首页|<'87>Sr/<'86>Sr Isotope Geochemistry of Groundwater System in the Hebei Plain，Northern China.
<'87>Sr/<'86>Sr Isotope Geochemistry of Groundwater System in the Hebei Plain，Northern China.
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The Hebei plain of Northern China is characterized by low and irregular rainfall． In such a semi-arid environment，ground water is the primary source for water supply．However，with the increasing population and economic growth,the utilization of this groundwater has resulted into over-exploitation and deteriorating water quality together with many other hydrogeological and environmental problems in the plain．This study was therefore carried out to further document the existing problem by utilizing the superiority of strontium sotopic technique to examine the influence of water-rock interaction(WRI) on the groundwater chemistry of the plain．Since WRI exerts an important control on groundwater chemistry，understanding of such groundwater is critical to the viability of water use in the region．In the study，data of 87 Sr/86 Sr ratio and ions chemistry of groundwater samples from the Hebei plain were used．Except some individual samples，it was shown that 87 Sr/86 Sr ratio increases with the increasing age and depth of groundwater and with increasing distance from the recharge area to the discharge area of the plain．87 Sr/86 Sr ratios are also found to be higher than that of the modem mean sea water．Geothermal waters with lower 87 Sr/86 Sr than the contemporary seawater was found to belong to Ordovician limestone which is particularly poor in Rb and radiogenic Sr although it is very old and has longer accumulation time．The primary sources of dissolved Sr in Hebei groundwater are from accession from the atmosphere(via Sr dissolved in rainfall and dust deposition) and dissolution of Sr bearing minerals in the unsaturated and saturated zones．Sr concentrations in rainfall ale generally low，and therefore， the high Sr concentrations measured in groundwater from the plain are therefore due to Evapo-concentration of rainfall-derived- Sr during transit through the upper few meters of the unsaturated zone and dissolution and re-crystallizationof Sr-bearing minerals．To discuss the relation between 87 Sr/86 Sr ratio and Sr2+ content,the groundwater is divided into three groups：moderate Sr2+ content and higher 87 Sr/86 Sr ratio (waterⅠ)；lower Sr2+ content and higher 87 Sr/86 Sr ratio (waterⅡ)；and higher Sr2+ content and lower 87 Sr/86 Sr ratio (water Ⅲ)，that is hot water．On the basis of integrated analysis，it was considered that the radiogenic Sr in the Quaternary groundwater (Q4-Q1) originates from weathering of silicate rich in Na and Rb，mainly from plagioclase；the radiogenic Sr of hot water in Central plain is attributed to carbonate dissolution．with lower 87 Sr/86 Sr ratio and higher Sr/Na ratio；the recharge area is laterally recharged by the groundwater flowing through igneous and metamorphic rocks，with moderate 87 Sr/86 Sr ratio．The tertiary geothermal water has higher initial Sr content and radiogenic Sr content is lower．The groundwater age is advanced and so the accumulative-time effect should be more notable．It’s therefore required that further studies be carried out to establish the formation mechanism of Tertiary groundwater with low 87 Sr/86 Sr ratio．Above a11．combining Sr data for groundwater and major ion chemistry has offered some new and unique evidence to the evolution of the groundwater in the Quaternary sediments in the Hebei Plain．
Odong Justine
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Groundwater System Hebei Plain Water-Rock Interaction Geochemistry
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