通风速率对土壤中四氯化碳污染物去除效率的影响研究

某重要岩溶地下水源地受到四氯化碳的严重污染,为此采用土柱通风试验模拟土壤气相抽提（SVE）净化四氯化碳污染物的过程,对通风速率为40mL·min-1和70mL·min-1两种条件下土壤四氯化碳的去除过程进行了试验模拟研究。结果表明,土柱通风能有效去除土壤中的四氯化碳污染物,通风条件下土壤中四氯化碳的去除过程符合一级反应动力学,土壤中四氯化碳浓度C的对数值ln[C（/μg·L-1）]与时间t呈良好的线性关系,相关系数均在0.95以上。通风速率为40mL·min-1的土柱A各取样口四氯化碳去除反应速率常数k值在0.0132～0.0155h-1之间,通风速率为70mL·min-1的土柱B各取样口k值在0.0178～0.0222h-1之间,说明增大通风速率能提高土壤中四氯化碳污染物的去除效率。     

生物通风法修复柴油污染土壤模拟实验研究

通过生物通风技术修复不同柴油浓度污染土壤的土柱模拟实验,研究了各土柱中土壤总石油烃(total petroleum hydrocarbon,TPH)的去除规律,并对影响柴油去除效果的因素进行了分析,结果表明:①经过3个月的生物通风后,初始柴油浓度为5(柱Ⅰ)、10(柱Ⅱ)、20(柱Ⅲ)、40(柱Ⅳ)g/kg的土柱柴油去除率为ⅡⅠⅣⅢ,柱Ⅱ的修复效果最佳,半衰期为60.05天,TPH最终去除率达65.3%;②挥发和生物降解作用影响土柱中柴油的去除,由于重力引起的向下迁移作用只对柴油在土柱中的空间分布产生影响,三者共同作用决定各土柱不同取样口柴油的去除规律;③在实验过程中,各土柱土壤pH变化不大,初始柴油浓度越高土柱水分损失率越小;有效磷和速效氮含量均有所降低,柱Ⅲ降低率最大,分别为58.27%和31.87%,柱Ⅰ最小;土柱上层土壤中的酶活性要低于下层,过氧化氢酶和脱氢酶活性均呈现出先升高后降低的趋势。实验结果为研究各土柱中柴油的生物降解规律提供了依据。     

不同土壤结构改良剂处理的磷淋溶特性的研究

研究了水动力作用下磷素在土壤剖面中的垂直迁移特征,聚丙烯酰胺(PAM)和羧甲基纤维素(CMC)两种改良剂处理土壤后,能够促进土壤中磷素在水动力作用下沿土柱垂直向下迁移,不仅使土柱下层对应层次的速效磷含量高于对照,且使磷淋失量增加。PAM处理和CMC处理相比,更有利于磷素沿土柱向下迁移和淋失,促进磷素在土壤中的垂直移动     

不同类型层状土壤持水能力的研究

为了了解不同类型层状土柱持水能力,利用砂土和砂黄土2种土壤,设置3种不同厚度分层土柱(11.25、22.5、45 cm)和2种匀质对照土柱,测定了土柱自初始饱和条件下的排水过程;同时利用匀质土柱测定结果标定2种土壤水力参数,通过Hydrus-1D模型对不同类型层状土柱排水过程进行模拟分析,获得了不同类型层状土柱的田间持水量。结果表明,层状土柱持水能力随着分层厚度的减小而增加,当分层厚度减小到一定程度时土柱持水能力不再随着分层厚度的减小而增加,该临界厚度取决于下层粗质土壤对上层细质土的吸力与上层细质土壤进气吸力之间的相对大小。本试验所用2种土壤分层临界厚度大约在5 cm左右;土柱失水主要来自下层较粗质地土壤,由饱和时的0.385 cm~3/cm~3减小到0.04 cm~3/cm~3。上层细质土壤含水量随着分层厚度的减小而增加。研究结果可为干旱半干旱地区矿区恢复和污染物填埋提供理论指导。     

