Methylmercury in ambient air. Method of determination and some measurement results

When air containing CH₃HgY (Y stands for a monovalent anion) is bubbled through pure water (MQ), part of the airborne CH₃HgY, depending on the actual distribution constant (air/water), will be retained in the liquid phase. The resulting concentration, although usually very low, is now in many cases possible to determine, using the very sensitive analytical procedure developed by Bloom and Fitzgerald (1988). By means of an evaluation method, described in this paper, the concentration data, obtained in this way, can be used to give the average original concentration of CH₃HgY in the air which had entered the bubbler and its distribution constant (air/water) as well.     

Physiological responses of soybean (Glycine max L. Merr) to simulated acid rain and ambient ozone in the field

Physiological processes in field-grown soybean (Glycine max L. Merr. 'Davis’) to determine if plant responses were altered by simulated acid rain and if the responses to acid rain were modified by the presence of gaseous pollutants. Applications of simulated acid rain (pH 3.2, 4.2, and 5.2), alone or in combination with gaseous pollutants, did not significantly affect photosynthesis, transpiration, stomatal conductance of water vapor, or chlorophyll content at periodic intervals during the 1984 season. Furthermore, in leaf samples collected during pod fill, the concentrations of 11 elements were not significantly affected by simulated acid rain, alone or in combination with gaseous pollutants. These data are evidence that combinations of ambient rain and gaseous pollutants at similar levels may not cause significant physiological disruption in field-grown Davis soybean, and provide mechanistic support for studies where no significant effects on yield were reported.     

Long term in situ measurements of gas exchange in a Norway spruce canopy at ambient and elevated ozone levels using a light weight chamber system — System designs and first results

The gas exchange system is computer controlled and is designed to measure and control 14 temperature regulated chambers enclosing spruce twigs for several months with minimum ozone absorption. The system is mounted on sun exposed single year classes of a Norway spruce stand in western Jutland, Denmark. Since July 1994 the temperature control system has been in function. Results show that 95% of the temperature measurements inside the cuvettes are within the range ?2 to +3 °C of the ambient temperature. Gas exchange measurements show that the current year shoots have a higher net photosynthesis than the older shoots. The net photosynthesis in current year needles on sunny days is significantly reduced by the 6 h daily 30–40 ppb ozone addition.     

用毛细吸渗原理快速测量土壤田间持水量的研究

田间持水量是衡量田间土壤保持水分能力的重要指标,视为对作物有效的土壤水分的上限,对农田灌溉和作物水分管理具有十分重要意义。该研究提出了能快速测量土壤田间持水量的新型毛细吸渗法。该方法以田间持水量为无地下水影响下土壤基质所能吸持的最大含水量为物理基础,设计了一套满足田间持水量要求的实验方法、装置和程序,采用5种不同土壤测量了其田间持水量,并与用威尔科克斯法测量得到的田间持水量进行了对比。结果表明：所提出的新型测量方法,无论是基本原理还是室内试验均可行。与威尔科克斯法相比,其测量值略微偏小;两种测量值相关性很好,相差约为9％,产生这种现象的原因主要是土壤的吸湿过程与脱湿过程中土壤含水率的滞后所致。与传统的测量方法相比,该方法可大大缩短测量时间,具有利用前景。     

Monitoring extra-matrical hyphae of a vesicular-arbuscular mycorrhizal fungus with an immunofluorescence assay and the soil aggregation technique

An immunofluorescence assay (IFA) was used to compare the amount of extra-matrical hyphae of the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus versiforme (Karst) Berch colonizing seedlings of White Cedar, Chamaecyparis lawsoniana (A. Murr.) Parl., with different root densities in three soil mixes. Restriction (binding) of the root mass with nylon screening decreased root density and also decreased the density of VAM hyphae detected per root length or per soil volume. Top growth of transplanted seedlings was not affected by root restriction. More VAM fungal external hyphae, determined by IFA and the sand aggregation method, formed in river sand than in silt loam with similar percentages of intraradical VAM colonization. More soil aggregates formed in silt loam than in sand regardless of the presence of VAM fungal hyphae. Depending on experimental design, the aggregation method for estimating VAM external hyphae may be limited to use in sandy soil. IFA reacted specifically with G. versiforme hyphae in mineral soil or sand, but was ineffective in peat soil due to nonspecific staining and autofluorescence of organic matter.     

