Forest Successional Stage Affects the Cortical Secondary Chemistry of Three Old Forest Lichens

Three epiphytic old forest lichens (Usnea longissima, Pseudocyphellaria crocata, and Lobaria pulmonaria) were transplanted along a natural shade–sun gradient comprising three successional stages in boreal spruce forests (dense young forest, open old forest, and clear-cut) for one summer. After harvest, extractable secondary compounds were analyzed by high-performance liquid chromatography, and the brown pigmentation in melanic species was quantified by reflectance measurements. Cortical compounds in all species increased from shady young forests to exposed clear-cuts. Usnic acid, the major cortical, secondary compound in U. longissima, showed consistently higher concentration in the clear-cut than in the two forested stands. Pseudocyphellaria crocata and L. pulmonaria, lacking extractable secondary compounds in the cortex, significantly increased their amounts of cortical melanins in well-lit stands. The medullary compounds showed more complex responses. Many were not influenced by environmental conditions during the transplantation, whereas the majority of those that responded showed the lowest concentration in clear-cut transplants. Only a few medullary compounds showed the highest concentration in the clear-cut, and at a low level of significance. The synthesis of UV-B-absorbing usnic acid and melanins seems to be part of an acclimation to increased light exposure. The medullary compounds in studied species barely function as solar screens despite their strong UV-B absorbance.     

DIA of centrifuge model tests on geogrid reinforced soil walls with low-permeable backfills subjected to rainfall

Geogrid reinforced soil walls (GRSWs) constructed using low-permeable backfills often experience failures when subjected to rainfall. The objective of this paper is to employ centrifuge modelling to investigate the effect of geogrid types on the performance of GRSW models constructed with low-permeable backfill, when subjected to rainfall intensity of 10 mm/h. A 4.5 m radius large beam centrifuge facility was used, and rainfall was simulated using a custom-designed rainfall simulator at 40 gravities. Digital Image Analysis (DIA) was employed to understand the deformation behaviour of GRSWs with low stiffness geogrid layers with and without drainage provision subjected to rainfall. Additionally, the effect of varying stiffness of geogrid reinforcement layers across the height of GRSW was also investigated. The interpretation of DIA helped to quantify displacement vector fields, face movements, surface settlement profiles and geogrid strain distribution with depth. Irrespective of drainage provision, GRSWs reinforced with low stiffness geogrid layers experienced a catastrophic failure at the onset of rainfall. However, GRSW reinforced with geogrid layers of varying stiffness was observed to perform well. This study demonstrates the effective use of DIA of GRSWs subjected to rainfall along with centrifuge-based physical model testing.     

植生袋复垦边坡在降雨入渗条件下的稳定性

对植生袋复垦边坡技术进行了详细介绍,采用极限平衡理论中的瑞典条分法、简化Bishop法对降雨入渗条件下的边坡稳定性问题进行了模拟分析。研究结果显示：在降雨入渗影响下,抗滑稳定性系数最低为1.848,明显高于规范规定的1.3,说明植生袋复垦边坡显著降低了边坡滑动趋势,边坡稳定性得到显著提高。     

Laboratory tests to evaluate effectiveness of wicking geotextile in soil moisture reduction

A new type of woven geotextile, referred to as wicking geotextile, was developed and introduced to the market. Since this wicking geotextile consists of wicking fibers, they can wick water out from unsaturated soils in a pavement structure thus resulting in an increase of soil resilient modulus and enhance performance of roadways. In this study, a physical model test was developed to evaluate the effectiveness of the wicking geotextile in soil moisture reduction for roadway applications. A test box with a dimension of 1041 mm in length, 686 mm in width, and 584 mm in height was used in this study. Two HDPE plastic panels were used to separate the box into two sections, one containing a dehumidifier and the other backfilled with soil. The dehumidifier was adopted to collect the water, which was wicked out from the soil by the wicking geotextile and evaporated into air. Test results show that (1) the wicking geotextile wicked water out from the soil even at the moisture content close to the optimum moisture content and (2) the comparison of soil moisture contents before and after rainfall demonstrated that the wicking geotextile maintained the soil moisture contents after rainfall close to those before rainfall and had an effective distance for the soil moisture reduction.     

