In this paper, we studied one of the largest coal mines in Mongolia, the Baganuur Coal Mine, in terms of environmental sustainability related to mining practices, with a focus on discharged water and waste sediments. The present quality and potential for future pollution were assessed. Based on World Health Organization and Mongolian guidelines, groundwater pumped from the mining operations could be used for drinking and domestic purposes. In addition, based on the Na absorption ratio, groundwater samples from GW-2 and GW-3 could be used as agriculture water supplies with salinity reduction, or used to grow halophytes as a measure for desertification control and pasture production. All waste soil samples appeared to have a desertification potential. Dust particles smaller than 150 μm comprised more than 80% of soil samples, which had arsenic levels higher than the Mongolian soil pollution standards. In addition, soil collected between coal seams (S-5) showed high sulphur content based on X-ray fluorescence (XRF) and scanning electron microscopy–energy dispersive X-ray (SEM-EDX) spectroscopy analyses, strong potential for producing acid mine drainage in the analysis of pH of net acid generation and net acid production potential, and potential for leaching of metals, such as Co. Therefore, the Baganuur Coal Mine requires soil pollution control measures to mitigate the risks of dust and desertification. In this perspective, mine groundwater could be used to reduce environmental stresses by supporting pasture crops such as halophytes on waste disposal sites, thereby preventing dust issues and desertification. Continuous efforts, including monitoring and enacting environmental management measures, are needed from both the mining company and the government to ensure sustainable mine development.

When groundwater drought occurs, baseflow discharges to surface-water bodies will be reduced and then domestic and agricultural water usage becomes at risk of insufficient supply. Thus, in this study, several methods for groundwater drought assessment were tested with long-term monitoring water-level data in the study area to preserve groundwater sustainability from drought, principally caused by reduced precipitation and propagated through agricultural drought and groundwater drought. Because of the Monsoon climate on the Korean Peninsula, the groundwater storage (or water-level) is secured until the end of summer, then falls by natural discharge during the dry seasons of autumn, winter and the following spring. Thus, the rainfall in the wet season seems to mainly influence groundwater storage until the spring of the following year. As the groundwater level (GWL) declines due to natural drainage and the use of agricultural water increases by the end of the dry season (October–May), the GWL will become lowered below the critical level. Below this level, sufficient water supply is not secured. Using the Standardized Precipitation Index (SPI), threshold method and 95% probability occurrence method, drought detection and the frequency of drought are compared. Groundwater drought using the threshold method results in more frequent occurrence than using the SPI method. The 95% occurrence method responds to severe drought but it also has weakness in missing the man-induced GWL decline in every spring season. For groundwater drought assessment, an appropriate drought index should be utilized according to climatic conditions and catchment characteristics. In the study area, variations of the both natural and anthropogenic effects are mixed and the threshold method is more suitable as a measure for preventing water resources shortage.

Seawater intrusion (SWI) is a critical issue for coastal aquifers, especially in islands where groundwater is the sole source of water supply. The objective of this study was to develop a straightforward approach to evaluating groundwater vulnerability to SWI, using a statistical method with spatial analyses applied to the four basins of Jeju volcanic island. In this study, five factors were parametrized, including hydraulic conductivity, groundwater level, distance from shoreline to wells, well depth and groundwater use. These parameters were spatially interpolated and correlated with groundwater electrical conductivity as a proxy for groundwater salinization, resulting in three parameters with significant relations: groundwater use, well depth, and groundwater level. Then, a numerical model for the SWI vulnerability assessment was constructed using ratings and weights, and by evaluating the vulnerability as weak, moderate and high with a numerical index. Regional conditions, including major land-use types, industrial activities, population and the degree of urbanisation, could affect parameters differently at each region. Based on the percentage of area with a high vulnerability, regions of Jeju Island followed the order of eastern > northern > western > southern, indicating that preventive measures for SWI and its influencing parameters could be applied more effectively in certain regions.

This study examined the spatiotemporal dynamics of nitrogen (N) sources and transport in the Gyeongancheon Stream mid-watershed. Stable isotopes of nitrate (δ¹⁵N-NO₃ and δ¹⁸O-NO₃) and boron (δ¹¹B), combined with a Bayesian statistical mixing model, indicate that manure/sewage and wastewater treatment plant (WWTP) effluent were the dominant N sources. However, due to isotopic overlap and complex mixing, precise source apportionment between WWTPs and groundwater pathways was difficult. To overcome this limitation, hydrograph separation using the recursive digital filter method was combined with water chemistry data to estimate the contributions of WWTP effluent, groundwater baseflow, and direct runoff to streamflow and N load under hydrological conditions. During the dry period, WWTP effluent dominated streamflow and N load in the main stream. Notably, during the growing season, the N load declined owing to biological uptake and streambed infiltration under losing stream conditions. In contrast, during the wet period, groundwater baseflow and direct runoff dominated both streamflow and N load following rainfall events. Under mid-range conditions, groundwater baseflow prevailed in the upper and middle reaches of the main stream, whereas the lower reach was almost entirely sustained by WWTP effluent, with substantial N load losses attributable to prolonged losing stream conditions. These findings underscore the critical role of hydrological variability and groundwater–surface water interactions in governing N dynamics in mixed-source watersheds, and demonstrate that isotope-based source apportionment alone is insufficient when end-member signatures overlap. Nutrient management strategies must be spatiotemporally differentiated to effectively mitigate N transport impacts under a changing climate.

Groundwater–surface water exchange is a key hydrological process that governs river water quality and aquatic ecosystems. However, the quantification of such exchange remains uncertain, especially within river island aquifers where exchange processes are highly heterogeneous. In this study, direct seepage meter measurements and indirect Darcy‐based estimates of exchange fluxes were compared under consistent spatiotemporal conditions within the aquifer of Jungsa Island, a river island in the lower West Nakdong River, South Korea. At the downstream low‐permeability site (SP‐3), Darcy‐based exchange fluxes ranged from −2.14 × 10 ⁻⁵ to 1.15 × 10 ⁻⁵ m/hr. Owing to these small magnitudes, net intrusion and discharge were not distinguishable. However, seepage meter measurements consistently indicated intrusion of surface water into the island aquifer, with fluxes ranging from −8.46 × 10 ⁻⁴ to −1.94 × 10 ⁻⁴ m/hr. At the upstream high‐permeability site (SP‐6), seepage meter measurements captured both transient groundwater discharge during short measurement periods and sustained surface water intrusion during longer measurements. Darcy‐based estimates at this site consistently indicated intrusion, indicating that both methods showed the same flow direction during longer measurements. Consequently, Darcy‐based approaches may underestimate exchange fluxes under low‐permeability conditions. These findings suggest that short‐term monitoring is favorable for capturing immediate, transient flow dynamics, whereas extended continuous measurements help buffer short‐term fluctuations to provide a more representative estimate of daily integrated exchange. Ultimately, by establishing a methodological framework that accounts for localized riverbed heterogeneity, this study provides practical guidelines for optimizing field investigation strategies in complex riparian environments.