Reduction in soybean yield after exposure to ozone and sulfur dioxide using a linear gradient exposure technique

A linear gradient field exposure system was modified from one originally described by Shinn et al. (1977) and used to expose field grown soybeans (Glycine max cv Hark) to a concentration gradient of a mixture of two gaseous pollutants: SO₂ and 0₃. Since this technique does not use enclosures, study plants experienced near ambient fluctuations in environmental conditions, including wind, and hence were exposed to widely fluctuating pollutant concentrations. Plants in the gradient system were exposed to both pollutants for 57 h on 12 days during the pod-filling period (31 August–17 September). Mean concentrations during the 57 h of exposure at the ‘high’ end of the gradient were 0.16 and 0.06 µl l^?1 (PPM) SO₂ and O₃, respectively, with 10 h at greater than 0.25 and 0.10 µl^?1 SO₂ and O₃, respectively. Total doses for these plants were estimated to be 9.0 and 3.5 µl^?1 · h SO₂ and O₃, respectively. Comparison with plants exposed to ambient air indicated that exposure to SO₂ and O₃ reduced total yield per plant and dry mass per bean by as much as 36 and 15 %, respectively. Since concurrent exposure to a much higher dosage of SO₂ alone (20.2 µl l^?1 · h) was observed in a separate experiment to have no significant effect on yield, 03, although present at moderately low levels, was probably responsible (alone or synergistically with SO₂) for the greatest reduction in seed size and yield.     

Modelling and measurement of the nitrogen cycle in a vegetable field in Switzerland II. Validation of the nitrogen model with field data

Field experiments were conducted over a period of two years on a commercial vegetable farm for calibration and validation of the nitrogen model (tables 1 and 2). Yield and nitrogen uptake of the crops were measured at least five times during crop growth. Soil water tension and nitrate concentration in the soil solution were assessed by frequent sampling of different soil layers. The volumetric soil water content was calculated from continuously measured water potential by means of a field desorption curve. The model was calibrated using a transfer factor for rapid and slow water transport corresponding to changes in water content observed during a leaching experiment in winter 1987/88. Other required input parameters were taken from existing knowledge about the growth of vegetable crops, an evaluation of the soil profile to assess water transport in the soil, and the results of an incubation experiment for the estimation of the net nitrogen-mineralisation. Yield and nitrate uptake of different vegetables are predicted with an accuracy of about 15% for yield and of about 20 kg N/ha for nitrate uptake (table 4, figure 1). Measurement of water and nitrate transport under fennel and a fallow plot (figure 2) reveals that the simulated net nitrogen-mineralisation is overestimated by about 30 percent, and that simulation of rooting depth and evapotranspiration should be improved. Nitrate leaching during summer takes place only after periods of very heavy rain. The accuracy of the agreement between simulated and measured data is within 10% for the water content, and within 25% for the nitrate concentration in the soil solution, while measured nitrate leaching exceeded the simulated values by up to 80 kg N/ha. The precision of the model seems to be satisfactory in view of the large amount of nitrogen and water cycled in a vegetable field (table 5). However with respect to water management improvements are necessary. Further validation of the model on other sites is required before a predictive model for practical purposes can be elaborated.     

Gradients of ozone at a forest site and over a field cropconsequences for the AOT40 concept of critical level

Ozone concentrations were measured at a wind-exposed edge of a 60 year-old 15–20 m tall Norway spruce forest in south-west Sweden and simultaneously over a barley field 5 km away for 27 days, At the forest site, measurements were performed at 3 and 13 m height 15 m in front of the forest edge, at 3 m height 15 m into the forest, and at 3 and 13 m height 45 m into the forest. Measurements at 3 m were made with three replicate tubes separated by 10 m. Differences between replicates were small. At 13 m height, the concentration (24-hr-average) 45 m into the forest was 95% of that in front of the forest edge. The average concentration at 3 m height did not vary strongly with the distance into the forest, but was 86% of that at 13 m in front of the forest edge. For AOT40 (Accumulated Exposure Over Threshold 40 ppb ozone), the differences between different positions were larger. At the 13 m level the AOT40 (day and night) was 88% of that in front of the forest 45 m into the forest. The AOT40 at 3 m was 71% of that at 13 m outside the forest. At the crop site, the ozone concentration at 1.1 m (0.1 m above the canopy), was 78% of that at 9 m (06.00–22.00). The AOT40 at 1.1 m above the ground, however, was only 50% of that at 9 m, indicating that serious errors can arise if ozone monitoring data are used uncorrnected in dose-response relationships based on measurements performed at plant height. The ozone concentration for the whole period differed very little between 9 m height at the crop site and 13 m height at the forest site outside the forest during daytime conditions (06.00–22.00). Night-time (22.00–06.00) values were only 21% at the crop site of those at the forest site due to the stronger night inversion development in the agricultural environment compared to the wind exposed forest edge. The results suggest that variations in topography and vegetation are important to consider when combining ozone monitoring data with dose-response functions.     

