The Application of Artificial Neural Networks for the Prediction of Water Quality of Polluted Aquifer

From hydrocarbon reservoirs, beside of oil and natural gas, thebrine is also produced as a waste material, which may bedischarged at the surface or re-injected into the ground. Whenthe wastewater is injected into the ground, it may be mixed withfresh water source due to to several reasons. Forecastingthe pollutant concentrations by knowing the historical data atseveral locations on a field has a great importance to take thenecessary precautions before the undesired situations arehappened.The aim of this study is to describe Artificial Neural Network(ANN) approach that can be used to forecast the future pollutantconcentrations and hydraulic heads of a groundwater source. Inorder to check the validity of the approach, a hypotheticalfield data as a case study were produced by using groundwatersimulator (MOC). Hydraulic heads and chlorine concentrationswere obtained from groundwater simulations. ANN was trained byusing the historical data of last two years. The future chlorineconcentrations and hydraulic heads were estimated by applyingboth the long-term and the short-term ANN predictions. Anapproach to overcome the effects of using the data of a singlewell was proposed by favouring the use of data set for aneighbour well. The higher errors for the long-term ANNpredictions were obtained at the observation wells, which wereaway from an injection well. In order to minimise the differencebetween the results of long-term ANN approach and flowsimulation runs; the short-term prediction was applied. The useof short-term prediction for the wells away from an injectionwell was found to give highly acceptable results when thelong-term prediction fails. The average absolute error obtainedfrom the shortterm forecasting study was 3.5% when compared to18.5% for the long-term forecasting.     

Sources of Riverine Litter: The River Taff,South Wales,UK

Riverine litter occupies a spatial and temporal position in any systematic analysis of river systems and is a problem that is increasing in scale. Quantifiable source factors of litter in the river Taff, South Wales, UK, system were found to be mainly two – sewage inputs through combined sewer overflows (CSO) and fly tipping. The greatest inputs of sewage derived solids were introduced to the river by malfunctioning CSO, the most numerous single component being sanitary towels. Whilst sewage-derived material constituted approximately 23% of all items on the river Taff, large quantities of waste, especially plastic sheeting, originated from fly tipping sites.     

Managing contaminated sediments

While remediation and storage of contaminated dredged materials is a key issue at harbour sites, there is another type of sediment pollution problem, which mainly originates from large-scale dispersion of contaminants in flood-plains, dike foreshores and polder areas. In recent years, catastrophic cases of sediment contaminations have occurred in connection with the failure of tailing dams from mines. Unlike problems related to conventional polluted sites, the risks here are primarily connected with the transporting and depositing of contaminated solids in a catchment area, especially in downstream regions. A special example demonstrating the dispersion of highly contaminated sediments in a large catchment area will be shown from the so-called Chemistry Triangle of the upper Elbe River system, Germany. The Spittelwasser area, situated there, was chosen by the organisers of the international conference ConSoil 2000 for a case comparison and four expert teams from Denmark, Germany, the Netherlands and the UK were invited to participate in this Case Study. Evaluation of the plan was done by members of the networks of NICOLE (Network for Industrially Contaminated Land) and CLARINET (Contaminated Land Rehabilition Network). In the study of the German team, five major groups of technical measures have been identified by the environmental authorities to be discussed in relation to the Spittelwasser case or for similar problem solutions in contaminated flood-plain areas. The team came to the conclusion that none of these techniques would be applicable as an individual measure. Instead, a stepwise approach combining different monitoring techniques and remediation measures was proposed. These would include point excavations of critical material, promotion of plant growth as an element for stabilising the soil and flood sediments, as well as the installation of sediment traps. At the Spittelwasser site, investigations are planned on the effects of natural attenuation processes of organic and inorganic contaminants in flood-plain sediments and soils. In the practice of this concept, non-destructive, ‘intrinsic’ bonding mechanisms and their temporal development have thus far found much less recognition compared to destructive processes such as biological degradation. Yet these so-called ‘diagenetic’ effects, which apart from chemical processes involve an enhanced mechanical consolidation of soil and sediment components by compaction, loss of water, and mineral precipitations in the pore space, may induce a quite essential reduction of the reactivity of solid matrices [see Part I ‘Improving Chemical and Biological Criteria’ (JSS - Journal of Soils and Sediments, Vol 1, No 1, pp 30-36)]. Part IV ‘Subaqueous Storage/Capping of Dredged Material’ will be published in JSS No. 4 (December issue).     

