Identification and evolution of hydrogeochemical processes in the groundwater environment in an area of the Palar and Cheyyar River Basins,Southern India   总被引：5，自引：0，他引：5  

N.?Rajmohan  L.?ElangoEmail author 《Environmental Geology》2004,46(1):47-61

The Palar and Cheyyar River Basins in Tamil Nadu state of Southern India are characterised by different geological formations, and groundwater is the major source for domestic, agricultural and other water-related activities. Hydrogeochemical studies were carried out in this area with the objective of identifying the geochemical processes and their relation to groundwater quality. Groundwater samples were collected once a month from 43 groundwater wells in this area from January 1998 to July 1999. Sampling procedures and chemical analysis were carried out as per the standard methods. Chemical data are used for mathematical calculations and graphical plots to understand the chemical process and its relation to the groundwater quality. The chemical composition of groundwater in the central part of the study area mainly depends on the recharge from lakes and the river, which is explained by a mixing mechanism. In addition, weathering of silicate minerals controls the concentration of major ions such as sodium, calcium, magnesium and potassium in the groundwater of this area. Further, the activity ratios indicate that the groundwater is in equilibrium with kaolinite, smectite and montmorrillonite. The reverse ion exchange process controls the concentration of calcium, magnesium and sodium in hard rock formations, and dissolution of carbonate minerals and accessory minerals is the source of Ca and Mg, in addition to cation exchange in the sedimentary formations. In general, the chemical composition of the groundwater in this area is influenced by rock–water interaction, dissolution and deposition of carbonate and silicate minerals, ion exchange, and surface water interactions.  相似文献   

基于²¹⁰Pb测年法的楚科奇海陆架北缘有机碳沉积通量研究          下载免费PDF全文

余雯何建华  李奕良苏健 《极地研究》2012,24(4):391-396

有机碳沉积作用在一定时间尺度上形成海洋碳汇作用的最终净效应,北冰洋陆架的有机碳沉积作用在全球碳循环中有着尤为重要的地位。为了测定楚科奇海陆架的有机碳沉积通量,本文应用210Pb测年法对中国第3次北极考察R17站位的沉积物样品的年龄及沉积速率进行了分析测定,并结合表层沉积物中有机碳的含量计算得到了楚科奇海陆架北缘的有机碳沉积通量。结果显示,该站位的沉积速率为0.6 mm/a,表观沉积质量通量为0.72 kg/m2/a,有机碳沉积通量为517 mmol C/m2/a。经估算,真光层输出的有机碳中约有29 %被长期封存在沉积物中,远高于中低纬度的正常值（~10 %）,说明楚科奇海陆架区具有高效的碳汇作用。  相似文献   

模拟氮沉降对三江平原湿地小叶章生物量及分配的影响     

赵光影  窦晶鑫  郝冬梅 《地理与地理信息科学》2012,28(4):103-106

在非淹水、淹水两种水分条件下模拟氮沉降变化(分别相当于氮沉降0g/(m2.a)、1g/(m2.a)、3g/(m2.a)、5g/(m2.a))对三江平原典型湿地植物小叶章生物量及其分配的影响。结果表明,不同水分状况下氮沉降均促进小叶章生物量的积累,且以N5水平下生物量增加最多(p<0.05)。小叶章各器官生物量增长程度对氮沉降的响应并不一致:非淹水条件下根生物量平均增长最大(54.5%),其次是叶(31%)、茎(19.2%);淹水条件下小叶章各部位的生物量增长更为显著,其中根生物量平均增长124.7%,叶、茎生物量分别增长62%和61.1%。氮沉降明显促进了根生物量的积累,提高根生物量的分配比例。生长季的氮沉降对于改变湿地的营养状况、刺激植物生长具有直接的生态意义。  相似文献   

降尘过程指示的沙尘循环过程   总被引：1，自引：0，他引：1  

贾晓鹏  石晓萌  王海兵 《中国沙漠》2012,32(3):600-603

 大气降尘过程受诸多因素的影响,如沙尘源区的性质、输送距离、降雨量等。利用甘肃省10个城市15 a间(1986—2000年)的降尘监测资料与气象资料,主要分析了沙漠戈壁区与黄土区降尘的差异及原因。结果表明：①西北干旱区的降尘量主要与沙尘事件频次有关;②沙漠戈壁区的大气降尘量大于黄土高原区;③降尘量在强沙尘源区,呈现出显著的高值中心。随着沙尘自西向东输送,降尘通量随输送距离的增加而减少。  相似文献   

基于RAMS/CFORS Ⅱ模式一次低空核试验放射性烟云扩散的数值模拟     

张彦  郑毅  王自发 《气候与环境研究》2008,13(6)

