Water

The Mahai Basin (MHB), situated in the northern Qaidam Basin on the Qinghai–Tibetan Plateau, hosts significant Quaternary potash resources. Nevertheless, the sources and evolutionary pathways of potash-forming fluids remain controversial. In this study, a comprehensive multi-isotope dataset and online-first publications spanning the period from 2015 to 2025 were compiled to constrain the end-member characteristics and evolution of brines in the MHB. δD-δ¹⁸O indicates that the initial fluids were derived mainly from Qilian Mountains precipitation and snowmelt, delivered via surface runoff and concentrated through prolonged evaporation under arid, semi-closed conditions, forming a river-lake-brine evolution sequence. δ⁷Li (+7‰ to +40‰) systematically increases with salinity and K content, reflecting long-term low-temperature water–rock interactions and selective ⁶Li adsorption by secondary clays, while deep Ca-Cl brines represent highly evolved endmembers. Elevated ⁸⁷Sr/⁸⁶Sr ratios (0.7113–0.7122) confirm silicate weathering contributions, with intercrystalline brines acting as key intermediate end members. B, S, and Cl isotopes further highlight deep fluid ascent along faults and anticlines, driving K co-enrichment, while sandy–gravel brines inherit highly evolved paleo-lake signatures. These multi-isotope constraints define an integrated evolutionary model involving surface runoff recharge, evaporation-driven concentration with water–rock interaction, deep fluid mixing, lateral migration, and final potash precipitation.

Climate change impacts on the Sado River (southwest Portugal) flow rates (FRs) were assessed for the first time under the 2041–2060 Shared Socioeconomic Pathways: 1–2.6 W/m² (SSP1-2.6), 3–7.0 W/m² (SSP3-7.0), and 5–8.5 W/m² (SSP5-8.5), using bias-adjusted and downscaled General Circulation Model (GCM) ensemble projections from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3b-Sado). ISIMIP3b-Sado was used to estimate future precipitation and temperature changes, and as input for Hydrological Simulation Program—FORTRAN (HSPF) simulations. The HSPF projected decreases in the Sado FRs, mainly under SSP3-7.0 and SSP5-8.5, due to temperature increases and autumn/spring precipitation decreases. The FR decreases may lead to 29%/33% reductions in yearly accumulated riverine water volume under SSP3-7.0/SSP5-8.5 and a 31% summertime riverine water deficit increase under SSP3-7.0. Surface-water demand fulfilment in the Sado Basin could suffer a 22-day delay, and the wintertime precipitation range is projected to increase. Hence, in the near-future, summertime surface-water needs and reservoir recharge in the Sado Basin could become more dependent on wintertime precipitation. With Sado being an agricultural region, our results should prompt agriculture stakeholders and decision makers to improve wintertime surface water storage and management to sustain summertime crop irrigation needs.

Phosphorus enrichment remains a major driver of eutrophication in lake-feeding rivers, yet effective regulation is hindered by insufficient understanding of the spatiotemporal variability and dominant sources of total phosphorus (TP) at the basin scale. The Xiangjiang River, a major inflow to Dongting Lake, provides a representative system for examining TP dynamics in a human-impacted watershed. An interpretable association rule mining framework was applied to multi-source water quality, hydrological, agricultural, and socio-economic data (2020–2024) to characterize TP variation and quantify source contributions. TP concentrations exhibit pronounced seasonal and hydrological variability, with higher levels during spring and the flood season and lower levels during autumn and low-flow periods, together with a longitudinal increasing pattern from upstream to downstream. Quantitative source apportionment indicates that agricultural non-point sources dominate TP contributions at the basin scale, domestic sources provide a stable secondary contribution, and industrial sources exert localized influences. The spatial organization of source contributions closely corresponds to land-use patterns, with relatively consistent source structures among sites despite local heterogeneity. These results demonstrate the utility of an interpretable association rule mining framework for resolving TP source structures in heterogeneous river basins. The proposed framework offers a transferable approach for phosphorus source identification and supports basin-scale nutrient management and targeted control of agricultural non-point source pollution.