Sedimentary characterization of Tagus estuarine beaches (Portugal)

Background, Aim and Scope  The distribution of sediments in estuarine beaches is controlled by the interactions between sediment supply, hydrodynamic processes and human intervention. The main purpose of this study is to characterize the sediments of Tagus estuarine beaches in order to understand their origin and to contribute to a better knowledge of the Tagus estuary sediment budget. Methods  Surface sediment samples were collected across beach profiles and sand grain size analysis was performed by dry sieving. Grain size statistics for the median (d₅₀) and standard deviation (SDM) were obtained using the Moment method. This study was complemented by a qualitative evaluation of the sediment composition. Cross-shore topographic surveys were conducted for selected sampling sites. Results  Tagus estuarine beach sediments are mainly composed of quartz sand particles which are fine-grained and well sorted near the mouth of the estuary and medium to coarse-grained and moderately sorted in the inner domain. Compositional results show evidence of active anthropogenic sediment sources, especially in the coarser fractions. Discussion  The analysis of the textural and compositional characteristics of beach sediments in the inner estuarine domain is compatible with local sedimentary sources, while a marine signature is present at the mouth and inlet channel sediments. In the inner domain, differences in the sedimentary processes are represented by the textural characteristics of the sediments, such as the sorting degree and the gravel content. Sediment characteristics also reflect human intervention in the system, with the introduction of anthropogenic and allochthonous particles and the mixture of sediments from different sources. Conclusions  The sediments of the inner Tagus estuarine beaches are derived from local Plio-Pleistocene outcrops while inlet and outer estuary beaches reveal a dominant marine source. Beach textural variability observed in the inner domain is not related to wave forcing gradients, but mainly to variations in the sedimentary processes along the estuarine margins and to human intervention. Results show that the Tagus estuarine beaches depended, almost exclusively, on sediment input from local sources until the last century. With increasing human occupation, sediment transfers became dominated by anthropogenically related activities mainly connected with the occupation of estuarine margins and dredging. Recommendations and Perspectives  Further studies should extend the present level of knowledge in what concerns sand transport patterns through additional compositional and geochemical analysis, and the development of new techniques in order to allow the quantitative evaluation of the impact of human activities on the sediment budget.     

The effect of land cover/vegetation on soil water dynamic in the hilly area of the loess plateau,China

Severe soil and water loss has lead to widespread land degradation in China's loess plateau. During the past decades, a great deal of effort was made on vegetation restoration to reduce soil and water loss in the loess plateau. However, due to water shortage the efficiency of vegetation restoration was not as satisfactory as expected. As part of a vegetation restoration project, we conducted research aiming to understand the relationship between vegetation pattern and soil water dynamics. The goal was to find vegetation types appropriate for the loess plateau with scarce water resources. In 1986, fifteen plots of land were planted with five vegetation types: pine woodland, shrubland, sloping cropland, alfalfa and semi-natural grassland. Soil water content, runoff, soil erosion were measured for each plot. Environmental variables, such as rainfall, evaporation and temperature, were recorded simultaneously by an automated meteorological station. The relationship between land cover pattern and soil water dynamic was evaluated by using statistical models. We found that: (1) soil water loss occurred during the growing season, and it reached the maximum in the second half of July; (2) soil water was not fully replenished from rainfall during the rainy season; (3) pine woodland induced the largest water loss to surface runoff, followed by sloping cropland, alfalfa, semi-natural grassland and shrubland; the poor capability of pine woodland for water conservation may be attributed to soil compaction and poor ground coverage under the tree; (4) in most cases, soil water of the five vegetation types was low except for shrubland and semi-natural grassland where it was moderate-high during a few periods. These conditions inhibit sustainable vegetation growth in the semi-arid loess hilly area of the loess plateau, China.     

