盐渍化灌区土壤盐分的时空变异特征及其与地下水埋深的关系

土壤盐分空间变异特征和地下水埋深状况是指导灌区合理用水和防治土壤盐碱化的重要依据。运用经典统计学和地质统计学方法,结合GIS技术,分析了河套灌区沙壕渠灌域0-20 cm、20-40 cm、40-60 cm土壤EC值的空间变异特征及地下水埋深对土壤盐分分布的影响。结果表明:沙壕渠灌域土壤盐分Cv值在不同灌溉时期和不同土壤深度均大于36%,表现为强变异特征;各灌水时期和不同土壤深度土壤EC值均表现为中等强度的空间自相关性,表层0-20 cm土壤空间自相关程度最高;秋浇前不同层次土壤EC值的空间分布在灌域内从南到北呈增大趋势,秋浇后土壤含盐量的高值区在西北部或东北部;土壤盐分受地下水埋深影响显著,灌域内地下水埋深南深北浅,土壤盐分随地下水埋深的增大而减小,二者之间满足指数关系。因此,应采取合理措施控制地下水埋深,防止区域土壤盐渍化加剧。     

蒸发条件下潜水埋深对土壤-柽柳水盐分布的影响

盐水矿化度下模拟设置4个潜水埋深(0.9、1.2、1.5、1.8 m),分析不同土层的土壤相对含水量(RWC)、含盐量(S_C)和土壤溶液绝对浓度(C_S)等水盐参数,及柽柳叶片和新生枝条的含水量及Na~+含量,探讨盐水矿化度下土壤-柽柳水盐参数对潜水埋深的响应规律。结果表明:各土层RWC与潜水埋深呈负相关,0.9 m潜水埋深下各土层的RWC均最高,且各土层RWC随土层深度的增加呈先降低后增加的趋势,其它潜水埋深下各土层RWC均逐渐增加,1.2 m是地下水所能上升且保持柽柳柱体土壤表层湿润的最高高度。各土层S_C和C_S与潜水埋深呈抛物线型,均表现为先增加后降低,潜水埋深1.2 m时,各土层S_C均最高。随土层深度的增加,各潜水埋深下S_C先降低后增加,而C_S呈现减少趋势;潜水埋深越高,土层间C_S变化幅度越激烈。潜水埋深对柽柳叶片和新生枝条的含水量无显著影响(P0.05),而随潜水埋深的增加,柽柳叶片Na~+含量逐渐增加,新生枝条Na~+含量则先增加后降低。从整个柽柳土柱看,随潜水埋深的增加,整个土壤剖面的RWC均值逐渐降低,而S_C和C_S均值先增加后降低,潜水埋深1.2 m是盐分变化的分界点,建议栽植柽柳的潜水埋深大于1.2 m。     

黄河三角洲典型植被与地下水埋深和土壤盐分的关系

土壤盐分和地下水埋深是影响黄河三角洲植被发育和分布的重要因素.本文通过野外调查与统计分析,研究了黄河三角洲区域典型植被(翅碱蓬 柽柳、刺槐、芦苇和棉花)、地下水埋深、土壤盐分之间的关系.结果表明: 研究区地下水埋深显著影响土壤盐分,平均影响系数为0.327,地下水埋深在0.5～1.5 m的土壤盐渍化最严重;整个研究区内植被发育较差,其中,研究区78%面积的归一化植被指数(NDVI)<0.4,地下水埋深、土壤盐分对天然植被分布有显著影响;土壤盐分对研究区翅碱蓬-柽柳、刺槐、芦苇及棉花NDVI的影响显著,地下水埋深对翅碱蓬-柽柳NDVI的影响显著,对芦苇、棉花、刺槐NDVI的影响不显著.     

