王家桥小流域综合治理模式及成效探析

王家桥小流域综合治理模式及成效探析余志训（湖北省秭归县水土保持办公室，４４３６００）秭归县王家桥小流域在综合治理水土流失中，针对本区域的环境特性，结合流域经济发展的要求，合理、优化配置防治措施，探索出了“山上林地封顶、山腰田林相间、山下水系配套”的与...     

Centres of Crop Diversity and/or Origin, Genetically Modified Crops and Implications for Plant Genetic Resources Conservation

The concept of centres of crop diversity and/or origin of agriculture is briefly reviewed. The conservation status of crop genetic resources, either ex situ or in situ, cultivated or wild, has been assessed for species of the Central American and Mexican centre, demonstrating that that region is indeed one of the important centres of crop diversity for human kind. Furthermore, biotechnological developments with regard to the creation and spread of genetically modified crops have been analyzed. The likelihood of unintentional introgression of genetically modified traits into conventional seed lots, crops as well as into germplasm collections have been assessed. Related biosafety measures as well as the possible implications of intellectual property rights on transgenic crops and/or genes are being discussed vis-a-vis the possible implications they might have for germplasm management. The Central American crop genetic resources situation has been used as a “case study” to illustrate the potential impact of the spreading of GM varieties on the genetic diversity in genebanks and farmers’ fields and the need for effective and efficient conservation efforts. Conservation management strategies and practices are being proposed of mitigate the potential negative impact of GM crops on the conservation efforts.     

Modeling studies on sulfur deposition and transport in East Asia

A three dimensional regional Eulerian model of sulfur deposition and tranport has been developed. It includes emission, transport, diffusion, gas-phase and aqeous-phase chemical process, dry depostion, rainout and washout process. A looking up table method is provided to deal with the gas-phase chemical process including sulfur transfer. Calculated values have reasonable agreement with observations. Distribution of sulfur deposition and transport in East Asia are also analyzed in the paper. Simulation shows that sulfate (SO ₄ ^2– ) is the main substance to transport in long range transport. Some amount of sulfur emission of different countries transport across boundaries, but the main origin of sulfur deposition in each country in East Asia is from herself. Furthermore, some transport paths on different layers and outlet or inlet zones are found.     

Acid deposition: Perspectives in time and space

Most acid-deposition investigations have been concerned with the impact of nitrogen oxides (NO_x) and sulfur dioxide (SO₂) emissions on Europe and North America. This paper examines three issues beyond this central focus. Major conclusions are 1) ammonia (NH₃) emissions and subsequent nitrogen (N) accumulation in terrestrial ecosystems have the potential to generate significant acidification in terrestrial and aquatic ecosystems; 2) sulfur (S) and N accumulation in environmental reservoirs will not only result in significant and extensive acidification but will also impact the earth's radiation balance, tropospheric oxidizing capacity, ecosystem nutrient balance and groundwater quality; and 3) future emissions will substantially increase in the developing world, especially in Asia. By 2020, Asian emissions of SO₂, NO_x and NH₃ will be equal to or greater than the combined emissions from Europe and North America.     

Factors and processes of gibbsite formation in Northern Thailand

Gibbsite is usually considered as end product of weathering in tropical environments with potentially high leaching rates. However, there are also hints towards gibbsite formation in initial stages of weathering in different climates. This study reports on a systematic approach based on soil forming factors in order to research the conditions of gibbsite formation in northern Thailand highlands. Therefore, three major study sites were chosen, which differ with respect to parent rock, relief, climate and vegetation. The results show that gibbsite is common in soils of the area. Reasons for its occurrence in soils are manifold. It can be a heritage of the parent rock, a result of initial weathering under free draining conditions or an accumulation under intense chemical weathering caused by high rainfall. Especially the investigation in granite and gneiss areas with a high share of primary minerals indicates that gibbsite can be an early and direct transformation without intermediates from micas and feldspars if free drainage is assured. With progressing soil genesis clay formation reduces drainage and favours kaolinite formation. Only sites with extremely high rainfall and low evaporation (high elevations in northern Thailand) show again a dominance of gibbsite in the clay fraction throughout the whole soil profile.     

Monitoring of gully erosion in the Central Ebro Basin by large-scale aerial photography taken from a remotely controlled blimp

Large deep gullies (Span. barrancos) are some of the most important sediment sources in the semi-arid environment of the Central Ebro Basin. They are incised into the Quaternary valley bottoms (Span. vales), which are characteristic landforms in this area. In the research project EPRODESERT ( valuation of cesses Leading to Land Degradation and ification under Extensified Farming Systems), the development of a large barranco system is being investigated by different methods, including documentation and monitoring by aerial photography.Geomorphological forms and processes, such as sheet wash, rill and gully erosion, cannot be documented sufficiently by conventional remote sensing methods. Spatial and temporal resolution of satellite sensors as well as of conventional aerial photography do not correspond to the scale and dynamics of geomorphological processes.With a specially designed hot-air blimp as a sensor platform, large-scale aerial photographs were obtained from the Barranco de las Lenas specifically aimed at the scientific demands (very high spatial and temporal resolution). The development of the gully is documented and its dynamics are evaluated by a sequence of six aerial photographs taken between 1995 and 1998.     

