农业集聚对农业面源污染的影响——基于中国地级市面板数据门槛效应分析   总被引：3，自引：0，他引：3  

邓晴晴  李二玲  任世鑫 《地理研究》2020,39(4):970-989

农业集聚的环境效应相比其他产业更为复杂,然而学术界对此探讨较少。在理论分析的基础上,利用2007—2015年中国337个地级市面板数据,核算农业集聚水平与农业面源污染排放量,并采用空间分析技术、计量模型,实证探究农业集聚与农业面源污染的时空特征及农业集聚对农业面源污染的门槛效应。结果显示：① 农业集聚与COD、TN、TP三种农业面源污染在时序变化、空间布局、空间关联以及空间趋势变化上特征相异。② 农业集聚对COD、TN、TP农业面源污染皆呈现正相关的单门槛效应。低于门槛值阶段,农业集聚水平的提高显著加剧了农业污染,集聚水平跨过门槛值后,污染加剧形势有所缓和。③ 农业集聚与农业面源污染之间经历的两个阶段,取决于规模效应、结构效应、技术效应、社会效应、累积效应分别对农业面源污染排放的加剧与制约作用。随着农业集聚水平提高,各效应增污作用明显,导致污染水平显著提高,进入高于门槛值的阶段,各效应对污染排放的抑制能力提升,削弱了部分负环境外部效应。④ 农业经济水平、农业生产条件在一定程度上加剧了COD、TN、TP污染;畜牧业结构、环境规制对COD、TP污染存在显著的正相关关系;生产者素质的提高可以影响农户生产行为并改善农业环境。⑤ 农业集聚对COD污染的降污效应较弱,农业COD污染较为严重且主要来源于畜牧业养殖,畜牧业污染防治亟待加强。  相似文献   

Cross-Correlation Detection of Point Sources in the WMAP First Year Data     

Jian-Yin Nie  Shuang-Nan Zhang  Department of Physics  Center for Astrophysics  Tsinghua University  Beijing  Key Laboratory of Particle Astrophysics  Institute of High Energy Physics  Chinese Academy of Sciences  Beijing 《中国天文和天体物理学报》2007,7(2):199-208

We apply a Cross-Correlation (CC) method developed previously for detecting gamma-ray point sources to the WMAP first year data by using the Point-Spread Function of WMAP and obtain a full sky CC coefficient map. We find that the CC method is a pow- erful tool to examine the WMAP foreground residuals which can be further cleaned accord- ingly. Evident foreground signals are found in the WMAP foreground cleaned maps and the Tegmark cleaned map. In this process 101 point sources are detected, and 26 of them are new sources additional to the originally listed WMAP 208 sources. We estimate the ?ux of these new sources and verify them by another method. As a result, a revised mask file based on the WMAP first year data is produced by including these new sources.  相似文献   

基于同轴差距测量法的南海深水海底沉积物声衰减特性研究   总被引：4，自引：3，他引：1  

邹大鹏  卢博  吴百海  梁润华  陈飞燕 《热带海洋学报》2009,28(3):35-39

通过分析沉积物声波测量过程能量损失的实质，阐述平行轴差距衰减测量法和垂直轴差距衰减测量法的研究基础——差动式衰减测量方法原理，并推导了其衰减系数公式。根据南海沉积物的柱状样品分装的特点，结合以上两种方法，提出了同轴差距衰减测量法，这种方法具有原理上的合理性并且其可操作性强；运用此方法测量了沉积物在常温和温度控制变化条件下的声波信号，计算了衰减系数，研究了温度对沉积物声波传播能量的影响，得出南海深水海底沉积物具有以下声衰减特性：沉积物含砂量高，声衰减系数大；随着温度的升高，沉积物的声衰减系数变化具有不均匀性，整体呈非线性减小趋势。以上研究将为声学遥测和反演海底沉积物的物理力学特性提供数据和方法支持。  相似文献   

Isotopic tracing of ore-forming source materials for Dexing porphyry copper deposit of Jiangxi, China     