超级电容动态容值测量与容值函数参数估计

针对目前的超级电容参数在线识别方法动态参数测量困难,通用性差,精度低的缺点,提出一种超级电容动态容值测量与参数识别方法。该方法中提出了动态电容值测量模型,通过电荷关系式与能量关系式联立推导动态电容值测量方程组,并采用限定记忆最小二乘法进行参数识别,应用时域仿真对该方法进行了验证。仿真结果表明,该文提出的电容值测量与参数识别方法适用于多种不同的容值函数。当测量信号存在噪声时仍可对电容测量,平均误差低于1%,参数估计相对误差低于20%,可以应用于超级电容动态容值测量。     

Preliminary results of a German field trial with different hemp (Cannabis sativa L.) accessions

Hemp is one of the oldest crops in the world and can be used in very different ways. Hemp cultivation was forbidden in Germany since 1982. Since 1996 hemp with less than 0.3 per cent THC content can be grown. To evaluate the available genetic hemp resources 14 monoecious and 26 dioecious hemp varieties and strains were grown in the field in 1996 and analysed for morphological traits. A large variability was found for plant height at different dates, blooming time, stem diameter, fresh and dry weight and seed yield. Plant density and plant height at maturity were negatively correlated. The initial growth rate is only of minor importance. There was no interaction between genotype and sex for dioecious accessions, though differences between sex types were important.     

Application of a novel method for soil aggregate stability measurement by laser granulometry with sonication

Aggregate stability is an important physical indicator of soil quality, and so methods are required to measure it rapidly and cost‐effectively so that sufficient data can be collected to detect change with adequate statistical power. The standard methods to measure water‐stable aggregates (WSA) in soil involve sieving, but these have limitations that could be overcome if the aggregates were measured with a laser granulometer (LG) instrument. We present a novel method in which a LG is used to make two measurements of the continuous size distribution (<2000 µm) of a sample of aggregates. The first measurement is made on the WSA after these have been added to circulating water (initial air‐dried aggregate size range 1000–2000 µm). The second measurement is made on the disaggregated material (DM) after the circulating aggregates have been disrupted with ultrasound (sonication). We then compute the difference between the mean weight diameters (MWD) of these two size distributions; we refer to this value as the disaggregation reduction (DR; µm). Soils with more stable aggregates, which are resistant to both slaking and mechanical breakdown by the hydrodynamic forces during circulation, have larger values of DR. We applied this method to six and ten sub‐samples, respectively, of soil aggregates (each ca. 0.3 g) from bulk soil material from two contrasting soil types from England, both under conventional tillage (CT). The mean DR values were, respectively, 178 and 30 µm, with coefficients of variation of 12.1 and 19% suggesting the DR value is reproducible for the small mass of soil used. We attribute the larger DR values to the greater abundance of micaceous clay minerals in one of the soils. The DR values computed for each Blackwater Drain (BD) sample after removal of organic matter (with hydrogen peroxide) were comparable to those subject to sonication suggesting that most of the aggregate structure is removed by sonication. We used aggregates (1000–2000 µm) from soil samples collected at 30 locations under CT (median soil organic carbon (SOC) = 1.4%) across two types of parent material in the Blackwater drain sub‐catchments of the Wensum catchment (Norfolk, UK). These soils had no coarse WSA, so we rescaled the size distributions to estimate DR for particle diameters <500 µm. Dithionite‐extractable iron concentration, plus a minor contribution from parent material class, accounted for 64% of the variation in rescaled DR highlighting the importance of crystalline iron oxyhydroxides for aggregate stability in this region where long‐term arable production has reduced top‐soil SOC concentrations. We discuss how this technique could be developed to monitor aggregate stability as a soil physical indicator.     

