非均匀土壤区域SVAT模型中土壤水动力学参数的整合研究

荷兰Cabauw地区一个 10km10km区域内的四种主要土壤的水动力学参数用一种实验室直接测定法 (Wind氏蒸发法 )和两种间接方法 (分段土壤推导函数、连续土壤推导函数)确定 ,而该区域水动力学特性参数的整合则采用两组方案 (聚合土壤参数法和有效土壤参数法 )进行。一个SVAT模型的模拟输出结果感热通量、潜热通量与实测数据的比较分析表明 :(1)对于用分段土壤推导函数确定的土壤水动力学参数的区域整合 ,以逆模拟法(有效土壤参数法 )较为可行 ,其模拟感热、潜热的精确性接近参比方案 (模拟 平均法) ;(2 )对于实验室直接测定的参数 ,则以几何平均vanGenuchten Mualem经验公式参数的方案 (聚合土壤参数法 )为佳 ;(3)对于连续土壤推导函数推导的水动力学参数 ,几何平均土壤组分方案 (聚合土壤参数法 )和逆模拟法方案 (有效土壤参数法 )二者均可得到优于参比方案 (模拟 平均法)的模拟结果 ,其中以前者最佳 ;(4 )所有区域化参数整合方案中 ,以水平几何平均区域内实验室直接测定的参数的方案最优 ;同时 ,连续土壤推导函数法的土壤组分几何平均方案的模型输出精确性接近该最优方案     

Alley coppice—a new system with ancient roots

Context

Current production from natural forests will not satisfy future world demand for timber and fuel wood, and new land management options are required.

Aims

We explore an innovative production system that combines the production of short rotation coppice in wide alleys with the production of high-value trees on narrow strips of land; it is an alternative form of alley cropping which we propose to call ‘alley coppice’. The aim is to describe this alley coppice system and to illustrate its potential for producing two diverse products, namely high-value timber and energy wood on the same land unit.

Methods

Based on a comprehensive literature review, we compare the advantages and disadvantages of the alley coppice system and contrast the features with well-known existing or past systems of biomass and wood production.

Results

We describe and discuss the basic aspects of alley coppice, its design and dynamics, the processes of competition and facilitation, issues of ecology, and areas that are open for future research.

Conclusion

Based on existing knowledge, a solid foundation for the implementation of alley coppice on suitable land is presented, and the high potential of this system could be shown.     

Colloidal hard-sphere crystal growth frustrated by large spherical impurities

Impurities affect the nucleation, growth, and structure of crystals. Here we report the effect of large, spherical, polymethylmethacrylate impurities on the crystal growth of monodisperse, hard, polymethylmethacrylate colloids in a density- and optically matching apolar solvent mixture. Crystal growth, initiated at the bottom of the sample, was studied by imaging sequences of two-dimensional xy slices in the plane of the impurity's center with a laser scanning confocal microscope. Impurities form the center of grain boundaries, and a single fluid particle layer around the impurity persists in all cases. The growth rate sensitively depends on the impurity's size. Crystal growth is inhibited to a greater extent near smaller impurities, pointing to local crystal frustration induced by the curvature of the impurity.     

On the Isotopic Composition of Pb in Cloud Waters in Central Germany. A Source Discrimination Study

Fifty seven (57) cloud water samples collected in 1 hr intervals during 9cloud events in 1997 at the summit of the Brocken (altitude 1142 m) in Central Germany were analyzed for their Pb concentrations and isotopic compositions. For comparison, filterdusts of such possible emitters as power plants, cement factories, waste incinerators, cars and others were also studied.Profiles over many hours reveal changes in composition correlatedwith changes in the origin of the air masses. Five main groups ofpossible sources of the Pb can be distinguished: most importantare (1) the European standard pollution ESP dominating the continent from Germany over France to Scandinavia and (2) industrial Pb (and soot from car exhausts) followed by (3) urban waste incinerators as well as (4) perhaps ores from Norilsk/Siberia, and, somewhat uncertain, (5) ores from PaleozoicEuropean deposits. Local and daily varying anthropogenic emissions of the sources (2–5) cause scatter of the points around the ESP correlation line. In soils all these variationsand individual signatures are levelled out so that specific sources of pollution cannot be identified anymore. Geogenic Pbfrom rocks and soils is the same as that from power plants and cement factories. It is one of the two nominal end components making up the mixture of the ESP. The less radiogenic end component of this mix which must contain Pb from very old deposits is somewhat elusive: none of the large Archaic or Proterozoic deposits could be identified. Most probably numerous sources contribute to this Pb. Pb from leaded gasoline seems to be absent or is hidden under the five components dominating the composition of the Pb in the European environment. This probably reflects phasing out of such gasoline in most European countries. The Pb in the clouds may contain a small component of old Proterozoic or even Archaic Pb, but it can also be modelled with Paleozoic Pb.     