苏干湖湿地土壤全盐含量特征及其与地下水的关联

地下水是内陆盐沼湿地生态水文过程及演变的关键因素,地下水位埋深和水质特征交互作用影响水盐运移过程和表层土壤盐渍化程度。根据2018年8月土壤盐分与地下水特征的监测数据,运用经典统计学、皮尔逊相关性和主成分分析等方法对苏干湖湿地（93°47''53″-94°04''26″E,38°50''07″-38°56''27″N）不同水位下表层0-10 cm土壤全盐含量、地下水水质特征及其间的关系进行定量分析。结果表明：（1）研究区0-10 cm土壤全盐含量的均值为204.41 g/kg,随地下水埋深的增加,土壤全盐含量的均值、变化幅度和变异系数呈先增加后降低的趋势。（2）地下水埋深介于0.17-6 m,pH在7.06-9.56范围,阳离子以Na⁺为主,阴离子以SO₄^2-和Cl^-为主,离子浓度变异系数从强到弱依次为Na⁺ > Mg²⁺ > Ca²⁺ > Cl^- > SO₄^2- > HCO₃^- > K⁺ > CO₃^2-。（3）关联分析表明,在水埋深<1 m、1-2 m的区域表层全盐含量与地下水埋深呈正相关,地下水埋深介于2-3 m和>3 m的区域两者间呈负相关;土壤全盐含量与地下水水质离子Na⁺、Mg²⁺、SO₄^2-、Cl^-间呈极显著正相关,与K⁺、CO₃^2-、HCO₃^-间的相关系数较低且不显著。内陆盐沼湿地表层土壤全盐含量与地下水埋深、地下水水质特征的关联分析,体现了内陆盐沼湿地土壤水盐运移过程的复杂性。     

Transformations of TNT and related aminotoluenes in groundwater aquifer slurries under different electron-accepting conditions

The transport and fate of pollutants is often governed by both their tendency to sorb as well as their susceptibility to biodegradation. We have evaluated these parameters for 2,4,6-trinitrotoluene (TNT) and several biodegradation products. Slurries of aquifer sediment and groundwater depleted TNT at rates of 27, 7.7 and 5.9 μM day⁻¹ under methanogenic, sulfate-reducing and nitrate-reducing conditions, respectively. Abiotic losses of TNT were determined in autoclaved controls. Abiotic TNT loss and subsequent transformation of the products was also observed. These transformations were especially important during the first step in the reduction of TNT. Subsequent abiotic reactions could account for all of the transformations observed in bottles which were initially nitrate-reducing. Other controls removed TNT reduction products at much slower rates than slurries containing live organisms. 2-Amino-4,6-dinitrotoluene was produced in all slurries but disappeared in methanogenic and in sulfate-reducing slurries within several weeks. This compound was converted to 2,4-diamino-6-nitrotoluene in all slurries with subsequent removal of the latter from methanogenic and sulfate-reducing slurries, while it persisted in autoclaved controls and in the nitrate-reducing slurries. Aquifer slurries incubated with either 2,4- or 2,6-diaminotoluene showed losses of these compounds relative to autoclaved controls under nitrate-reducing conditions but not under sulfate-reducing or methanogenic conditions. These latter compounds are important as reduced intermediates in the biodegradation of dinitrotoluenes and as industrial chemicals. In experiments to examine sorption, exposure to landfill sediment resulted in losses of approximately 15% of diaminotoluene isomers and 25% of aminodinitrotoluene isomers from initial solution concentrations within 24 h. Isotherms confirmed that the diaminotoluenes were least strongly sorbed and the amino-dinitrotoluenes most strongly sorbed to this sediment, while TNT sorption capacity was intermediate. In our studies, 2,4,6-triaminotoluene sorption capacity was indeterminate due to its chemical instability. Coupled with biodegradation information, isotherms help describe the likelihood of contaminant removal, persistence, and movement at impacted sites. Received 11 March 1996/ Accepted in revised form 24 July 1996     

不同土壤水分条件下北方稻田耗水规律研究

采用田测法研究不同土壤水分条件下稻田需水规律．试验采用淹灌、湿润灌和间歇灌3种灌水处理．结果表明,在整个生育期内由田测法测得的淹灌、湿润灌和间歇灌3种处理的蒸散量分别为889．1、635．9和775．9mm．蒸散速率分别为6．9、4．9和6．0mm·d^-1．与淹灌处理相比．湿润灌和间歇灌处理分别节水28．5％和12．7％．在充分供水的情况下,由Penman法计算的潜在蒸散值分别比田测法小29．30％．淹灌、湿润灌和间歇灌3种处理的生物产量分别为16438．22、15887．94和15757．88kg·hm^-2．经济产量分别为8014．01、7828．91和7853．93kg·hm^-2．统计分析结果表明．3种处理间的产量差别不显著．淹灌、湿润灌和间歇灌3种处理的水分利用效率(WUE)分别为9．01、12．31和10．12kg·hm^-2·mm^-1．淹灌的WUE分别比湿润灌和间歇灌减少26．8％和11．0％．对比分析结果表明．湿润灌的节水效果最好．     

