Abstract:Desiccation of the deep soil layer under forest and grass vegetation is one of the crucial topics in scientific research for eco-environmental construction of the Loess Plateau.Soil water balance of grassland in gully regions on the Loess Tableland in various hydrological years was simulated numerically with simulated rainfall. The results show that soilwater balance of grassland with high vegetation cover ratio could be studied with WAVES model, and the simulated values of soil water storage capacity agree well with the measured values but how to determine correlative parameters need to be studied further. To keep in balance the supply and the demand of soil water, the rainfall amount during the rainy season and in the whole year should at least be 507.0 mm and 747.6 mm respectively, higher than the multi-year average value, respectively, indicating that soil water tends to have deficit in drought and average years on the Loess Plateau, leading to formation of the dry soil layer.

Abstract:Even though the numerical solution of the unsaturated water flow in soil has been widely applied, the analytical solution cannot be replaced in understanding the intrinsic mechanism of water flow in soil Considering the nonlinear in nature of unsaturated water flow in soil, analytical solutions should be extremely difficult to obtain, especially as the gravity is taken into consideration Thus, so far, there is not any analytical solution available for those issues with both the gravitational effect and the nonlinearity under consideration In this contribution, a coordinate transformation approach is suggested, enabling us to avoid the obstacle of the gravity by removing the item of gravitational effect in the equation Subsequently, the equation for describing unsaturated water flow in the gravitational field bears the same form as the equation neglecting the gravitational effect As a result, for the first time, an analytical solution that can be expressed with the algebra form is obtained The relational theoret ical results, including the new method of coordinate transformation and the analytical solution advanced in this paper, have been verified in experiments.

Abstract:Crop Water Stress Index (CWSI) that was firstly suggested by Jackson and Idso to evaluate water status was expressed as a function of (T_c-T_a).Since remote sensed thermal radiation is a mixture information of soil and canopy, CWSI is not applicable at the pixel scale.On the assumption that land surface temperature (T_S) is a linear function of canopy temperature (T_C), soil surface temperature (T_soil) and vegetation cover fraction (f_v) and that there is no coupling between soil and canopy, Water Deficit Index (WDI) that was extended from CWSI was used to evaluate regional drought.In the paper, air temperature (T_a) spat ial patterns in the first ten days of April and second ten days of May in 2000 were firstly figured out with NDVI-T_s (where NDVI is Normalized Difference Vegetation Index) space with Terra MODIS land surface temperature and vegetation index product.Then Water Deficit Index (WDI) was calculated based on (T_s-T_a) and NDVI.The comparison between WDI and topsoil moisture show that WDI can reach a satisfactory estimation of field water deficit for both full-covered and partially vegetated sites and have overcome the shortage of CWSI that can only work for the site of fully covered by vegetation.

Abstract:Relationship between crop water stress index(CWSI) and soil water content in irrigated winter wheat field was investigated at the Irrigation Experiment Station of the Northwestern Science and Technical University of Agriculture and Forestry during the cropping season from October 2000 to July 2001.Based on the formula for calculation of evapotranspiration of a crop under water stress and the definition of CWSI, a CWSI-and SWCC-based equation for estimat ion of soil water content in the winter wheat field at different vegetative stages was worked out using the Dooreboos model (D-M) and Kang Shaozhong model (K-M).The experiment results show: the D-M and K-M both overestimated soil moisture during the seedling-regreening stages and the error ratio reached 70% and 50%, respectively; and the K-M was inclined to overestimate while D-M was inclined to downestimate soil moisture during the regreening-maturing stage and the error ratio could reach 15% and 30%, respectively.

