汤屯高速公路路堑边坡土质特征与生态防护植物配置 研究

汤屯高速公路边坡土壤具有偏酸性、有机质低、磷缺乏、铜过量等土质特征。边坡生态防护具有边坡高陡、原生植被彻底破坏、土质贫瘠、缺水、缺肥、生物气候干热胁迫、水土流失严重等难点,遵循交通安全性、景观协调性、生态适应性、生物多样性、经济实用性的原则,提出了以草本植物为主,草、灌、藤有机结合的边坡生态防护植物配置方案,针对全岩质边坡、碎裂结构边坡、土质边坡及边坡的顶部、下沿、平台等部位提出了不同的植物群落配置原则及物种配比方案,对类似工程具有借鉴意义。     

Interactive influence of water level,sediment heterogeneity,and plant density on the growth performance and root characteristics of Carex brevicuspis

Water level, sediment heterogeneity, and plant density are important factors that determine plant growth, distribution, and community structure. In the present study, we investigated the effects of these factors on the growth and root characteristics of Carex brevicuspis. We conducted an outdoor experiment to monitor biomass accumulation and allocation, relative root distribution mass ratio, longest root length, and total N and P contents of C. brevicuspis plants. We used a factorial design with two water levels (0 cm and −15 cm relative to the soil surface, named high and low water level treatments, respectively), three sediment types (sand/clay sediment with 0–15 cm of sand and 15–30 cm of clay; mixed sediment with 0–30 cm mixture of sand and clay with 1:1 volumw ratio; and clay/sand sediment with 0–15 cm of clay and 15–30 cm of sand), and three plant densities (88 plants per m², 354 plants per m², and 708 plants per m²). Biomass accumulation decreased with increasing plant density and was significantly higher in the low water level and the clay/sand sediment than in the high water level and the other two sediment types. The shoot:root ratio was markedly higher in the high water level than in the low water level and decreased with increasing plant density; further, in the high water level, it was significantly lower in the sand/clay sediment than in the other two sediment types. The relative root distribution mass ratio was markedly higher in the high water level treatments than in the low water level treatments. Further, in the high water level treatments, the relative root distribution mass ratio increased with increasing plant density in the clay/sand sediment and was lower in the sand/clay sediment than in the other two sediment types. The longest root length was significantly lower in the high water level than in the low water level and increased with increasing plant density in the sand/clay sediment in the high water level. Total N content in the plants was influenced only by sediment type; on the other hand, total P content was markedly higher in the high water level than in the low water level. Our data indicate that growth of C. brevicuspis was limited by higher water level, higher density and sand/clay sediment. Plants can increase shoot:root ratio and develop shallow root system to acclimate to high water level and thus could adjust shoot:root ratio and root characteristics, e.g. decrease their shoot:root ratio and allocating more root and increasing root length to the nutrient rich layer to acclimate to conditions of higher density and sediment heterogeneity.     

Response of a warm temperate peatland to Holocene climate change in northeastern Pennsylvania

Studying boreal-type peatlands near the edge of their southern limit can provide insight into responses of boreal and sub-arctic peatlands to warmer climates. In this study, we investigated peatland history using multi-proxy records of sediment composition, plant macrofossil, pollen, and diatom analysis from a ¹⁴C-dated sediment core at Tannersville Bog in northeastern Pennsylvania, USA. Our results indicate that peat accumulation began with lake infilling of a glacial lake at ~ 9 ka as a rich fen dominated by brown mosses. It changed to a poor fen dominated by Cyperaceae (sedges) and Sphagnum (peat mosses) at ~ 1.4 ka and to a Sphagnum-dominated poor fen at ~ 200 cal yr BP (~ AD 1750). Apparent carbon accumulation rates increased from 13.4 to 101.2 g C m^? 2 yr^? 1 during the last 8000 yr, with a time-averaged mean of 27.3 g C m^? 2 yr^? 1. This relatively high accumulation rate, compared to many northern peatlands, was likely caused by high primary production associated with a warmer and wetter temperate climate. This study implies that some northern peatlands can continue to serve as carbon sinks under a warmer and wetter climate, providing a negative feedback to climate warming.     

Securing forests from the scourge of chestnut blight: The biopolitics of nature and nation

Bringing a biopolitical framework to bear on historical geographies of nature, this article traces the recent history of the American chestnut, with a focus on the pivotal time period in the early 20th century (1905–1925) during which the tree’s ecological, economic, and cultural roles changed dramatically. Once an ecologically dominant and culturally important forest tree in eastern North America, the American chestnut was rendered functionally extinct following the accidental introduction of a fungal pathogen, known as the chestnut blight, at the turn of the 20th century. Calling attention to the historical ties between nature and nation, I demonstrate how blight control, chestnut breeding, and restoration efforts were formulated in conversation with broader anxieties about the fate of the American nation in the wake of social, environmental, economic, and racial change. Through an exploration of three themes distilled from archival research—chestnut blight as national threat, fear and desire for exotic nature, and the shared histories of plant breeding and racial improvement—this paper illustrates the role that nature has played in the construction and circulation of biopolitical discourses, nationalist sensibilities, and gendered and racial logics.     