基于叶面积指数（LAI）的小麦变量施氮模型研究

为探讨基于叶面积指数变化的小麦变量施氮技术,依据养分平衡原理和"作物-土壤-环境-技术"整体原则,采用土壤空间信息数据与小麦需氮量和各生育阶段叶面积指数相结合的方法,设计了小麦播前施氮总量和播后精确追氮的数量模型.根据拔节期和抽穗期小麦的长势,对施氮量的初值进行订正,确定小麦的最适追氮量.在河南郑州市和鹤壁市两地的试验验证结果表明:小麦产量模拟值与实测值间的相关系数分别为0.7799和0.7169,达显著水平.与传统施肥技术相比,在相同产量下,使用模型后每公顷施氮量减少43.5 kg.该研究提出的基于模型的变量施氮技术,可以兼顾天气、地力和作物长势三方面因素,最终实现小麦的精确施氮,对促进精确农业的发展具有重要意义.     

农村社区动态交互式三维虚拟漫游系统的实现

为了提高农村社区规划建设的可视化宣传效果,为用户提供直观的操作工具辅助实现农村社区规划建设信息的管理,提出了一种基于虚拟建模现实语言(VRML)的农村社区动态交互三维虚拟漫游系统的实现方法.在本方法中,农村社区三维虚拟场景是通过社区布局VRML建模、社区纹理数据和层次化数字高程模型(DEM)数据的VRML表达两个过程建立;通过将社区中建筑物、树木等对象实体设置为具有三维坐标和属性集的锚点,并利用Java与虚拟现实建模语言对锚点的操作实现空间定位、距离分析、三维虚拟场景属性和空间位置查询等实时动态交互过程.该方法已经在北京房山八十亩地村网络虚拟漫游系统的实现中得到应用,应用效果表明系统仅需在带宽100 kB网络条件下即可快速响应用户的各种操作请求,适合在大都市周边农村地区大规模推广应用.     

Soil compaction and forest floor removal reduced microbial biomass and enzyme activities in a boreal aspen forest soil

Soil enzymes are linked to microbial functions and nutrient cycling in forest ecosystems and are considered sensitive to soil disturbances. We investigated the effects of severe soil compaction and whole-tree harvesting plus forest floor removal (referred to as FFR below, compared with stem-only harvesting) on available N, microbial biomass C (MBC), microbial biomass N (MBN), and microbial biomass P (MBP), and dehydrogenase, protease, and phosphatase activities in the forest floor and 0–10 cm mineral soil in a boreal aspen (Populus tremuloides Michx.) forest soil near Dawson Creek, British Columbia, Canada. In the forest floor, no soil compaction effects were observed for any of the soil microbial or enzyme activity parameters measured. In the mineral soil, compaction reduced available N, MBP, and acid phosphatase by 53, 47, and 48%, respectively, when forest floor was intact, and protease and alkaline phosphatase activities by 28 and 27%, respectively, regardless of FFR. Forest floor removal reduced available P, MBC, MBN, and protease and alkaline phosphatase activities by 38, 46, 49, 25, and 45%, respectively, regardless of soil compaction, and available N, MBP, and acid phosphatase activity by 52, 50, and 39%, respectively, in the noncompacted soil. Neither soil compaction nor FFR affected dehydrogenase activities. Reductions in microbial biomass and protease and phosphatase activities after compaction and FFR likely led to the reduced N and P availabilities in the soil. Our results indicate that microbial biomass and enzyme activities were sensitive to soil compaction and FFR and that such disturbances had negative consequences for forest soil N and P cycling and fertility.     

Genetic characterization of a collection of chayote, <Emphasis Type="Italic">Sechium edule</Emphasis> (Jacq.) Swartz,in Costa Rica by using isozyme markers

We established protocols for the analysis of genetic diversity in chayote (Sechium edule) by using isozyme markers, thereby determining the level of genetic diversity present in 42 accessions of chayote from Costa Rica. We obtained clear and reproducible zymograms for eight enzyme staining systems: PGM, 6-PGD, PGI, IDH, MDH, SOD, SKD, and EST, and were able to score 14 putative loci. Eight of the 14 loci examined were polymorphic. We found 35 distinct multilocus genotypes among these accessions. Five of these multilocus genotypes were homozygous for all loci. In addition, our data also revealed that most of the multilocus genotypes (24) were heterozygous for only one of the eight loci, and the rest were heterozygous for two or three loci (9 and 4 accessions, respectively). Seven multilocus genotypes were found in two different accessions. Dice similarity coefficient was used to study the relationship between accessions. This analysis, based on the presence and absence of alleles, revealed that accessions collected in the same location seldom shared the same multilocus genotype. The value of isozyme polymorphisms as tools to continue studies on the characterization of chayote is discussed.     

