Attenuation of arsenic in a karst subterranean stream and correlation with geochemical factors: A case study at Lihu,South China

Arsenic （As） pollutants generated by human activities in karst areas flow into subterranean streams and contaminate groundwater easily because of the unique hydrogeological characteristics of karst areas. To elucidate the reaction mechanisms of arsenic in karst subterranean streams, physical-chemical analysis was conducted by an inductively coupled plasma mass spectrometer and an X-ray fluorescence spectrometer. The results show that inorganic species account for most of the total arsenic, whereas organic arsenic is not detected or occurs in infinitesimal amounts. As（III） accounts for 51.0% ± 9.9% of the total inorganic arsenic. Arsenic attenuation occurs and the attenuation rates of total As, As（III） and As（V） in the Lihu subterranean stream are 51%, 36% and 59%, respectively. To fully explain the main geochemical factors influencing arsenic attenuation, SPSS 13.0 and CANOCO 4.5 bundled with CanoDraw for Windows were used for simple statistical analysis and redundancy analysis （RDA）. Eight main factors, i.e., sediment iron （SFe）, sediment aluminum （SAI）, sediment calcium （SCa）, sediment organic matter （SOM）, sediment manganese （SMn）, water calcium （WCa^2＋）, water magnesium （WMg^2＋）, and water bicarbonate ion （WILCOX） were extracted from thirteen indicators. Their impacts on arsenic content rank as： SFe〉SCa〉WCa^2＋〉SAl〉wHCO3^-〉SMn〉SOM〉WMg^2＋. Of these factors, SFe, SAl, SCa, SOM, SMn, WMg^2＋ and WCa＆2＋ promote arsenic attenuation, whereas WHCO3^- inhibits it. Further investigation revealed that the redox potential （Eh） and pH are adverse to arsenic removal. The dramatic distinction between karst and non-karst terrain is that calcium and bicarbonate are the primary factors influencing arsenic migration in karst areas due to the high calcium concentration and alkalinity of karst water.

The roles of phosphate in shaping the structure and dynamics of Antarctic soil microbiomes

One major consequence of global warming in the Antarctic region is increased ice-free zones.Subsequent colonization of these ice-free areas by penguins alters their biogeochemistry,with one prominent example being elevation of inorganic phosphate concentrations around feces depositions.The complex soil biochemistry in the region makes it difficult to define the causal factors of these changes using common research approaches.Here,we addressed the effects of phosphate alone on microbiome structure and dynamics over time by adding external phosphate to selected soils in the Antarctic region.We then analyzed the soil bacterial community composition and diversity using 16S rRNA amplicon sequencing and compared these data with phosphate levels.Parallel geochemical analysis revealed changes in nine soil geochemical factors upon phosphate addition,all of which were relevant to microbiome structure,with soil pH showing the highest correlation.Links between geochemical factors and composition were identified,as were interactions between bacterial taxa.Additionally,Sphingobacteriia,Sphingobacteriales and Chitinophagaceae were found to be more abundant in phosphate-treated soils.Co-occurrence network analysis revealed significantly increased levels of associations in all major network properties over time after phosphate supplementation.Therefore,we conclude phosphate addition has diverse effects on Antarctic soil microbiomes.

Sequence of the main geochemical controls on the Cu and Zn fractions in the Yangtze River estuarine sediments

Metal speciation can provide sufficient infor- mation for environmental and geochemical researches. In this study, based on the speciation determination of Cu and Zn in the Yangtze Estuary sediments, roles of eight geochemical controls （i.e., total organic carbon （TOC）, clay, Fe/Mn in five chemical fractions and salinity） are fully investigated and sequenced with correlation analysis （CA） and principal components analysis （PCA）. Results show that TOC, clay and Fe/Mn oxides are key geochemical factors affecting the chemical speciation distributions of Cu and Zn in sediments, while the role of salinity appears to be more indirect effect. The influencing sequence generally follows the order： TOC 〉 clay 〉 Mn oxides 〉 Fe oxides 〉 salinity. Among the different fractions of Fe/Mn oxides, residual and total Fe content, and exchangeable and carbonate Mn exert the greatest influences, while exchangeable Fe and residual Mn show the poorest influences.