References： 《东北亚地学研究》2008,11(1):25-31

Dexing copper deposit is the biggest porphyry copper deposit in China. By researching isotopes of C, Si and Cu from the samples of Tongchang and Fujiawu ore-field, the authors found that δ^13 CpDB values of siderite were close to the δ^13 CpDB value of original magma; δ^30Si values of the samples at the ore-forming stage were close to the δ^30 Si value range of magma, δ^30Si values of partial samples were far away from it; Cu isotopic compositions of massive chalcopyrite formed at the early ore-forming stage are higher than that of veinal chalcopyrite formed at the later ore-forming stage. The results show that ore-forming materials were mainly derived from the porphyry body, and part of them were from wall rock materials.  相似文献   

Detecting environmental change in estuaries: Nutrient and heavy metal distributions in sediment cores in estuaries from the Gulf of Finland,Baltic Sea     

S. Vaalgamaa  D.J. Conley 《Estuarine, Coastal and Shelf Science》2008

Historical sediment nutrient concentrations and heavy metal distributions were studied in four estuaries in the Gulf of Finland, Baltic Sea to examine the response of these estuaries to temporal changes in human activities. Cores were collected using a 1-m Mackereth corer and dated using ²¹⁰Pb and ¹³⁷Cs. The cores were analyzed for total carbon (TC), total nitrogen (TN), total phosphorus (TP), organic phosphorus (OP), inorganic phosphorus (IP), biogenic silica (BSi), loss-on-ignition (LOI), Cu, Zn, Al, Fe, Mn, K, Ca, Mg and Na. Principal component analysis (PCA) was used to summarize the trends in the chemical variables and to compare the trends at the different sites. Applying the 1986 ¹³⁷Cs date as a reference point, ²¹⁰Pb chronologies were constructed for the sites using either the CRS model or a composite model (using both CIC and CRS). Significant increases were observed in sedimentation rates, TP and TN concentrations in all of the cores. Copper showed clear increases from 1850 towards present at all sites. Furthermore, redundancy analysis (RDA) was used to correlate environmental variables (catchment land use, catchment size, estuary surface area, depth and lake percentage) to sediment geochemistry. Based on redundancy analysis (RDA), the percentage of agriculture in the catchment was the most important factor affecting the sediment accumulation rate. Urban land-use types and industry correlate well with sediment Cu and Ca concentrations. Forest areas were related to high sediment BSi concentrations. Catchment land use was the most significant factor affecting sediment geochemical composition and sediment accumulation rates in these coastal embayments. Our results demonstrate that the coastal estuaries of the Gulf of Finland respond to the increased nutrient loading with the increased sedimentation and nutrient accumulation rates.  相似文献   

Comparative studies on carbon origin of dawsonite between Hailaer Basin in China and Bowen-Gunnedah-Sydney basin system in Australia     

Yuqiao GAO  Li LIU  Qi'an MENG  Yan XU  Xiyu QU  Xianmei JIN 《世界地质(英文版)》2007,10(2)

Dawsonite, NaAlCO3(OH)2, is widespread as a cement, replacement and cavity filling in Hailaer Basin in China and Bowen-Gunnedah-Sydney (BGS) basin system in Australia. The origin of dawsonite is emphatically contrasted and analyzed through stable isotopic composition. Dawsonite δ13C values ranging from -4.0×10-3 to 4.1×10-3 are remarkably consistent through the BGS basin system. The calculated δ13C values of CO2 gas in isotopic equilibrium with dawsonite range from -11.3×10-3 to -4.6×10-3. These values indicate carbon of dawsonite came from inorganic CO2 gas accompanied by magmatic activity. In Hailaer Basin, the Dawsonite δ13C values ranging from -4.64×10-3 to 2.12×10-3 are also consistent. The calculated δ13C values of CO2 gas in isotopic equilibrium with dawsonite range from -11.82×10-3 to -5.11×10-3. According to the coincidence of dawsonite-bearing well and CO2 gas well with mantle source,lying along deep fracture within or adjacent to Yanshanian granite,it is concluded that CO2 gas forming dawsonite is derived from mantle related to magmatic process during the Yanshanian. A little biologic origin carbon owing to petroleum charging intervened when dawsonite formed.  相似文献   

