Modeling the risk of nitrate leaching and nitrate runoff loss from intensive farmland in the Baiyangdian Basin of the North China Plain

The water movement and soil nitrogen cycle of the Baiyangdian Basin were simulated, and the risk of nitrate leaching and nitrate runoff loss from intensive farmland was assessed by using the distributed hydrological soil and water assessment tool (SWAT) in this study. The model assessment showed that SWAT was able to simulate water and nitrate movement in the region with satisfactory results. The modeling analysis indicated that fertilizer application was the overriding source of soil nitrogen and might result in a large amount of nitrate accumulation in soils; this nitrate might be lost by leaching or runoff driven by water movement. In 2009, nitrate nitrogen leaching represented 19.5 % of the total amount of nitrogen fertilizer application, while nitrate nitrogen runoff represented 1.7 % only. Thus, it showed that the nitrate leaching was the main approach of soil nitrogen movement in farmland because of strong percolation. It also showed a significant variation of nitrate leaching from different soil depths, with the largest amount leached from surface soil layers and the smallest amount leached from lower soil layers. Therefore, it could be further revealed that the nitrate concentration was very low at soil layers lower than the root zone of crops (1.2 m). Validated by groundwater observations, groundwater pollution by nitrate derived from fertilizers was not serious because of the deep groundwater level in the study plain. However, the risk of groundwater pollution would increase significantly if precipitation increased.     

宁芜盆地白象山铁矿床成矿作用过程数值模拟

白象山铁矿床是宁芜火山岩盆地钟姑矿田中典型的玢岩型铁矿床,主矿体赋存于闪长岩和黄马青组砂页岩接触带部位的内带-正带,呈似层状产出。本文采用数值模拟的方法研究探讨白象山铁矿床成矿过程的动力学机制以及汇流容矿空间的形成。在建立白象山矿床典型剖面以及三维实体模型的基础上,选取典型剖面,基于FLAC 3D系统,对白象山铁矿床的充填过程进行数值模拟。模拟结果显示,白象山铁矿床存在容矿汇流空间,其形成受力-热-流体的耦合作用制约;扩容空间的形成可为矿质的沉淀以及交代作用提供有利的成矿空间,并为流体的汇聚提供有利场所,也表明白象山铁矿床的成矿过程与力学作用密切相关。本文的模拟研究充分揭示了白象山铁矿床成矿过程中的物理过程,岩石不同的力学性质以及接触带的形态是控矿的重要因素,这为进一步的找矿工作提供了依据。     

从洋壳俯冲到陆壳俯冲和碰撞：来自羌塘中西部地区榴辉岩和蓝片岩地球化学的证据

羌塘中部晚三叠世低温/高压变质带是目前青藏高原内部延伸规模最大的高压变质带,但大量关键高压变质岩石出露地区地球化学资料匮乏,严重制约了对高压变质带原岩建造以及构造演化的全面认识。本文以羌塘中西部地区尚无地球化学资料的果干加年山榴辉岩和红脊山蓝片岩为研究对象,进行了系统的地球化学以及原岩恢复工作。研究表明,果干加年山榴辉岩呈透镜状产于围岩石榴石多硅白云母片岩和少量大理岩中,其原岩为亚碱性玄武岩,具有较低的稀土总量(∑REE=51.19×10-6~59.43×10-6)和轻稀土亏损的特征[(La/Yb)N=0.59~0.70],不具有Nb、Ta、Ti的亏损,与典型的N-MORB特征一致,暗示其原岩可能来源于亏损的地幔源区,形成于洋中脊环境。红脊山地区基性蓝片岩的原岩为碱性玄武岩-亚碱性玄武岩,具有高的TiO2(2.97%~4.14%)和P2O5(0.29%~0.48%)含量,富集轻稀土元素[(La/Yb)N=6.10~11.6]和高场强元素,地球化学特征类似于OIB。但是这些基性蓝片岩与大量的陆源碎屑岩伴生产出,且具有明显的硅铝质上地壳物质混染的特征,与南羌塘地区二叠纪大陆板内基性岩墙的产出特征以及地壳混染特征一致,可能是其俯冲消减的产物。通过本文研究结果并结合区域内已识别出的E-MORB型洋壳和洋岛/海山物质深俯冲的证据,我们认为羌塘中部晚三叠世高压变质带以洋壳物质深俯冲为主,同时亦保留了部分陆壳物质俯冲的证据,暗示大洋向北俯冲消减结束之后,又牵引至少一部分南羌塘北缘陆壳物质经历了随后的俯冲过程。     

叠覆式三角洲——一种特殊的浅水三角洲

不同于常规三角洲以分流河道体系所形成的分流河道、河口坝、席状砂等微相为三角洲朵体的基本单元,叠覆式三角洲以内部结构简单的朵体为基本构成单元,朵体相互叠置,形成复合叠合体,进而构成三角洲骨架。单个朵体由河道扫描或扩展而成,复合朵体则是由单朵体侧向迁移或前(退)积而成。三角洲因大量朵体叠置而形成厚层状、内部结构复杂的复合砂体。不同朵体形成于不同时期,因而不存在统一的分流体系,单一沉积体具有层状特征,但不同期朵体受可容空间和地貌控制,呈三维叠置,而非简单的层状叠加,从而使得三角洲内部呈现出拼合式、立体式特点。单朵体是结构的基本单元,发育范围有限,与相邻朵体发育于不同时间单元,因而只能在复合体约束下小范围追踪。单一朵体接触关系及接触界面的渗流能力决定了油气富集和注水开发响应特征。朵体迁移、叠置造成大面积、巨厚的砂层可形成大型油气藏,而同时朵体间泥岩的不均匀分布也造就了砂体局部不连通或朵体间连通性变化,为岩性油气藏形成创造了条件,并且影响了注水开发中的注采对应性,进而影响水驱采油效果。     

