Abstract:Soil properties change dramatically during urbanization. However, recent knowledge about properties of urban soils is still scarce. The purpose of this paper is to deliver some data of soil organic matter (SOM) properties of urban soils and to describe environmental consequences of human activities in urban environment. For the above objectives, organic carbon (OC) and black carbon (BC) were analyzed of 60 soil samples collected from 0～10 cm and 10～30 cm soil layers in five different function zones in Nanjing city, China. The method used to analyze OC and BC is chemical oxidation treatment (acid dichromate), in which removal of OC is a critical process in determination of BC. The results suggest that SOM (e. g. OC and BC) is significantly different among function zones in chemical nature and concentration. The highest concentration of OC reaches 29.09 g kg^-1 (0～10 cm layer), and the highest concentration of BC 13.67 g kg^-1(0～10 cm layer) in roadside soils, suggested its substantially different human activity and pollution source. Especially, pollution compounds emitted from gasoline and diesel vehicles are found to be the main source of BC in roadside soils. The BC/OC ratio may be related to changing pollution intensity due to local biomass and fossil fuel burning. Based on the present data, the high BC/OC ratios and BC concentrations observed in roadside soils indicate that they are the result of direct human activity (e. g. vehicles). In other words, the BC/OC ratio in different functional zones may show different intensity of human activities. Further comparison shows that BC is probably the main part of total organic carbon in urban soils, contrary to that in natural soils. This knowledge is essential for qualitative assessment of SOM properties of urban soils and urban environment.

Abstract:Partitioning of subpopulations in bulk grain-size distribution and identification of their sedimentary implications has become a fundamental task for further studies on quantitative reconstruction of the sedimentary environment. The subpopulations were identified through calculating standard deviation of each grain-size class of the six profiles of the loess-paleosal formed during the last interglacial-glacial cycle in the west of the Loess Plateau, Hexi Corridor and the west of Henan Province, China. The peak values of standard deviation corresponded to the modal grain-sizes of each environmentally sensitive grain-size population. Findings of the study indicate that the two major grain-size populations (coarse and fine) varied from profile to profile, suggesting different sedimental implications. Distance of material resources and post-sedimental pedogenesis are the two major affecting factors on environmentally sensitive grain-size populations. The sensitive grain-size populations of Binggou and Luojiawan profiles were coarser because they were more influenced by the distance of material resources; whereas the sensitive grain-size populations of Nuanhuowan and Kouma profile were finer as they were more influenced by the pedogenesis. The results showed similar populations and subpopulations. The analysis of the standard deviation of each grain-size class of Koma profile demonstrated comparability between the population and L₁, which deposited during the last glacial period, and that big difference between the population and S₁, which deposited during the last interglacial period, suggesting close relationship with pedogenesis.

Abstract:With the theory of sustainable development as guide for the agriculture of China, farmland in Houhu region of the Jianghan Plain was selected for case-study on introduction of the niche 2 fitness theory into multi-suitability evaluation of cultivated land. Quantitative analyses of niche fitness of and restrictive factors for rice, wheat, cotton and rape, were carried out by means of weighted average and limiting factor models. The results indicate that the niche-fitness value in this area is in medium on the high side with the peak value reaching 0.958, suggesting the region meets the basic requirements of the crops; and farm-lands in Grade 1 and 2 account for 75%; rice ranks first in terms of acreage of niche-fitness, amounting to 65.54%, and wheat comes the next. CEC, soluble phosphorus and accessibility to roads are the primary niche factors that restrict land productive potential in this area. These results of the study can find direct application to supervision of agricultural production, to reasonable utilization and scientific management of cultivated land resources.