Abstract:The spat ial patterns of soil organic carbon (SOC) are closely related to changes in the global climate In order to quantify spatial patterns of SOC density in Hebei Province, China, three different methods, i e mult iple linear regression (MLR), universal kriging (UK) and regression-kriging (RK), coupled with auxiliary topographic factors extracted from a 1:250 000 DEM (cell size is 100 m) were applied to predict spatial patterns of SOC density for Hebei Province The results show that the sum squared error (SSE) of the MLR method was quite large with only 18 6% of the total variation explainable, the UK method lowered SSE but widened the range of SOC density as compared with the MLR method However, it can explain 53% of the total variation and detect local variation of lower SOC density in southeast of Hebei Province When the RK method was applied, the SSE decreased significantly It not only explained 65% of the total variation, but also better reflected the relationship between SOC density and landform and local variation, indicating that it is the best one for predicting spatial patterns of SOC density.

Abstract:The research on urban expansion in Yixing city shows that the city's growth is greatly affected by river systems and communicat ion networks (roads and bridges).Since they occupy certain land spaces, modeling of urban expansion can be transformed into analysis of their spatial relationships with the city's growth.Based on distance analysis by using grid GIS, this paper is trying to simulate spatial distribution of Yixing city by firstly calculating spatial distances from each cell to the river system, roads, and the former city zone in the whole region to determine the priority of each cell in expansion, and then filling in the whole region according to each cell's priority in expansion.When the total area of the filled cells is near the real urban area then stop filling in and thus the simulated city distribution would be determined.The case study of Yixing city in China shows that the precision of spatial simulat ion can be as high as 80% as compared with the real city.The precision is expected to be improved by taking into account more factors that might affect town sprawl.

Abstract:Deposition of sediments on river floodplains is accompanied by the deposition of sediment-associated nutrients and pollutants Using the ¹³⁷Cs measurement to provide a chronology for sediment cores, in combination with information on downcore variations of the total-P content of floodplain sediment cores, affords a means of investigating recent changes in the total-P content of the suspended sediment deposited on the river floodplains and of documenting recent rates of phosphorus accumulation Results are presented for sediment cores collected from eight floodplain reaches of River Culm, Devon, UK The average values of total-P concentration of fine sediment deposited since 1963 for individual cores range from 0.60 to 1.96 g kg^-1, and the values of total-P storage since 1963 range from 18.6 to 435 g m^-2, showing a trend of total P concentration increasing from upstream to downstream and from the 1960s to the present.

Abstract:Fecal Coliform (FC) is an indicator pathogen for evaluating safety of land application of sewage sludge In the present study, forty-eight sewage sludge samples were collected from 15 cities in the Yangtze River Delta region Both FC and water content were determined in the fresh samples and in some selected samples when being air-dried for 7, 14, 21 and 28 days, respectively, in order to investigate counts of FC in the sludges, their pollution risks and dynamics following air-drying The results show that the counts of FC in the sludges ranged from 0 to 3.41×10⁶ (MPN g^-1, DW), with an average of 3.79×10⁵ (MPN g^-1, DW) FC was found in 89.6% of the samples River sludges and products thereof were much lower in FC count than the domestic and domestic industrial mixed sewage sludges The counts of FC dropped markedly at first with the time of air-drying but rebounded after 3~4 weeks It can be concluded that majority of the sewage sludges from wastewater treatment plants in the Yangtze River Delta region had pathogenic bacteria, but their counts varied with the wastewater sources, treatments and sludge disposals FC in some sewage sludges exceeded a guidance level of 2×10⁶ (MPN g^-1, DW), indicating potential risk to eco-environmental safety and public health upon land application without appropriate pasteurization.

Abstract:The main objective of this project is to study distribution and concentration of selenium (Se) and its affecting factors in Hong Kong soils.Soil samples were collected from fifty-one soil profiles and 44 surface soil layers at 44 sampling sites throughout Hong Kong for analysis of total Se with the aid of the induct ively coupled plasma spectrophotometry.The results indicate that Se was mainly distributed in B and C horizon.Concentrations of total Se in all the soil samples ranged from 0.07 mg kg^-1 to 2.26 mg kg^-1 (dry wt.), with the lowest and highest concentrat ions recorded in Orthic Anthrosols (average 0.45 mg kg^-1, dry wt.) and Udic Ferralisols (average 1.05 mg kg^-1, dry wt.) respectively.In terms of land use, the highest and lowest concentrations were recorded in forest soil (average 1.36 mg kg^-1, dry wt.), and agricultural soil (average 0.36 mg kg^-1, dry wt.) respect ively.The main factor that influences Se concentration and distribution in Hong Kong soils was the parent material.Other soil factors such as soil pH, organic matter, clay fraction, iron and aluminum also played relatively important roles.