宁夏引黄灌区盐渍化土壤在改良剂作用下的水力特性试验

为了研究宁夏引黄灌区盐渍化土壤在施加有机改良剂和无机改良剂后的水力特性,选取宁夏引黄灌区典型区域进行土壤改良并进行种植试验。将改良后的土壤分5层取样在实验室中进行土柱入渗试验,利用压力膜仪和自循环达西渗流试验仪,测量了土壤含水率与压力水头之间的关系和渗透系数;根据实测数据,选取van Genuchten （VG）模型进行参数反演,对不同改良剂处理后各层土壤水分特征曲线进行了对比分析。研究发现：①各层土壤在水吸力相同时,施加不同改良剂后的土壤含水率一般大于对照组,而有机改良剂处理组要大于无机改良剂处理组;②改良后水分特征曲线及相应VG模型中的参数发生了较大变化;③有机改良剂处理后土壤容重有所减小,而无机改良剂处理后土壤容重变化不太明显;④不同改良剂处理后土柱中水分入渗的湿润锋推进速度和土壤渗透系数有不同程度增大,有机改良剂处理组增大幅度大于无机改良剂处理组。综上所述,不同改良剂对土壤容重、含水率、水分入渗速度及其他水力参数都有较大影响,说明改良剂在一定程度上改变了土壤结构。土柱试验及种植试验均表明,有机改良剂（牛粪和糠醛渣）处理组的性态要优于无机改良剂（脱硫石膏和粉煤灰）处理组。     

非均质饱和土壤盐分优先运移的随机模拟

在室内使用特殊形状的土柱隔板成功地填装了在水平横截面上呈“川”字型分布、由质地相差较大的两种土壤相间构成的非均质土柱。当土柱出流达到稳态后，灌入CaCl2溶液，监测土柱出流液的浓度动态。通过计算表征氯离子迁移时间随机特征的概率密度函数，对出流盐分的优先运移采用传递函数模型进行仿真，并对构成非均质土柱的两种均质土壤分别进行了条件类似的水盐入渗实验和模拟。在此基础上获得了参与氯离子输运的土壤水运移体积和可动体积以及土壤溶液中氯离子的体积平均驻留浓度。     

黑麦有机氮在土壤中矿化与淋洗的研究

采用土柱和变温培养方法研究黑麦的机Ｎ在土壤中的矿化及淋洗。结果表明，培养八周后约７１％的有机Ｎ被矿化。有机Ｎ矿化明显受温度影响，培养温度由低到高的处理比由高到低的处理更利于矿化Ｎ在土壤中积累。淋洗试验的水分平衡及Ｎ的淋洗也受温度影响。     

地下水作用条件下土壤积盐规律研究

用粉砂壤土土柱进行了为期一年的室内模拟试验 ,对不同地下水埋深及其矿化度作用条件下 0～ 40cm深度土壤的盐分运动规律进行了深入研究。地下水埋深 85cm、1 0 5cm情况下 ,0～ 40cm深度土壤电导率与地下水矿化度呈良好正相关关系。地下水埋深 1 5 5cm、试验设定条件下 ,各土柱 0～ 40cm深度土壤积盐强度都较小 ,并且相互之间差异不明显。获得了各土柱 0～ 40cm深度土壤电导率关于地下水埋深、地下水矿化度的统计模型。对土壤电导率动态规律进行了深入分析 ,并建立了地下水明显影响到该深度土壤后土壤电导率动态模型。     

应用^35S研究模拟酸雨硫在土壤中的渗透流失规律

应用＾３５Ｓ研究模拟酸雨硫在土壤中渗透流失规律，结果表明：酸雨硫在中性紫色土的土柱中，硫的流失量多，酸性黄壤次之，酸性紫色土的土柱中硫的流失量少。供试三种土壤的土柱随着酸雨浓度的增加，酸雨硫的流失百分率增加；随着气温升高，酸雨硫的流失百分率增加。酸雨浓度大的土柱，残留硫量多，酸雨浓度小的土柱，残留硫量少。ｐＨ５．６酸雨随土柱深度增加，残留硫量有所增加，而ｐＨ４和ｐＨ２．５酸雨土柱，随深度增加残留硫     

草甘膦对重金属污染土壤中铜、锌淋溶的研究

草甘膦分子结构中含有膦酸基、羧基和胺基等,具有强的络合重金属离子的能力,从而影响重金属在土壤中的环境化学行为.本文采用土柱淋溶方法,研究了不同浓度草甘膦溶液( 0、5 、20 和 50 mg/L)对污染土壤中重金属溶出的影响.草甘膦的存在降低了淋滤液的pH,增加了淋滤液中Cu和Zn的含量.逐层采样并分析了土壤中重金属的生物有效性含量,发现草甘膦的存在增加了土柱下层土壤重金属的生物有效性浓度.大量使用草甘膦会导致污染土壤中重金属的溶出,进而污染地下水.     