Abstract:Transport of bacteria through subsurface environment was studied from different perspectives, including the fate of genetically engineered microorganisms in the environment, waste management, public health, microbially enhanced oil recovery and in-situ remediation of contaminated subsurface. The objective of this study was to investigate transport and sorption of bacteria in saturated sandy loam. Escherichia coli and Cl^-1 tracer solution were introduced separately into saturated soil columns as a pulse function under steady water flow. A mathematical model based on one-dimensional convection-dispersion equation (CDE), including the local equilibrium assumption and non-equilibrium assumption, was formulated to describe E. coli's transport. The CXTFIT program was used to fit mathematical solutions of different theoretical transport models, based upon the CDE, to experimental results. The results show transport of E. coli through sandy loam was well described by the chemical nonequilibrium two-sites model when a first-order kinetic removal process was assumed. Bacteria were removed at a significantly greater rate than Cl^-1 tracer. Breakthrough Curve (BTC) of E. coli was retarded and had a longer elution tailing when it was compared with that of Cl^-1 tracer, and the relative concentration of E. coli at the peak of BTC was much lower than that of the tracer. The total breakthrough of E. coli was also much smaller than that of the tracer. The increase in flow velocity from 0.214 to 0.470 cm min^-1 resulted in marked increase in E. coli from 0.05 to 0.2 at the peak of BTC, but decrease in retention coefficient.

Abstract:The Green Ampt infiltration model is extensively applied in many aspects, and a common means used for simu lation of rainfall infiltration and stream production on slope. Average potential suction S_f and general saturation water conductivity K_s are key parameters of this model. In this paper the mean water content increment Δθ(t) in wetted zone during ponded infil tration was defined. A ponded infiltration experiment was carried out on brown earth in Yantai, indicating Δθ(t) was a constant of 0.34. The relation between general wetting front and actual wetting front was quantified based on the water balance principle, and methods of determining S_f and K_s were put forward on the basis of the relationships of infiltration rate i(t) with cumulation infiltration I(t) or with actual wetting front Z_f^a in graphic characteristics. Compared with the field data, the calculation of infil tration rate and accumulation infiltration based on graphic characterization of i(t)~I(t) and i(t)~Z_f^a was relatively high in accuracy with overall relative error being less than 6%.

Abstract:The use of a two-flow domain model improves description of soil solute breakthrough curves, especially in preferential flows. But all parameters of the model currently can only be figured out by the inverse method, thus restricting its application. In recent years, development of the capillary theory and the model of soil hydraulic property make it possible to expose mechanisms of soil water and solute movement from a more microcosmic angle, and use a new method to determine parameters of the convection-dispersion model. Based on the Brooks-Corey model, pore velocity distribution is deduced from soil water suction curve in this paper, relationship between the geometrical coefficient of the Brooks-Corey model and the parameters of the two-flow domain model established with the average pore velocity set as the critical velocity between the two flow domains, and hence a method for determining parameters of the two-flow domain model proposed in this paper. Data measured in field observation are used to test the reliability of this method either considering immobile water in soil or not. The results indicate that the predicted breakthrough curves are far from the observed without taking into consideration immobile water;and quite close to the observed with immobile water taken into account. Errors would not be too great for loam soils and sand loam soils in the prediction based on the two-flow domain model, and the model parameters determined through the method proposed above.

Abstract:Effects of traffic on soil properties are poorly understood, and very few methods are available for measurement of these effects. In this paper, dusting rate under vehicles different in velocity and destruction of structures of the soils were measured to explore impact of traffic on physical properties of soils of arid grasslands. Experiments were conducted with vehicle simulation under field conditions. These experiments involve four velocities (V=20, 30, 40, and 50 km h^-1), seven frequencies of crushing (0, 5, 10, 15, 20, 25 and 30 times) and four soil surfaces (heavily eroded land, mediumeroded land, newly eroded land and grassland). The results indicate that under the impact of wheels, soil structures would be destroyed forming soils particles 0.063~1.0 mm in size in the soil surface. With frequent crushing of wheels, soil particle sizes would vary in the range of 0.125~0.18 mm, and the amount of broken soil mass would increase. Also, the dusting rate would increase with the velocity of the vehicles, showing a quadratic function relationship. Moreover, vehicles could affect bulk density and compression strength of the soils, and they would increase with frequency of the compaction of wheels.