Abstract:Nitrate content of groundwater was surveyed from 1999 to 2000 in the rural plain areas of Beijing.The mean value of NO₃^--N content of groundwater sampled from 481 wells was 5.74 mg L^-1, NO₃^--N content in 48 1 4% of the wells was above 2 mg L^-1, implying that the quality of groundwater was affected by human activities, 21.0% above 10 mg L^-1, which is the maximum permissible limit for drinking water, and 8.1 percent above 20 mg L^-1.The surveyed wells were grouped into two types based on depth and utilizat ion, that is, drinking wells(DW), about 120 to 200 meters in depth, and irrigation wells(IW), about 70 to 100 meters in depth.NO₃^--N contents of groundwater from 145 DWs and 336 IWs averaged 5.16 mg L^-1 and 5.98 mg L^-1 respectively, and 13.8% of DW and 24.1% of IW exceeded 10 mg L^-1.Nitrate contamination of groundwater in the suburbs of Beijing, such as Haidian, Fengtai and Chaoyang Districts, is much worse than that in the exurbs of Beijing, such as Shunyi, Tongzhou, Changpin, and Daxing Districts.For suburban areas, NO₃^--N content in 38.7% of DW and 52.6% of IW were above 10 mg L^-1, but for exurban areas, only 3.0% of DWs and 15.3% of IWs above 10 mg L^-1.It is confirmed that nitrate contaminated wells were mainly located in the long-term vegetable cultivation regions.In general, nitrate contamination of groundwater in Beijing is more serious than in developed countries, and hence it is necessary to take countermeasures to control nitrate pollution.

Abstract:Karst soil rocky desertification is not only a geo-ecological disaster induced by Karst geomorphy, but also a critical factor restraining social and economic development of Southwest China.Soil mechanical composition, physical features, chemical propert ies, microbial feature and chemical composition of soils were measured for studying the Karst rocky desertification.The results indicate that fine soil particles decrease propressively with soil erosion, leading to disappearance of surface soil layer and replacement of a sand layer.The absence of weathering parent material between soil and rocks makes calcareous soil unstable.Soil erosion at the rock-soil interface is a distinct character.Soil texture tends to be desertified.As a result, soil organic matter and nutrients in the surface soil layer reduce progressively and so do the soil's nutrient and moisture retention and functional diversity of the soil microbial communities.Soil formation is at the stage of chemical erosion and sand deposition.It could be concluded that rocky desertificat ion is the final result of a vicious cycle of social economic stress and environmental deterioration.

Abstract:Stationary soil-moisture-observation was carried out in Xiuwen County, Guizhou Province, which lies in the karst mountainous area of Southwest China.Based on the two year observation from June 13, 2001 to July 23, 2003, impacts of gradient and land use on soil moisture are analyzed systemically.The result shows that gradient and land use have a marked effect on soil moisture.Comparison of change in soil moisture between soils under three different kinds of land uses shows that it is the most remarkable in soil under vegetable, and there is no significant difference between bared soil and soil under wheat or corn.But in terms of effect of slope on soil moisture, surface runoff shows a decreasing order of 16°>9.5°>6.5° in gradient field while soil moisture has a decreasing order of 9.5°>16°>6.5° in gradient field.According to a preliminary analysis, the difference in soil profile structure is the potential cause.Soil profile soil moisture increases with the depth in the soil profile.In conclusion, the impact of gradient and land use on soil moisture is mostly effect ive in the soil layers above the BC layer, and is quite weak in the C layer.And the impact of gradient on moisture distribution in depth is lower than that of land use.