Rapid,objective measurement of soil color with a tristimulus colorimeter

Abstract

The color of 100 soil sanples collected in Florida and Brazil was measured conventionally with Munsell color charts and with a tristimulus colorimeter (Minolta Chroma Meter 200) progranmed to record reflected color in Munsell notation. The instrument‐derived color readings were highly reproducible and more precise than the visual determinations. It appears that the Chroma Meter 200, an instrument usually used for fruit and juice color measurenent, can be used to get objective soil color measurenents, free of individual color perception differences, and with better interpolated values.     

Isotope (C and C) analysis of deep peat CO2 using a passive sampling technique

We developed and tested a new method to collect CO₂ from the surface to deep layers of a peatland for radiocarbon analysis. The method comprises two components: i) a probe equipped with a hydrophobic filter that allows entry of peat gases by diffusion, whilst simultaneously excluding water, and, ii) a cartridge containing zeolite molecular sieve that traps CO₂ passively. We field tested the method by sampling at depths of between 0.25 and 4 m at duplicate sites within a temperate raised peat bog. CO₂ was trapped at a depth-dependent rate of between ∼0.2 and 0.8 ml d⁻¹, enabling sufficient CO₂ for routine ¹⁴C analysis to be collected when left in place for several weeks. The age of peatland CO₂ increased with depth from modern to ∼170 BP for samples collected from 0.25 m, to ∼4000 BP at 4 m. The CO₂ was younger, but followed a similar trend to the age profile of bulk peat previously reported for the site (Langdon and Barber, 2005). δ¹³C values of recovered CO₂ increased with depth. CO₂ collected from the deepest sampling probes was considerably ¹³C-enriched (up to ∼+9‰) and agreed well with results reported for other peatlands where this phenomenon has been attributed to fermentation processes. CO₂ collected from plant-free static chambers at the surface of the mire was slightly ¹⁴C-enriched compared to the contemporary atmosphere, suggesting that surface CO₂ emissions were predominantly derived from carbon fixed during the post-bomb era. However, consistent trends of enriched ¹³C and depleted ¹⁴C in chamber CO₂ between autumn and winter samples were most likely explained by an increased contribution of deep peat CO₂ to the surface efflux in winter. The passive sampling technique is readily portable, easy to install and operate, causes minimal site disturbance, and can be reliably used to collect peatland CO₂ from a wide range of depths.     

旋流泵含气混输数值计算及涡室流场探针测量

为探索旋流泵内部流场及气液两相流混输特性,该文通过32WB8-12型旋流泵外特性试验和泵最优工况流场五孔探针测量,得出泵性能曲线和5个测点静压ps、绝对速度v、圆周速度vu、径向速度vr和轴向速度vz分布情况。针对N-S方程中四项力在气液两相流动中的具体表现特性进行力学分析,说明了泵内部两相流动特点及关联因素之间约束关系。阐明了旋流泵含气混输抽吸和扬程形成的基本原理,及空化和气液两相流混输的不同特点。选择性能试验最优工况,基于改进重组化群k-ε湍流模型(RNG k-ε模型),应用Fluent软件对泵内部流场进行数值模拟,得到了3个轴面静压、速度矢量和含气率分布图。证明泵进口轴向运动为主流,气体主要集中在压力较低的进口区域。气相的引入,其微团与液相尺寸、形状及弹性模量的不同,造成两相流场惯性力、摩擦力和浮力发生变化,由此解释了外特性变化及气液抽吸与内部流动之间定性的因果关系。探讨了旋流泵内部气液两相流动速度场和过流通道发生畸变的基本原理,为建立旋流泵内部气液及空化流动模型提供实例。     

Initial results from a long-term, multi-site field study of the effects on soil fertility and microbial activity of sludge cakes containing heavy metals

In a long‐term study of the effects on soil fertility and microbial activity of heavy metals contained in sewage sludges, metal‐rich sludge cakes each with high Zn, Cu or Cd concentrations were applied annually for 4 years (1994–1997) to nine sites throughout Britain. These sites were selected to represent agricultural soils with a range of physical and chemical properties, typical of those likely to be amended with sewage sludge. The aim was to establish individual total Zn (approx. 60–450 mg kg^?1), total Cu (approx. 15–200 mg kg^?1) and total Cd (approx. 0.2–4 mg kg^?1) metal dose–response treatments at each site. Sludges with low metal concentrations were added to all treatments to achieve as constant an addition of organic matter as possible. Across the nine sites, soil pH was the single most important factor controlling Zn (P < 0.001; r² = 92%) and Cd extracted with 1 m NH₄NO₃ (P < 0.001; r² = 72%), and total iron content the most important factor controlling Cu extracted with 1 m NH₄NO₃ (P < 0.001; r² = 64%). There were also positive relationships (P < 0.001) between soil organic carbon (C) concentrations and soil biomass C and respiration rates across the nine sites. Oxidation of sludge C following land application resulted in approximately 45% of the digested sludge cake C and approximately 64% of the ‘raw’ sludge cake C being lost by the end of the 4‐year application period. The sludge cake applications generally increased soil microbial biomass C and soil respiration rates, whilst most probable numbers of clover Rhizobium were generally unchanged. Overall, there was no evidence that the metal applications were damaging soil microbial activity in the short term after the cessation of sludge cake addition.     