Abstract:Persistent organic pollutants (POPs) listed in the Stockholm Convention of 2000 all belong to the category of organochlorine chemicals and deserve high priority for investigation. However, researches on organochlorines in Hong Kong area used to be focused mainly on those in sediments, marine organisms and human milk in the past, and little was reported on their presence in soils. Forty six samples of surface (0～10 cm) soils typical in Hong Kong were collected and analyzed for organochlorine pesticides and polychlorinated Biphenyls with the aid of GC/ECD (gas chromatograph/electronic capturer detector), six Stockholm Convention substances including pesticides and PCBs as well as HCH were detected in the samples and they were lined up in a decreasing sequence of HCH > dichlorodiphenylthrichloroethane (DDT) > hexachlorobenzene (HCB) = Endrin = PCBs > α-endosulfan in terms of concentration. The major components of the organochlorine pesticide residues were β-HCH and p, p'-DDE due to their stable molecular structures compared with other homologues. The average contents of these two compounds were only 6.12 μg kg^-1 and 0.41 μg kg^-1, respectively, which was much lower than the corresponding target values in the Dutch List. As for the PCBs, five samples were detected to have PCB28 and PCB138, which were lower than 0.1 μg kg^-1 in content. Moreover, the regression analysis results presented that residual contents of HCH in the soils were related to pH (KCl) and total organic carbon (TOC) content, but such relationship was not found with the other detectable organochlorines.

Abstract:A study was carried out to investigate mechanisms of the removal and accumulation of phenanthrene and pyrene by Zea Mays L. Pot experiment was conducted with a series of concentrations of phenanthrene and pyrene in a greenhouse. The results showed that maize significantly removed phenanthrene and pyrene from soils. At the end of the 60-day experiment, the extractable phenanthrene and pyrene were lower in planted soil than in non-planted soil. About 69.76%～91.16% of phenan-threne and 76.97%～88.37% of pyrene were removed from the soils, respectively. As compared to control 1 (with addition of NaN₃), maize removed on average 63.56% of phenanthrene and 72.27% of pyrene from the soils and relative to control 2 (without NaN₃), 15.13% of phenanthrene and 38.15% of pyrene were removed. Maize did take up PAHs from the soils, and generally the higher the concentration of PAH in soil, the more maize took up. Bioconcentration factors (BCFs) for phenanthrene and pyrene tended to decrease with increasing concentrations of the contaminants in soil, and the BCFs for pyrene were large than those for phenanthrene. The BCFs for phenanthrene in shoots were 0.79～2.45 (leaves) and 0.17～1.76 (stems), higher than in roots (0.42～1.21) in the same treatment. However, the BCFs for pyrene in shoots were 1.03～3.31 (leaves) and 0.2～2.17 (stems), much lower than in roots (2.07～6.40). Maize can grow in soils higher in PAHs, and accumulate phenanthrene and pyrene. The results indicate that removal of PAHs from contaminated soils by Zea mays L may be a feasible approach to remediation of the soils.

Abstract:Pot experiments were carried out to evaluate effects of soil amendments on heavy metal uptake and distribution in different organs of tobacco plants, which were planted in soil containing Pb 330 mg kg^-1 and Cd 1 mg kg^-1 of extraneous sources. Three different kinds of soil amendments were applied separately, Pb and Cd contents in and biomasses of different parts of the plants during different growth periods were investigated to determine effects of the amendments on heavy metal uptake by the tobacco. The results show that the translocation factor (TF) of Pb is lower than that of Cd, indicating that Cd in tobacco moved more easily than Pb. Cd in the tobacco leaves is more harmful to human health than Pb; Compared with control, pots treated with amendments had more Cd and Pb left in the soil, suggesting that all the three kinds of soil amendments more or less reduced Cd and Pb contents in different parts of the tobacco plants, and increased biomass of the tobacco. Therefore, they had positive effects on tobacco growth and reduction of Pb and Cd uptake by tobacco. Among all the amendments, attapulgite was the best modifier, and bone powder was better than activated carbon.

Abstract:In the Ecological Experimental Station of Red Soil of Chinese Academy of Sciences, a six-year (1991~1996) stationary experiment had been carried out on a red soil slope land with different forests to study systematically dynamic circulation of N, P and K and establish a compartment model of nutrient circulation. The results indicate that a major part of N, P and K was stored in the soil compartment in different forest lands, amounting to above 97%. The annual total net accumulation of N, P and K was positive for six-year old broadleaf forest and conifer forest, being 36.51 kg hm^-2 and 29.70 kg hm^-2, respectively. The entire system was gaining in nutrient reserve, and N, P and K were all accumulating, showing surplus in the system. As a contrast, the annual total net accumulation of N, P, K in control (nature wild slope) was -9.59 kg hm^-2, suggesting an out flow of nutrients, N, P and K from the system. Meanwhile, simulation of N, P, K circulation in different compartments of the forest slope land and wild slope land within 0~10 years was described. The results indicate that N, P and K were in surplus in the broadleaf forest and conifer forest systems, and their accumulation in the ground parts of the plants was significant, but, in the soil compartment N was losing, and P and K were gaining. The results also show that nutrients in the soil compartment on the nature wild slope suffered slight loss.