变饱和带条件下污水灌溉对土壤氮素运移和冬小麦生长的影响

为了研究地下水浅埋区污水灌溉对土壤环境及作物生长的影响,设置地下水埋深(2、3m和4m)和灌水水量(900m3·hm-2和1200m3·hm-2)2个因素,对冬小麦全生育期土壤氮素和冬小麦生长发育指标进行试验,试验在地中渗透仪中进行.结果显示:灌水后,不同处理土壤中硝态氮含量均显著增加,灌水水平越高,土壤中硝态氮含量增加越多;灌水后,灌水水平B1(900 m3·hm-2)不同潜水埋深地下水硝态氮分别增加34.67%、24.94%、20.88%;灌水水平B2(1200 m3·hm-2)不同潜水埋深地下水硝态氮分别增加58.42%、38.98%、27.21%.潜水埋深越浅,地下水中硝态氮的浓度增加越大,这也就表明由于淋溶和硝化作用产生的硝态氮造成浅层地下水污染的风险越大.污水灌溉对冬小麦的生长发育指标和产量有促进作用;相同灌水水平(B1 和B2),地下水埋深影响冬小麦生长发育指标的大小顺序为:2m＞3m＞4m.     

Mercury translocation in and evaporation from soil. III. quantification of evaporation of mercury from podzolized soil profiles treated with Hg Cl

Mercury evaporation from undisturbed iron‐humus podzol lysimeters was measured over 3 months after treatment with HgCl₂ spiked with radioactive ²⁰³Hg. The relative evaporation rate from HgCl₂ treated soils followed the sum of two exponential functions. Because evaporation asymptotically approaches zero with time, the integral of the fit curve represents the evaporative loss in percent of atmospheric deposition. For the soil investigated, about 5% of atmospheric Hg deposition was reemitted into the atmosphere. It is hypothesized that mercury evaporation can decrease the leaching of mercury in and from soil significantly; this effect is probably increasing with decreasing rain acidity or soil acidity. Mercury deposited as soluble salt remains susceptible to reemission to air for 300 d after incorporation into the soil matrix. Indications are found that Hg evaporation from soils in geological background areas predominantly derives from recent atmospheric Hg deposition and not from geological sources.     

Ameliorative role of zinc on maize growth (Zea mays L.) under salt-affected soil conditions

A greenhouse experiment, growing maize for six weeks, was conducted to evaluate the ameliorative role of Zn (0 and 10 ppm Zn) under saline (ECe4, 8 and 12 mmhos/cm), Sodic (ESP 10, 20 and 30) and saline-sodic (all possible combinations of above salinity and sodicity levels), and normal soil conditions using a sandy loam (Typic Ustochrepts) soil sample.Zinc ameliorated plant growth under salt-affected soil conditions. Ameliorative effect was more under sodic than under saline or saline-sodic soil conditions. Shoot yield decreased with Salinity level of 12 mmhos/cm, and ESP 30 and adverse effects were accentuated with increasing level of ESP and Salinity, respectively.Shoot Zn increased with applied Zn. Increasing sodicity in soil under Zn deficient or low salinity conditions generally decreased shoot Zn, whereas the low level of soil salinization counteracted the adverse effect of high sodicity. Shoot Na increased but K decreased with increasing sodicity and salinity in soil. Shoot Na decreased but K increased with applied Zn. Shoot Ca increased with salinity levels of 4 and 8 mmhos/cm, but decreased with 12 mmhos/cm at 0 Zn level. Sodicity decreased shoot Ca, whereas Zn counteracted adverse effect of high sodicity. Shoot Mg generally increased with increasing salinity, but decreased with increasing sodicity. Zinc had no definite effect. Shoot Ca/Na and K/Na ratios were widened with Zn and narrowed down with high ESP.The effects of salinity, sodicity, and Zn on plant growth and its composition were generally associated with their respective roles in dry matter production, and inter-ionic relationships among Ca, Mg, K, Na and Zn in soils and plants.Contribution from the Department of Soils, Haryana Agricultural University, Hissar, 125004, Indiaformer Research Fellow, respectively.     