Vegetation change in the coastal-lowland rainforest at Avai'o'vuna Swamp, Vava'u, Kingdom of Tonga

Avai'o'vuna Swamp, a small coastal wetland in Vava'u, Kingdom of Tonga, produced a 4500-year pollen and sediment record. Results are: (1) a mid-Holocene sea level highstand is confirmed for Tonga between about 4500 and 2600 ¹⁴C yr B.P.; marine clay contains pollen from mangroves (Rhizophora mangle), coastal forest trees (Barringtonia asiatica and Cocos nucifera), and rainforest trees (Alphitonia, Rhus, Hedycarya and Calophyllum). (2) Microscopic charcoal first appeared at 2600 ¹⁴C yr B.P., coincident with the arrival of Polynesians. (3) Cocos, Pandanus, Excoecaria, Macaranga, and Elaeocarpaceae pollen reflects the establishment of a mixed coastal-lowland rainforest in the last 2500 years. (4) The loss of Hedycarya, Elaeocarpus, Calophyllum, and Guettarda and the reduction of Terminalia and taxa in the Papilionaceae family by about 1000 years ago may be due to habitat destruction and the loss of dispersal capabilities of some species through the extinction of the two largest pigeons in Tonga.     

彭水地下电站围岩稳定性分析

在分析彭水地下厂房地质条件的基础上,采用3DEC程序建立了3#机组部位三维离散元数值计算模型,对地下厂房开挖支护全过程进行了计算,详细分析了围岩变形情况、应力状态、塑性区分布及稳定性影响因素。计算结果反映：按基本计算条件,地下厂房开挖支护后,围岩整体稳定性良好。受开挖及结构面空间组合作用,上、下游边墙部位变形量在15? 35 mm左右;边墙变形主要发生在从其开挖往下的2?3级开挖步之内,从整个厂房开挖来分析,223.0?201.0 m高程开挖阶段对围岩稳定影响最重要;围岩稳定主要受层面、软弱夹层及贯通节理特性及其切割块体在开挖临空面的位置控制,局部分布的页岩本身变形及地应力因素对围岩稳定性影响相对较小。     

Large-Eddy Simulation of Coherent Turbulence Structures Associated with Scalar Ramps Over Plant Canopies

Large-eddy simulations were performed of a neutrally-stratified turbulent flow within and above an ideal, horizontally- and vertically-homogeneous plant canopy. Three simulations were performed for shear-driven flows in small and large computational domains, and a pressure-driven flow in a small domain, to enable the nature of canopy turbulence unaffected by external conditions to be captured. The simulations reproduced quite realistic canopy turbulence characteristics, including typical ramp structures appearing in time traces of the scalar concentration near the canopy top. Then, the spatial structure of the organised turbulence that caused the scalar ramps was examined using conditional sampling of three-dimensional instantaneous fields, triggered by the occurrence of ramp structures. A wavelet transform was used for the detection of ramp structures in the time traces. The ensemble-averaged results illustrate that the scalar ramps are associated with the microfrontal structure in the scalar, the ejection-sweep structure in the streamwise and vertical velocities, a laterally divergent flow just around the ramp-detection point, and a positive, vertically-coherent pressure perturbation. These vertical structures were consistent with previous measurements made in fields or wind tunnels. However, the most striking feature is that the horizontal slice of the same structure revealed a streamwise-elongated region of high-speed streamwise velocity impacting on another elongated region of low-speed velocity. These elongated structures resemble the so-called streak structures that are commonly observed in near-wall shear layers. Since elongated structures of essentially similar spatial scales were observed in all of the runs, these streak structures appear to be inherent in near-canopy turbulence. Presumably, strong wind shear formed just above the canopy is involved in their formation. By synthesis of the ensemble-averaged and instantaneous results, the following processes were inferred for the development of scalar microfronts and their associated flow structures: (1) a distinct scalar microfront develops where a coherent downdraft associated with a high-speed streak penetrates into the region of a low-speed streak; (2) a stagnation in flow between two streaks of different velocities builds up a vertically-coherent high-pressure region there; (3) the pressure gradients around the high-pressure region work to reduce the longitudinal variations in streamwise velocity and to enhance the laterally-divergent flow and lifted updrafts downstream of the microfront; (4) as the coherent mother downdraft impinges on the canopy, canopy-scale eddies are formed near the canopy top in a similar manner as observed in conventional mixing-layer turbulence.     

植被微气象的数值模拟

综合考虑梯度输送和阵性穿透作用，并对植被上方的过渡层作适当处理，提出了植被微气象的一阶闭合模型。它对温、湿、风等物理量垂直分布的模拟精度良好。引用系统优化理论和方法，对模型中参数作多维非线性搜索，结果客观可靠。由于植物本身的调节适应能力和反馈作用，大气与植被间的动量与水热交换机制和过程不尽相同。在动量输送过程中，梯度产生项和阵性穿透皆不可忽视，尤其在群体下部，更为重要；而在热量和水分输送过程中，阵性穿透作用在低矮密集植被中的贡献甚微，梯度产生项起主导作用。     

Effects of Compost Addition on Pyrene Removal from Soil Cultivated with Three Selected Plant Species

A greenhouse pot experiment was conducted to investigate the effect of compost addition on the phytoremediation ability of Medicago sativa, Brassica napus, and Lolium perenne in soils contaminated with pyrene. Pyrene concentrations were evaluated after 90 days in contaminated uncultivated amended‐soil, cultivated amended‐soils, and shoots and roots of the three plant species. The addition of compost enhances significantly pyrene dissipation from 16 to 26% in uncultivated soil, whereas in cultivated soils it appears not to have any significant effect on pyrene dissipation, neither pyrene was detectable in shoots and roots of the three species examined. The high partition coefficient of pyrene to compost dissolved organic matter (DOM) and the molar absorptivity values at 280 nm (ε₂₈₀) indicate a high affinity of pyrene to compost DOM molecules, likely due to their aromatic character. These results suggest that compost improves pyrene removal from soil, possibly by promoting its adsorption onto compost DOM. This property is very important in indicating that compost can be used, besides for its amendment capacity, also as a potential tool for remediation of contaminated soils.