Abstract:Through field sampling and investigation, spatial distribution of soil organic carbon, total nitrogen, total phos-phorus and total potassium in annular wetlands of the Sanjiang Plain was studied preliminarily. The results showed that horizontally it varied sharply, but followed a certain law, that is, soil organic matter, total nitrogen and total phosphorus gradually decreased in content, but total potassium content and C/N ratio gradually increased along the direction from center to edge of the wetlands. Vertically these soil chemical elements also varied, showing obvious stratification and enrichment. In a soil profile, organic matter declined in content with the depth; soil organic carbon under all the five vegetation communities gradually decreased; soil total nitrogen increased first and then decreased under all the vegetation communities except under Ass. Carex pseudocuraica; total phosphorus and total potassium under most vegetation communities decreased first and then increased. The results of correlation analysis between soil organic matter, total nitrogen, total phosphorus and total potassium suggest that soil organic carbon and total nitrogen showed a similar pattern in distribution; the spatial distribution pattern of total potassium was completely different from that of soil organic carbon and total nitrogen; and total phosphorus had its own unique pattern of distri-bution. The distribution law of soil organic carbon, total nitrogen, total phosphorus and total potassium of the wetlands was mainly impacted by element contents of the plants, biological processes and hydro-geomorphological processes. The study on the distribution laws of soil organic carbon, total nitrogen, total phosphorus and total potassium of the annular wetlands is not only helpful in perfecting the theory of wetland soil formation and development, and proving up ecological processes and function of wetlands, but also provides scientific basis for reasonable exploitation and protection of the wetland resources.

Abstract:In nature irrigated rice fields fix about N 27 kg hm^-2 more than upland rice fields, which means that the crop needs less N fertilizer in irrigated rice paddy than in upland rice field and that growing rice in paddy fields may lower the production cost, save valuable resources and relieve environmental pressure. Results indicate that irrigated rice paddy is a sink of N because it gains N 2～20 kg hm^-2 in balance from N cycling with water flowin 7.5% of the non-point source N loading in South Jiangsu plain, suggesting that N runoff from rice paddy is not a major contributor of the problem. N leaching from irrigated rice paddy is less than from upland fields. Since the mid 2 1980s, the over 2 limit rate of nitrate N in well water has remained almost unchanged even though the N fertilizer application rate has dramatically increased, which implies that nitrate in well water is not directly related to N fertilization. N loss through ammonia volatilization accounted for about 6%～21% of the urea N applied in paddy field in the rice growing season, and only 3.1%～6.5% in the winter wheat season;On the other hand, N input through wet deposition was also much larger in the rice season than in the winter wheat season. Overall, irrigated rice paddy is a N sink, but not a N source to its surrounding environment. "Paddy field Ring" works as an artificial wetland and protects our environment from the view point of N cycling

Abstract:Studies were carried out on influences of replacement of 25% NO₃^--N with NH₄⁺-N in nutrient solution (enhanced ammonium nutrition) on tomato growth and activity of such key enzymes in N assimilation and organic acids as nitrate reductase (NR), glutamine synthetase(GS) and phosphoenolpyruvate carboxylase (PEPcase) in tomato leaves and fruits sampled at different developmental stages. The results showed that the replacement of 25% NO₃^--N with NH₄⁺-N led to a significant increase in fruit fresh weight, NH₄⁺-N content in both leaves and fruits and soluble protein content in fruits, while led to decrease signifi cantly in NO₃^--N content in tomato leaves. Meanwhile, significant enhancement of the activity of PEPcase in both leaves and fruits and of GS in leaves were observed but not much change in GS activity in tomato fruits was. NR activity was of ten observed to decrease dramatically in both fruit and leaves in enhanced ammonium treatment.

