模拟雨水连续淋洗下土壤化学性状动态变化特征的研究

本文从研究正常降雨对土壤性状的影响出发,进行了模拟雨水对酸性紫色土和石灰性紫色土的连续淋洗试验。试验结果表明在模拟雨水连续淋洗150天的过程中,土壤中钙、镁、钾、钠等盐基离子几乎都显示出一定程度的净淋溶特征,土壤中各盐基离子的动力学变化特征几乎都与抛物线扩散方程吻合。淋洗结束后土壤酸度未发生显著变化,但两种土壤CEC值均有所降低。     

模拟酸雨对酸性土壤铝溶出及其形态转化的影响

通过采样、酸雨模拟试验和样品分析，研究了我国南方酸沉降区主要土壤类型在模拟酸雨影响下，土壤中铝离子释放及铝形态转化的特点。结果表明，酸雨淋洗造成土壤中铝离子释放；酸雨pH值越低，则铝离子释放量越大。酸雨淋洗还造成土壤中铝形态发生变化；酸雨pH值越低，则土壤中羟基态铝和腐殖质铝含量越低，交换态铝含量越高，从而导致土壤中的铝对植物和生态系统的危害性也越大。     

几种低分子量有机酸淋溶对土壤铝、硅及盐基离子淋失的影响

采用50cm原状土柱进行模拟淋溶实验,比较研究了模拟酸雨和几种低分子量有机酸对红壤Al、Si及盐基离子淋失的影响。结果表明,模拟酸雨淋洗后土壤中有极少量的Al和一定量的Si及盐基离子淋出。与去离子水对照相比,pH3.5和pH4.5模拟酸雨处理Si的淋出总量分别增加了6.52%和3.26%;K 、Na 、Ca2 和Mg2 等盐基离子淋出量增加了2.41%~96.80%。100μmol/L的柠檬酸、苹果酸和草酸处理Al、Si的淋出量与模拟酸雨处理相差不大,而10mmol/L的柠檬酸、苹果酸和草酸处理则比模拟酸雨处理有显著的增加。有机酸淋洗后淋出液中各盐基离子含量均要高于模拟酸雨处理,盐基离子淋出总量是模拟酸雨处理的1.58~9.27倍。实验结果说明低分子量有机酸在酸化土壤方面比酸雨有更大的威胁。由于盐基离子的大量淋失,模拟酸雨和有机酸淋洗后淋出液pH均要高于原淋洗液pH。     

短期和长期中水灌溉对绿地土壤理化性质的影响

采用短期室内中水灌溉土柱模拟和长期中水灌溉区大田定位调查,对中水灌溉后对植物体内营养元素、毒害离子以及重金属的增减变化进行对比分析。结果表明,与清水对照相比,中水灌溉使绿地土壤pH值降低,土壤有机质含量增加,孔隙度增大,容重及田间持水量减小;全氮、全磷含量随土层厚度的增加而呈减少的趋势;碱解氮、有效磷和速效钾含量增加且与清水对照之间差异显著（P〈0.05）;盐离子在土壤中得以积累,含量增加;毒害离子和重金属含量呈增大或减少的趋势,与不同离子种类有关,但其含量极少,累积效应变化缓慢,且由于自然降水等因素的稀释和植物、土壤微生物等因素的吸收及降解,一般不会造成对土壤的污染及对植物的生长胁迫。     

基于COMSOL软件的绿洲盐渍化土壤中多离子耦合运移模型构建

了解盐分离子在土壤中的迁移规律可以为盐渍土的综合治理以及高效利用提供科学依据,在COMSOL多孔介质和地下水流模块模拟非饱和土壤水流的基础上,自定义偏微分方程组构建盐渍化土壤SO42–、Ca2+、Na+、Cl–、Mg2+耦合运移模型,考虑阳离子交换过程以及硫酸钙的沉淀溶解反应,并通过新疆绿洲膜下滴灌田间试验对模型进行检验,对比不同活度系数估算方法对模拟结果的影响。结果表明,各离子模拟值与实测值吻合较好,平均相对误差介于9.15%~28.57%,决定系数介于0.41~0.88,该模型能够较好地反映土壤中盐分离子的动态变化规律;在膜下滴灌条件下,膜下0~40 cm土层的盐分离子有不同程度的淋洗,Cl–和Na+的淋洗效果好于Ca2+和SO42–;活度系数的估算对模拟结果的准确性有重要影响,尤其是盐分含量较高时,采用通用的函数关系可能会带来较大的模拟误差。     