琼东南盆地深水区中央峡谷天然气成藏条件与成藏模式

利用钻井岩芯、岩屑地质化验资料及测井、二维、二维地震数据,综合分析了琼东南盆地深水区中央峡谷储层的发育特征、天然气成藏条件及成藏主控因素.结果表明,峡谷中、下部堆积的多期浊积砂岩,储集物性好,是该区带的优质储层;峡谷内发育的大量岩性、构造-岩性复合型圈闭为天然气聚集造就了重要场所;凹陷中的渐新统崖城组煤系烃源岩及广厚的半封闭浅海泥岩生气潜力大,提供了丰富的烃源基础;峡谷下方的底辟/微裂隙是深部崖城组烃源岩生成的天然气向上运移的重要通道.可见,中央峡谷成藏条件优越,圈闭有效性和运移是该区天然气成藏的关键要素;由于峡谷内圈闭大多数定型于上新世莺歌海组沉积时期,与下伏崖城组烃源岩主生气期形成合理配置,因此,天然气成藏较晚,L1、L2和L3气田的重大发现就是很好的例证.     

С��Ⱥ���봨�����ʼ���ѵ�˺�ѵ�����ͼ��

??????M8.0????????????????????С???????????????????о???????????λ????????????????????ν???ие???????????????????1??M8.0??????????????????????????????????????С????????????????????????????????????????????????42°????????????????????????????20 km??2?????????????????????????????????????10 km?????????????????С??????????????????????????????????????????????????????λ?????????7 km??3??2??14??
ML3.7?????????????????93°?????????????????????С??????????????????????????????????2???????￡????????????????????????????????????????????????????????????????4??2??28??ML3.8?????????λ?????????????????????????????????????????????????????????￡????????????     

Nutrient export via overland flow from a cultivated field of an Ultisol in southern China

Understanding the influence of complex interactions among hydrological factors, soil characteristics and biogeochemical functions on nutrient dynamics in overland flow is important for efficiently managing agricultural nonpoint pollution. Experiments were conducted to assess nutrient export from Ultisol soils in the Sunjia catchment, Jiangxi province, southern China, between 2003 and 2005. Four plots were divided into two groups: two peanut plots and two agroforestry (peanut intercropped with citrus) plots. During the study period, we collected water samples for chemical analyses after each rainfall event that generated overland flow to assess nutrient export dynamics. The concentrations of potassium (K) and nitrate‐N (NO₃^––N) in overland flow were higher during the wetting season (winter and early spring). This reflects the solubility of K and NO₃^––N, the accumulation of NO₃^––N during the dry season and an increase in desorption processes and mixing with pre‐event water caused by prolonged contact with soil in areas with long‐duration, low‐intensity rainfall. In contrast, concentrations of total nitrogen (TN) and total phosphorus (TP) were higher during the wet season (late March to early July) and during the dry season (mid‐July to the end of September or early October). This was due to the interaction between specific hydrological regimes, the properties of the Ultisol and particulate transport processes. Variations in nutrient concentrations during storm events further identified that event water was the dominant source of total nitrogen and total phosphorus, and pre‐event water was the dominant source of NO₃^––N. In addition, the results obtained for the different land uses suggest that agroforestry practices reduce nutrient loss via overland flow. Copyright © 2012 John Wiley & Sons, Ltd.     

Rocking vibrations of a rigid embedded foundation in a poroelastic half‐space

This paper presents an analysis of the rocking vibrations of a rigid cylindrical foundation embedded in poroelastic soil. The foundation is subjected to time‐harmonic rocking excitation and is perfectly bonded to the surrounding soil. The soil underlying the foundation base is represented by a homogeneous poroelastic half‐space, whereas the soil along the side of the foundation is modeled as an independent poroelastic stratum composed of a series of infinitesimally thin layers. The behavior of the soil is governed by Biot's poroelastodynamic theory. The contact surface between the foundation base and the poroelastic soil is assumed to be smooth and either fully permeable or impermeable. The dynamic interaction problem is solved by employing a simplified analytical method. Some numerical results for the nondimensional rocking dynamic impedance and nondimensional angular displacement amplitude of the foundation are presented to show the effect of nondimensional frequency of excitation, poroelastic material parameters, hydraulic boundary condition, depth ratio and mass ratio of the foundation. Copyright © 2009 John Wiley & Sons, Ltd.     

鄂尔多斯盆地及其周边的新构造运动

本区新构造运动十分活跃,表现出多次波动性,周边山系呈不均衡抬升,盆地则呈不均衡沉降,因此使盆地呈现不对称的簸箕状,盆地中的水系结构也呈现不对称性。区内构造变形主要有褶皱、断裂、新隆起、新坳陷、拱曲和掀斜等,并产生现代地震、地热和火山活动。不均衡掀斜是导致上述现象的根本原因。