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Guo F.,Chang'an University | Guo F.,Institute of Karst Geology | Wang W.,Chang'an University | Jiang G.,Institute of Karst Geology | Ma Z.,East China Mineral Exploration and Development Bureau of Jiangsu Province
Shuikexue Jinzhan/Advances in Water Science | Year: 2014

Lihu subterranean river in South China was selected to study the contaminant transport behavior and self-purification capacity of a karst aquifer. The subterranean river was investigated through water sampling along the stream reach for one year. Analysis of inorganic ions and trace elements in different seasons and at different locations showed the major contaminants are NO2 --N, NH4 +-N, COD, As, Cd, and Hg, due to domestic waste, mining industrial waste, and fertilizer application in the recharge area. Along the course of the karst conduit, a self-purification process was observed because of significant decrease in some ions concentration. The mechanism of self-purification was caused by dilution and nitrification, which was determined by the suterranean river's structure and hydrogeological condition. By comparing the attenuation quantity and percentage of ions, it was found that ammonium had the highest, while chloridion had the lowest percentage. According to the attenuation rate, four types of attenuation character could be classified. Firstly, the ions decayed completely after they entered the karst aquifer, such as TFe, Zn, and Al; secondly, the ions had the highest attenuation rate when they traveled underground through the aquifer, such as K, Na, Mg, F, Cl, HPO4, and TP; thirdly, the concentration gradually decreased from upstream to downstream, which was represented by NH4 +-N, CODCr, and BOD5; and finally, they had the highest attenuation rate when transformed from surface stream to underground stream, but secondary suspension of contaminants could happen in the cave, such as Mn, Ba, and Hg.

Li X.,Nanjing University | Li X.,Chengdu University of Technology | Jenkyns H.C.,University of Oxford | Zhang C.,Nanjing University | And 3 more authors.
Geological Magazine | Year: 2014

Lower Cretaceous pedogenic carbonates exposed in SE China have been dated by U-Pb isotope measurements on single zircons taken from intercalated volcanic rocks, and the ages integrated with existing stratigraphy. δ13C values of calcretes range from -7.0‰ to -3.0‰ and can be grouped into five episodes of increasing-decreasing values. The carbon isotope proxy derived from these palaeosol carbonates suggests pCO2 mostly in the range 1000-2000 parts per million by volume (ppmV) at S(z) (CO2 contributed by soil respiration) = 2500 ppmV and 25°C during the Hauterivian-Albian interval (c. 30 Ma duration). Such atmospheric CO2 levels are 4-8 times pre-industrial values, almost double those estimated by geochemical modelling and much higher than those established from stomatal indices in fossil plants. Rapid rises in pCO2 are identified for early Hauterivian, middle Barremian, late Aptian, early Albian and middle Albian time, and rapid falls for intervening periods. These episodic cyclic changes in pCO2 are not attributed to local tectonism and volcanism but rather to global changes. The relationship between reconstructed pCO2 and the development of large igneous provinces (LIPs) remains unclear, although large-scale extrusion of basalt may well be responsible for relatively high atmospheric levels of this greenhouse gas. Suggested levels of relatively low pCO2 correspond in timing to intervals of regional to global enrichment of marine carbon in sediments and negative carbon isotope (δ13C) excursions characteristic of the oceanic anoxic events OAE1a (Selli Event), Kilian and Paquier events (constituting part of the OAE 1b cluster) and OAE1d. Short-term episodes of high pCO2 coincide with negligible carbon isotope excursions associated with the Faraoni Event and the Jacob Event. Given that episodes of regional organic carbon burial would draw down CO2 and negative δ13C excursions indicate the addition of isotopically light carbon to the ocean-atmosphere system, controls on the carbon cycle in controlling pCO2 during Early Cretaceous time were clearly complex and made more so by atmospheric composition also being affected by changes in silicate weathering intensity. Copyright © Cambridge University Press 2013.

Li X.,Nanjing University | Li X.,Chengdu University of Technology | Xu W.,Chengdu University of Technology | Liu W.,Nanjing Institute of Geology and Mineral Resources | And 4 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2013

Carbon and oxygen isotopic ratios were determined from ~100 Lower Cretaceous samples from four carbonate-bearing facies in Southeast (SE) and Northwest (NW) China for palaeoclimatic and palaeoenvironmental analyses. The samples were interpreted as sediments within sublithofacies of distal alluvial ponds (SF1), open shallow lakes (SF2), littoral lakes (SF3), and marshes (SF4). Results of analyses show in SE China, δ13C values range between -5.0‰ and 3.0‰ with a negative trend through time, and δ18O values are all negative (-19.3‰--7.4‰); in NW China, δ13C values range from -4.0‰ to 4.0‰ with periodic change, and δ18O values range between -18.0‰ and 1.5‰.Both relatively heavy values and pronounced covariances of most δ13C and δ18O indicate semiarid climate and domination of closed brackish lakes, marshes, and ponds in NW and SE China during the Early Cretaceous. Of them, positive δ13C (0.0‰ to 4.0‰) and relatively heavy δ18O (-5.0‰ to 1.5‰) values suggest interruptions of arid-evaporation in intermittences of the early Hauterivian in SW Fujian, of the middle Aptian in West Jiuquan basin, of the late Aptian in SW Ordos basin, and of the late Aptian-early Albian in Liupanshan basin. In a short interval of the early Aptian, the hot and humid climate occurred in local SW Zhejiang by high kaolinite content and in West Jiuquan basin by warm flora could be an exception. Particularly, extremely negative δ18O values (mainly -19.0--9.0‰) indicate relatively low temperature in SE Fujian in the Berriasian-Barremian, in Liupanshan basin in the late Aptian, in SW Ordos basin in the late Albian, and in West Jiuquan basin in the mid-late Aptian, which is supposed to attribute to the presence of 2500m-4500m in elevation. More positive values and more covariance ratios of δ13C and δ18O in NW China than in SE China and in mainland China than in America indicate a arider climate in former than in later, probably attributing to the palaeogeography in distance to sea.A tentative correlation of the Early Cretaceous δ13C value excursion of calcretes shows a good compatibility between marine OAEs and terrestrial carbonate sediments and between NW China and America continents, implying a global response to carbon cycle in both marine and terrestrial environments. The feature suggests the potential of global correlation and application of terrestrial calcrete δ13C excursions in pre-Cenozoic. © 2013 Elsevier B.V.

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