采用RAMS／CFORS Ⅱ模式模拟了一次低空核试验烟云的传输和沉降过程。CFORS Ⅱ模式是在RAMS／CFORS模式的基础上开发的,可用于对核试验放射性烟云长距离输送和沉降过程的模拟研究。模拟表明：对流层中低层的低压槽系统对本次低空核试验烟云的水平传输和垂直扩散起着重要的影响作用;烟云的长距离传输速度呈现出随高度递减而减小的趋势,在6000m以上,烟云在爆后48h即东移入海,6000m以下,烟云在中国大陆的扩散和沉降维持了5d以上;爆后2天内以大粒子沉降为主,其后以小粒子沉降为主,小粒子的放射性远小于大粒子,在爆后第4天,放射性沉降就减小了3个量级,而小粒子的沉降范围是大粒子的5倍以上。通过模拟和观测对比表明,模拟结果基本符合实际烟云的传输和沉降态势。  相似文献   

Coeval versus reciprocal mixed carbonate–siliciclastic deposition, Middle Devonian Baltic Basin, Eastern Europe: implications from the regional tectonic development     

KATI TÄNAVSUU-MILKEVICIENE  PIRET PLINK-BJÖRKLUND†  KALLE KIRSIMÄE  LEHO AINSAAR 《Sedimentology》2009,56(5):1250-1274

The Middle Devonian Narva succession in the Baltic Basin represents a significant turnaround in the history of the basin. The detailed study of core and outcrop sections and the three‐dimensional correlations across the Baltic Basin reveal a carbonate‐dominated, mixed retrogressive succession, overlain by a siliciclastic‐dominated, progradational succession. The palaeogeographic reconstructions show how the shallow, tide‐influenced basin expanded from south‐west to north‐east and, later during the transgression, also to the north, south and east. The transgressive portion of the basin fill is dominated by carbonate‐rich sabkha and supratidal to intertidal deposits on the basin margins, and subtidal carbonates in the basin centre. Siliciclastic material was derived by tidal currents and storm waves from the south‐west through a tidal inlet and flood‐tidal delta complex. This initial transgressive phase is characterized by the lack of subsidence or even episodic uplifts in the northern/north‐western part of the basin margin, shown by convergence of timelines and the thin (30 m) transgressive succession. In contrast, on the southern margin, the facies associations stack vertically into a 70 to 80 m thick succession, indicating significantly higher subsidence rates. The upper part of the transgressive phase indicates subsidence across the whole basin. The upper, progradational portion of the basin fill is dominated by coarse, siliciclastic, tide‐influenced deltaic deposits that rapidly prograded from north‐west to south‐east. This detailed study on the Narva succession shows that siliciclastic and carbonate deposition was coeval and that mixing occurred at different temporal and spatial scales. The mixing was controlled by grain‐size, volume and location of siliciclastic input rather than relative sea‐level changes as suggested in widely used reciprocal mixing models. It is suggested that the forebulge of the Scandinavian Caledonian fold‐and‐thrust belt migrated to the north‐western margin of the Baltic Basin during the earliest Eifelian, as indicated by the lack of subsidence and probable uplift in the northern/north‐western margin during the early transgressive phase. The forebulge migration ceased although the forebulge had already started to subside during the later stages of the transgressive phase. The deltaic progradation is interpreted to be associated with the orogenic collapse and uplift in the Scandinavian Caledonides that caused the erosion of the foreland basin fill and the coarse sediment transport into the Baltic Basin.  相似文献   

苏北南通海涂近期冲淤动态及其开发   总被引：5，自引：1，他引：5  

陈宏友 《海洋科学》1990,14(2):28-35

  相似文献   

Channel response to a dam-removal sediment pulse captured at high-temporal resolution using routine gage data     

Matthew J. Cashman  Allen C. Gellis  Eric Boyd  Mathias J. Collins  Scott W. Anderson  Brett D. McFarland  Ashley M. Ryan 《地球表面变化过程与地形》2021,46(6):1145-1159

In this study, we captured how a river channel responds to a sediment pulse originating from a dam removal using multiple lines of evidence derived from streamflow gages along the Patapsco River, Maryland, USA. Gages captured characteristics of the sediment pulse, including travel times of its leading edge (~7.8 km yr⁻¹) and peak (~2.6 km yr⁻¹) and suggest both translation and increasing dispersion. The pulse also changed local hydraulics and energy conditions, increasing flow velocities and Froude number, due to bed fining, homogenization and/or slope adjustment. Immediately downstream of the dam, recovery to pre-pulse conditions occurred within the year, but farther downstream recovery was slower, with the tail of the sediment pulse working through the lower river by the end of the study 7 years later. The patterns and timing of channel change associated with the sediment pulse were not driven by large flow or suspended sediment-transporting events, with change mostly occurring during lower flows. This suggests pulse mobility was controlled by process-factors largely independent of high flow. In contrast, persistent changes occurred to out-of-channel flooding dynamics. Stage associated with flooding increased during the arrival of the sediment pulse, 1 to 2 years after dam removal, suggesting persistent sediment deposition at the channel margins and nearby floodplain. This resulted in National Weather Service-indicated flood stages being attained by 3–43% smaller discharges compared to earlier in the study period. This study captured a two-signal response from the sediment pulse: (1) short- to medium-term (weeks to months) translation and dispersion within the channel, resulting in aggradation and recovery of bed elevations and changing local hydraulics; and (2) dispersion and persistent longer-term (years) effects of sediment deposition on overbank surfaces. This study further demonstrated the utility of US Geological Survey gage data to quantify geomorphic change, increase temporal resolution, and provide insights into trajectories of change over varying spatial and temporal scales.  相似文献   

