The inertial range “outer scale” and optical turbulence

The crucial parameter used to calculate turbulence effects upon light waves propagating through the atmosphere is known as the structure constant, . As Tatarski has shown, this parameter depends upon the “outer scale” of the inertial sub-range of the turbulence. Recently there have been successful predictions of astronomical “seeing” conditions at Mauna Kea Astronomical Observatory which have increased interest in this subject and in the use of the so-called “Dewan Optical Turbulence Model”. In the case of the Air Force, there has been a longstanding need for such optical turbulence prediction, especially in the stratosphere. In the past researchers have used a relation due to Tatarski, (which plays a prominent role in this model) in order to deduce values of the “outer scale” from measurements. When doing this, they have been surprised to find values very much smaller than expected. The goal of the paper is to explain this unexpected result. As we will show, this result can be explained by two factors: (a) the average turbulent layer thicknesses are smaller than originally believed, and, more importantly, (b) only a minor fraction of the stratosphere is turbulent. In order to arrive at this conclusion, we used the high-resolution (10 m) wind profiles that were originally used to formulate the previously mentioned optical turbulence model. The U.S. Government’s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

城市滨水区的生态恢复研究

城市滨水区的生态恢复具有着重要的生态、经济和社会意义。通过探讨和分析城市滨水区生态恢复的基础理论和主要内容,综述了国内外城市滨水区生态恢复的研究现状,指出我国为做好城市滨水区生态恢复工作尚需加强滨水区生态恢复的基础理论、关键技术、景观生态学的应用和示范推广等方面的研究,以滨水区的生态恢复带动开发,保证城市的可持续发展。     

上海城市土地利用转变类型及其空间关联分析

基于多时段TM遥感影像资料,通过地图代数和空间关联分析、相邻度分析等空间分析手段的综合应用,论文对上海地区近10年来城市土地利用变化类型、形成过程和相关空间机制进行了研究,结果表明:①近10年来上海城市土地利用扩展经历了“单核扩展”模式为主(1987～1990年)到“单核扩展”、“多核扩展”与“点-轴”扩展模式并存(1990～1995年),直至“多核扩展”及“点-轴”等复杂扩展模式为主(1995～2000年)的变化过程,导致上海中心城区和郊县城镇规模急剧扩张,交通干道沿线区域城市化过程明显增强,并形成整个上海地区城市化网络结构;②面积贡献率较大、转变频率较低的城市土地利用变化类型,与其他类型之间具有较高的关联度和空间亲和性,构成中心城区或卫星城、郊区城镇的扩展核心;③面积贡献率较低的类型,其转变频率较高,分布零散,构成扩展核的外围部分,这些城市周边地区存在一定程度紊乱、不合理的土地利用、开发活动;④城市化过程的内在空间机制与土地利用类型的面积和转变频率有密切关系。在更精细的尺度上依据转变频率划分的类别在一定程度上能更好体现城市土地利用变化类型的空间分异,及其作为宏观驱动机制的社会经济因子所具有的空间差异性。     

黄土丘陵区“梯田退耕”生态重建规划方法——以燕沟流域为例

论文在阐述“梯田退耕”生态重建规划指导思想、内容、标准及宜遵循的基本原则的基础上,借助GIS空间分析技术,提出并探讨了针对黄土丘陵区中小尺度流域或行政村合理布建梯田和经济林果园地等的规划方法及技术流程,进而将其应用于燕沟流域,研究结果表明业已探讨的规划方法是可行的和实用的。按规划结果,燕沟流域至少需新修梯田295.06hm2、果园4.61hm2,使其基本农田达到359.23hm2、果园面积达到622.69hm2;森林覆盖率48.87%,林灌草植被覆盖率可达75%,坡地减沙效益在80%以上。农业发展预计每年可实现粮食总产1645.13t、苹果总产9340t以上,载畜量可达7500只羊单位。     

Macroinvertebrate Responses to Constructed Riffles in the Cache River,Illinois, USA

Stream restoration practices are becoming increasingly common, but biological assessments of these improvements are still limited. Rock weirs, a type of constructed riffle, were implemented in the upper Cache River in southern Illinois, USA, in 2001 and 2003–2004 to control channel incision and protect high quality riparian wetlands as part of an extensive watershed-level restoration. Construction of the rock weirs provided an opportunity to examine biological responses to a common in-stream restoration technique. We compared macroinvertebrate assemblages on previously constructed rock weirs and newly constructed weirs to those on snags and scoured clay streambed, the two dominant substrates in the unrestored reaches of the river. We quantitatively sampled macroinvertebrates on these substrates on seven occasions during 2003 and 2004. Ephemeroptera, Plecoptera, and Trichoptera (EPT) biomass and aquatic insect biomass were significantly higher on rock weirs than the streambed for most sample periods. Snags supported intermediate EPT and aquatic insect biomass compared to rock weirs and the streambed. Nonmetric multidimensional scaling (NMDS) ordinations for 2003 and 2004 revealed distinct assemblage groups for rock weirs, snags, and the streambed. Analysis of similarity supported visual interpretation of NMDS plots. All pair-wise substrate comparisons differed significantly, except recently constructed weirs versus older weirs. Results indicate positive responses by macroinvertebrate assemblages to in-stream restoration in the Cache River. Moreover, these responses were not evident with more common measures of total density, biomass, and diversity.     

