Sulfate sources constrained by sulfur and oxygen isotopic compositions in the upper reaches of the Xijiang River,China

While it is critical to accurately understand the sources and transformation of sulfate based on time-series analysis, there are limited studies on temporal variation of sulfate in rivers and on rock weathering by sulfuric acids.We conducted a monthly sampling campaign in the Beipan, Nanpan, and Hongshui Rivers over the course of one hydrological year. This study examined seasonal variations in riverine sulfate impacted by the monsoon climate in the upper reaches of the Xijiang River basin. In general, the SO_4^(2-) contents in these rivers dropped from relatively high levels to low values during the high-flow season, in response to increasing discharge. The sulfate was generally enriched in heavy isotopes during the low-flow season compared to the high-flow season. The calculated results indicate that the riverine sulfate was mainly derived from sulfide oxidation, but that evaporite dissolution could be an important source during the low-flow season, based on isotopic evidence. Mine drainage is likely an important source of sulfate to these rivers during the high-flow season due to contributions from fast surface flow, which responds to frequent heavy rain in monsoonal climate regions. Arelatively high proportion of HCO_3^- was found to be derived from rock weathering by sulfuric acid during the high-flow season when compared to that observed during the low-flow season. The results suggest that approximately one quarter of the HCO_3^- in the Hongshui River originated from carbonate weathering by sulfuric acid derived from the oxidation of sulfide. Such information on the specific dual isotopic characteristics of riverine sulfate throughout a hydrological year can provide unique evidence for understanding the temporal variability of sulfate concentrations and weathering processes in rivers.

Variations of trace elements under hydrological conditions in the Min River, Eastern Tibetan Plateau

In order to better understand the relative importance of hydrologic variation and anthropogenic disturbance and their complex interactions within the trace elemental geochemical cycle, water samples were collected monthly over 1 year in the Min River, eastern Tibetan Plateau, and analyzed for trace element composition. The dissolved trace elements exhibited different relationships with increasing discharge compared with major elements.The elements analyzed can be divided into three groups according to their behavior in response to changing discharge:(1) elements that showed weak positive correlation with discharge, e.g. Cu, V, and Ba;(2) elements that exhibited weak negative correlation with discharge,including Rb, Sr, Pb, Sb, Zn, Cr, Cd, and U; and(3) elements that displayed no significant correlation with variation in discharge, e.g. Ti, Fe, Co, Ni, and As. Cu was strongly affected by anthropogenic activities and flushed into the river with increasing discharge. Ba has a strong solubility in the terrestrial environment, dissolved quickly,and was released into the river. The positive relationship between V concentration and discharge may be attributed to secondary reactions, such as precipitation and adsorption on oxides and aluminosilicate clays. Conservative behavior had an impact on the geochemical behavior of Sr and Rb across hydrologic variation. Pb, Zn, Sb, Cd, and Cr underwent a mild dilution effect connected with anthropogenic activities. The chemostatic behavior of U was regulated by carbonate dissolution and biological uptake.In addition, higher temperatures enhanced biotic activities,affecting the concentrations of Fe and Ni. The relationship between power law slopes and coefficient of variation for discharge and solute concentration suggests that concentrations of trace elements vary significantly with increasing discharge compared with major elements. Silicate mineral weathering had less effect on the fluvial solutes with increasing discharge. Mining activity may exert an additional control on concentration–discharge dynamics of anthropogenic trace elements.

Superconductivity of the FeSe/SrTiO3 Interface in View of BCS–BEC Crossover

In paired Fermi systems,strong many-body effects exhibit in the crossover regime between the Bardeen–Cooper–Schrieffer(BCS)and the Bose–Einstein condensation(BEC)limits.The concept of the BCS–BEC crossover,which is studied intensively in the research field of cold atoms,has been extended to condensed matters.Here by analyzing the typical superconductors within the BCS–BEC phase diagram,we find that FeSe-based superconductors are prone to shift their positions in the BCS–BEC crossover regime by charge doping or substrate substitution,since their Fermi energies and the superconducting gap sizes are comparable.Especially at the interface of single-layer FeSe on SrTiO3 substrate,the superconductivity is relocated closer to the crossover unitary than other doped FeSe-based materials,indicating that the pairing interaction is effectively modulated.We further show that hole-doping can drive the interfacial system into the phase with possible pre-paired electrons,demonstrating its flexible tunability within the BCS–BEC crossover regime.

Collective excitations and quantum size effects on the surfaces of Pb(111)films:An experimental study

Pb(111)film is a special system that exhibits strong quantum size effects in many electronic properties.The collective excitations,i.e.,plasmons,in Pb(111)films are also expected to show signatures of the quantum size effect.Here,using high-resolution electron energy loss spectroscopy,we measured the plasmons on the surface of Pb(111)films with different film thicknesses and analyzed the plasmon dispersions.One surface plasmon branch exhibits prominent damping in the small momentum range,which can be attributed to the interaction between the top and bottom interfaces of the Pb(111)films.With the film thickness increasing,the critical momentum characterizing the damping in Pb(111)films decays not only much slower in Pb(111)films than in other metal films,and even in films with the thickness up to 40 monolayers the damping still exists.The slow decay of the surface plasmon damping,manifesting the strong quantum size effect in Pb(111)films,might be related to the strong nesting of the Fermi surface along the(111)direction.

Metamorphic fluxes of water and carbon in rivers of the eastern Qinghai-Tibetan Plateau

Geothermal activities are common in active orogenic zones and play an important role in surface-earth geochemical processes.Here we analyzed the water chemical compositions,stable and radioactive carbon isotopes of dissolved inorganic carbon(δ^(13)CDICandΔ^(14)CDIC)of hot springs and large rivers in the eastern Qinghai-Tibetan Plateau(QTP).The hot springs had major ions’concentrations varying in a wide range,and most hot springs’alkalinities resulted from high-temperature silicate alteration.The observed hot springs’waters were affected by the mixing of metamorphic fluids and surface waters,which altered the water chemistry andΔ^(14)CDICof the hot springs.Because the observedΔ^(14)CDICin hot springs was much higher than the theoreticalΔ^(14)CDICin metamorphic fluids(i.e.,-1000‰),we used an isotopic mass balance approach(i.e.,Δ^(14)CDIC)to quantify the contribution of surface waters to the hot springs.After the ions of metamorphic fluids were calibrated byΔ^(14)CDIC,the metamorphic water fluxes were calculated by the chemical mass balance approach of Ge/Si ratios,using the Monte-Carlo method.We found that the proportion of metamorphic water fluxes to the river discharge ranged from 0.17%for the Yellow River to 0.52%for the Jinsha River,and it would be much higher in some tributaries.The horizontal metamorphic contributions of alkalinity to the large rivers ranged from 0.87%to 3.96%in eastern QTP,and the vertical metamorphic carbon outgassing would be much higher.The metamorphic fluids fluxes estimated in this study were much lower than previous estimations extrapolated from small Himalayan rivers,and thus we thought that the previous estimations of metamorphic carbon fluxes in QTP were likely over-estimated.We propose that systematic studies are needed to be conducted to constrain the metamorphic carbon flux in QTP.This study shed light on the release of metamorphic carbon in the orogenic zone,placing limits on the results of orogenic forcing on chemical weatherability.