland are distributed from north to south along the western margin of the Kanto Plain, in which the Tokyo Metropolitan Area is located. Each of these regions has largely different land use characteristics. In the Musashino Upland, the land use of the Tokyo Metropolitan Government area is urban, but there are also green spaces, parks, and small farmlands scattered. From the Saitama Prefectural area of the Musashino Upland to the Higashimatsuyama Hills, the land use transits from urban to suburban, and the area of farmland increases. On the other hand, farmlands extend and livestock farming is conducted in the Arakawa River Fan.
We have been studying the influence of human activities on the groundwater environment such as sources of groundwater, groundwater flow regime, chemical compositions and its evolution, etc., in these regions with different degrees of urbanization, using multi-tracer techniques, to clarify the influence and mechanism of human activities on the groundwater environment. As for multi-tracers, the major dissolved ions, environmental isotopes, PPCPs, artificial sweeteners, E. Coli and coliforms, and groundwater age indicators are used. We conducted a field survey in November 2023 and collected water samples from 22 points of springs and artesian wells scattered in the above-mentioned regions. In this presentation, we report on the properties of SO42- and δ34S in these samples.
The SO42- concentrations of the samples ranged from 15.6 to 55.4 mg/L. The land use type in the recharge area of each site estimated based on topography and geology was classified into five categories using satellite photos: urban type, mainly urban and includes farmland type (urban main type), urban and farmland type, mainly farmland and includes urban type (farmland main type), and unknown type. Only one sample obtained from an artesian well of unknown depth was classified as the unknown type. SO42- concentrations of these types were as follows; urban type: 23.2 - 31.5 mg/L; urban main type: 15.6 - 27.1 mg/L; urban and farmland type: 29.4 - 46.5 mg/L; farmland main type: 32.9 - 55.4 mg/L; and unknown type: 33.2 mg/L. As these results show, the SO42- concentrations are relatively low at the sites where urban land use is dominant whereas relatively high at the sites where agricultural land use is major. Here, the SO42- concentrations in the river water that is the source of the tap water and the tap water in these regions are 24 - 34 mg/L (Tokyo Metropolitan Government, 2019; Saitama Prefecture, 2019, etc.). Therefore, in the areas where agriculture is the major land use, the source of SO42- is considered to be not only leaked tap water and domestic wastewater but also fertilizers and Livestock manures in the farmland. This is supported by the fact that the tendencies of relationships in the correlations of SO42- vs NO3- and SO42- vs Cl- are different between the samples of the urban/urban main types and the farmland main type.
On the other hand, the δ34S values of the samples ranged from -0.2 to +7.5 ‰. However, only three sites showed δ34S less than 2‰. The δ34S values by land use types were as follows; urban type: 2.5 - 7.5 ‰, urban main type: 3.2 - 6.0 ‰, urban and farmland type: 2.1 - 4.9 ‰, farmland main type: -0.2 - 4.7 ‰, and unknown type: 0.6 ‰. Thus, the sites of urban land use types have relatively high isotope ratios (δ34S > 2.5‰), while lower isotope ratios below 1.0 ‰ were found in the areas of the farmland main type. Here, according to a study in northwestern Chiba Prefecture, the δ34S of groundwater, chemical fertilizers, and synthetic detergents in the area where agriculture is the major land use ranges from 1.1 to 5.3 ‰, -2.7 to 3.5 ‰, and -4.2 to -0.7 ‰, respectively (Muramatsu et al., 2010). Considering these values and SO42- concentrations, in the sites of δ34S less than 2 ‰ found in the farmland main types, sulfur is considered to be mainly supplied from chemical fertilizers.
This work was supported by JSPS KAKENHI Grant Number 19K12293.
We have been studying the influence of human activities on the groundwater environment such as sources of groundwater, groundwater flow regime, chemical compositions and its evolution, etc., in these regions with different degrees of urbanization, using multi-tracer techniques, to clarify the influence and mechanism of human activities on the groundwater environment. As for multi-tracers, the major dissolved ions, environmental isotopes, PPCPs, artificial sweeteners, E. Coli and coliforms, and groundwater age indicators are used. We conducted a field survey in November 2023 and collected water samples from 22 points of springs and artesian wells scattered in the above-mentioned regions. In this presentation, we report on the properties of SO42- and δ34S in these samples.
The SO42- concentrations of the samples ranged from 15.6 to 55.4 mg/L. The land use type in the recharge area of each site estimated based on topography and geology was classified into five categories using satellite photos: urban type, mainly urban and includes farmland type (urban main type), urban and farmland type, mainly farmland and includes urban type (farmland main type), and unknown type. Only one sample obtained from an artesian well of unknown depth was classified as the unknown type. SO42- concentrations of these types were as follows; urban type: 23.2 - 31.5 mg/L; urban main type: 15.6 - 27.1 mg/L; urban and farmland type: 29.4 - 46.5 mg/L; farmland main type: 32.9 - 55.4 mg/L; and unknown type: 33.2 mg/L. As these results show, the SO42- concentrations are relatively low at the sites where urban land use is dominant whereas relatively high at the sites where agricultural land use is major. Here, the SO42- concentrations in the river water that is the source of the tap water and the tap water in these regions are 24 - 34 mg/L (Tokyo Metropolitan Government, 2019; Saitama Prefecture, 2019, etc.). Therefore, in the areas where agriculture is the major land use, the source of SO42- is considered to be not only leaked tap water and domestic wastewater but also fertilizers and Livestock manures in the farmland. This is supported by the fact that the tendencies of relationships in the correlations of SO42- vs NO3- and SO42- vs Cl- are different between the samples of the urban/urban main types and the farmland main type.
On the other hand, the δ34S values of the samples ranged from -0.2 to +7.5 ‰. However, only three sites showed δ34S less than 2‰. The δ34S values by land use types were as follows; urban type: 2.5 - 7.5 ‰, urban main type: 3.2 - 6.0 ‰, urban and farmland type: 2.1 - 4.9 ‰, farmland main type: -0.2 - 4.7 ‰, and unknown type: 0.6 ‰. Thus, the sites of urban land use types have relatively high isotope ratios (δ34S > 2.5‰), while lower isotope ratios below 1.0 ‰ were found in the areas of the farmland main type. Here, according to a study in northwestern Chiba Prefecture, the δ34S of groundwater, chemical fertilizers, and synthetic detergents in the area where agriculture is the major land use ranges from 1.1 to 5.3 ‰, -2.7 to 3.5 ‰, and -4.2 to -0.7 ‰, respectively (Muramatsu et al., 2010). Considering these values and SO42- concentrations, in the sites of δ34S less than 2 ‰ found in the farmland main types, sulfur is considered to be mainly supplied from chemical fertilizers.
This work was supported by JSPS KAKENHI Grant Number 19K12293.