Abstract:In metal mining areas, mine tailings, as an accessory product, are usually stored in a big tailings dump, destroying original vegetations and seriously damaging ecological systems To restore vegetations over metal mine tailings is very difficult because they are often high in heavy metal concentrat ion, low in nutrient content and small in water retention capacity Pot experiments were conducted to investigate effects of application of natural montmorillonite and zeolite as amendments to mine tailings on ryegrass growth and uptake of Cu and Zn in this paper The results indicate that the biomass of the ground part of ryegrass did not change much but its root weight changed with the applicat ion of the two clays, respectively Chemical fertilizer was extremely necessary for ryegrass growth in the mine tailings Application of montmorillonite decreased available Zn in the mine tailings, but did not affect much available Cu; application of zeolite significantly decreased both available Cu and Zn in the mine tailings The pHs of the mine tailings decreased with the application, but did not correlate with the change in available Cu and Zn in the mine tailings Copper and Zn concentrations in ryegrass root decreased with the application of the clays However, application of montmorillonite increased Cu uptake but did not affect Zn uptake of the ground part of ryegrass in the first and the second harvest Application of zeolite did not change the Cu and Zn concentrations in the ground part of ryegrass, either.

Abstract:Ananaerobic incubation and field experiment of fertilize-rN application of different rates were conducted in the Taihu region to determine effects of fertilize-rN on soil N supply, rice N uptake and groundwater.The results show that soil N availability could be considerably enhanced after years of N-fert ilization.N content in rice and N uptake by rice increased with the N application rate, but the rate of N transferred to grain decreased.The optimum fert ilize-rN application rate ranged from N225 to 270 kg hm^-2 for rice in this region.The concentrations of both NH₄⁺-N and NO₃^--N in the surface water of paddy field rose temporarily as a result of fertilize-rN application, but they were not significantly correlated.NO₃^--N was the main form of nitrogen in the leachate from paddy field.Its concentration rose quickly arriving at a peak around 1.62~2.75 mg L^-1 within the first 7 days after the field was flooded for transplanting, and then dropped to below 0.5 mg L^-1 after 10 days or so.NH₄⁺-N concentration in the leachate seemed increasing with the N application rate and peaked at the end of the rice tillering stage, but usually remained lower than 0.2 mg L^-1 in the rest of the growing season.

Abstract:Intracellular measurement of nitrate activity in leaf cells of Chinese cabbage in vivo using double barreled nitrate selective microelectrode was reported for the first time in China These microelectrodes showed a typical log linear response to nitrate concentration from 100 mol m^-3 to 0.01mol m^-3 with a slope of 48~ 58 mV and the nitrate act ivity detectable was very low The microelectrode was characterized by a high selectivity and sensitivity of ion and a good economy compared with other intracellular measurements In addition, the in vivo method is better than the chemical analysis of the samples The detected results showed that nitrate activity in leaf cell of Chinese cabbage induced with 5 mol m^-3 nitrate for 48h fell into two different populat ions, i e 0.24 mol m^-3~10 mol m^-3 in cytosol and 20 mol m^-3~110 mol m^-3 in vacuole Since vacuolar volume accounts for 90% of a whole cell, most of the nitrate in plants is stored in vacuoles And, thus it is of great importance to study the remobilization of the nitrate in vacuoles both in increasing nitrogen use efficiency and in decreasing the nitrate content of vegetables.

