黄土塬区浅层地下水化学特征及其碳循环意义

对甘肃省灵台县独店镇秋射村黄土剖面浅层地下水的水化学组成、溶解无机碳(DIC)、溶解有机碳(DOC)、颗粒有机碳(POC)等进行了取样分析,对其δ~(13)CDIC和δ~(13)CPOC的特征及其控制因素进行了探讨,并评估了降雨补给过程中的碳酸盐风化碳汇强度。结果表明,研究区地下水的水化学类型为HCO3-Ca·Mg型,其方解石饱和指数SIC大于0,已经饱和,但尚未达到大规模沉淀的程度。研究区黄土浅层地下水的DIC变化范围为5.25~5.45mmol/L,DOC含量为0.59~0.62mg/L,明显低于地表水体;而POC稍高,这是因为黄土颗粒物的混入造成。泉水和井水的δ~(13)CDIC变化范围在-9.19‰~-8.90‰之间,其较高的δ~(13)C与碳酸盐风化-沉积过程中反复的碳同位素交换有关。而δ~(13)CPOC变化范围在-19.99‰~-18.87‰之间,与黄土有机碳同位素特征基本一致。地下水中的HCO-3、Ca2+和Mg2+主要来源于碳酸盐的化学风化。根据风化反应的离子平衡关系,计算得到研究区的风化碳汇为2.82mmol/L,即每有1L的降水入渗到零通量面以下,就会产生2.82mmol的碳汇。     

Strontium isotopic geochemistry of the Changjiang estua-rine waters: Implications for water-sediment interaction

The Sr concentrations and 87Sr/86Sr ratios have been measured for the Changjiang es-tuarine waters with a main purpose to understand physical and chemical processes at the estuary. The result shows that the Changjiang River water has higher Sr concentration (150 ng/g) and lower 87Sr86Sr ratio (0.7105) when compared with the average values (0.7119 for 87Sr/86Sr and 78ppb for Sr, respectively) of large world rivers. In the mixing process, no simple mixing of two end-members has been found according to the variations of Sr concentration and isotope ratios. There is an abrupt rise of Sr isotope ratios at the salinity about 1 mg/g during river-sea water mixing at the estuary. This abrupt rise of Sr isotope ratios is mostly ascribed to the strong water-sediment interaction, because there exists the same rise of suspended particulate materials due to energetic resuspension of bottom sediments.     

Enrichment and Release of Rare Earth Elements during Weathering of Sedimentary Rocks in Wujiang Catchments, Southwest China

Thirteen weathering profiles of sedimentary rocks such as limestone, dolomitic limestone, dolomite, sillicalite, black shale and purple sandrock from Wujiang catchments were selected for study on enrichment and release behavior of rare earth elements （REE） during weathering, and its impact on plant growth and riverine REE distribution in the catchments with methods of hierachical cluster analysis and mass balance calculation in order to set a basis for riverine material source research and agricultural production. The results show that the enrichment degree of REE in calcareous soils from the Wujiang catchments is much higher than that of limestone, yellow soil, upper continental crust （UCC）, China soil （CS） and world soil （WS）. The ability of enrichment and release of REE is partly controlled by distribution of REE in bedrocks, contents and adsorption ability of organic matters, clay minerals and Fe-oxides/hydroxides in weathering profiles. The REE released from weathering of carbonate rocks and clastic rocks can be absorbed and utilized by local plants. The results also reveal that release of REE and Fe mainly from weathering of carbonate rocks and partly from clastic rocks exerts an important control on riverine REE distribution.     

Isotopic compositions of strontium in river water of Guizhou karst areas, China

We have carried out a study on the variation of strontium isotope composition of river waters, Wujiang and Yuangjiang River, in karst areas of Guizhou Province, China. The results obtained permit us to characterize the geochemistry of the river draining karst terrain and obtain a better understanding of main controls of catchment geology, chemical weathering of different rocks, and evaluate impact of human activities on the environment. The isotopic ratios of dissolved Sr in all rivers are between 87Sr/86Sr =0.7077 and 0.7110, totally lower than the weighted average of 87Sr/86Sr =0.7119 for the world large rivers. The Wujiang River waters have Sr concentrations from 1.0 to 6.1 μmol/L, while the Yuanjiang River waters have much lower Sr concentrations ranging from 0.28 to 1.3 μmol/L. Most of the river waters from the Wujiang river are characterized by low Ca/Sr and Mg/Sr, and 87Sr/86Sr ratios, in which a majority of river waters are of 87Sr/86Sr ratios lower than the average Sr isotope ratio (87Sr/86Sr