Abstract:Characteristics of phosphorus adsorption by upland red soils different in fertilization and their affecting factors were studied with X_m-value calculated out of the Langmuir curve as index. The results show: (1) X_m-value is always lower in soil fertilized with inorganic or organic phosphorus than in soil not fertilized with phosphorus. Livestock manure is an effective fertilizer because it makes X_m-value lower than other fertilizers. (2) Organic matter and available-Al significantly influence soil P absorbing capacity, which rises with the increase in available-Al content in soil, but it declines with the increase in organic matter content. pH and available-Fe are minor factors affecting X_m-value in this research. The above-listed results are testified by data reduction-analysis, indicating the content of organic matter was the most influential factor found. (3) Because of the good relationship between X_m-value and ff-value, which can be used as a basis for recommendation of P fertilization in practice, X_m-value may be an index to judge the amount of P fertilizer needed in the field primarily. In a word, these results contribute to research on transformation of phosphorus and determination of P application rate in red soil regions.

Abstract:With the buried glass filter paper bag method a field experiment was carried out in a tobacco field to study mineralization of green manure and its effect on tobacco leaf quality. Results show that about 81% of the organic C and 54% of the organic N in alfalfa, 63% of the organic C and 22% of the organic N in rye grass were mineralized throughout the growth period of tobacco. However, more than 92% of the mineralized N in alfalfa and 74% in rye grass were released in the first 6 weeks after they were incorporated into the soil. In the whole growth period of the plant, about N 43 kg hm^-2 was released from alfalfa. In order to control of over-supply of N nutrient in the late growth period and resultant higher nicotine content in tobacco leaves at upper stalk position, it is recommended that alfalfa should be ploughed into the field earlier and the total N fertilizer application rate should be reduced by deducting the amount of mineralized N released from the alfalfa. Rye grass released only N 10.5 kg hm^-2 in the same period of time because of its low N content. So rye grass could totally be ploughed and incorporated into the soil unless its biomass production is getting too high. When the application rate of chemical N fertilizer remained unchanged, the alfalfa treatment resulted in slightly higher nicotine content, lower total sugar and lower reducing sugar content in tobacco leaves at the upper stalk position in this experiment, while the rye grass treatment reduced the nicotine content and kept sugar contents in a proper range, thus improving quality of the tobacco leaves.

Abstract:Soil coleopteras in agro-habitats in the plain, mid-west Jilin Province were investigated with emphasis on species richness and abundance in relation to land 2 use patterns i. e. residential garden, farmland, and Sanbei Windbreak Forest Belts in July and September, 2003. Soil coleopteras were hand-sorted and identified to the families level. A total of 955 soil colepoterous individuals was captured and fell into 26 families. Scarabaeidae larvae,Carabidae and Carabidae larvae were the dominant groups that account for 65.03% of the total captured. The results suggest that land use affects the species abundance and diversity, and there was significant difference in soil coleoptera community between the plains in the middle and in the west of Jilin Province. Agricultural activity reduced soil coleoptera abundance and diversity in residential garden and farmland, while forests improved soil coleptera diversity in agro-habitats.

Abstract:Short term effect of mefenacet, an acetanilide herbicide, on soil microbial communities in paddy soil was stud ied. The Biolog method (a kind of colour development assay) was used to determine substrate utilization potential of microbial communities for assessment of biological communities. The results show that functional diversity of the microbial communities decreased, and capability of the microbes of utilizing substrate of simple carbon sources reduced in mefenacet-polluted soils compared with those in non polluted soil. However, this effect was transient, and functional diversity of the microbial communities in mefenacet polluted soils came back at the end of the experiment. Supplementation of strain Y1 had a positive effect on metabolic potential of the soil microbial communities. A kinetic method was presented for characterizing the physiological state of microorganisms capable of carrying out specific metabolic function in paddy soils. Test well dye reduction was non linear in microplates inoculated with duration of the incubation, and the color development curve was generally sigmoidal in shape. Test well OD values over time suggested a kinetic model based on the density-dependent logistic growth equation. The kinetic parameters generated by the model can be used as surrogates for single-time-point data in constructing carbon source utilization patterns. And a and x₀ were more sensitive to indicate the effects of mefenacet and strain Y1 on functional diversity of the microbial communities. Shannon index (H) was more sensitive than the index of microbial community richness (S) to show the microbiological change in contaminated environment.