Assessment of wheat productivity responses and soil health dynamics under brackish ground water

The continuous use of brackish groundwater for irrigation is detrimental for soil and crop attributes. A three-year research study was designed for the wheat crop to assess the effects of brackish groundwater on crop yield and soil health under a surface irrigation system. Three sites were selected in different cropping zones of Pakistan. The treatments comprised of irrigation with moderately brackish water having 0.8, 1.3 & 2.7 dSm^?1 of salinity and canal water. The results indicated that EC, SAR, bicarbonates, Ca²⁺ and Mg²⁺ levels increased in the soil for consecutive years and this increase was more at site S3 followed by S2 and S1. As soil depth is concerned, the increase was more pronounced in upper layers of soil (0–15 cm) as compared to 15–30 cm depth. Growth and yield were also affected by the consecutive use of this water, the number of plants, plant height, the number of spikes per plant, and yield was reduced at all the three sites. However, the impact was less pronounced at the site S1 whereas S3 was the most affected one. Grain weight and dry matter weight were observed to be maximum at S1. Water productivity was also calculated for all the three sites. Maximum water productivity was observed at S1 followed by S2 & S3. It was concluded that the continuous use of brackish water would have an adverse effect on crop yield and subsequently, soil health is also affected by it significantly.     

Spatial distributions and net deposition rates of mineral elements in the elongating wheat (Triticum aestivum L.) leaf under saline soil conditions

Wheat leaf growth is known to be spatially affected by salinity. The altered spatial distribution of leaf growth under saline conditions may be associated with spatial changes in tissue mineral elements. The objective of this study was to evaluate the spatial distributions of mineral elements and their net deposition rates in the elongating and mature zones of leaf 4 of the main stem of spring wheat (Triticum aestivum L. cv. Lona) during its linear growth phase under saline soil conditions. Plants were grown in an illitic-chloritic silty loam with 0 and 120 mM NaCl. Three days after emergence of leaf 4, sampling was begun at 3 and 13 h into the 16-h light period. Spatial distributions of fresh weight (FW), dry weight (DW), and Na⁺, K⁺, Cl⁻, NO⁻ ₃, Ca²⁺, Mg²⁺, total P, and total N in the elongating and mature tissues were determined on a millimeter scale. The patterns of spatial distribution of Na⁺, Cl⁻, K⁺, NO₃ ⁻, and Ca²⁺ in the growing leaves were affected by salinity, while those of Mg²⁺, total P, and total N were not. Sodium, K⁺, Cl⁻, Ca²⁺, Mg²⁺, and total N concentrations (mmol · kg⁻¹ FW) were consistently higher at 120 mM NaCl than at 0 mM NaCl along the leaf axis from the leaf base, whereas NO₃ ⁻ concentration was lower at 120 mM NaCl. Deposition rates of all nutrients were greatest in the elongation zone. The elongation zone was the strongest sink for mineral elements in the leaf tissues. Local net deposition rates of Na⁺, Cl⁻, Ca²⁺, and Mg²⁺ (mmol · kg⁻¹ FW · h⁻¹) in the most actively elongating zone were enhanced by 120 mM NaCl, whereas for NO₃ ⁻ this was depressed. The lower supply of NO⁻ ₃ to growing leaves may be responsible for the inhibition of growth under saline conditions. Higher tissue concentrations of Na⁺ and Cl⁻ may cause ion imbalance but probably did not result in ion toxicity in the growing leaves. Potassium, Ca²⁺, Mg²⁺, total P, and total N are less plausibly responsible for the reduction in leaf growth in this study. Higher tissue K⁺ and Ca²⁺ concentrations at 120 mM NaCl are probably due to the presence of high Ca²⁺ in the soil of this study. Received: 13 March 1997 / Accepted: 9 June 1997     