受污农田中农作物对重金属镉的富集特征研究

采用湿法消化法研究了浙江省不同地区农田污水灌溉后水体、土壤和多种农作物各器官的镉含量,分析了土壤污染状况及农作物对重金属镉的富集特征。结果表明：污水和受污土壤镉含量极显著相关（R^2=0．617,P〈0．01）。不同农作物对镉的吸收程度不同,富集系数为紫云英〉水稻〉大豆〉大麦〉玉米〉小麦。未受污染农作物和受污农作物根系及地上部镉含量差异明显,但镉富集系数差异不明显。同一农作物不同器官对镉的累积规律为根系〉茎叶〉果实。不同农作物果实的富集系数为紫云英〉大麦〉大豆〉水稻〉小麦〉玉米。对几种农作物富集系数和吸收系数的比较发现,玉米和小麦根系及茎叶等营养器官富集镉的能力较强,但果实富集量却很低。6种农作物对镉的转移系数为玉米〉大麦〉紫云英〉小麦〉大豆〉水稻,且转移系数介于0．50～0．95之间,说明这几种农作物均对镉有很好的耐性。     

不同降雨强度对营养盐垂向迁移过程和淋失量的影响

云南抚仙湖流域农田面源污染日益严重,土壤污染物主要随地表径流进入湖泊,使湖泊受到污染。但目前的现场观测表明,农田区浅层地下水也已受到污染,地下水已成为污染物输移的路径之一。通过四组不同降雨强度作用下的室内土柱试验模拟土壤污染物向地下水的淋失迁移量,对降雨入渗过程中总氮、总磷、铵态氮和硝态氮的垂向迁移过程进行了分析,通过分时段处理来对各组实验中营养盐累积淋失量进行了计算。结果表明,硝态氮的垂向迁移能力和出流浓度均大于铵态氮,总氮和总磷的累积淋失量与累积降雨量呈自然对数关系;降雨强度对总氮的淋失作用明显,对总磷淋失量的影响则相对较弱。实验结果有助于揭示抚仙湖流域降雨作用下农田土壤中污染物的垂向迁移过程及其对农田浅层地下水的污染机制,并为污染物垂向迁移的数学模拟提供数据基础。     

电渗析技术在大豆低聚糖溶液脱盐上的应用

从甜浆中提取的大豆低聚糖粗提液中含有很多的盐类,影响糖液的纯度。该试验通过离子交换膜辅助的电渗析法对大豆低聚糖模拟溶液进行脱盐处理,确定了较好的试验操作参数。试验结果表明:电渗析法对大豆低聚糖模拟液进行脱盐是可行的,且脱盐效果较好,脱盐率达到96.07%;该试验条件下较佳的工作电压为20 V,流量为60 L/h,样品稀释倍数为15倍。通过以上条件处理后,大豆低聚糖的保留率达到83.82%。     

GIS在中国土壤侵蚀定量研究中的应用

土壤侵蚀定量研究一直是土壤侵蚀学科的热点和难点问题,GIS在我国土壤侵蚀定量研究已有20年之久,回顾和总结过去的研究成果对于今后更好地开展研究工作具有重要意义。本文系统地分析和总结了GIS在我国土壤侵蚀信息管理、土壤侵蚀测报和土壤侵蚀模型等定量化研究中应用的现状与进展,针对目前研究中存在的问题,探讨了GIS在我国土壤侵蚀定量研究和应用工作中的展望。