Are salinity tolerances of non-native macroinvertebrates in France an indicator of potential for their translocation in a new area?

Because of its geographic and economic position, the Western part of Europe and France is prone to biological invasions. Among the aquatic species non-native to France, a high proportion of these species are considered to be salt-tolerant. To verify this assumption, we compared the salinity tolerance of 18 native and non-native species in France in order to determine whether the introduced non-native species are more salt-tolerant than the native ones. Contrary to our expectations, our study shows that both native and non-native macroinvertebrate species from the same taxonomic group which had originated from within Eurasia had very similar salinity tolerance. Our results show that species originate from outside Eurasia (introduced by the ballast or drinking water on ships) were more salt tolerant than native from France and non-native species originated from Eurasia. Thus, derivation of the acute test of the salinity tolerance in native ranges may give good indications of their potential ability to survive during the translocation by shipping from the area of origin to another area. Our approach does provide empirical evidence for potential of non-native species to survive translocation in saline water using standard, quick and inexpensive protocols.     

我国防控外来物种入侵的立法思考

我国防控外来物种入侵相关法律缺乏应有的系统性和协调性,各职能部门基本上是"各立各的法、各管各的事",有时甚至相互矛盾。相关法律、法规比较分散,立法角度也不相同,不能全面地解决和控制外来入侵种对我国可能造成的生态、经济和健康的破坏,需要着手研究《防止外来物种入侵法》的立法。本文尝试性地对外来物种入侵的相关法律、法规进行考察和分析,并对构建防止外来物种的入侵提出立法思考,为制定《防止外来物种入侵法》提出立法原则和理论参考。     

任意方向发射源在柱状多层介质中的电磁场的理论计算

针对柱状多层介质测井模型,本文给出了井轴上沿任意方向的发射源在介质空间的电磁场的理论公式,利用递推方法可以很方便地进行数值计算.文中还分别对轴向与径向的电偶极子源和磁偶极子源共4种情况,给出了井轴上接收区磁场强度与侵入半径的关系曲线.     

泥浆滤液侵入孔隙地层径向导电特性的模拟实验

研究了泥浆滤液侵入孔隙地层的模拟实验理论和相似条件，并用砂盘模型对泥浆滤液侵入油、气、水层进行了模拟实验，得到了侵入地层径向剖面的高侵、低侵、低阻环带和非台阶型的电性特征。     

Detection and mapping the spatial distribution of bracken fern weeds using the Landsat 8 OLI new generation sensor

Bracken fern is an invasive plant that presents serious environmental, ecological and economic problems around the world. An understanding of the spatial distribution of bracken fern weeds is therefore essential for providing appropriate management strategies at both local and regional scales. The aim of this study was to assess the utility of the freely available medium resolution Landsat 8 OLI sensor in the detection and mapping of bracken fern at the Cathedral Peak, South Africa. To achieve this objective, the results obtained from Landsat 8 OLI were compared with those derived using the costly, high spatial resolution WorldView-2 imagery. Since previous studies have already successfully mapped bracken fern using high spatial resolution WorldView-2 image, the comparison was done to investigate the magnitude of difference in accuracy between the two sensors in relation to their acquisition costs. To evaluate the performance of Landsat 8 OLI in discriminating bracken fern compared to that of Worldview-2, we tested the utility of (i) spectral bands; (ii) derived vegetation indices as well as (iii) the combination of spectral bands and vegetation indices based on discriminant analysis classification algorithm. After resampling the training and testing data and reclassifying several times (n = 100) based on the combined data sets, the overall accuracies for both Landsat 8 and WorldView-2 were tested for significant differences based on Mann-Whitney U test. The results showed that the integration of the spectral bands and derived vegetation indices yielded the best overall classification accuracy (80.08% and 87.80% for Landsat 8 OLI and WorldView-2 respectively). Additionally, the use of derived vegetation indices as a standalone data set produced the weakest overall accuracy results of 62.14% and 82.11% for both the Landsat 8 OLI and WorldView-2 images. There were significant differences {U (100) = 569.5, z = −10.8242, p < 0.01} between the classification accuracies derived based on Landsat OLI 8 and those derived using WorldView-2 sensor. Although there were significant differences between Landsat and WorldView-2 accuracies, the magnitude of variation (9%) between the two sensors was within an acceptable range. Therefore, the findings of this study demonstrated that the recently launched Landsat 8 OLI multispectral sensor provides valuable information that could aid in the long term continuous monitoring and formulation of effective bracken fern management with acceptable accuracies that are comparable to those obtained from the high resolution WorldView-2 commercial sensor.     