Streambank dewatering for increased stability     

F. Douglas Shields Jr  Andrew Simon  Seth M. Dabney 《水文研究》2009,23(11):1537-1547

Streambank erosion is often the dominant source of sediment leaving modified watersheds. Mass failure of high, steep banks is one of the most serious forms of streambank erosion. The risk of a given bank experiencing mass failure is a function of bank height, angle, and soil strength, which is governed by soil moisture. Two methods for bank dewatering were tested in adjacent sections of streambank bordering a deeply incised channel in northern Mississippi: a low‐cost pump system and subsurface horizontal drains. Pore water pressures (both positive and negative pressures, or matric suction) were continuously monitored for 2 years at the pumped site, at an adjacent untreated control section, and for 1 year at the site stabilized with horizontal drains. Resulting data were used to calculate a time series of the factor of safety using a computer model. Over the course of two wet seasons, average bank retreats for the control and pumped plots were 0·43 and 0·21 m, respectively. More limited monitoring revealed that the site with passive drains retreated about 0·23 m. At the pumped site pore water pressure was 3–4 kPa lower than at the control site during the most critical periods. Accordingly, computed factors of safety were above the failure threshold at the pumped site, but fell below unity at the control site on 11 occasions over the period of observation. Similarly, the drained site displayed generally lower pore water pressure and higher safety factors except for two events when drains were evidently overwhelmed with the volume of local surface and subsurface flows. These results suggest, but do not prove, that bank dewatering promoted lower rates of bank retreat and higher levels of stability since the three sites had slight differences in soils, geometry and boundary conditions. Initial cost of the dewatering treatments were significantly less than orthodox bank stabilization measures, but operation and maintenance requirements may be greater. Published in 2009 by John Wiley & Sons, Ltd.  相似文献   

Numerical calculation of free-surface potential flow around a ship using the modified Rankine source panel method     

Md. Shahjada Tarafder  Kazuo Suzuki 《Ocean Engineering》2008,35(5-6):536-544

A modified Rankine source panel method is presented for solving a linearized free-surface flow problem with respect to the double-body potential. The method of solution is based on the distribution of Rankine sources on the hull as well as its image and on the free surface. An iterative algorithm is used for determining the free surface and wave resistance using upstream finite difference operator. A verification of numerical modeling is made using the Wigley hull and the validity of the computer program is examined by comparing the details of wave profiles and wave making resistance with Series 60 model.  相似文献   

鄂尔多斯盆地塔巴庙地区上古生界源岩热演化特征     

戴世立  杨智  李弘  杨姣 《海洋地质译丛》2009,(1):15-20

鄂尔多斯盆地北部主力气源岩太原组、山西组煤系地层热成熟史的研究对本区天然气充注过程和有利目标区预测具有重要的参考价值。在对研究区烃源岩评价和一维、二维地质建模研究的基础上。利用BasinMod盆地模拟软件对单井以及研究区内二维剖面、平面进行了煤系烃源岩热演化史模拟研究。研究结果表明：（1）该区在中三叠世进入生烃门限，中侏罗世以后，烃源岩持续埋深，早白垩世末期至最大埋深（4000m左右），绝大多数的天然气都在这一阶段生成，早白垩世末构造抬升以后只有少量天然气生成；（2）研究区上古生界太原组和山西组煤系源岩最大累积生烃强度可达到2200×10^8m^3／km^2，对现今天然气的分布具有较强的控制作用。  相似文献   

西湖凹陷平北地区烃源岩特征及生排烃史     

陆俊泽  叶加仁  黄胜兵  吴娟 《海洋地质译丛》2009,(4):38-43

为了综合确定平北地区的主力烃源岩，深化其油气成藏动力学过程研究，在烃源岩分布特征及有机质丰度、类型和成熟度分析的基础上，应用舍油气盆地数值模拟技术，定量恢复了研究区主要烃源岩层系的生排烃历史。研究表明，平北地区主要发育始新统平湖组、渐新统花港组两套烃源岩系，其中平湖组暗色泥岩为主力烃源岩，具较高的有机质丰度、成熟度、生排烃强度与排烃效率；以平湖组为源岩的油气系统应是本区油气勘探的主要目标。  相似文献