Pollution of quaternary cover on aquafers of eocene chalk in Ramat Hovav Industrial Area in Israel

Ramat Hovav in the Northern Negev of Israel was selected as a site for an industrial park because it had been believed to have a potential capacity to absorb in the loess layer large amounts of hazardous chemical waste liquid and solid materials. The lithology of this site is composed of calcareous loess, sand dunes and underlying limestones. Its soils are loessial serozems, brown lithosols, sandy regosols and arid brown soils. The geomorphology includes specific forms of the Negev desert, such as differentiated relief, slightly dipping level structures, ‘V’ shaped canyons, parabolic and sief sand dunes. The hypothetical time span required to totally fill the pore space in the loess, in the total area draining the site selected for study, is more than 400 yr. The problem lies in the ability of the rock formations to act as conduit and storage for the toxic waste in such a way that will protect the inhabitants from the toxic dangers. Microstructural data are lacking on the 130 m between the Eocene saline water chalk aquifer that lies immediately below the loess, and the Cenomanian meteoric water limestone and dolomite aquifer below. Outcrops of the Eocene chalk, however, do show fractures which, if present also in the buried Eocene rocks, may serve as passages for quick leakage of the waste liquids into the underlying rocks.     

风电场建设对周边扰动区域土壤养分和植被的影响

研究了风电场的建设对周边扰动区域土壤养分和植被的影响。结果表明:风电场的建设增加了扰动区域土壤容重、pH和总孔隙度,降低了土壤电导率、含水量和全盐,同时也降低了植被生长各指标和土壤养分（除了土壤全磷）等;在扰动区域（0~3 km）,植被生长各指标和土壤养分均随远离风电场距离的增加而增加,距离风电场4 km时,植被生长各指标和土壤养分基本与未扰动区域达到一致,初步表明了风电场对于植被和土壤养分的影响范围均在方圆3 km以内;风电场扰动区域土壤微生物量的变化幅度和变异系数最大,说明风电场对土壤微生物量的空间变异影响较大;风电场扰动区域和非扰动区域土壤养分均随土层深度的增加而逐渐降低趋势,表现出明显的“表聚性”,而土壤深层（40—60 cm）未扰动区和扰动区土壤养分基本一致,表明了风电场的建设并没有改变土壤养分的垂直分布特征,也并未影响深层土壤养分含量;风电场未扰动区域植被与土壤因子相关性基本与扰动区域相一致,表明风电场对周边区域植被和土壤均有影响,而此影响具有同等的重要性,也即同等程度下影响了植被和土壤因子,同时也体现了植被和土壤因子的互作效应。     

Effects of dredging operations on sediment quality: contaminant mobilization in dredged sediments from the Port of Santos, SP, Brazil

Background, aim, and scope  

Contaminated sediments are a worldwide problem, and mobilization of contaminants is one of the most critical issues in environmental risk assessment insofar as dredging projects are concerned. The investigation of how toxic compounds are mobilized during dredging operations in the channel of the Port of Santos, Brazil, was conducted in an attempt to assess changes in the bioavailability and toxicity of these contaminants.     