下层土壤反硝化作用的研究

在夏玉米生长期间 ,采用乙炔抑制 -原状土柱培养方法研究了北京褐土下层 (15～ 6 0cm)土壤的反硝化作用 ,并探讨影响该层土壤反硝化作用的主要因素。试验结果表明 ,施氮量越高 ,反硝化量越大。随着土壤层次的加深 ,反硝化量呈直线下降 ,但在亚表层土壤 (15～ 30cm)反硝化值仍保持了较高的量 ,约相当于表层的 10 .7%～ 33.5 % ;下层土壤 (15～ 6 0cm)的总反硝化量约相当于表层土壤的 14%～ 51%。加入碳源无论对表层土壤还是下层土壤 ,其反硝化损失氮量大大增加 ,尤其是对下层土壤增加的趋势更为明显。在计算夏玉米季土壤反硝化损失氮量时 ,如果忽略下层土壤的反硝化作用 ,肯定会低估其数值     

A gas-flow soil core method to measure field denitrification rates

A method was developed for rapid measurement of soil denitrification under conditions where natural soil structure and aeration status is maintained. Air was continuously recirculated by means of a membrane pump through a soil core and a sample loop of a gas chromatograph equipped with an electron capture detector. Addition of acetylene to the recirculating air permitted measurement of denitrification in the soil core. Because of the rapid distribution of C₂H₂ and removal of N₂O provided by the gas flow, denitrification rates could usually be determined in less than 2 h. By means of external 6-way and 8-way valves, four soil cores could be simultaneously analyzed on one gas Chromatograph equipped with dual detectors. Soil cores could also be stored at 4°C for later analysis without affecting the denitrification rate. The detection limit for denitrification rate measurements was 0.5 ngN g^?1 soil day^?1 or approximately 2.6 g N ha^?1 day^?1. Coefficients of variation for repeated measurements on the same soil core were usually less than 15%, but coefficients of variation for repacked or natural cores of the same soil were much higher (70–90%) Disruption of the natural soil structure by sieving increased the denitrification rate in an aggregated clay loam soil, but decreased the rate in a non-aggregated sandy soil. These results illustrate the importance of maintaining natural soil structure during denitrification measurements. The effect of pumping gas through soil was evaluated by comparing denitrification rates in soil cores where C₂H₂ was allowed to distribute into the soil by passive diffusion with rates obtained by pumping. Lower denitrification rates were observed in the static incubation presumably due to limited diffusion of C₂H₂ into or N₂O out of the denitrifying sites in the soil. This diffusion limitation could be overcome in the static incubations if C₂H₂ was initially distributed through the soil by pumping. This gas flow method is well suited to the study of soil denitrification rates under nearly natural conditions because the indigenous substrates and anaerobic microsites are preserved, the rapidity in which denitrification rates can be measured, and the high sensitivity and relatively low analytical variability of the method.     

Comparison of two versions of the acetylene inhibition/soil core method for measuring denitrification loss from an irrigated wheat field

 Two versions of the acetylene inhibition (AI)/soil core method were compared for the measurement of denitrification loss from an irrigated wheat field receiving urea-N at a rate of 100 kg ha^–1. With AI/soil core method A, the denitrification rate was measured by analysing the headspace N₂O, followed by estimation of N₂O dissolved in the solution phase using Bunsen absorption coefficients. With AI/soil core method B, N₂O entrapped in the soil was measured in addition to that released from soil cores into the headspace of incubation vessels. In addition, the two methods were also compared for measurement of the soil respiration rate. Of the total N₂O produced, 6–77% (average 40%) remained entrapped in the soil, whereas for CO₂, the corresponding figures ranged from 12–65% (average 44%). The amount of the entrapped N₂O was significantly correlated with the water-filled pore space (WFPS) and with the N₂O concentration in the headspace, whereas CO₂ entrapment was dependent on the headspace CO₂ concentration but not on the WFPS. Due to the entrapment of N₂O and CO₂ in soil, the denitrification rate on several (18 of the 41) sampling dates, and soil respiration rate on almost all (27 of the 30) sampling dates were significantly higher with method B compared to method A. Averaged across sampling dates, the denitrification rate measured with method B (0.30 kg N ha^–1 day^–1) was twice the rate measured with method A, whereas the soil respiration rate measured with method B (34.9 kg C ha^–1 day^–1) was 1.6 times the rate measured with method A. Results of this study suggest that the N₂O and CO₂ entrapped in soil should also be measured to ensure the recovery of the gaseous products of denitrification by the soil core method. Received: 12 May 1998     