Abstract:Two contrasting rice (Oryza sativa L.) cultivars, i.e.Wuyujing No.3 (salt-tolerant) and IR36 (salt-sensitive), were used for investigating effects of exogenous calcium (Ca) on antioxidant enzyme activity and lipid peroxidation in leaves of rice growing hydroponically under salt stress.The results show that content of malondialdehyde (MDA) as well as membrane permeability were enhanced under salt stress.Salt stress decreased activities of antioxidant enzymes and contents of antioxidants.Addition of Ca significantly enhanced activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) in the leaves of salt stressed rice but reduced concentration of MDA and permeability of cell membrane.Furthermore, exogenous Ca enhanced ascorbic acid (AsA) content and root activity.Treatment with higher Ca (10 mmol L^-1 Ca²⁺) was observed to have better alleviat ing effect than that with lower Ca (5 mmol L^-1 Ca²⁺) in the two contrasting rice cultivars differing in salt tolerance, but the reverse was observed in the experiment of APX activity.The degree of increase or decrease in the above mentioned parameters was smaller in salt tolerant cultivar than in salt sensitive one under single NaCl stress.The results seem to suggest that the elimination of active oxygen species (AOS) and maintenance of membrane stability accounted to some extent for the mechanisms of Ca-mediated enhancement of salt tolerance in rice growing under salt stress.

Abstract:The present paper addresses changes in uptake, transport and allocation of potassium and sodium, SOD (superoxide dismutases) activity and H₂O₂ content in leaves of Bt (Bacillus thuringiensis) transgenic cotton (Sukang 103) induced by different levels of salt stress as compared with those in its conventional parent (Sumian 12) at the early growth stage.The results showed that after receiving Bt gene the cotton increased its demand for potassium; more potassium was accumulated in shoot while the potassium content in roots was lowered as compared with the regular cotton.It seems to indicate that potassium transport ability is enhanced.On the other hands, when both regular and Bt cotton seedlings were exposed to salt stress, the ability of selecting potassium for transport from root to shoot was weakened in the Bt transgenic cotton, consequently more sodium was accumulated in the shoot and salt tolerance was lower than that in the control.Furthermore, SOD activity in leaves of the Bt cotton decreased significantly under salt stress, which might lead to reduced ability of eliminating superoxide radicals (O₂^-).Results of the research suggest that Bt cotton is more sensitive to salt stress than regular cotton and may not be suitable for cultivation in saline soils.

Abstract:Laboratory incubation experiments in constant temperature were implemented to study influence of humic-acid and fulvic-acid on fixation and release of potassium in cultivated brown soil.The results indicate that application of humic acids accelerated potassium release from the soil, showing a tendency of the rate of K release increasing with the rate of humic acid addition.After incubating at 25℃ for 21days, K release increased by 6.25% in the soil treated with 40 g kg^-1 fulvic-acid, but only by 2.26% in the soil treated with humic-acid.Application of humic acids may reduce the rate of the soil fixing extraneous K.After application of 400 mg kg^-1 K, the soils treated with humic acids differed significant from the soil in the control in Kfixation.But the effect of humic acids reducing K fixation rate was affected by how K was applied.In the treatments where humic acids-treated soils were incubated in constant temperature for 7days before application of potassium, the K fixation rates were lower than that in the treatment of applying potassium and humic acids at the same time.The effect of humic acids on fixation and release of potassium in soil was accomplished by dissolving K-bearing minerals or blocking interlayers and adsorbing K.