Forest operations and environmental protection

Increased mechanisation in forestry usually means increased traffic over the ground, which also is a substrate for growth. Soil compaction, rut formation, and damage to stems and roots may all result in growth reduction. To reduce soil disturbance and tree damage, smaller machines or machines with less ground pressure must be considered. Today the traffic may cover 10–30% of the site area. This is mainly due to skidding during clear-felling and thinning. If present trends of heavy mechanisation continue, in the future there could be as many as six machine entries onto the site by the time a stand has reached an age of 50 years. Rut formation from forwarders and skidders is a problem. Harvesters seem to cause minor problems. The engine torque powering the driving wheels adds considerably to the influence of the total weight of the vehicle on the ground. High traction forces and slipping may contribute twice as much to soil disturbance as the vehicle ground pressure. When designing forest machinery for transportation of timber the payload itself is the most complicated problem. During the XIX World Congress of the International Union of Forestry Research Organisations (IUFRO) in Montreal, Canada, 1990, a Project Group on Forest Operations and Environmental Protection was established within IUFRO Division 3. From the author's point of view, concern about biodiversity is not taken into account through single-track and profit-oriented forestry in some areas and total preservation in other areas. It is the manifold of different ways of forestry that is the answer to sustainable development and conservation of biodiversity.     

Managing contaminated sediments

Remediation techniques on contaminated sediments are generally much more limited than for most other solid waste materials, except for mine wastes. The widely diverse contamination sources in larger catchment areas usually produce a complex mixture of contaminants that is more difficult to treat than an industrial waste. In the first two chapters, additional information will be presented onin- situ treatment methods, which were the central topic in the Spittelwasser Case Study (JSS - Journal of Soils and Sediments, Vol. 1, No. 3, pp. 181–187), and on the development of ecologically sound dredging and processing techniques, where practical applicability had to be demonstrated as part of an integrated remediation chain. In the latter respect, mechanical separation of less strongly contaminated fractions may be a useful step prior to the final storage of the residues (chapter 2, Treatment of Strongly Contaminated Dredged Materials) For most sediments from maintenance dredging, there are more arguments in favor of ‘disposal’ rather than ‘treatment’ (chapter 3, Subaqueous Storage and Capping). Consideration about the comparative assessment of the two basic management options ofin- situ capping and dredging followed by sub-aqueous disposal are discussed on a legislative, economic and technical-environmental basis. The concept of capping of contaminated sedimentsin- situ has been developed in the last two decades as an ecologically sound and economic alternative to more costly remediation techniques. The main characteristics are related to the passive character of this concept, which minimizes labor and process costs. Mechanisms of contaminant retention in sediment caps is discussed with special regard to the chemical isolation component. From this consideration, the development of the active barrier concept is derived that denotes the use of reactive additives in capping layers to chemically bind one or more contaminants specifically.     

Field Investigation of Controlling Acid Mine Drainage Using Alkaline Paper Mill Waste

To verify in situ laboratory test results for the control of acid mine drainage using alkaline paper mill waste, five demonstration cells were built on the Ascot mine site in Sherbrooke (Québec, Canada). A monitoring program was set up to record temperature, leached water quality, oxygen concentration and electrical conductivity.Monitoring results showed that mixing mine residueswith alkaline paper mill waste and covering mine residues with paper mill waste allows an efficient control of acid mine drainage. The paper mill waste cover generates an alkaline front which results in metal precipitation as hydroxides. Also, an increase in pH results in an inhibitionof bacterial catalytic activity. Chemical analyses conducted on the collecting water shows a high reduction of leachingmetals to under ground water. Moreover, a significant reduction of diffusion of oxygen to the mine residue is observed.     

基于层次分析法和模糊综合评价的沼气工程技术筛选

不同沼气工程技术对地域自然条件、环境制约条件、原料种类等因素的适应性有较大差异,科学客观的沼气工程技术筛选方法,是保证沼气工程长期稳定发挥其最大能效的重要基础。该文提出了基于层次分析法(analytic hierarchy process,AHP)和模糊综合评价的沼气工程技术筛选方法和决策流程,构建了沼气工程技术筛选的指标体系;以领域专家实地调查结果为基础,通过AHP法获得沼气工程技术筛选不同指标的权重,然后采用模糊综合评价方法对沼气工程技术进行排序。利用该方法筛选的结果与武汉地区的实际运行效果一致。采用AHP和模糊综合评价方法相结合解决复杂的多因素决策问题,既能克服AHP指标不易量化的主观性,又能避免模糊综合评价方法对指标权重的忽视,可为沼气工程技术筛选提供科学方法。     