Laboratory vs. in situ resin‐core methods to estimate net nitrogen mineralization for comparison of rotation and tillage practices

Properly estimating soil nitrogen (N) mineralization as a consequence of different agronomic practices would result in better soil N fertility management. In this study, we tested the differences between laboratory and in situ resin‐core incubation methods for estimating soil net N mineralization for long‐term burley tobacco (Nicotiana tobacum L .) tillage and rotation systems. The laboratory incubation method used crushed, homogenized, litter‐free soil samples, and the in situ resin‐core incubation method used an intact soil core with the inclusion of any plant residue below or above ground. Comparisons showed that no‐tillage had significantly increased soil net N mineralization compared to conventional tillage with the laboratory incubation method, while there was no significant difference between tillage methods with the in situ resin‐core method. This indicates that soil pretreatment in the laboratory incubation method can create an “artificial tillage effect” for soil previously managed with no‐tillage, resulting in overestimated soil net N mineralization. The rotation comparison showed that different crop sequences had no impact on measured net N mineralization with the laboratory incubation method. However, a preceding soybean crop did significantly increase net soil N mineralization compared to preceding corn when measured with the in situ resin‐core method. This suggests that discarding plant residue in the laboratory incubation method can neglect the potential effect of plant residue on soil N mineralization. Therefore, it is important to be aware that soil pretreatment may influence soil N mineralization estimates, potentially resulting in flawed decisions for soil N fertility management.     

A SYSTEM FOR MEASURING THE RATES OF EVOLUTION OF NITROUS OXIDE AND NITROGEN FROM INCUBATED SOILS DURING DENITRIFICATION

An incubation system is described for studying denitrification rates in incubated soil by measuring the gaseous products removed in a stream of helium flowing across the soil. The system has been used to demonstrate the effect on denitrification of air-drying a soil. A constant rate of denitrification occurs in soil pre-incubated aerobically at 50% water holding capacity for a period of 3 weeks prior to the denitrification assay. By contrast, air-dry soil wetted immediately prior to denitrification measurement showed a rapid increase in denitrification rate to a maximum at 1–3 days and a decline thereafter until a steady state is reached about 2–4 weeks after rewetting. Nitrous oxide was the dominant product from both soils studied: the ratio of N₂O to N, in the gases evolved changed little with time for the pre-incubated soil, but diminished with time of incubation for the air-dried soil.     

In Situ Batch Denitrification of Nitrate-Rich Groundwater Using Sawdust as a Carbon Source—Marydale, South Africa

Batch experiments were performed to denitrify groundwater using sawdust as a carbon source at Marydale, South Africa. Alkalinity, pH, electrical conductivity, nitrate, nitrite, ammonia, SO ₄ ^2? , heterotrophic plate count (HPC), dissolved organic carbon (DOC), potassium and chloride were monitored. Two soil depths, 75 to 100 and 165 to 200 cm, respectively, from the Marydale area were used as matrix material during denitrification based on contrasting chemical composition with respect to major ion composition and moisture to consider different denitrification rates for varying soil depths. Different N to C ratios were used to evaluate the denitrification efficiency and the least undesirable products, e.g., elevated SO ₄ ^2? , H₂S and other reduced compounds. DOC is directly proportional to the N to C ratio used. Nitrite was produced for most of the treatments as incomplete denitrification occurred. The incubation periods were 28 and 43 days, respectively. N to C ratios were 12.6:1, 24:1, 34:1 and 54:1. Longer incubation period and higher N to C ratio resulted in total removal of both nitrate and nitrite. The reaction was carbon-limited for lower N to C ratios. The denitrification rate was proportional to the carbon availability at any time during the experiment. There was no significant difference in denitrification using heterogeneous and homogeneous particle sizes for sawdust. Soil depth of 75–100 cm displayed a greater denitrification rate than 165–200-cm soil depth due to higher initial soil nitrate concentration. The method showed some specificity, as DOC, nitrite, nitrate, alkalinity and HPC were the only parameters that showed a change in concentration over the duration of the denitrification experiment under constant temperature and nitrogen gas atmosphere. DOC and HPC were unacceptable for domestic use, but methods such as boiling or chlorinating water can rid it of bacteria.     