Development of a technique for the measurement of root geometry in the soil using resin-impregnated blocks and image analysis

A method is described that permits the measurement of roots in situ in the soil using computerized image analysis to process images obtained from planar faces cut from a resin-fixed pot. Soil sample pots are initially impregnated with rapid-curing epoxy resin. Blocks are then cut from the impregnated pot with a diamond saw to expose a planar face. Modification of the present resin-impregnation procedure is necessary as impregnation results were mostly unsatisfactory. Roots are contrasted from the soil matrix by enhancing autofluorescence using longwave ultraviolet light and appropriate filters. After image capture and segmentation to show regions of root material, measurements of volume fraction of roots, volumetric surface area, horizontal root length and horizontal root separation, were made with a larger resolution with soil depth than previously.     

稻麦玉米秸秆残留还田量定量估算方法及应用

为了解秸秆残留还田是秸秆直接还田的基本形式。该文通过逐步推导,给出了秸秆残留还田量定量估算的系列公式,并将秸秆残留还田量定量估算建立在5个参数的基础上,即农作物平均株高、收割留茬高度、叶部生物量比例、枝叶脱落率和秸秆机械收集损失率;以实地调查为基础,结合对试验数据收集整理,给出了小麦、玉米、水稻三大农作物秸秆残留还田量定量估算的参数体系,并估算出了三大农作物的秸秆残留还田量,分别为7 106.92、4 543.48和6 392.95万t,合计为18 043.35万t,占三大农作物的秸秆总产量的31.13%;三大作物人工收获秸秆残留还田量为1724.47万t,机械收获秸秆残留还田量为16 318.88万t,后者是前者的9.46倍;进而以农作物面积为权重,推算出全国的秸秆残留还田量为25 330.08万t,计算出单位面积耕地的残留还田量为1.87 t/hm2,与基本还田量的最低需求3.0 t/hm2相比尚需增加60%以上,与基本还田量的一般需求4.5 t/hm2相比尚需增加1.41倍。论文最后指出了秸秆残留还田量定量估算需要继续深入开展的主要研究工作:一是开展更广泛的田间实测,进一步提高小麦、玉米、水稻三大农作物秸秆残留还田量定量估算参数的精准度,尤其是收割留茬高度和秸秆机械收集损失率这两大参数的精准度,以便更确切地估算三大农作物的秸秆残留还田量;二是针对棉花、大豆、油菜等主要经济作物进行秸秆残留还田量定量估算研究,建立全国主要粮经作物秸秆残留还田量定量估算的参数体系;三是建立区域性的秸秆残留还田量定量估算的参数体系,逐步实现各区域秸秆残留还田量的定量估算。     

Nitrogen oxides,regional transport,and ozone air quality: Results of a regional-scale model for the midwestern United States

An overview of the role of NO _x in the formation of rural O₃, regional transport and its potential impact on urban air quality is presented. An analysis of a specific O₃ excursion in southeast Michigan (8-2-90) is performed based on a combined urban and regional-scale model. The regional component of the model represents transport and photochemistry from sources as far away as Texas. Results suggest that rural O₃ and regional transport sensitive to NO _x emissions and relatively insensitive to changes in volatile organic carbon (VOC) emissions. This differs from the situation in urban areas, where O₃ is sensitive to both NO _x and VOC. Regional transport and upwind NO _x emissions have a significant impact on peak O₃ in Detroit. Implications for urban and regional-scale abatement strategies are discussed.     

Effects of elevated carbon dioxide on metal transport in soil-crop system: results from a field rice and wheat experiment

Journal of Soils and Sediments - Climate changes have significant impacts on crop yield, and also on crop quality related to food safety and human health. This study investigated the influences of...