亚热带花岗岩地区土壤矿物风化过程中盐基离子的释放特征

矿物风化过程中盐基离子释放遵从一定的化学计量关系,这种化学计量关系一般只能通过模拟实验来获取。本研究采用pH 7.0的EDTA-乙酸铵溶液将土壤中的交换性盐基离子完全洗脱出来,然后用Batch方法模拟不同pH溶液淋溶洗脱盐基和未洗脱盐基土壤,旨在消除土壤中交换性盐基离子的影响后更为准确地判断土壤矿物风化的盐基离子释放特征。结果表明:未洗脱盐基土壤的淋出液pH由3.73±0.14逐渐上升到4.23±0.06,主要原因是淋溶液中有高浓度的NH_4~+;洗脱盐基土壤矿物风化后淋出液pH从7.39±0.02逐渐下降到5.39±0.17,主要是由于土壤中可风化矿物减少。土壤交换性盐基离子会改变盐基离子释放特征、释放总量:未洗脱盐基土壤经酸雨淋溶后,各盐基离子释放均呈现急速下降后逐渐平缓的趋势,洗脱盐基土壤矿物风化后,K~+及盐基离子释放总量呈波动上升趋势,且盐基离子释放总量比未洗脱盐基土壤低。土壤交换性盐基离子的存在还会改变淋出液中的盐基离子化学计量关系:未洗脱盐基土壤的K~+︰Ca~(2+)︰Mg~(2+)︰Na+化学计量关系为11︰13︰4︰1(当量比),而洗脱盐基土壤为7︰2︰2︰1。K~+是盐基离子中风化释放量最多的,大部分K~+来自于土壤中云母的风化。因此,只有利用洗脱盐基土壤的盐基离子释放量才能准确计算矿物风化速率并获得准确的化学计量关系。土壤矿物风化作用随着淋溶液酸度增大而增强,但模拟一年降雨量的情况下,p H 3.5、4.5和5.5三种不同p H溶液对矿物风化后盐基离子的释放在实验期间没有显著性影响,较长时间后的差异性有待观察。本研究表明,可以通过预洗脱盐基土壤然后模拟酸雨淋溶的方法,观察矿物风化特征,特别是盐基离子释放的化学计量特征。     

黄土高原土壤物理性质对养分迁移速率的影响

采用一维饱和稳定流易混置换试验,用Cl-和K 为对象模拟黄土高原地区4种典型土壤对养分运移阻滞因子R的影响。试验结果表明对于不同质地的土壤,随着土壤质地变细,运移阻滞因子增大;对于同种质地土壤,随着容重增加,运移阻滞因子增大;对于同种质地而粒级不同的土壤,运移阻滞因子随着粒级的增大而增大;受土壤排斥的离子较受土壤吸引的离子容易穿透土壤。     

模拟再生水灌溉下污灌土壤中盐分离子交换运移的试验研究

为研究再生水灌溉下原污灌区土壤中主要盐分离子交换运移规律,采用有污水灌溉背景的两种质地土壤,根据再生水的基本性质及其盐分离子组分,配制4种浓度水平的入渗液,进行土柱模拟试验。结果表明,不同质地土壤在低Na^＋配制液淋洗下的穿透曲线都出现下凹现象,但Na^＋在壤土中富集的表现并不显著,而在粉质砂壤土中部分Na^＋吸附累积时间较长;模拟再生水入渗溶液中不同组分的盐分离子在不同程度上影响污灌土壤中发生的离子化学反应的进行,导致各处理下Na穿透时间发生显著差异;长期再生水灌溉会对HCO3^-含量较高且粉粒比重大的土壤的入渗等性能产生更为不利的影响。     