基于Landsat系列数据的盐分指数和植被指数对土壤盐度变异性的响应分析——以新疆天山南北典型绿洲为例

基于不同地理区域,借助目前已有或者构建新的盐分和植被指数定量评估研究区的土壤盐度状况。但多数指数并未在盐渍化较为严重的中国新疆地区进行系统性对比分析。因此,以新疆阜北地区(采样数=37),玛纳斯河绿洲(采样数=68)和渭干河-库车河绿洲(采样数=38)为研究区,以灌区农田和盐渍地采样数据和Landsat TM/ETM+/OLI为数据源,利用线性模型和多个非线性模型(10个)测试上述指数(14个指数)和原始波段对于研究区土壤盐度的敏感性。结果显示,阜北地区基于遥感获取的扩展的增强型植被指数Extented Enhanced Vegetation Index(EEVI)在全样本和部分样本(盐渍化样本,土壤盐度0.3%)两种模式下(0—10cm),较其他指数和波段而言较为敏感。在全样本和部分样本(土壤饱和溶液电导率2ds/m)两种模式下,与玛纳斯流域各层土壤盐度最为敏感的为band 2,部分样本模式下土壤盐度变异性显著性探测最大下探深度为30cm。渭干河-库车河绿洲全样本模式下,最大土壤盐度变异性显著性探测深度为40cm,0—10cm和10—20cm深度表现最为敏感的是土壤盐分指数SI-T,20—40cm深度则为植被指数TGDVI。部分样本下(土壤饱和溶液电导率2ds/m),0—10cm深度最为敏感的为band5,10—20cm深度最为敏感的为TGDVI,20—40cm深度则为EEVI。其他指数因地理环境的差异性(气候,土壤盐分类型,土壤类型,采样时间),与土壤盐度之间并未达到显著性(sig=0.05或者0.01)的水平。以上结果只是初步结论,但也暗示其中的某些指数在本区具有一定土壤盐度的识别潜力。此外,由于土壤本身的复杂性,需要采集更多的样本以深入分析不同盐度等级下上述指数的具体表现。     

Root dynamics in a salt marsh over three consecutive years

The minirhizotron technique has been used to study root development in a salt marsh in the western part of the Nationalpark Niedersächsisches Wattenmeer during a three-year period. The objective of our study was to evaluate root depth distribution and seasonal changes in growth activities of natural plant root systems. Root number was counted at monthly intervals in the top soil layer (0–0.2 m) for every 2 cm soil depth. The number of roots was regarded as an easily detectable parameter reflecting root growth and decay.In general, highest rooting intensity was found in the soil's subsurface layer (0–0.08 m). The number of roots significantly decreased in deeper horizons of the soil. There was also a significant increase and decrease in the number of roots in the course of a year. The highest rooting intensity was found in late winter to early spring, which substantially decreased towards mid summer when the plants were in their reproductive phase. The data indicate that there is a clear seasonal pattern of root growth of salt marsh species.     

干旱区不同地下水埋深下胡杨细根空间分布特征

细根空间分布特征能够反映植物对环境的利用程度和适应性,这对评价植物适应逆境至关重要。为了探究胡杨细根空间分布在干旱环境下的适应性特征,以塔里木河下游极端干旱区不同地下水埋深条件下的成年胡杨(Populus euphratica Oliv.)为对象,采用人工挖掘法,对胡杨细根(D≤2 mm)空间分布及其与地下水埋深和土壤水分的关系进行了研究。结果显示:(1)在水平方向上(550 cm范围内),胡杨细根的根长密度(RLD)、表面积密度(SAD)、根质量密度(RMD)随水平距离的增加未发生显著变化;(2)在垂直方向上,土壤表层基本无细根分布,随土壤深度加深,胡杨细根RLD、RMD呈先增加后减少的分布特征,并且在地下水埋深较深处,胡杨细根在较深土壤层(280 cm)仍保持较高的比根长(SRL)和比表面积(SRA);(3)胡杨细根RLD、RMD与上层土壤(0~180 cm)含水量存在较高的正相关关系,而与深层土壤(180 cm以下)含水量存在空间差异。本研究表明生长在上层土壤(0~180 cm)的胡杨细根主要受水分的限制,而生长在土壤深层的细根很可能受地下水埋深的影响,同时为了应对干旱环境,胡杨根系不仅具有较强的水平扩展能力,也会向深层湿润的土壤发展。研究结果可为极端干旱环境下胡杨适应机制的研究提供参考。     