Comparing Deterministic and Probabilistic Risk Assessments. A case study at a closed steel mill in southern Sweden (7 pp)

Background, Aims and Scope   Contaminated land is a high priority environmental problem in most of Europe and North-America. Sweden is no exception and generic guideline values have been developed for the initial assessment, but site-specific assessments are also needed. The generic guideline values are not applicable when the exposure conditions are different from the typical Swedish conditions or when the site contains a particularly sensitive ecosystem. The Swedish guideline values have, like in many other countries, been set by using deterministic point estimates for all variables and constants in the used multimedia model. The same approach is common also for site-specific assessments, and a limitation is that it fails to quantify variability and uncertainty. Probabilistic risk assessment provided a method to deal with this problem. Variability and uncertainty in the input parameters (variables or constants) are described by probability distributions, and likewise the output (risk or exposure) is presented as a probability distribution. A substantial number of probabilistic risk assessments for contaminated land at sites in North America, Europe and Asia have been published. However, an extensive review of the literature did not identify any study where probabilistic risk assessment was applied to a site contaminated by an iron or steel industry. Here we will describe such a case, where we have compared a deterministic point estimate with a probabilistic risk assessment for six elements and benzo[a]pyrene. Methods   The site had different metallurgical plants in operation for more than 100 years. Most parts of the steel mill were closed by the mid 1980s, and today the site is used by small-sized enterprises. The soil is contaminated with metals from the previous industrial operations. The present owner plans to develop the site and has therefore initiated extensive investigations of soil contamination. Sixty-two soil samples collected between 1997 and 2000 provided a good coverage of the whole site, and were analyzed for the content of different elements and polycyclic aromatic hydrocarbons (PAH). The exposure assessments were focused on six elements with high concentrations compared to the generic guideline values; arsenic (As), lead (Pb), cadmium (Cd), chromium (Cr), copper (Cu) and zinc (Zn). In addition, benzo[a]pyrene was included due to the high toxicity and comparatively high concentrations. Variability and uncertainty were characterized in a Monte Carlo simulation of exposures (10 000 iterations), and the exposures were evaluated with two land use scenarios; less sensitive use and sensitive use. Results and Discussion   The deterministic point estimates and the probabilistic estimates of the 95th percentile are in approximately the same ranges in the scenario of less sensitive land use. It is only the exposure for arsenic that is slightly above the toxicological reference value (TRV) in the deterministic assessment. In the probabilistic assessment, the exposure for all elements is below the TRV. The results for sensitive land use are applicable to a scenario where the site is developed for general housing. The deterministic point estimates and the probabilistic estimates of the 95th percentile are also here in approximately the same ranges, but the exposure exceeds the TRV for arsenic, cadmium and lead. Drinking water, vegetables grown on site and soil ingestion are the major exposure pathways for this scenario. In this assessment, the estimated intake distributions are applicable to a randomly selected individual. The probability distributions used here to characterize the different soil parameters are typically representing both variability and uncertainty, and the same is true the majority of the exposure variables. We therefore decided not to attempt to separate variability and uncertainty at this stage, but with additional data from a more in-depth site investigation it might be possible to achieve this. Conclusions and Outlook   To the best of our knowledge, this study is the first report on a probabilistic risk assessment on a former iron and steel works site. The materials handled by this industry were less toxic than for many other metallurgical operations, but contaminants may still severely limit the options for future land use. This case study shows that probabilistic exposure estimates for a set of soil contaminants can be quite similar to deterministic point estimates. The main difference is instead to be found in the additional information obtained with the probabilistic assessment. The sensitivity analyses show pathways and input variables that contribute most to variations in the total intake of each contaminant, e.g. dermal contact and ingestion of soil, vegetables and drinking water. This information can be used both in the planning of future land use and for active measures to reduce current exposure. The probabilistic assessment also provides information on the magnitude of exposure and the margin of safety. This information may facilitate risk communication between decision-makers and stakeholders. The presentation of results from probabilistic risk assessments is only briefly discussed in the literature and here we see a need for research and opportunities for enhancement. The choice of data analytical tools may then be of importance, since more complex multimedia models are rather difficult to decipher when implemented within traditional spreadsheet software. Some of the research needs are identified here and in a previous review article in this journal.     