Abstract:An improved method was used to extract soil microbial DNA by indigenous silica gel instead of imported glass beads. A new degenerate PCR-primer pair P1/P2 was designed to amplify directly xylanase gene fragments from soil microbial DNA. PCR products were ligated with pMD18T vector. Transformants were got by transforming ligation product into E. coli. Ten different recombinants that were confirmed by RFLP were sequenced. The sequence analysis shows that all of the ten fragments encode partial xylanase. The BLAST of deduced amino acid of fragments show that eight out of the ten were high in sequence homology with xylanase from Actinomycetes, two with Pseudomonas. Asn27 was found in all partial xylanase based on the alignment of deduced amino acid sequences, which means that all xylanase fragments were alkali-tolerant. Phylogenetic tree shows that all xylanase fragments were positive and over 70% of similarity.

Abstract:Mechanism of corn plant residue (CPR) improving soil was studied through a soil culture experiment. After CPRs were applied into soil, contents of biomass C and N were augmented, cation exchange capacity of the soil, five-carbon sugar and six-carbon sugar were increased significantly, content of loosely combined humic substances, unitedly combined humic substances and tightly combined humic substances also were enriched. However, content of stably combined humic substances was reduced, and five-C sugar was apt to change. CPRs improved activity of soil colloid. Corn stalk is different from corn stubble in effect on improving the soil.

Abstract:Pathogens such as bacteria and viruses are widely spread in septic tanks, sewage sludge, wastewater and other sources. Groundwater contamination with viruses has caused great concerns in various countries because viruses are much smaller in size than bacteria or protozoan cysts and not easy to be filtered out through the porous soil matrix. Many scientific studies have been conducted in the past decades and much information is available in the literature about virus transport in the subsurface and its mechanisms. The purpose of this study is to review the literature from China and foreign countries with a focus on factors that influence virus transport in the subsurface, which include (1) general hydrodynamic factors that may affect fate and transport of viruses, (2) factors influencing virus adsorption and their mechanisms, (3) factors influencing virus inactivation and their mech 2 anisms. Soil physical heterogeneity is one of the main factors that cause dissimilarities between microorganisms and conservative solute tracers in transport behavior. Factors such as soil type, virus type, pH, ionic strength and the multivalent cations, organic matter, temperature, soil moisture content, particulate matter and soil, and microbial activities have been found to influence virus adsorption and inactivation in the subsurface. Each influencing factor is described and explained in detail. As for selection of indicator viruses, bacteriophages such as MS2, PRD1, and ΦX174 have been used extensively to study virus transport in columns and fields various in conditions and are considered to meet the requirements as indicator viruses. Based on the review, recommendations are made for future research activities.

Abstract:Soil fauna is a main component of the terrestrial ecosystem and its ecological characteristics and functions has recently aroused more and more concerns from researchers. Much of the interest has come from the need to understand the critical roles of soil fauna in material cycling and energy flow. The review firstly summarizes the ecological characteristics of soil fauna in the following three aspects: (1) definition and classification of soil fauna. (2) abundance, diversity, community structure and distribution pattern of soil fauna. (3) factors influencing these ecological characteristics including natural factors, artificial factors and the global changes. And then the paper reviews the functions of soil fauna in different aspects, focusing mainly on its functions of litter decomposition and ecological indicator. Principles of the litter decomposition function of soil fauna and main research contents in this field are discussed in detail. In the end, the authors point out some scientific problems in the present research of soil fauna and suggest a direction for the future research. This paper aims to have a further understanding of soil fauna and to provide necessary theoretical basis for biodiversity protection, consummation of the ecological index system, reasonable exploitation of the soil resources and realization of sustainable development of the agriculture and ecology.

Abstract:土壤侵蚀预报是进行水土流失监测、指导水土保持措施合理配置、优化水土资源高效利用的重要工具,自20世纪60年代以来,国内外学者对此进行大量研究,建立一系列经验统计模型^[1,2]和物理成因模型等^[3,4]。以上模型复杂性及适用性各异:如经验统计模型主要从侵蚀产沙因子角度入手,建立径流产沙与降雨、植被、土壤、土地利用、耕作方式、水保措施等之间的多元回归因子关系式,一般比较简单,便于应用,但模型中经验参数适用范围有限,模拟精度难以控制;物理机理模型主要以土壤侵蚀物理过程为基础,利用水文学、水力学、土壤学及其他相关学科基本原理,根据降雨、径流条件来描述土壤侵蚀过程,预报给定时段内的土壤侵蚀量,具有一定,但其限制因素较多,应用不便^[5];人工神经网络(ANN)中的BP网络模型具有较强的自学习能力和处理非线性问题能力,近年来已在有关工程领域得到广泛应用^[6～9]。本文以土壤侵蚀较为严重的陕西淳化县泥河沟流域坡耕地为例,引入BP网络模型这一新的定量研究方法对坡面土壤侵蚀产沙规律进行研究。

