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[O08-P51] Changes in water quality and watershed environment of Minowa spring, northwestern Shimousa upland
Keywords:Spring, Minowa spring, Shimousa upland
Thi et al (2009) examined the effects of groundwater recharge and spring water conservation in the rainwater infiltration facilities at Minowa Spring, located in the northeastern part of Ichikawa City, Chiba Prefecture. However, this study did not mention any changes in water quality, although it has examined relationship between water injection and runoff.
Therefore, the aim of this study is to clarify the relationship between precipitation and water quality and seasonal changes in Minowa spring water, which were not shown in Thi et al (2009). In addition, we attempted to clarify the watershed environment by comparing the water quality of seven springs located on the Shimosa upland (Minowa Spring, Futagofuji Pond, Futagoura Pond, Shichimen Daimyojin pond, Benten Pond Park, Akiyama Spring, and Rakan-no-i spring).
We studied the Minowa spring from September 18, 2020 to January 28, 2022. Measurement items are air temperature, water temperature, pH, RpH, and electrical conductivity. As a result, the water temperature showed small seasonal changes except in summer, and the average annual water temperature was 17.6℃. Also, the average annual air temperature is 17.8℃. According to Arai (2004), the temperature at the upper limit of the thermostatic layer in Japan is usually about equal to the annual mean temperature or 1 to 3℃ higher. This indicates that the Minowa spring flows through an upper limit of the isothermal layer (a layer in which seasonal changes in the ground temperature disappear) on the Shimosa upland.
The coefficient of water permeability of the Narita Formation and Kanto Loam layer, each of that is 1.58×10^-3 cm/s, 4.35×10^-4 cm/s, and hydrodynamic slope is 1/100, as shown by Thi et al (2009) and Ida (2019) found that when the hydraulic conductivity is 10^-3, the porosity is about 40%. In addition, the porosity of the Kanto loam layer is 76% to 79% and the vertical permeability is 3 to 20 times greater than the horizontal one due to the presence of tubular pore spaces, as shown by Yasuike and Suzuki (1986). Based on these facts, we proposed that the Minowa spring may be a piston flow, in which rainwater infiltrates and pushes out groundwater that is stagnant in the aquifer. This is consistent with the fact that the value of RpH–pH is almost constant throughout the year.
The water quality of seven springs located on the Shimosa upland around Ichikawa City was investigated on November 14, 2021. The results of the survey and the estimated catchment area based on the topographic relief revealed that the springs in the northwestern part of the Shimosa upland have a small recharge area and many of them have a fast water cycle.
Therefore, the aim of this study is to clarify the relationship between precipitation and water quality and seasonal changes in Minowa spring water, which were not shown in Thi et al (2009). In addition, we attempted to clarify the watershed environment by comparing the water quality of seven springs located on the Shimosa upland (Minowa Spring, Futagofuji Pond, Futagoura Pond, Shichimen Daimyojin pond, Benten Pond Park, Akiyama Spring, and Rakan-no-i spring).
We studied the Minowa spring from September 18, 2020 to January 28, 2022. Measurement items are air temperature, water temperature, pH, RpH, and electrical conductivity. As a result, the water temperature showed small seasonal changes except in summer, and the average annual water temperature was 17.6℃. Also, the average annual air temperature is 17.8℃. According to Arai (2004), the temperature at the upper limit of the thermostatic layer in Japan is usually about equal to the annual mean temperature or 1 to 3℃ higher. This indicates that the Minowa spring flows through an upper limit of the isothermal layer (a layer in which seasonal changes in the ground temperature disappear) on the Shimosa upland.
The coefficient of water permeability of the Narita Formation and Kanto Loam layer, each of that is 1.58×10^-3 cm/s, 4.35×10^-4 cm/s, and hydrodynamic slope is 1/100, as shown by Thi et al (2009) and Ida (2019) found that when the hydraulic conductivity is 10^-3, the porosity is about 40%. In addition, the porosity of the Kanto loam layer is 76% to 79% and the vertical permeability is 3 to 20 times greater than the horizontal one due to the presence of tubular pore spaces, as shown by Yasuike and Suzuki (1986). Based on these facts, we proposed that the Minowa spring may be a piston flow, in which rainwater infiltrates and pushes out groundwater that is stagnant in the aquifer. This is consistent with the fact that the value of RpH–pH is almost constant throughout the year.
The water quality of seven springs located on the Shimosa upland around Ichikawa City was investigated on November 14, 2021. The results of the survey and the estimated catchment area based on the topographic relief revealed that the springs in the northwestern part of the Shimosa upland have a small recharge area and many of them have a fast water cycle.