Dynamic modelling for linear erosion initiation and development under climate and land-use changes in northern Laos

Linear erosion (LE) induced either by piping or overland flow is one of the most active factors in the evolution of soils. During single storm events LE may remove enormous amounts of soil material from the uplands to the bottomlands and has thus become a broad challenge for food supply, food security, and human health. Recent and rapid changes in land-use and climate patterns in the sloping lands of tropical areas may dramatically increase LE. Our main objective was to investigate to what extent one could use direct flow velocity estimations from dynamic models for predicting LE initiation and development at the event level. The second objective was to estimate the impact of expected land-use and climate changes on LE. The study was conducted in the 0.62 km² watershed of northern Laos presented inChaplot et al. (2005). Field observations of the formation and the development of LE features throughout 2001 were compared to flow velocity estimations from an existing surface water routing algorithm developed at Utrecht University ([De Roo, A.P.J., Wesseling, C.G. and Ritsema, C.J. 1996. LISEM: a single event physically based hydrologic and soil erosion model for drainage basins. I: theory, input and output. hydrological processes 10 (8): 1107–1117.]). In 2001, two main rainfall events were responsible for the formation or development of 14 linear features with a total length of 972 m and an erosion rate of 3.5 Mg ha^{− 1}. The water routing algorithm was calibrated using the water and the sediment hydrographs observed at the watershed outlet during the first rainfall event. Assuming realistic estimations of flow velocity in hillslopes, a threshold of 0.062 m s^{− 1} for linear erosion estimated over 10-m cells was defined. This threshold, validated using the remaining rainfall event, accurately predicted the length (mean error of estimate of less than 15%) and location of LE features. Using this simulation tool, an increase of the percentage of land under cultivation from 9% to 100% resulted in 600% increase in linear erosion. The tested scenarios of climate changes had less impact on linear erosion.     

Fungal communities associated with the decomposition of a common leaf litter (Quercus leucotrichophora A. Camus) along an elevational transect in the Central Himalaya

Summary We studied the fungal communities associated with decomposing common leaf litter (Quercus leucotrichophora A. Camus) placed in five forests of Central Himalaya between the elevations of 330 and 2150 m. During the initial period of decay, conciding with the rainy season, a progressive increase in fungal counts and species diversity was observed in all forest sites. The sal forest site had a greater weight loss and supported the largest fungal densities, whereas the pine forest had a lower weight loss and the smallest fungal densities. Deuteromycetes were the dominant group in all the forest sites. Most of the species isolated during the annual cycle of the forest sites were of the accidental type. Species diversity and fungal counts on the common leaf litter were markedly affected by the environmental changes brought about by the native leaf litter. This effect was most obvious in the chir pine forest site where the leaf litter of the native dominant species was distinctly more resistant to decay than those of the other sites, making the soil environment of the site markedly different from that of other sites. The pattern of fungal-species changes with progressive decay of the substrate was similar to that suggested by the tolerance model of Connel and Slatyer.     

Effects of landscape change on clutches of Phyllomedusa tarsius, a neotropical treefrog

Phyllomedusa tarsius is an arboreal frog species that suspends its eggs on leaves above water in order to achieve the high relative humidity necessary for embryo development. I compared the hatching success of P. tarsius in ponds located in pasture, Vismia spp. regrowth, Cecropia spp. regrowth, forest fragments and continuous forest at a site in central Amazônia. Reproductive success of P. tarsius is measured as percentage of clutches producing at least one tadpole and number of tadpoles produced per clutch. Reproductive success was higher in Cecropia regrowth, forest fragments and continuous forest, compared to pasture and Vismia regrowth. Desiccation and flooding were the main causes of clutch loss in pasture and Vismia regrowth, while predation was more frequent in forest and Cecropia regrowth. The levels of successful of P. tarsius clutches observed across all habitat types suggests that a landscape mosaic including pasture, secondary growth and forest fragments may allow for recolonization and genetic exchange to occur in isolated forest patches.     

Allium vavilovii M. Popov et Vved. and a new Iranian species are the closest among the known relatives of the common onion A. cepa L. (Alliaceae)

A wild onion species from Karaj valley east of Tehran istaxonomically described as Allium asarense R. M.Fritsch et Matin. Sharing the bubble-like inflated lower scapewith A. vavilovii, the newspecies differs by semi-cylindrical leaves and small flowerswith translucent greenish-yellow tepals from all other knownspecies of Allium sect.Cepa. Molecular data suggest a closerelationship to A. cepa(but to a lesser degree than A.vavilovii) and indicate a still weakerphylogenetic connection of A.oschaninii to the common onion. The questionabout the possible wild ancestor of A.cepa is discussed against this background, and akey for determination of the Oschaninii-alliance of sect.Cepa is presented.