The Effect of Yatagan Thermal Power Plant (Mugla,Turkey) on the Quality of Surface and Ground Waters

Yatagan thermal power plant consumes annually 5.4 million tons of coal and the annual production capacity of the plant is 3.78 billion KWh. The thermal power plant uses 15 000 tons of coal and discharges 5000 tons of fly and bottom ash daily to the disposal site. The waste is dumped using conveyer belts and pipes into a dam founded on metamorphic rocks. However, as the waste hills formed, the water level reached the karstic marbles that over lay schist. Water leaches through dried waste hills and karstic marbles, ultimately adversely affecting the quality of ground and surface waters. The concentrations of major and minor ions were determined on water samples taken at 2 points in the dam, 5 points in surface water and at 21 points in groundwater located in the vicinity of the waste disposal site, total of 28 samples, for three years. The chemical analyses revealed that the concentrations of Ca²⁺, Cd²⁺, Pb²⁺, Sb²⁺ and SO₄ ^2- in some samples exceed the Turkish Drinking Water, the U.S. EPA and WHO limits. Isotope analyses were carried out to determine the origins of waters, which showedthat contamination is taking place in the vicinity of the waste disposal site.     

Recycling Newsprint on Agricultural Land with the Aid of Poultry Litter

The large volume of cellulose products, primarily newsprint and yard waste, that are disposed of in landfills and the resistance of these products to decomposition led to an evaluation of the disposal of ground newsprint on agricultural land. A field study was conducted with cotton to evaluate the effects of trenching and mixing the excavated soil with ground newsprint and/or poultry litter. Decomposition rate of newsprint and potential for environmental contamination were investigated in a Cahaba-Wickham-Bassfield sandy loam (Typic Hapludult) soil. The experimental variables included different ratios of soil, ground newsprint, and/or poultry litter applied on the soil surface and in trenches 0.61 m or 1.22 m deep. When ground newsprint and excavated soil were mixed without adjusting the C:N ratio of the backfill, the newsprint was still present seven months after application. However, adjusting the C.N ratio of the excavated soil and ground newsprint with poultry litter provided the nitrogen necessary to completely decompose the ground newsprint within seven months. Soil surface application of ground newsprint required adjusting the C:N ratio to control the occurrence of plant pathogenic organisms. Extractable soil nutrients were increased when poultry litter was added, including P and K which are of concern with respect to surface and groundwater contamination. Extractable Zn, Cu, and Mn levels were increased by the addition of poultry litter, but their levels were in the ranges that most row crops will tolerate. The metals Cr and Pb, found in some printer's ink, may be of concern if repeated application of newsprint is made to the same site. Soil organic matter content was increased from 11.9 g kg-1 to 23.8 g kg-1 in the 50:40:10 backfill mixture of soil, newsprint, and poultry litter seven months after application.     

Exploring Ground Vegetation Change for Different Deposition Scenarios and Methods for Estimating Critical Loads for Biodiversity Using the ForSAFE-VEG Model in Switzerland and Sweden

The ForSAFE-VEG model was used to investigate the impacts of climate change and air pollution scenarios on soil chemistry and ground vegetations composition. In particular, the model involves a ground vegetation model incorporating plant changes to ambient site conditions in terms of climate and chemistry, but the model also incorporate competition between the different plant groups. The model was validated against observed values and reproduced observations of tree growth, soil chemistry, and ground vegetation compositions to satisfaction. The results show that the ground vegetation reacts strongly to changes in air pollution, in particular nitrogen as well as to climate change with major shifts in plant composition. A procedure for estimating critical loads for nitrogen, using ground vegetation biodiversity as criterion, was tested and the method seems operable. It suggests that if we want to protect the present biodiversity of the ground vegetation, this will face significant difficulties because of permanent climate change that induced changes in the ecosystem. We conclude that the reference state for ground vegetation biodiversity is rather to be sought for in the future, hopefully using models, than in the past or present.     