自然降雨对粤北岩溶区土壤钙、镁离子流失影响模拟试验北大核心CSCD

采用土柱模拟试验,分析自然降雨对粤北岩溶区土壤钙、镁离子流失的影响。结果表明：土壤钙、镁离子流失量与降雨量变化趋势基本一致,呈现倒＂U＂形季度变化趋势,第2,3季度明显高于第1,4季度;降雨量与土壤钙、镁离子流失量之间存在极显著正相关关系,相关系数在0.891-0.944之间;大雨以上的雨强是造成土壤钙、镁离子流失的主要降雨类型;70%以上的土壤钙、镁离子流失量都是由酸雨造成,酸雨引起土壤贫瘠化、石漠化的问题不容忽视;土壤钙离子与镁离子流失量之间存在极显著正相关关系,相关系数在2011年为0.971,在2012年为0.923。     

三峡库区消落带土壤中施用磷肥对环境激素铅吸附-解吸的影响

采用室内模拟施肥、恒温振荡平衡法研究了磷肥种类、磷肥浓度、铅离子浓度、离子强度和酸度影响三峡库区消落带土壤对铅离子的吸附量和解吸量。结果表明：（1）磷肥种类与铅离子的吸附量和解吸量显著相关,施用Ca（H2PO4）2使铅离子的吸附量和解吸量相对较小;（2）土壤铅离子的吸附量和解吸量与施用磷肥浓度呈显著相关,建议选用磷酸二氢钙、磷酸二氢铵、磷酸二氢钾3种磷肥,施用量在3.4066～8.5164kg P2O5·666.6m-2之间较为合适;（3）铅离子浓度极显著地影响土壤吸附和解吸铅离子,随着铅离子浓度的增加,吸附量和解吸量都呈逐渐增加的趋势;（4）离子强度和酸度都极显著地影响土壤吸附和解吸铅离子,建议选用磷酸二氢钙盐、钾盐和铵盐作为磷肥,可以减小土壤铅离子的环境风险。     

Sediment transport rate-based model for rainfall-induced soil erosion

A one-dimensional mathematical model, termed sediment transport rate-based model, is developed for determining rainfall-induced soil erosion and sediment transport. The model is comprised of (1) the kinematic-wave equation for overland flow, (2) a transport rate-based advection equation for rainfall-induced soil erosion and sediment transport, and (3) a semi-Lagrangian algorithm for numerical solution of the soil erosion and sediment transport equation. A series of soil flume experiments under simulated rainfalls were conducted to simulate the overland flow and sediment transport and to test the sediment transport rate-based model. Numerical results of sediment transport rate-based model indicate that (i) hydrographs display an initial rising limb, followed by a constant discharge and then a recession limb; (ii) sediment transport rate graphs exhibit the distributions similar to the hydrographs; and (iii) sediment concentration graphs show a steep-receding limb followed by a constant distribution and a receding tail. The numerically simulated hydrographs, sediment transport rate and concentration distributions are in good agreement with those measured in laboratory experiments, demonstrating the efficacy of the transport rate-based model.     

不同坡度坡面径流输沙能力对集中流流量变化的响应

坡面水流的输沙能力是影响土壤侵蚀过程的重要参数之一,加强坡面集中水流输沙能力的研究有助于深入理解集中流发生机理,并为防治集中流侵蚀发生提供科学依据。采用室内集中流放水冲刷试验,以黄土高原典型黄绵土为研究对象,研究了集中流输沙能力与放水流量和坡度以及与单宽流量和坡度之间的关系,同时对集中流水力参数和输沙能力的相应关系进行了研究。结果表明:集中流输沙能力随着坡度和放水流量的增加而增加。多元统计分析建立输沙能力与坡度和放水流量之间的幂函数关系发现坡度指标对输沙能力相对放水流量影响更大,而在坡度和单宽流量作用下,由于集中流在大坡度时汇集作用的影响下,坡度指标影响减小。水流功率是描述集中流输沙能力最好的水动力学参数,其次为单位水流功率和水流剪切力,过水断面单位能描述效果最差。总体来说各水动力学参数均能够较好地拟合描述集中流输沙能力。     