Spatial and seasonal variability of sediment accumulation potential through controlled flooding of the beels located in the polders of the Ganges-Brahmaputra-Meghna delta of Southwest Bangladesh     

Md Feroz Islam  Hans Middelkoop  Paul P. Schot  Stefan C. Dekker  Jasper Griffioen 《水文研究》2021,35(4):e14119

The Ganges-Brahmaputra-Meghna (GBM) delta plain within Bangladesh is one of the most vulnerable to relative sea level rise (RSLR) in the world especially under current anthropogenically modified (i.e., embanked) conditions. Tidal river management (TRM) as practiced in coastal regions of Bangladesh may provide an opportunity to combat RSLR by raising the land level through controlled sedimentation inside beels (depression within embanked polders) with re-opening of polders. To date, TRM has been applied to tide-dominated coastal regions, but the potential applicability of TRM for the beels within the polders of river-dominated and mixed flow (MF) regimes remains to be assessed. We apply a calibrated 2D numerical hydromorphodynamic model to quantify sediment deposition in a beel flooded through breaching of the polder dike under conditions of river-dominated, tide-dominated and MF regimes for different seasons and applying different regulation schemes for the flow into the beel. Simulation results show considerable seasonality in sediment deposition with largest deposition during the monsoon season. The potential of controlled flooding is highest in the tide-dominated region, where sediment accumulation can be up to 28 times higher than in the river-dominated region. Regulating flow into a beel increases trapping efficiency, but results in slightly lower total deposition than without regulation. We conclude that re-establishing flooding of the beel within the polder without regulating the flow into the beel through breaching of the polder dike is a promising strategy for the mixed and tide-dominated flow regions in the delta as the sediment accumulation can raise the land surface at a higher rate than RSLR and effective SLR (ESLR). In the more upstream river-dominated section of the delta, accumulation rates would be much lower, but the pressure of sea level rise on these areas is lower as well. Owing to the abundant availability of sediment, application of controlled flooding like TRM therefore provides an opportunity to counteract the impact of RSLR and ESLR by means of land raising, particularly along the tidal river reaches in the GBM delta.  相似文献   

Geological and Fluid Inclusion Constraints on Gold Deposition Processes of the Dayingezhuang Gold Deposit,Jiaodong Peninsula,China   总被引：1，自引：0，他引：1  

CHAI Peng  ZHANG Zhiyu  HOU Zengqian 《《地质学报》英文版》2019,93(4):955-971

The Dayingezhuang gold deposit, hosted mainly by Late Jurassic granitoids on Jiaodong Peninsula in eastern China, contains an estimated 170 t of gold and is one of the largest deposits within the Zhaoping fracture zone. The orebodies consist of auriferous altered pyrite–sericite–quartz granites that show Jiaojia-type (i.e., disseminated and veinlet) mineralization. Mineralization and alteration are structurally controlled by the NE- to NNE-striking Linglong detachment fault. The mineralization can be divided into four stages: (K-feldspar)–pyrite–sericite–quartz, quartz–gold–pyrite, quartz–gold–polymetallic sulfide, and quartz–carbonate, with the majority of the gold being produced in the second and third stages. Based on a combination of petrography, microthermometry, and laser Raman spectroscopy, three types of fluid inclusion were identified in the vein minerals: NaCl–H2O (A-type), CO2–H2O–NaCl (AC-type), and pure CO2 (PC-type). Quartz crystals in veinlets that formed during the first stage contain mainly AC-type fluid inclusions, with rare PC-type inclusions. These fluid inclusions homogenize at temperatures of 251°C–403°C and have low salinities of 2.2–9.4 wt% NaCl equivalent. Quartz crystals that formed in the second and third stages contain all three types of fluid inclusions, with total homogenization temperatures of 216°C–339°C and salinities of 1.8–13.8 wt% NaCl equivalent for the second stage and homogenization temperatures of 195°C–321°C and salinities of 1.4–13.3 wt% NaCl equivalent for the third stage. In contrast, quartz crystals that formed in the fourth stage contains mainly A-type fluid inclusions, with minor occurrences of AC-type inclusions; these inclusions have homogenization temperatures of 106°C–287°C and salinities of 0.5–7.7 wt% NaCl equivalent. Gold in the ore-forming fluids may have changed from Au(HS)0 as the dominant species under acidic conditions and at relatively high temperatures and fO2 in the early stages, to Au(HS)2– under neutral-pH conditions at lower temperatures and fO2 in the later stages. The precipitation of gold and other metals is inferred to be caused by a combination of fluid immiscibility and water–rock interaction.  相似文献