Microbial ethylene production and inhibition of methanotrophic activity in a deciduous forest soil

Production of C₂H₄, but not of CH₄, was observed in anoxically incubated soil samples (cambisol on loamy sand) from a deciduous forest. Ethylene production was prevented by autoclaving, indicating its microbial origin. Ethylene production gradually decreased from 4 to 12 cm soil depth and was not affected by moisture or addition of methionine, a possible precursor of C₂H₄. Oxidation of atmospheric CH₄ in soil samples was inhibited by C₂H₄. Ethylene concentrations of 3, 6 and 10 μl l⁻¹ decreased CH₄ uptake by 21, 63 and 98%, respectively. Methionine and methanethiol, a possible product of methionine degradation, also inhibited CH₄ oxidation. Under oxic conditions, C₂H₄ was consumed in the soil samples. Ethylene oxidation kinetics exhibited two apparent K_m values of 40 μl l⁻¹ and 12,600 μl l⁻¹ suggesting the presence of two different types of C₂H₄-oxidizing microorganisms. Methanotrophic bacteria were most probably not responsible for C₂H₄ oxidation, since the maximum of C₂H₄ oxidation activity was localized in soil layers (2-8 cm depth) above those (8-10 cm depth) of CH₄ oxidation activity. Our observations suggest that C₂H₄ production in the upper soil layers inhibits CH₄ oxidation, thus being one reason for the localization of methanotrophic activity in deeper soil layers.     

Microbial populations and phenolic acids in soil

Populations of bacteria, fungi and actinomycetes in Portsmouth A₁- and B,-soil material were affected in different ways by repeated enrichment with ferulic, p-coumaric, p-hydroxybenzoic or vanillic acids. Responses varied with type of soil material and phenolic acid, phenolic acid concentration, and inorganic nutrient status of the soil. Populations changed more frequently in B₁- than in A₁-soil material. Phenolic acids were readily metabolized by microorganisms, sometimes without detectable population changes, when adequate mineral nutrients were present. Induction of enzymes or selection of organisms capable of degrading individual phenolic acids were clearly evident. Results imply that microbial activity in bioassay systems should be defined for allelopathic studies, particularly when results from various bioassay systems are to be compared     

The Isotopic Composition of Anthropogenic Pb in Soil Profiles of Northern Germany: Evidence for Pollutant Pb from a Continent-wide Mixing System

Seventy-five samples of six soil profiles from forests on different substrates plus one next to a motorway were analyzed for the variation of Pb concentration and isotopic composition with depth. A substantial fraction of the anthropogenic Pb (peak concentrations between 74 and 300 ppm) is still stored in the organic top soil, and seldom penetrates deeper than 20–30 cm. In (²⁰⁸Pb/²⁰⁶Pb) vs. (²⁰⁷Pb/²⁰⁶Pb)-diagrams the Pb in the uppermost layers of the profiles plots on an excellent correlation line (R = 0.99) indicating essentially a two-component mixing system. Values for the dust on Scottish plants, Norwegian and Swiss bogs as well as for aerosols collected over the North Atlantic (data from the literature) plot on the same correlation line showing that the Pb was deposited from a continent-wide mixing system with two apparent end members: The radiogenic one is similar to geogenic Pb and could consist of contributions from certain European ore deposits and from different soil components (e.g. silicates and Fe-oxides), power plants and cement factories. The less radiogenic component must contain or consist of Pb from Proterozoic or even Archaic ore deposits. However, the sources of this Pb remain somewhat elusive. In any case, this isotopic pattern is so consistent all over Europe that the correlation line may serve as a line of reference for quasi normal or European Standard Lead Pollution (ESLP). The gasoline derived Pb in the soils is swamped by Pb of other provenances.     

Protonenpuffersubstanzen in Böden

Proton buffer compounds in soils A classification of solid soil buffer substances according to the type of proton accepting sites, viz. carbonate buffer, variable charge buffer, silicate buffer and hydroxide buffer is proposed. The buffer reactions are discussed in some detail and so are formation and transformation processes of buffer. An association of pH-ranges to various buffer compounds is hampered by an insufficient knowledge of the acid strength of the different functional groups.