Abstract:Based on test ing results of topsoils, distribut ion characteristics of plant-growth elements, such as N, P, K, Ca, Mg, S, B, Fe, Mn, Mo, and Cl etc, were discussed by types of soils and rocks, elevations, degrees of slope, and vegeta-tion covering.It can be concluded that calcareous soil is the highest in content of nutritional elements such as B, Ca, Mg, Mn, Mo, N, P, and Fe; where as yellow soil the lowest in content of nutritional elements, such as Ca, Mg, K, P, S, Cl, and Fe.Purple soils are the highest in content of P, K and Cl, but the lowest in content of N, Mo and S.Parent rocks play an important role in distribution of elements in soils.In the limestone area the soils are abundant in nutritional elements except for P, K, and Cl.On the other hand, in the sandstone districts the contents of most nutritional elements in the soils are lowest, but only Ca and B higher than that of greywacke district and siltstone district respectively, and Mo lower than that of the limestone area.Among soils formed from the mudstone, siltstone, greywacke, and sandstone, soils developed from mudstone are highest in most nutrition elements, such as K, Mg, Fe, B, P, and Mn, but relatively lower in Mo and N.The contents of nutritional elements in soils developed from siltstone are higher than those in soils developed from mudstone and lower than those from sandstone.In terms of the degree of slope, the contents of N, S, Mo, Fe, Mn, and P in the purple soils increase with the decline of the degree of slope, but the contents of Ca, Mg, and K do not show such a trend.When the elevation decreases, the contents of P and S in the purple soils increase remarkably, while Mn and Mo increase somewhat, and other elements show irregular change.When the parents, climate and topography are similar, the contents of elements in purple soils are determined by the types of plantcover.Soils in the mixed forest area and tussock area contain more nutritional elements relatively, than soils in the conifer forest area.In areas with little vegetation cover, the soils are higher in S and lower in B and Ca.

Abstract:An orthogonal quadratic regression rotation combinatorial design with 4 factors, i.e.nitrogen(N), phosphor (P), potassium(K), and boron(B), was adopted in field experiments.Fert ilization models were built up and analysed for yield, oil content, oil yield and protein of yellow-seeded rape.The single factor effect analysis shows that in terms of effect of fertilization on seed yield and oil yield, the four single factor fertilizers were in the order of X₁(N)>X₂(P₂O₅)>X₄(B)>X₃(K₂O); while in terms of effect on oil content and protein, they were in the order of X₁ (N) > X₄ (B) > X₂ (P₂O₅)>X₃(K₂O) and X₁ (N)>X₄(B)>X₃(K₂O)>X₂(P₂O₅), respectively.Based on the fert ilization models for oil yield and protein, in order to get an oil yield higher than 1 000 kg hm^-2 and a protein content higher than 40% in the rapeseed cakes, the optimum fertilization rate should be recommended as N 163.7~179.2 kg, P₂O₅ 85.0~95.0 kg, K₂O 100.7~124.3 kg and B 6.7~8.3 kg per hm²; and to get a protein content higher than 45%, the fertilization rate as N 236.6~255.4 kg, P₂O₅ 80.3~ 99.7 kg, K₂O 103.2~126.8 kg, and B 8.9~ 10.3 kg per hm².

Abstract:Yellow earth, yellow rendzina and neutral purplish soil are typical soils for tobacco cultivation in Guizhou province and selected for studying community structures of microorganisms and their dynamics in the rhizosphere of flue-cured tobacco.During the growing periods of tobacco plants, the lowest count of bacteria was found at the rosette stage.Thereafter, it increased and peaked at the budding stage and then decreased till the mature stage.Actinomycetes and fungi showed a constantly increasing tendency from the rosette stage to the maturestage.The count of bacteria and actinomycetes in the rhizosphere differed between the soils, which are in the sequence of yellow earth > yellow rendzina > neutral purplish soil.In regard to the count of fungi, there existed the following tendency: neutral purplish soil > yellow earth > yellow rendzina.The microorganism population diversities and their dynamics in the tobacco rhizosphere also varied from soil to soil.In purplish soil, the number of dominant microbial populations in the rhizosphere was greater than in the other two soils, and the population diversities of bacteria and act inomycetes were even greater and more constant, suggest ing that the community structures of microorganisms in neutral purplish soil were more reasonable than in both yellow earth and yellow rendzina, which was probably related to the low incidence of tobacco bacterial wilt in the neutral purplish soil.

