Two-stage aquifer pumping subject to slow desorption and persistent sources

This work focuses on improving pump-and-treat remediation by optimizing a two-stage operational scheme to reduce volumes extracted when confronted with nonequilibrium desorption, low-permeability units, and continuous contaminant sources such as non-aqueous phase liquids (NAPL). Q1 and Q2 are the initial short-term high pumping rate and later long-term low pumping rate, respectively. A two-dimensional ground water flow and transport management model was used to test the proposed strategy for plumes developed from finite (NAPL-free) and continuous (NAPL-driven) contaminant sources in homogeneous and nonhomogeneous (zoned) aquifers. Remediation scenarios were simulated over durations of 2000, 6000, and 15,000 d to determine (1) the optimal time to switch from a preset Q1 to Q2 and (2) the value of Q2. The problem was constrained by mass removal requirements, maximum allowable downgradient concentrations, and practical bounds on Q2. Q1 was fixed at preset values 50% to 200% higher than the single-stage pumping rates (i.e., steady pumping rates during entire remediation period) necessary to achieve a desired cleanup level and capture the plume. Results for the NAPL-free homogeneous case under nonequilibrium desorption conditions achieved the same level of cleanup as single-stage pumping, while reducing extracted volumes by up to 36%. Comparable savings were obtained with NAPL-driven sources only when the source concentration was reduced by at least 2 orders of magnitude. For the zoned aquifer, the proposed strategy provided volume savings of up to 24% under NAPL-free and reduced source conditions.     

A sediment quality triad assessment of the impact of copper mine tailings disposal on the littoral sedimentary environment in the Atacama region of northern Chile

A sediment quality triad (SQT) assessment was made of the impact of copper mine tailings disposal on littoral meiofaunal assemblages in the Atacama region of northern Chile. This situation is unusual in that the disposal is direct into the high-energy coastal system and not via a river estuary or other low-energy environment. This situation also allows for the examination of the impact of copper mine tailings in the absence of confounding effects from other pollutants. The three components of the SQT were: 1. an analysis of the bioavailable metals in both the sedimentary porewater and the adjacent seawater, 2. a microcosm bioassay of both sediments and seawaters using meiofaunal assemblages, and 3. quantitative field samples of the meiofaunal assemblages. Twelve study sites with varying degrees of impact were used, including three reference sites. The study identified that both the meiofaunal assemblage densities and taxa diversities decrease with increasing levels of bioavailable copper, that the Foraminifera and Harpacticoida are sensitive to copper, and that otoplanid Turbellaria are often characteristic of impacted sites; tailings also have both chemical and physical impacts on the environment. In some cases the physical impact of tailings is more important in excluding some organisms e.g. the interstitial polychaete, Saccocirrus sonomacus, from a site than is their chemical impact.     

Spatial distribution and ecotoxicity of petroleum hydrocarbons in sediments from the Galicia continental shelf (NW Spain) after the Prestige oil spill

The distribution of aliphatic and aromatic hydrocarbons was determined in surface sediments collected at 36 stations along the Galicia continental shelf (NW Spain), following the Prestige oil spill. Sampling was performed in December 2002, just after the accident, and in February and September 2003. Concentrations of PAHs (summation operator 13 parent components) were in the range of 0.9-422 microg/kgdw, the highest values being close to coastal urban areas (e.g. Pontevedra and A Coru?a), whereas in the stations of the area most heavily impacted by the spill (off Costa da Morte) concentrations were in the range of 14.8-89.6 microg/kgdw, with a certain predominance of alkylated compounds, which may suggest a mixture of petrogenic and pyrolytic sources. The detailed study of petrogenic molecular markers (e.g. steranes and triterpanes) showed the occurrence of an old (weathered) petrogenic chronic pollution in the shelf sediments but not of the Prestige oil, with the possible exception of few stations in the area of Costa da Morte. This was attributed to the heavy nature of the spilled oil that was barely dispersed in the water column and mainly stranded on the coast or sedimented in the form of oil patches. The addition of increasing amounts of fuel oil to a representative sediment sample showed that the molecular indices were indicative of the presence of the Prestige oil when the amount was above 1g/kg of sediment. The toxicity of selected samples (showing the higher PAH concentrations) was tested using the bivalve embryogenesis bioassay. Embryogenesis success reached high values in all cases (80-88%, with 86% in the control), indicating a lack of toxicity in the sediments and supporting the conclusion that the patchiness of the fuel eventually reaching the seafloor reduced its impact on the benthic communities of the Galician shelf.     

