Soil water erosion is frequently reported as serious problem in soils in Southeast Asia with tropical climates, and the variations in pH affect the development of the erosion. This study investigated the effects of changes in pH on soil water erosion based on changes in the physical properties of the simulated soils with pH adjusted from 2.0 to 10.0 through artificial rainfall tests. The zeta potential was entirely shifted to positive direction at each pH condition due to Al, Ca, and Mg. In the pH range of 6.0 to 2.0, the aggregation of soil particles resulting from the release of Al³⁺ from clay minerals and/or molecular attraction between soil particles caused the plastic index (I_P) of the soil to decrease. The decrease in I_P led to the development of soil water erosion at the pH range. When the pH exceeded 6.0, the repulsive force generated by the negative charges on soil particles decreased I_P, resulting in accelerated erosion by water. The results suggest that changes in pH causes physical properties of the soil to change through changes of the zeta potential in the clayey soil rich in Al, Ca, and Mg, leading to the development of soil water erosion.

The increase in the number of coal-fired power plants with the increase in coal production and its consumption has caused the problem of the treatment of a large amount of coal ash in Indonesia. In the past studies, coal ash was applied to postmine land with the aim of improving soil conditions for plant growth; however, heavy rain in the tropical climate may cause soil erosion with the change in soil conditions. This study presents the effects of application of coal ash to postmine land on soil erosion by performing the artificial rainfall test as well as physical testing. The results indicate that the risk of soil erosion can be reduced significantly by applying the coal ash which consists of more than 85% of sand to topsoil in the postmine land at the mixing ratio of over 30%. Additionally, they reveal that not only fine fractions but also microporous structures in coal ash enhance water retention capacity by retaining water in the structure, leading to the prevention of soil erosion. Thus, the risk of soil erosion can be reduced by applying coal ash to topsoil in consideration of soil composition and microporous structure of coal ash.

Characterization of mine waste rocks and prediction of acid mine drainage (AMD) play an important role in preventing AMD. Although high-tech analytical methods have been highlighted for mineral characterization and quantification, simple testing methods are still practical ways to perform in a field laboratory in mines. Thus, this study applied some simple testing methods to the characterization of mine wastes and AMD prediction in addition to a leaching test and the sequential extraction test with HCl, HF, and HNO₃, which have not been applied for these purposes, focusing on the form of sulfur and the neutralization effects of carbonates. The results of the Acid Buffering Characteristic Curve test supported the changing trend of the pH attributing carbonates only during the first 10 leaching cycles in the leaching test. The change in the Net Acid Generating (NAG) pH in the sequential NAG test reflected the solubility of sulfur in the rocks, providing information on the form of sulfur in the rocks and the acid-producing potential over time. Consequently, the sequential NAG test and sequential extraction with the acids in combination with the current standards tests (Acid Base Accounting and NAG tests) provided important information for preventing AMD.

A qualitative assessment of groundwater resources is significant in islands that largely depend on individual aquifers. In Okinawa Island, Japan, limestone aquifers are valuable groundwater reservoirs. However, these aquifers are sensitive to contamination due to high permeability in the conduit network. Although human activity has increased in recent decades, there remains insufficient hydrological information to assess the impact of anthropogenic loading on groundwater quality in Okinawa Island. To address this, we analyzed 4 seepage, 16 river, and 14 shallow (<10 m in depth) groundwater samples to obtain baseline chemistry and anthropogenic impact information on groundwater resources in central Nago City, northern Okinawa Island. We divided the region into three landscape units: lowland (<30 m asl), eastern, and western areas. Except for a limited number of water samples collected in the eastern mountain and coastal section of the lowland, the hydrochemistry was characterized by Ca-HCO₃ type, indicating carbonate weathering within limestone-bearing lithology and Quaternary deposits. Divergent water ⁸⁷Sr/⁸⁶Sr values (0.707723-0.712102) with lower Sr concentrations (0.1-1.6 μmol/L) in the mountains and convergent values (0.708859-0.709184) with higher Sr concentrations (0.3-17.6 μmol/L) in the lowland suggest that the water-rock interactions in the lowland aquifer composed of Quaternary deposits are mostly responsible for the hydrochemistry of groundwater resources. The local meteoric water line (δD = 6.38 δ¹⁸O + 3.36) indicated that the water originates from precipitation, the altitude effect, and evaporation. The δ¹⁵N and δ¹⁸O in NO₃^- indicated the addition of manure and septic waste in the lowland aquifer. The results imply that detecting source areas of anthropogenic NO₃^- prior to serious groundwater pollution is important (regardless of the NO₃^- concentration), and isotope analyses would aid in developing appropriate action plans to mitigate or prevent future water pollution by NO₃^- in island regions.

Understanding seasonal groundwater quality changes in temperate continental climate waste rock dumps (WRDs) is necessary for sustainable environmental risk prevention and legacy mine contamination management. Therefore, we conducted a field investigation of a WRD to determine the mechanisms controlling its groundwater quality dynamics. The research aimed to understand the impact of seasonal changes on heavy metals released from the WRD. Three monitoring wells were installed in the WRD to investigate the pH, electrical conductivity (EC), and groundwater level (GL). The mineral composition of the waste rock was determined. Groundwater and river water samples from the monitoring wells and rivers surrounding the WRD were collected for chemical analysis. The sphalerite and galena concentrated in the WRD were assumed to be the main sources of Zn, Pb, and Cd contamination. Summer rainfall was the dominant recharge source of river water, which rapidly infiltrated to the WRD, altering the pH, EC, and GL of the groundwater. The pH, EC, and GL were stable in winter because snowpack covering the surface soil prevented groundwater recharge to the WRD. However, snow melting affected the pH, EC, and GL in the WRD. The sources of groundwater recharge (rainfall, river water, and snowmelt) altered the behaviour of the heavy metals in the WRD through two main mechanisms: the dissolution of sulphide minerals and efflorescent salts upon contact with the recharge water, and the dilution effect of the recharge water, which mixes with the groundwater in the WRD, reducing the heavy metal concentration. Sulphide mineral and efflorescent salt dissolution were significant in the deepest monitoring well and rainfall was the dominant recharge source which increased sulphide mineral and efflorescent salt dissolution in the WRD.