基于穷举法的雨水管渠设计流量计算方法研究

[目的]找出雨水管渠设计流量常用计算方法——面积叠加法和流量叠加法中存在的问题,对计算方法进行改进,使雨水设计流量计算结果更加合理。[方法]从下游管段暴雨强度的计算入手,对流量叠加法进行改进,同时提出基于穷举法的最大流量法。[结果]实例计算表明,除起始管段外,改进后的流量叠加法的各管段设计流量均小于面积叠加法,最大流量法各管段设计流量较面积叠加法平均增长7.0%,最大增长13.0%。[结论]运用最大流量法对雨水管渠进行设计,计算结果更合理,更安全,对缓解城市内涝具有重要意义。     

竖直埋管换热器热响应半径计算方法

随着能源压力的日益增大,世界各国都十分重视可再生能源的利用与开发,地源热泵技术作为一种清洁、高效的可再生能源,近年得到了较快的发展。该文利用无限长线热源传热计算模型,讨论了介质内过余温度场的分布特性。结果表明：介质内温度响应在孔壁处最大,随离孔壁距离的增加呈指数衰减,随时间的增加而增大;热传播区域随时间的增加而增大,随介质的热扩散系数的增加而增大。针对工程中群埋管换热器情况,利用叠加原理计算群埋管的孔壁温度,定义换热器的热响应半径为其他钻孔引起的过余温度影响系数≤5％时相邻钻孔中心线之间的垂直距离。在大量计算分析基础上,提出了竖直埋管换热器热响应半径计算方法。计算结果表明该文方法具有较好的计算精度,竖直埋管换热器的热响应半径随岩土热扩散系数增大而增大,随持续运行时间增加而增大,随钻孔排数增加而增大,随着钻孔孔径增大而增大;钻孔布置方式不同对钻孔热响应半径的影响较明显,相同布置方式下钻孔直径对其热响应半径的影响较小。针对工程中常见的115和135 mm 2种孔径,绘制了不同岩土介质下钻孔单排、双排和三排以上布置时热响应半径-运行时间的关系曲线。工程算例表明该文方法简单方便,为工程设计提供了便利。     

Prolonged Testing of Metal Mobility in Mining-Impacted Soils Amended with Phosphate Fertilisers

The aim of the study was to determine whether the application of superphosphate fertiliser to soils contaminated with mine wastes can inhibit metal and metalloid mobility (Cu, Pb, Zn, Cd, Fe, Mn, As, Sb) in the long term. Contaminated soils contained sulfide- and sulfate-rich waste materials from the Broken Hill and Mt Isa mining centres. Results of long-term (10 months) column experiments demonstrate that fertiliser amendment had highly variable effects on the degree of metal and metalloid mobilisation and capture. Rapid release of metals from a sulfate-rich soil showed that phosphate amendment was ineffective in stabilising highly soluble metal-bearing phases. In a sulfide-rich soil with abundant organic matter, complexing of metals with soluble organic acids led to pronounced metal (mainly Cd, Cu and Zn) release from fertiliser-amended soils. The abundance of pyrite, as well as the addition of fertiliser, caused persistent acid production over time, which prevented the formation of insoluble metal phosphate phases and instead fostered an increased mobility of both metals and metalloids (As, Cd, Cu, Sb, Zn). By contrast, fertiliser application to a sulfide-rich soil with low organic carbon content and a sufficient acid buffering capacity to maintain near-neutral pH resulted in the immobilisation of Pb in the form of newly precipitated Pb phosphate phases. Thus, phosphate stabilisation was ineffective in suppressing metal and metalloid mobility from soils that were rich in organic matter, contained abundant pyrite and had a low acid buffering capacity. Phosphate stabilisation appears to be more effective for the in situ treatment of sulfide-rich soils that are distinctly enriched in Pb and contain insignificant concentrations of organic matter and other metals and metalloids.     

