Fluoride and arsenic hydrogeochemistry of groundwater at Yuncheng basin,Northern China

High fluoride and arsenic concentrations in groundwater have led to serious health problems to local inhabitants at Yuncheng basin, Northern China. In this study, groundwater with high fluoride and arsenic concentration at Yuncheng basin was investigated. A majority of the samples (over 60%) belong to HCO₃ type water. The predominant water type for the shallow groundwater collected from southern and eastern mountain areas was Ca/Mg-Ca-HCO₃ types. For the shallow groundwater from flow through and discharge area it is Na-HCO₃/SO₄-Cl/SO₄/Cl type. The predominant water type for the intermediate and deep groundwater is of Na/Ca/Mg-Ca-HCO₃ type. According to our field investigation, fluoride concentration in groundwater ranges between 0.31 and 14.2 mg/L, and arsenic concentration ranges between 0.243 and 153.7 μg/L. Out of seventy collected groundwater samples, there are 31 samples that exceed the World Health Organization (WHO) standard of 1.5 mg/L for fluoride, and 15 samples exceeds the WHO standard of 10 μg/L for arsenic. Over 40% of high fluoride and arsenic groundwater are related to the Na-HCO₃ type water, and the other fifty percent associated with Na-SO₄-Cl/HCO₃-SO₄-Cl type water; little relation was found in calcium bicarbonate type water. A moderate positive correlation between fluoride and arsenic with pH were found in this study. It is due to the pH-dependent adsorption characteristics of F and As onto the oxide surfaces in the sediments. The observed negative correlation between fluoride and calcium could stem from the dissolution equilibrium of fluorite. The high concentration of bicarbonate in groundwater can serve as a powerful competitor and lead to the enrichment of fluoride and arsenic in groundwater. Most of the groundwater with high fluoride or arsenic content has nitrate content about or over 10 mg/L which, together with the observed positive correlations between nitrate and fluoride/arsenic, are indicative of common source of manmade pollution and of prevailing condition of leaching in the study area.     

Assessment of Impact of Storm on Point Source Pollutant Transport in Estuary by Dissolved Tracer Modeling

A continuously discharged dissolved conservative tracer was simulated with the Chesapeake Bay Estuary Model Package to study pollutant transport in the estuary in response to point source loads and the impact of the November, 1985 storm. A visualization technology is applied to show 3-dimensional concentration variations in a continuous daily time sequence. The differential responses of daily net transport during storms versus inter-storm periods can be observed from an MPEG movie. It may take 2–3 months for a tracer to travel from the fall-line to the mouth of a river during relatively dry seasons, only 2 weeks in some medium storms, and less than 5 days in a big storm. Plots of daily concentrations from eleven selected locations in the estuary provide quantitative information on the response of tracer concentration to flows. The magnitude and time of tracer peaks related with different weather events in these locations reflect the combined effects of flows from various directions to these locations. The lower tributaries (which are closer to the Bay mouth) are affected more than the upper tributaries by a source discharged at a mid-tributary. A storm can transport materials more effectively to the Bay and affect adjacent tributaries more severely.     

Zircon U-Pb geochronology,geochemistry and Sr-Nd-Pb isotopes from the metamorphic basement in the Wuhe Complex:Implications for Neoarchean active continental margin along the southeastern North China Craton and constraints on the petrogenesis of Mesozoic g

We report zircon U-Pb geochronology,geochemistry and Sr-Nd-Pb isotope data from mafic granulites and garnet amphibolites of the Wuhe Complex in the southeastern margin of the North China Craton (NCC).In combination with previous data,our results demonstrate that these rocks represent fragments of the ancient lower crust,and have features similar to those of the granulite basement in the northern margin of the NCC.A detailed evaluation of the Pb isotope data shows that Pb isotopes cannot effectively distinguish the role of the Yangtze Craton basement from that of the NCC basement with regard to the source and generation of magmas,at least for southeastern NCC.The age data suggest that the protoliths of the granulites or amphibolites in the Wuhe Complex were most likely generated in Neoarchean and that these rocks were subjected to Paleoproterozoic(1.8-1.9 Ga) high-pressure granulite facies metamorphism. This study also shows that the Precambrian metamorphic basement in the southeastern margin of the NCC might have formed in a tectonic setting characterized by a late Neoarchean active continental margin.