Effect of degree of fluid saturation on transport coefficients in disturbed soils

To improve the predictive capability of transport models in soils we need experimental data that improve their understanding of properties at the scale of pores, including the effect of degree of fluid saturation. All transport occurs in the same soil pore space, so that one may intuitively expect a link between the different transport coefficients and key geometrical characteristics of the pores such as tortuosity and connectivity, and pore‐size distribution. To understand the combined effects of pore geometry and pore‐size distribution better, we measured the effect of degree of water saturation on hydraulic conductivity and bulk soil electrical conductivity, and of degree of air saturation on air conductivity and gaseous diffusion for a fine sand and a sandy loam soil. To all measured data were fitted a general transport model that includes both pore geometry and pore‐size distribution parameters. The results show that both pore geometry and pore‐size distribution determine the functional relations between degree of saturation, hydraulic conductivity and air conductivity. The control of pore size on convective transport is more for soils with a wider pore‐size distribution. However, the relative contribution of pore‐size distribution is much larger for the unsaturated hydraulic conductivity than for gaseous phase transport. For the other transport coefficients, their saturation dependency could be described solely by the pore‐geometry term. The contribution of the latter to transport was much larger for transport in the air phase than in the water phase, supporting the view that connectivity dominates gaseous transport. Although the relation between effective fluid saturation and all four relative transport coefficients for the sand could be described by a single functional relation, the presence of a universal relationship between fluid saturation and transport for all soils is doubtful.     

Mechanisms of solute transport affect small-scale abundance and function of soil microorganisms in the detritusphere

In the detritusphere, particulate organic matter offers new sites for microorganisms, whereas soluble substrates are transported into the adjacent soil. We investigated how mechanisms of solute transport affect microbial abundance and function in the detritusphere. In a first experiment, transport was restricted to diffusion, whereas in a second experiment it was dominated by convection. Two soil moisture contents were established in each experiment. When diffusion was the exclusive transport mechanism, the addition of maize litter induced distinct gradients in enzyme activities, soil organic C content and microbial biomass to a depth of 1.5–2.8 mm. Convection enlarged these gradients to 2.5–3.0 mm. The moisture regime modified the temporal pattern of diffusive C transport, microbial growth and enzyme release by inducing faster transport at large water contents. Convective transport seemed to be unaffected by soil moisture content. Using a convective‐diffusive transport model with first‐order decay, it was possible to simulate the observed activity profiles. The results indicate that the spatial dimension of the detritusphere is governed by the ratio between decay rate of available substrates and transport rate. Bacteria and fungi showed differing utilization strategies as revealed by coupling phospholipid fatty acid (PLFA) analysis with stable isotope techniques. Fungi assimilated C directly in the litter, whereas bacteria took up the substrates in the soil and therefore depended more on transport processes than fungi. Our results demonstrate the impact of physicochemical conditions on the abundance and function of microorganisms in the detritusphere. Furthermore, the combination of enzymatic measurements and mathematical transport modelling may offer a new way to measure substrate decay rates in soil.     

Virus Transport Experiments in a Sandy Aquifer

The occurrence of human enteric viruses in ground water has been well documented in the literature. Bacteriophages such as MS-2 and PRD1 have properties similar to pathogenic human viruses suggesting that bacteriophages can be used as proxies for virus transport. The objective of this study is to investigate a “worst case scenario” for virus transport in a ground water aquifer, i.e., sand and gravel aquifer under a forced-gradient, by using bacteriophages. Field studies have been conducted to trace large-scale (34 m) and small-scale (10 m) virus transport under natural- and forced-gradients through a sand and gravel aquifer at a ground water research site at the Texas A&M University. Virus transport was monitored under natural and forced-gradient conditions using MS-2 and PRD-1 as virus tracers and bromide as a conservative tracer. Results indicate virus and bromide transport to down-gradient monitoring wells in both the large- and small-scale field tests. During the tests conducted, MS-2 transport appears to exhibit little longitudinal dispersion, showing a narrow peak at the well nest 34 m down-gradient in 13 days which is 20 days before the bromide breakthroughs, indicating that bacteriophage transport through the aquifer was mainly by advective flow. Differences in tracer transport can be attributed to the heterogeneity of the sand and gravel aquifer at the site, different injection methods, different sampling methods, and different tracer properties. Heterogeneity of the aquifer would cause virus transport through preferential flow paths.     

