The actual conditions of groundwater use in an irrigated paddy area in the Echi River alluvial fan with multiple water resources were clarified to evaluate influencing factors of groundwater use and to consider how to establish its sustainable use. Groundwater is managed by two kinds of organizations, the land improvement district that has the responsibility for sending irrigation water to the entire command area through principal distributing systems, and the farmers or the water users associations that irrigates paddy plots in the terminal command areas controlling terminal division works and groundwater pumping wells. Groundwater use in the entire command area compensates for the shortage of surface water intake and complements the fluctuation of surface water intake due to meteorological conditions. Water managers use groundwater with excellent handleability responding to the changes in precipitation and situation of rice growth stages in the terminal plots. The appropriate division of roles and cooperative works among the two different organizations are important for desirable agricultural groundwater management.
In the previous studies, the acute toxicity effects of alkanes, which are the main components of gasoline, on luminous bacteria have evaluated for the purpose of developing a soil contamination evaluation method for petroleum hydrocarbons. On the other hand, alkanes are known to be converted to alcohols by microbial decomposition. Therefore, in this study, in addition to investigating the acute toxicity effects of alcohols on luminous bacteria, the effects on the soil pollution evaluation for alkanes in the coexistence with the produced alcohols were examined. The strength of the acute toxicity effect in the test using the test solution with alcohol concentration of 100 vol% was methanol ＜ ethanol ＜ 2-methyl-1-propanol < 2-propanol ＜ 1-propanol ＜ 2-methyl-2-propanol ＜ 1-butanol ≒ 2-butanol. That means the acute toxicity effect was higher with increasing carbon number among the straight-chain alcohols and was higher with straight-chain types than with branched-chain ones. On the other hand, the alcohols tested in this study were shown to have no acute toxic effects on luminous bacteria at low concentrations (1 vol% in the test solution). In the method, which uses methanol as a solvent for extracting petroleum hydrocarbons from contaminated soil, the presence of alcohols in contaminated soil is considered not to affect the soil pollution evaluation for petroleum hydrocarbons such as alkanes.
To evaluate changes in hot spring water quality and estimate the flow paths from its vertical distribution, multivariate analysis (Hierarchical cluster analysis and Factor analysis) and hydrological analysis were conducted using 52 hot spring wells in the Beppu hydrothermal area, Japan. Hot spring water quality was classified by five groups (G1, G2a, G2b, G2c, and G3). G1 and G2a are distributed in the Kamegawa thermal zone, and G3 and G2c are mainly found in the Beppu thermal zone. G2b is observed in both thermal zones. The water types of the hot springs were almost consistent with those in the 1980s but changed from Cl to HCO3 type in the Beppu thermal zone. The vertical distribution of the hot springs implies that there are two distinct flow paths in the Beppu thermal zone, and confirmed the seawater mixing in the well located near the shore. The mixing rate between the seawater and hot spring water was calculated by Cl－ concentration, which was 12% of seawater.
Transition in effective precipitation, land use change and discharge of hot spring reveals the long term changes in the unconfined groundwater level in the southern Beppu volcanic fan from 1971 to 2019. The unconfined groundwater level was periodically fluctuated between 40 m and 50 m above sea level and indicated the maximum value in October or November and the minimum value in April or May. Annual effective precipitation was related to the maximum groundwater level in each year and it had decreased 0.7 mm every year. The urban area was slightly increased from the 1970s to 2016, but it was not a factor to decrease the unconfined groundwater level. The hot spring yield was inversely related to the maximum groundwater level in each year and it had increased 7.9 mm/y, which is approximately 11 times higher than the effective precipitation. Thus, it could conclude that the increase of the hot spring yield mainly affected the decline of the unconfined groundwater level from 1971 to 1999.