Water

Integrating an end member catchment offers a mechanistic foundation for interpreting large basin hydrology. This critical aspect is rarely evident in Malawi’s river basin studies. This study characterizes the hydrochemistry of surface and groundwater and stable isotopes of water to gain a regional picture of how the Ruo River Transboundary Catchment (RRC) influences the Shire–Zambezi River Basin. Hydrochemistry (2013 to 2024) and stable isotope (2020 to 2022) data are used. Both Gibbs and Piper diagrams were used to interpret surface and groundwater facies and hydrogeochemical processes controlling mineralization of water. SI biplots were used to trace water sources, mixing signals, and evaporation trends. Low to moderate mineralization is noted in surface and groundwater sources, and electrical conductivity varied between 19 and 622 µS/cm and 31 and 1930 µS/cm for surface (12 sites) and groundwater (151 boreholes), respectively. Piper diagram analysis reveals a Ca-Mg-HCO₃ water type dominance. Gibbs plots suggested dissolution of silicate minerals and interaction of surface and groundwater. Stable oxygen (δ¹⁸O) and hydrogen (δ²H) isotope ratios in precipitation, surface, and groundwater exhibit a similar pattern, indicating a common meteoric input, variability in moisture source, and significant interaction of surface water and groundwater. SI plots indicate mixing of precipitation, surface, and groundwater of RRC. Finally, the Ruo River at flood stage reverses the flow of the Shire River sub catchments, impacting the water quality and quantity of the Zambezi, and, therefore, should be considered an important mixing end member in the Lower Shire Basin.

Peloid maturation is governed by geological settings, duration of water–sediment interaction (microbial reworking), and thermomineral water properties, with molecular distributions providing insights into transformation mechanisms. To assess site-specific biomarker maturity, geochemical parameters were applied to five Serbian therapeutic muds, including spa peloids (Bujanovac, Jošanica, Kanjiža) and natural systems (Vrujci, Rusanda). Mineralogy was determined via X-ray diffraction, and organic matter (OM) was characterized by gas chromatography–mass spectrometry of n-alkanes, steranes and hopanes. Samples are mostly clay-rich, providing favorable catalytic conditions for biomarker transformations. Bujanovac shows a higher plant OM signature (n-C₂₉ maximum) and elevated biomarker maturity (high Ts/Tm, near-equilibrium C₂₉ S/(S + R)), likely inherited from volcanically influenced source material. Jošanica exhibits high CPI but low Ts/Tm and C₂₉ S/(S + R), indicating largely immature OM despite four years of spa aging. Kanjiža shows unexpectedly high apparent maturity after one-day aging, with a pronounced UCM and C₃₁ S/(S + R) (0.58), consistent with incorporation of migrated petrogenic hydrocarbons. Vrujci displays coherent maturity due to prolonged water–sediment interaction, clay-rich mineralogy, extended aging, and regional geothermal gradients. Rusanda exhibits decoupled parameters (CPI 3.91, C₂₉ S/(S + R) 0.69), indicative of hydrocarbon overprinting. Overall, integrating biomarker geochemistry with mineralogy, depositional context, and local thermal/geological conditions provides a robust framework to evaluate peloid maturation.

In our research we analyzed a series of water quality parameters and conducted a metagenomic analysis of the microbial community in the Chishui River (in southwestern China), aiming to explore the microbial driving mechanisms of the phosphorus cycle in the river ecosystem. The research results indicated that the concentrations of total phosphorus (TP) and soluble reactive phosphorus (SRP) were higher in summer, suggesting seasonal differences in exogenous input and water body biogeochemical processes. The concentration of manganese (Mn) is higher in autumn, and it shows a significant positive correlation with Soluble reactive phosphorus (SRP). This may indicate the contribution of endogenous release from sediments to phosphorus in the water body. There were significant differences in the abundance of phosphorus cycling functional genes between summer and autumn. For example, in summer, the abundances of high-affinity phosphate transporter (pstB), inorganic phosphate dissolution (pqqC), and polyphosphate decomposition (ppx) were significantly higher. This might be to adapt to high productivity and the potential lack of phosphorus, or it could be that the microorganisms carrying these genes have a greater advantage during the summer. In contrast, the relative abundance of phosphonate (phn) and glycerophosphate (ugpQ) was significantly higher in autumn, indicating that the metabolic focus of the microorganisms has shifted towards the utilization of organic phosphorus, or that the microorganisms that are adept at utilizing organic phosphorus have taken the dominant ecological position in this situation. Moreover, the analysis of the microbial community showed that the Proteobacteria phylum (Pseudomonad phylum) was the main phylum, and the relative abundance of key functional bacterial genera (such as Limnohabitans, Acinetobacter) reflected seasonal changes, which was consistent with the above functional gene patterns. Spearman correlation analysis indicated that environmental physical and chemical parameters (such as iron, dissolved oxygen, dissolved organic carbon, pH value) jointly regulated the composition and distribution of phosphorus cycling functional genes. Our research results demonstrated that the microbial community plays a crucial regulatory role in the biogeochemical cycle of the river ecosystem through the transformation of functional genes and the changes in community structure. The research results emphasize that attention must be paid to the phosphorus cycling process regulated by microorganisms and its impact, in order to control water body eutrophication and maintain the stability of the ecosystem.