Experimental and theoretical investigations of drainage in horizontal rough-walled fractures with different correlation structures

Experiments on the immiscible displacement of water by air were performed in two horizontal artificial open rough-walled fractures with different correlation structures. The aperture field of the first fracture has a Gaussian variogram with a finite correlation length, while that of the second one has a power-law variogram, for which no finite correlation length can be assigned. We simulated the displacement process using an invasion percolation model, which takes the in-plane curvature of the interface between water and air into account. The correlation structure of the aperture field has no effect on the irregularity of the shape of the air clusters. However, the correlation structure in combination with the in-plane curvature influences the density of the air clusters and thus has an impact on characteristic properties of the flow. We analyze the model parameters and properties with respect to the fracture properties. The stochastic average of the air clusters for models with different curvature numbers and fields with different correlation lengths is then calculated in order to analyze their influence on continuum approach models.     

双侧向测井曲线形状与地层侵入关系研究

通过对具有不同侵入特征地层的双侧向理论曲线的计算,研究双侧向测井曲线的形状与泥浆侵入地层状态的关系.发现双侧向视电阻率曲线在高侵剖面的地层界面处出现‘反冲’,曲线‘峰’和‘谷’均较尖锐,而在低侵剖面,深侧向和浅侧向视电阻率曲线在地层界面处出现‘过渡’趋势,且曲线形状较圆滑.研究表明：产生上述现象的原因是由于原状地层对电流的吸引和排斥,使主电极和屏蔽电极供出的电流增大或减小,因而屏流比变化,进而导致视电阻率的变化.     

Leaf nitrogen productivity as a mechanism driving the success of invasive annual grasses under low and high nitrogen supply

Invasion of the historically perennial-dominated landscapes in the Great Basin by exotic winter annual grasses is one of the most serious plant invasions in North America. Evidence suggests invasive annuals outperform native perennials under N-poor and N-rich conditions. The objective of this study was to identify key traits contributing to the success of invasive annual grasses in these environments. Three invasive annual grasses, two native perennial grasses and one introduced perennial grass were exposed to three levels of N supply. Root biomass, root length, root N uptake rate, root and leaf morphology, leaf nitrogen productivity (leaf NP) as well as biomass and N allocation were quantified over four harvests. Path analysis indicated that leaf NP was the key trait contributing to variation in N capture among the species. Species with a higher leaf NP produced more root length and consequently captured more N under a range of soil N availability. This suggests variation in leaf NP may be one critical trait determining the ability of the resident plant community to resist establishment of these invaders. Restoration programs may be able to increase weed resistance by specifically selecting for this trait in revegetation efforts.     

Hyperslow drainage in a porous medium: Influence of retention curve

We investigate the process of very slow drainage from pore network simulations in relation with the study of the repository of radioactive waste materials in deep geological formation. The process is characterized by a quite low desaturation of the medium. Considering the special case of a constant stabilizing gradient, we study the sensitivity of the solution given by the classical continuum two-phase flow model to the shape of the retention curve. The solution is found to be very sensitive to the evolution of the retention curve in the range of the high wetting fluid saturations. We show how to construct the retention curve so as to minimize the prediction error with the classical two-phase flow model.     

The effect of spontaneous gas expansion and mobilization on the aqueous-phase concentrations above a dense non-aqueous phase liquid pool

The spontaneous expansion and mobilization of discontinuous gas above dense non-aqueous-phase liquid (DNAPL) pools can affect the aqueous-phase concentrations of the DNAPL constituents above the pool. The results of an intermediate-scale, two-dimensional flow cell experiment showed that the discontinuous gas flow produced by spontaneous expansion, driven by the partitioning of 1,1,1-TCA from the surface of a DNAPL pool, resulted in detectable aqueous-phase concentrations of 1,1,1-TCA well above the pool surface. In comparison to a conventional model for DNAPL pool dissolution in the absence of a discontinuous gas phase, these concentrations were greater than expected, and were present at greater than expected elevations. Additionally, this study showed that the discontinuous gas flow produced transient behavior in the aqueous-phase concentrations, where the elevated concentrations occurred as short-term, pulse-like events. These results suggest that the spontaneous expansion and mobilization of discontinuous gas in DNAPL source zones could lead to the misdiagnosis of source zone architecture using aqueous concentration data, and that the transient nature of the elevated concentrations could further complicate the difficult task of source zone characterization.