黄土坡面细沟水流输沙能力变化特征

水流输沙能力是土壤侵蚀过程极其重要的参数之一,精确计算细沟水流输沙能力可以有效揭示细沟侵蚀过程机理,为建立坡面细沟侵蚀过程模型奠定重要基础。采用细沟水槽试验方法对黄土坡面细沟水流输沙能力变化特征进行研究。结果表明:不同坡度下,细沟水流输沙能力随流量增加而平缓增大,可用幂函数方程很好地描述;不同流量下,细沟水流输沙能力随坡度的增加而增大,可以用指数方程很好地描述;细沟水流输沙能力随流量及坡度变化的因子模型为二元幂函数方程,其中流量对细沟水流输沙能力的影响大于坡度的影响;ANSWERS模型中的输沙能力方程不能用于计算黄土陡坡细沟水流输沙能力。     

Zur relativen Bedeutung von Massenfluß und Diffusion beim Nitrattransport zur Wurzel

Relative contribution of mass flow and diffusion to nitrate transport towards roots Experimental data from a field experiment with oats and faba beans were used to quantify the contribution of mass flow to nitrate transport towards roots. Two different approaches were used. The first was the calculation of apparent mass flow from average nitrate concentration and water uptake rate. The second was the computation of the increase of nitrate transport rate caused by mass flow. This was done using a mathematical model for nutrient transport. A comparison was made for a reference situation of transport by diffusion only. Calculation of apparent mass flow resulted in a nitrate transport to faba bean roots of 88 and 42 kg N-ha^?1 in 1982 and 1983, respectively. This accounted for 27 and 16% of total N accumulation of the faba bean shoots. For oats a transport of 38 and 23 kg N-ha^?1 by mass flow was calculated. These values correspond to 30 and 16% of total N uptake of oats in both years. The model calculations, however, showed that apparent mass flow overestimated the contribution of mass flow drastically when the nitrate concentration at the root surface is much lower than the average nitrate concentration of the soil solution as was found for faba beans in the soil layer 40–60 cm depth. In that case apparent mass flow overestimated the real increase of nitrate transport to roots by mass flow by a factor of 2.7. Under the given conditions diffusion was the more important process involved in the nitrate transport towards roots. The increase in maximum nitrate transport rate towards roots is much lower than apparent mass flow.     

温室表层土壤硝态氮运移的水、热耦合效应研究

为了探讨温室作物生产水肥管理和温度环境对土壤NO3--N向表层迁移的影响,选用5 a的温室土壤样品进行土柱蒸发模拟试验,研究蒸发温度、土壤初始含水量、初始NO3--N含量及其耦合效应对温室土壤迁移速率及其垂直剖面分布的影响。试验结果表明:蒸发温度和土壤初始含水量明显影响NO3--N向土壤表层的迁移,并随蒸发温度和土壤初始含水量的增加而加强;通过正交回归分析得出影响NO3--N迁移速率的因素依次为初始含水量、蒸发温度以及温度与含水量的交互作用;土壤初始NO3--N含量以及它与蒸发温度、土壤初始含水量的交互作用对NO3--N迁移速率的影响不显著,但它影响土壤中各层的NO3--N绝对含量;经过5 d蒸发后,NO3--N沿垂直剖面分布出现上高下低,并出现一小的回升后逐渐趋于稳定。本文建立了蒸发条件下NO3--N迁移速率的回归模型,利用该回归模型,可为温室土壤在不同环境及水肥条件下NO3--N向表层迁移速率的预测提供依据。