优化施肥下华北冬小麦/夏玉米轮作体系农田反硝化损失与N2O排放特征

在田间条件下,应用乙炔抑制-原状土柱培养法测定优化施肥下华北冬小麦/夏玉米轮作体系土壤反硝化和N2O的排放特征。研究表明:冬小麦和夏玉米整个生育期反硝化速率和N2O排放通量均表现出明显的季节性变化,且均与土壤水分和无机氮浓度呈显著正相关。小麦季和玉米季的反硝化损失量及N2O排放量均表现出随施肥量的降低而降低,夏玉米季的反硝化损失量和N2O排放量均高于小麦季。小麦季的反硝化损失量和N2O排放量习惯施肥处理是氮肥减量后移处理的1.62和1.67倍,玉米季分别为2.01和2.00倍。氮肥减量后移可能是通过改变土壤无机氮浓度而降低反硝化损失量和N2O排放量。     

Effect of cow urine upon denitrification

The influence of urine application upon the zone and rate of denitrification of a pastoral soil was studied using a short term incubation technique. Under the condition of full enzyme induction, no increase in denitrification activity was measured with the addition of cow urine. The zone of maximum denitrification activity was within the top 30 mm and did not shift with increasing C and N substrate at the 60–90 mm depth.     

Denitrification activity in the vadose zone beneath a sludge‐amended semi‐arid soil

Abstract

Soil cores were collected to a depth of 14 m from a Southwest semi‐arid soil amended with either anaerobically digested sludge or inorganic fertilizer. Twenty sections partitioned from each core were characterized for their physical and chemical properties. Denitrification potential was estimated in each core section in the laboratory using the acetylene reduction method. The sludge‐amended soil had significantly higher denitrification rates within and below the root zone than the fertilizer‐amended soil. Additionally, significant correlation values were obtained in both cores between denitrification rates and particle size distribution, moisture, and total organic carbon (C). Sludge applications in semi‐desert soils may add much needed organic C in the soil profile. This additional soluble organic C may help control nitrate (NO₃) ground water pollution by providing substrate C for denitrifying bacteria below the root zone.     

Direct Estimation of Nitrogen Gases Emitted from Flooded Soils During Denitrification of Applied Nitrogen

Denitrification losses measured by direct method (measuring the evolution of (N2 N2O)-^15N) were compared with the apparent denitrification losses (calculated from the difference between the total N loss and ammonia loss), for fertilizers applied to flooded soils.The direct measured denitrification losses from potassium nitrate were 23.0%,40.0%,and 63.1-79.7% of applied N in rice field,and in incubations of 7 cm deep layer of soil and 2 cm deep layer of soil,respectively;while the corresponding apparent denitrification losses were 96.0%,98.4%,and 97.7-97.9%,respectively.In field experiments with urea,the direct measured denitrification losses ranged from 0.1-1.8%,which were much less than the apparent denitrification losses (41.3-45.7%).Such discrepancies were primarily due to the entrapment of the gaseous products of denitrification in the soil as revealed by the facts:(1) stirring the floodwater and the surface soil markedly increased the fluxes of (N2_N2O)-^15N from urea or potassium nitrate applied to the flooded rice field,and (2) reducing the pressure in the headspace of the incubation bottle with the 7 cm soil layer during gas sampling decreased the discrepance between the direct measured and apparent denitrifecation losses from 58.4% to 21.2%.The advantage of reducing the pressure in the headspace is that there is minimal disturbance of the soil.Further testing of this technique in rice field is needed to determine its effectiveness in releasing the entrapped gaseous products of denitrification so that denitrification losses can be quantified directly.