Abstract:对应分析,又称对应因子分析(Correspondence Factor Analysis,CFA),是由法国学者Jean-Paul Benzecri在20世纪70年代提出的一种几何分析技术^[1~4],是主成分分析技术的拓广^[2]。CFA依靠主成分分析的降维手段,使高维问题变为低维问题;采取独特的数据预处理方式使样本矩阵Q和变量矩阵R呈对称性,并从数学上证明了R与Q具有正交关系,有相同的特征值,从而可以在相同标度的因子轴坐标系中同时标度变量和样本^[1~7]。CFA依据被标注点群的聚散状况,解释与判断变量之间、样本之间以及变量与样本之间的多重内在联系,已在众多领域得到了广泛的应用。

Abstract:尽管我国从1983年就开始禁用有机氯农药,但环境中仍有大量残留存在。土壤中污染物的残留是吸附、降解和迁移等各种理化作用和生物作用的综合结果,其中降解是制约其残留量的关键过程^[1~5]。大量研究表明,影响土壤中农药降解的主要环境因素包括土壤有机质、土壤温度、土壤pH和土壤含水量等^[6~8],因为这些因素显著影响着土壤微生物的数量和活性。微生物代谢所需的营养物质有一部分来自农药和土壤有机质,土壤中微生物对其降解起着重要作用。胡敏酸(HA)是土壤有机质的主要组分,因此以HA代表土壤有机质对农药降解的影响是合理的,也有很多关于HA对农药在土壤中吸附等环境行为影响的研究报道。

Abstract:横断山北部是我国地理环境独特和生物多样性最丰富的地区之一^[1~3],其生态恢复与重建对整个长江流域的水土流失治理及生态安全具有重要的现实意义,故一直受到国内外学术界的高度关注^[4,5]。但由于近40年来人类活动和气候环境的变化,其林木蓄积量大幅度减少,水土流失日趋严重,生态环境破碎化,部分野生动植物资源已濒临灭绝,已有研究表明属生态脆弱区^[6]。尽管该区实施退耕还林工程和天然林保护工程已四年,但因该区域有关生态环境(包括土壤钾素养分等)的基础研究资料较少,生态重建进度仍很缓慢。

Abstract:土壤对疏水性有机污染物的吸附实际上是土壤中矿物和有机质两部分共同作用的结果。土壤有机质的作用相当重要,因为与矿物相比,它通常对疏水性有机污染物具有较大的热力学亲合力。因此,土壤吸附有机污染物机理的研究主要是从土壤有机质的角度进行的^[1~5]。土壤有机质组成复杂,主要包括非特异性有机质和腐殖质^[6],其中腐殖质约占有机质总量的50%~80%,包括胡敏酸、富里酸和胡敏素。早期的实验研究认为疏水性有机污染物在土壤有机质相中表现为线性分配,可以用平衡分配系数来描述^[4]。

Abstract:稻草在分解过程中产生有机酸。高浓度的有机酸一方面对水稻生长产生毒害作用^[1,2],另一方面,有机酸可通过酸溶、螯合和竞争吸附等机制活化土壤难溶态磷,提高磷的生物有效性^[3,4]。所以,研究稻草分解过程中有机酸和有效磷的动态变化,对于评价稻草还田在水稻营养中的作用,指导秸秆管理具有十分重要的意义。在以往的土壤有机酸研究工作中,大多采用水提取法来获得土壤有机酸溶液^[2,5]。这一方法改变了土壤溶液原来的化学平衡和化学环境,因而在一定程度上影响了有机酸分析结果的可信度,而且也不适合土壤有机酸的动态测定。Al-berto等^[6]设计了一种适用于原位动态取样的方法(多孔聚酯管溶液采集器采样法)。