Influence of the oceanographic conditions during spring 2003 on the transport of the Prestige tanker fuel oil to the Galician coast

Hydrographic data collected during the cruise HIDROPRESTIGE were combined with meteorological and dynamic data provided by remote sensors and drifting/moored buoys, to describe the surface circulation of the Northern Iberian basin in March-April 2003. Sea surface winds transported the floating Prestige oil slicks from the sinking area to the continental slope off the Rías Baixas in 1/2 month: the surface current intensity was 2% of the wind intensity and it was rotated clockwise 5 degrees from the wind direction. Mesoscale cyclonic and anticyclonic structures west of 10 degrees W increased the residence time of oil patches in the Northern Iberian basin, as compared with the expected southwards flow of the Iberian current (IC). On the other hand, the Iberian poleward current (IPC) formed a marked surface front with coastal waters, preventing the entry of fuel oil into the rías. PAHs in the surface layer during the cruise were <0.5 microgL(-1), except in the Galicia bank (approximately 1 microg L(-1); where the Prestige tanker was still leaking) and the vicinity of Cape Fisterra (approximately 1.5 microg L(-1); where the convergence front between the IPC and coastal waters vanished).     

乡村转型发展特征评价及地域类型划分——以“苏南-陕北”样带为例

以"苏南-陕北"样带为案例区,评价分析了该区2000～2005年、2005～2008年乡村转型发展态势,并揭示了样带乡村转型发展的地域空间格局。结果表明:(1)2000～2005年期间,样带各县乡村发展度普遍较低但转型度普遍较高,低水平的乡村发展度与较高转型度造成样带各县不同程度的城乡不协调发展;2005～2008年期间,样带乡村系统普遍较快发展,各地城乡系统间的差异化发展局面得到初步改善;(2)"苏南-陕北"样带乡村转型发展呈现显著的地带性演变特征,各地转型发展的特征与结果同其所处的区位条件、经济基础、发展模式、政策要求等基本属性相匹配;(3)基于样带乡村转型发展评价结果,将样带划分为8个乡村转型发展地域类型区,各类型区之间因区位条件和资源禀赋的差异而选择不同乡村转型发展模式,并由此驱动资源环境和城乡经济系统的差异性变化。     

金沙县大运煤矿雷电风险评估

该文通过查阅贵州近5a的雷电监测网资料以及金沙县大运煤矿所在县45 a气象观测资料,对该矿可能存在的雷电危险进行分析,提取雷击灾害风险评估参数,对金沙县高坪乡大运煤矿进行雷击灾害风险评估,指出隐患,提出防雷保护装置设计的补充和完善的对策、措施,以满足安全生产的要求.     

模糊Hough变换算法在城市道路提取中的应用

采用形态学细化算法,将二值化影像形态学细化之后再进行峰值检测,有效地去除了虚假峰值,提高了道路提取精度及计算效率,为此,利用用模糊Hough变换算法提取遥感影像中的城市道路。试验表明,其方法在计算效率、提取精度以及内存占用方面具有明显优势。     

中国近54年来夏季极端降水事件特征研究

利用1960~2013年中国6~8月无缺测的571站逐日降水资料,定义7个极端降水指数,研究中国夏季极端降水事件特征。结果表明:(1)极端降水事件空间分布存在明显的区域性差异,长江中下游地区、华南地区、西北地区表现为增加趋势,东北地区、华北地区、西南部分地区表现为减少趋势;时间分布表现出具有显著的年际和年代际变化特征,极端降水事件有增加趋势,在20世纪90年代初期有明显转折。(2)M-K检验表现出极端降水事件在20世纪90年代初发生突变,突变前(后)偏弱(强)。(3)极端降水指数周期振荡不完全一致,准15年周期振荡为主,其次是准7年周期,最强振动出现在1998年。(4)除持续干期指数外,其他极端降水指数间存在较好的相关性。     

1953-2005年内蒙古东部产粮区气候变化特征研究

利用系统聚类分析和相关分析方法,根据1953--2005年内蒙古东部产粮区48个气象站的气象资料．进行了气候相似区划分;并得出各区在热量、水分的时间变化上具有较高的区域一致性。据此,以区域内各站点的温度、降水和日照时数的平均值作为区域热水光时间序列,分析了各气候要素变化特征及其对农业可能产生的影响。结果表明：各区域温度呈上升趋势,增温速率（平均增温为0．3-0．4℃／10a）高于中国平均增温速率（0．22℃／10a）,增温幅度呈从西向东递增的趋势,平均最低气温增幅最大,平均最高气温增温幅度与海拔呈正相关,尤以1988年以后变暖趋势最为明显;降水量基本呈减少趋势,年代际波动较大;20世纪90年代至今,内蒙古东部产粮区生长季降水明显减少,气温迅速升高,暖千化趋势表现明显,温差减小和日照时数减少,水热匹配格局发生改变,粮食产量出现减少趋势的可能性较大。