Effects of Riparian Vegetation and Watershed Urbanization on Fishes in Streams of the Mid‐Atlantic Piedmont (USA)1

Abstract: The joint influences of riparian vegetation and urbanization on fish assemblages were analyzed by depletion sampling in paired forested and nonforested reaches of 25 small streams along an urbanization gradient. Nonforested reaches were narrower than their forested counterparts, so densities based on surface area differ from linear densities (based on reach length). Linear densities (based on number or biomass of fish) of American eel, white sucker and tesselated darter, and the proportion of biomass of benthic invertivores were significantly higher in nonforested reaches, while linear densities of margined madtom and the number of pool species were significantly higher in forested reaches. Observed riparian effects may reflect differences in habitat and algal productivity between forested and nonforested reaches. These results suggest that relatively small‐scale riparian restoration projects can affect local geomorphology and the abundance of fish. Dense vegetative cover in riparian zones and similar or analogous habitats in both forested and nonforested reaches, the relatively small scale of the nonforested reaches, and the low statistical power to detect differences in abundance of rare species may have limited the observed differences between forested and nonforested reaches. There was a strong urbanization gradient, with reductions of intolerant species and increases of tolerant species and omnivores with increasing urbanization. Interactions between riparian vegetation type and urbanization were found for blacknose dace, creek chub, tesselated darter, and the proportion of biomass of lithophilic spawners. The study did not provide consistent support for the hypotheses that responses of fish to riparian vegetation would be overwhelmed by urban degradation or insignificant at low urbanization.     

Projecting Cumulative Benefits of Multiple River Restoration Projects: An Example from the Sacramento-San Joaquin River System in California

Despite increasingly large investments, the potential ecological effects of river restoration programs are still small compared to the degree of human alterations to physical and ecological function. Thus, it is rarely possible to “restore” pre-disturbance conditions; rather restoration programs (even large, well-funded ones) will nearly always involve multiple small projects, each of which can make some modest change to selected ecosystem processes and habitats. At present, such projects are typically selected based on their attributes as individual projects (e.g., consistency with programmatic goals of the funders, scientific soundness, and acceptance by local communities), and ease of implementation. Projects are rarely prioritized (at least explicitly) based on how they will cumulatively affect ecosystem function over coming decades. Such projections require an understanding of the form of the restoration response curve, or at least that we assume some plausible relations and estimate cumulative effects based thereon. Drawing on our experience with the CALFED Bay-Delta Ecosystem Restoration Program in California, we consider potential cumulative system-wide benefits of a restoration activity extensively implemented in the region: isolating/filling abandoned floodplain gravel pits captured by rivers to reduce predation of outmigrating juvenile salmon by exotic warmwater species inhabiting the pits. We present a simple spreadsheet model to show how different assumptions about gravel pit bathymetry and predator behavior would affect the cumulative benefits of multiple pit-filling and isolation projects, and how these insights could help managers prioritize which pits to fill.     

地下水环境中甲基叔丁基醚运移过程的动力学模型

建立了地下水环境中甲基叔丁基醚(MTBE)运移过程的变系数动力学模型,并对模型进行了验证和参数灵敏度分析.模拟结果表明,地下水流速和阻滞系数对于MTBE的运移过程影响最为显著,而水动力弥散系数的影响较小,忽略其变化不会对预测地下水环境中污染物运移的环境动力学行为造成太大误差.由此得到的结论可定量研究MTBE在地下水环境中的对流.扩散特征,还可为MTBE污染地下水的预测预报、修复治理等研究提供科学依据.     

Ecological effects of cultivation on the machair sand dune systems of the Outer Hebrides, Scotland

The machair sand dune systems of the Outer Hebrides of Scotland are a unique habitat, which is rare within both a global and European context. Unusually, the machair habitat also represents an agricultural resource that is very important to the Hebridean people, having been subject to both grazing and cultivation throughout the historical period. Following designation as an Environmentally Sensitive Area (ESA) in 1988, the machairs of South Uist have been studied with the aim of understanding the links between agricultural practice and their plant community and ecosystem dynamics. This research focused primarily on the effects of cultivation practices and their role in maintaining plant species richness and community and ecosystem stability. Within two carefully selected areas, the successional plant communities of machair at different stages of recovery following ploughing and cultivation of cereals and potato patches or ‘lazy beds’ were identified at both a macro- and micro-level. Investigations of the vegetation recovery processes on turves taken from newly ploughed land indicated that the initial stages of recolonization are characterized primarily by rapid vegetative reproduction and growth, although re-vegetation by seeds is also an important factor. The implications of these findings for the long-term management of machair plant communities are discussed and in particular the need to maintain old cultivation practices such as shallow ploughing. The need for more detailed research into both seed banks and seed rain and into processes of vegetative reproduction is stressed. Nomenclature: Clapham et al. (1981) and Stace (1991, 1997) for vascular plants; Hubbard (1984) for grasses; Pankhurst & Mullin (1991) for the regional flora; Dobson (1992) for lichens; Watson (1981) for mosses and liverworts.     

满洲里市景观生态修复与重建

受到自然和人为因素的影响,满洲里市生态环境十分脆弱。其基本景观型包括城镇、水域、垦殖地和矿区景观。根据各类景观破坏的原因和现状,将产业生态学与流域生态学的原理相结合,提出重建、修复的措施或对策。