Localized Enrichment of PCB Levels in Street Dust Due to Redistribution by Wind

As part of a project to identify PCB sources in combined sewer overflows discharging to the Buffalo River, NY, nine street and two unpaved aggregate parking lot dust and dirt samples were collected and analyzed for selected PCB congeners and total PCBs. Without exception, the dust and dirt samples had greater concentrations associated with the higher-chlorinated homologue groups. PCB-congeners 153, 138, 101, 118, and 180 contributed >50% of the total PCBs mass in each sample, suggesting contamination with Aroclors 1254 and 1260. Total PCB concentrations for the dust and dirt samples ranged between 90 and 1700 ng g^-1. Samples with the highest concentrations were located across the street and downwind from an industrial lot that had been remediated for PCB contamination in 1988. The industrial lot had been contaminated with Aroclors 1254 and 1260, indicating that contaminated soil had been locally redistributed through natural and vehicle-generated wind. Calculations based on the particle size of the street dust confirm the possibility of wind-induced redistribution. Street and aggregate lot dust and dirt potentially contribute to Buffalo River PCBs loadings through combined sewer overflows and stormwater runoff. Best management practices such as more frequent street sweeping may be useful in reducing these loadings.     

考虑地表粗糙度改进水云模型反演西班牙农田地表土壤含水率

土壤含水率是农业、环境、气象等领域进行建模的重要参数。该研究将微波遥感与光学遥感相结合,利用Sentinel-1数据交叉极化比及变换土壤调节植被指数对地表粗糙度进行估计,构建了一种改进的水云模型(modifiedwatercloud model, MWCM)。分析将NDVI、NDWI和NDWI1725,2200等植被指数作为植被冠层含水率时,水云模型(water cloud model,WCM)及MWCM农田地表土壤含水率的反演精度。结果表明:从总体精度上来看,MWCM的反演精度优于WCM。在不同植被覆盖度情况下:当植被覆盖度为中、低程度(NDVI0.5),MWCM具有较高的反演精度;在较高的植被覆盖度情况下(NDVI≥0.5),WCM与MWCM的反演精度较为接近。MWCM可有效的建立微波后向散射系数与地表土壤水分的关系,提高土壤含水率反演精度,为各种地表覆盖类型的土壤含水率反演提供研究思路及理论支持。     

Experimental determination of climate‐change effects on above‐ground and below‐ground organic matter in alpine grasslands by translocation of soil cores

We used the soil‐core translocation method to investigate the effect of increased temperature on above‐ and below‐ground phytomass and organic matter in cool alpine areas. The translocation of undisturbed soil cores from a high alpine site (2525 m a.s.l.) to an alpine site near the timberline (1895 m a.s.l.) achieved an effective artificial warming of 3.3 K. From a methodological point of view, the translocation of soil cores was performed successfully. Soil cores moved to a new site at the same altitude showed no change in above‐ and below‐ground vegetation, bulk density, and soil skeleton. At both sites, soils were Haplic Podzols with a similar chemistry and clay mineralogy. At the lower elevation site, however, podzolization processes seemed to be more pronounced. As a consequence, the translocation of the soil cores probably led to a disturbance of the actual steady state that had been established after about 10,000–13,000 years of soil formation. This might have affected the adaptability of the vegetation system. Therefore, it cannot be fully excluded that the experimental design influenced the results. Translocation of soil cores from a very cool to a warmer site led to a distinct decrease in above‐ground phytomass (about –45%) over the experimental period of two years. Below‐ground phytomass significantly decreased (up to –50%) in the topsoil (0–5 cm) after artificial warming. Possible mechanisms are that roots reduced photosynthesis and hence C flow below‐ground, a reduction of soil moisture that would have led to root death (not a very probable cause, however) or an abrupt change in the radiation duration and flux which affected root growth (also not very probable). Fast climate change exceeded the ability of the above‐ground and below‐ground phytomass to adapt quickly. Whether the decrease in phytomass was a short‐term or a long‐term response to climate warming remains uncertain. Based on a gradient study (climosequence at the same locality), we hypothesize that the decreased plant productivity might be a short‐term effect.