宝鸡市雨水径流岸边渗滤系统设计与应用

城市雨水径流污染对城市河湖水体污染的贡献越来越受到关注.针对城市雨水径流,采用岸边砂渗滤系统处理,进行了工程设计和建设,建成"宝鸡市金渭湖雨水岸边渗滤系统示范工程".运行结果表明,渗滤池对水中有机物和悬浮物的去除率达80%以上.该工程将城市雨水管网、集蓄、处理及排放连为有机整体,为解决雨水径流污染城市河湖水体提供示范.     

Quantification of fecal coliform inputs to aquatic systems through soil leaching

In order to assess the fecal contamination of rivers in the Seine watershed through soil leaching, 78 small streams located in rural areas were sampled upstream from any wastewater outfall. Culturable fecal coliforms (FC) and beta-D-glucuronidase activity (specific of Escherichia coli) were measured in the samples. Data showed a significant correlation between both estimates of fecal contamination. In the two different areas of the Seine river watershed investigated, most of the small streams were significantly contaminated by fecal bacteria. In general, the streams flowing through areas partly or fully covered with pastures were more contaminated than those flowing through forest and cultivated areas. Rainfall increased the suspended solid content of small streams as well as their fecal contamination, as an important fraction of FC was adsorbed on particles. Calculations showed that, at a large watershed scale, the input of FC in rivers through soil leaching was very low when compared to the input through the discharge of treated domestic wastewater but this could not be true at local scale.     

Rainfall-triggered debris flows following the Wenchuan earthquake

On 24 September 2008, 72 debris flows were triggered by heavy rainfall in the central part of the area affected by the Wenchuan Earthquake. This paper describes the process of debris-flow initiation and transport in the study areas and presents field observations on the roles of rainfall, lithology and the presence of faults. It is likely that following the ground shaking, the critical amount of accumulated precipitation and the hourly rainfall intensity necessary to initiate debris flow was reduced compared with values before the earthquake. A case study in the Xishanpo gully is presented; the debris flow from which caused a thick accumulation in the already devastated city of Beichuan. It is concluded that the whole of the area shaken by the Wenchuan Earthquake is now more susceptible to debris flows, which may be initiated by localized heavy rainfall. Care must be taken to properly assess this new type of geo-hazard.     

The importance of the relationship between scale and process in understanding long-term DOC dynamics

Concentrations of dissolved organic carbon have increased in many, but not all, surface waters across acid impacted areas of Europe and North America over the last two decades. Over the last eight years several hypotheses have been put forward to explain these increases, but none are yet accepted universally. Research in this area appears to have reached a stalemate between those favouring declining atmospheric deposition, climate change or land management as the key driver of long-term DOC trends. While it is clear that many of these factors influence DOC dynamics in soil and stream waters, their effect varies over different temporal and spatial scales. We argue that regional differences in acid deposition loading may account for the apparent discrepancies between studies. DOC has shown strong monotonic increases in areas which have experienced strong downward trends in pollutant sulphur and/or seasalt deposition. Elsewhere climatic factors, that strongly influence seasonality, have also dominated inter-annual variability, and here long-term monotonic DOC trends are often difficult to detect. Furthermore, in areas receiving similar acid loadings, different catchment characteristics could have affected the site specific sensitivity to changes in acidity and therefore the magnitude of DOC release in response to changes in sulphur deposition. We suggest that confusion over these temporal and spatial scales of investigation has contributed unnecessarily to the disagreement over the main regional driver(s) of DOC trends, and that the data behind the majority of these studies is more compatible than is often conveyed.     

Evaluation of Surficial Stability for Homogeneous Slopes Considering Rainfall Characteristics

Shallow slope failures in residual soil during periods of prolonged infiltration are commonly occurring in the world. This study examines an infinite slope analysis to estimate the influence of infiltration on surficial stability of slopes by the limit equilibrium method. An approximate method that accommodates the boundary condition of a uniform rainfall has been proposed to evaluate the likelihood of shallow slope failure that is induced by a particular rainfall event. The method based on the Mein and Larson model, which provides an explicit solution for preponding infiltration, has been applied to various types of soil having measured unsaturated hydraulic properties. To compare results with those obtained from the approximate method, a series of numerical analyses were carried out. According to the results, with the use of properly estimated input parameters, the approximate method was found to give results that compare reasonably well with those of more rigorous finite element analyses.