Abstract:The δ¹³C method, which is a new technique for researching on soil organic matter (SOM) dynamics in recent years, possesses not only virtues of the radioactive ¹⁴C labeling methods, but also some specific merits.For instance, it is nonradioactive and long-term in labeling, and is able to evenly and economically label all SOM fract ions and be carried out directly on samples collected from an experimental site.So δ¹³C method has been ut ilized extensively to study origin of SOM and its fractions, to quantify C turnover, and to investigate historical changes in C₃/C₄ vegetation.With the quick development of this method and cont inuous improvement of various analytical techniques of the δ¹³C values, the δ¹³C method displays a new vitality in studying soil processes, especially soil carbon cycling.In order to promote the application of the δ¹³C method in researches at home, a comprehensive summary is made in this article of factors affecting δ¹³C values of SOM, and applications of the method in researching on SOM at home and abroad and the δ¹³C values analytical technique.

Abstract:结皮是土壤表面普遍存在的致密层,厚约数毫米至几厘米,其表面强度较大,孔隙较细,且导水性较差^[1～3]。土壤结皮在坡面侵蚀过程中占据重要的地位,其直接导致入渗量的减少和地表径流量的增加,从而极大地增加了诱发细沟侵蚀的可能性,导致侵蚀量剧增^[2]。也有研究表明,结皮形成对土壤具有一定的保护作用,在一定程度上可以减少溅蚀量、抑制风蚀、降低土壤表面水分蒸发速率^[4,5]。土壤结皮是在物理分散力和化学分散力作用下形成,而且土壤质地是影响其形成的最重要因素。

Abstract:由富营养化导致的地表水和地下水水质的恶化是当今全球关注的主要环境问题之一。富营养化主要是由于磷在地表径流、生活污泥和流向地表水和地下水体的土壤渗滤液中的迁移。近年来随着大量的有机废弃物在土壤中的应用,磷在土壤表层和亚表层中的活动性显著增加^[1～3]。这不仅归结于有机废弃物中的有机磷和无机磷^[4,5],也归结于由植物根系所分泌的和土壤中植物残体分解所产生的可溶性有机大分子和低分子量有机酸与磷的相互作用^[6～9](1)、有机配位体与钙的络合作用^[10,11]以及有机分子对土壤表面电荷的影响等^[12]。

Abstract:在城市生态系统中,城市土壤重金属积累状况对城市绿地建设、城市区域环境质量及人类健康都有十分重要的影响^[1]。国外研究证明城市土壤中重金属元素已有不同程度积累^[2～6]。我国也有这方面的研究报道,但这些研究大都集中在研究重金属含量和单个污染物污染程度方面^[7～10],一些研究也涉及到重金属的分布^[8]、城市重金属的影响因子分析^[11]。但对城市不同功能区重金属元素的分布特性、重金属与环境之间以及重金属相互之间关系的研究报道甚少。然而这些研究又是城市土壤质量研究的基础^[1],只有认清不同重金属元素在城市各功能区土壤的地球化学过程,才能有效地控制和降低城市土壤的重金属含量和活性,提高城市土壤质量。

Abstract:随着三峡工程的顺利进行,库区的文物保护、考古发掘愈加紧迫,处于三峡库区腹地的忠县中坝遗址始得以发掘,因其文化层包含了新石器时代、夏商周时期、直到唐、宋、明、清,而被誉为地下“二十四史”。遗址延续时间之长,遗迹和遗物之丰富在中外遗址中实属罕见,可以说中坝遗址是重庆三峡库区5000a来历史的缩影。

Abstract:漂白湿润淋溶土,存在一障碍层次——白浆层,是山东省的主要低产土壤之一。小麦是该土壤上种植的重要粮食作物。影响小麦生长和产量的因素数量多,且相互关联^[1～3]。对这类问题的统计分析,以往多使用回归分析和相关分析。这些方法往往事先指定待考察的因素,对其他因素则进行严格控制^[3～6],如此得到的相互关系由于舍弃了某些因素以及固定了某些指定因素的作用而存在局限性。近年来在生物科学中应用较多的主成分分析方法为探索和阐明这类问题提供了手段^[7～12]。植物生长需要养分的支持,不同养分对植物生长的影响不同;即使同一养分,在不同的层次,影响也不同。