Hydrogeochemical characteristics and its role in controlling arsenic mobilization in a shallow aquifer

The relevance of groundwater hydrogeochemistry to explain the occurrence and distribution of arsenic in groundwater is of great interest.The insightful discussions on the control of shallow groundwater(<50 m)hydrogeochemistry in arsenic mobilization are known to be a viable tool to explain the arsenic menace in shallow groundwater.The present investigation emphasizes the hydrogeochemical driver and/or control over the reductive dissolution of Fe-bearing host minerals and thereby releasing arsenic into the shallow groundwater of the study area.The study suggests that hydrogeochemical evolution is mainly governed by carbonate minerals dissolution,silicate weathering,and competitive ion-exchange processes in the shallow aquifers(<50 m).The present study also indicates the prevalence of carbonate minerals dissolution over silicate weathering.The emergence of Cl^(-)concentration in the shallow groundwater founds the possibilities of anthropogenic inputs into the shallow aquifers(<50 m).The reducing environment in shallow aquifers(<50 m)of the study area is evident in the reductive dissolution of Febearing shallow aquifer minerals which absorb arsenic in the solid phase and mobilize arsenic onto shallow groundwater.The study opted for many statistical approaches to delineate the correlation among major and minor ionic constituents of the groundwater which are very helpful to understand the comprehensive mechanism of arsenic mobilization into shallow groundwater.

Changes of marine productivity and sedimentary environment recorded by biogenic components in the Antarctica Ross Sea since the last deglaciation

Changes in the marine productivity and sedimentary environment since the last deglaciation in the Ross Sea are presented in this paper.Opal has replaced calcium carbonate as the major biogenic component and has a significantly positive correlation with total organic carbon(TOC),which indicates that siliceous phytoplankton controlled the absorption and release of carbon by the biological pump and was the main producer of marine organic matter.Using the AMS 14C age framework,foraminiferal fossils and redox sensitive elements(RSEs),we found that both the sedimentary environment and marine productivity changed clearly in^11 cal ka BP,which is more likely related with the melting and retreat of the Ross Ice Shelf.In addition,the increase of marine productivity promoted the sinking of more organic-matter to the seabed.A large proportion of oxygen in the bottom water body was consumed and more carbon dioxide was produced during the decomposition of organic matter,making the bottom water body more soluble to calcium carbonate.

Molecular biomarker record of paleooceanographic environment in the East China Sea during the last 35000 years

By reference of the δ18O and δ13C isotopic compositions of G.sacculifer and accelerator mass spectrometry (AMS)14C dates, the U K 37 , ∑C – 21 /∑C +- 22 and Pr/Pn in core DGKS9603 have been used to characterize the changes of paleooceanographic environment occurring in the East China Sea (ECS) during the last 35000 years. The stratigraphic records of these proxies have shown that during the last 35 ka the Okinawa Trough has gone through 7 stronger cold-climate events (C1–C7) and 9 terrigenous matter-decreasing events (e2–e9), of which, the C1 corresponds to the cold episode occurring in the middle late Holocene, C2–C4 and C7 correspond to the H1–H4 events, respectively. e1 and e3–e8 correspond to the decrease of sea surface temperature (SST), respectively. The terrigenous inputs increased when Heinrich events occurred. Climate colding resulted in the decrease of terrigenous matter transported by rivers, and the increase of that transported by winter monsoon. Heinrich events are closely related to East Asia monsoon. During the Last Glacial Maximum (LGM, 15.5–25.8 Cal ka BP), reduction environment fluctuated strongly, bringing forth three stronger reduction events (R1–R3) and one weaker reduction event (O), of which, R1–R3 correspond to the decrease of SST and increase of terrigenous nutrient and O corresponds to the decrease of terrigenous nutrient. The fluctuation of reduction condition must be related to the change of sea surface productivity.