半干旱区不同垄沟集雨种植马铃薯模式对土壤蒸发的影响

通过垄沟集雨种植马铃薯试验,研究了不同垄沟集雨种植模式对土壤蒸发的影响.结果表明,在马铃薯全生育期,垄上覆盖塑料薄膜(CR)处理土壤蒸发量为122.9～165 mm,垄上原土夯实不覆膜(UR)处理土壤蒸发量为90.9～101.2 mm,无垄带状种植(CK) 土壤蒸发量为80.7 mm.其中,覆膜垄处理CR₆₀在马铃薯成熟期土壤蒸发强度最大,达2.6 mm·d^-1,平均为1.46 mm·d^-1,而对照的土壤蒸发强度为0.65 mm·d^-1;不覆膜土垄处理(UR₃₀)土壤蒸发强度苗期最小,只有0.2 mm·d^-1,平均为0.39 mm·d^-1,而对照的土壤蒸发强度为0.58 mm·d^-1.在马铃薯生长的现蕾期和开花期,水面蒸发量最大,日平均水面蒸发量分别为8.3和9.0 mm,与土壤蒸发不同步.马铃薯成熟期,各处理棵间土壤蒸发量都达到最大值.覆膜垄蒸发量最大,集雨效果显著,所以应采取抑制土壤蒸发措施,以便进一步提高水分利用效率.     

不同水分条件下毛果苔草枯落物分解及营养动态

于2009年5月至2010年5月采用分解袋法,研究了三江平原典型湿地植物毛果苔草枯落物分解对水分条件变化的响应,探讨了典型碟形洼地不同水位下枯落物分解1a时间内的分解速率与N、P等营养元素动态。分解1a内,无积水环境下枯落物失重率为34.99%,季节性积水环境下为27.28%,常年积水环境下随水位增加枯落物失重率分别为26.99%与30.67%,表明积水条件抑制了枯落物的分解。枯落物的分解随环境变化表现出阶段性特征,分解0—122 d内随水位增加枯落物失重率分别为16.09%、24.25%、23.53%与26.60%,即生长季内积水条件促进了枯落物有机质的分解及重量损失。而随实验进行,分解122—360 d内随水位增加毛果苔草枯落物的失重率分别为18.90%、3.02%、3.46%、4.03%,即在非生长季土壤冻融期积水条件抑制了枯落物分解(P<0.05)。水分条件对毛果苔草枯落物N元素的影响表现为积水条件促进生长季内枯落物的N固定,水位最高处毛果苔草N浓度显著高于无积水环境(P<0.05)。但进入冻融期后积水环境下枯落物N浓度与含量降低;其中季节性积水限制了枯落物的N积累能力,至分解360d时与初始值相比表现出明显的N释放(P=0.01)。毛果苔草枯落物分解61d时P出现富集,其中积水条件下P的富集作用增强,但与水位不相关。分解1a后毛果苔草枯落物表现为P的净释放,不同水分条件下枯落物P元素损失没有明显差异(P>0.05)。     

Community dynamics within a bacterial consortium during growth on toluene under sulfate-reducing conditions

A sulfate-reducing bacterial consortium was enriched from an anoxic aquifer contaminated with BTEX compounds, using toluene as a growth substrate. Total cell counts, protein contents and sulfide production were determined to follow growth at the in situ temperature (14 °C) and at 25 °C, respectively. Community members were identified by 16S rRNA gene cloning and sequencing. Phylogenetic analysis revealed 12 sequence types belonging to Deltaproteobacteria (several groups) , Epsilonproteobacteria, Bacteroidetes, Spirochaetaceae and an unclassified bacterial clade. The most prominent phylotype comprising 34% of all clones was affiliated to the Desulfobulbaceae and closely related to environmental clones retrieved from hydrocarbon-contaminated aquifers. Flow-cytometric methods were applied to analyze the community dynamics and to identify key organisms involved in toluene assimilation. Flow-cytometric measurement of DNA contents and scatter behavior served to detect and quantify dominant and newly emerging clusters of subcommunities. Up to seven subcommunities, two of them dominant, were distinguished. Cell sorting was used to facilitate the analysis of conspicuous clusters for phylogenetic identity by terminal restriction fragment length polymorphism profiling of the 16S rRNA genes. The Desulfobulbaceae phylotype accounted for up to 87% in proliferating subcommunities, indicating that it represents the key organism of toluene degradation within this complex anaerobic consortium.     

Solute dynamics in soil water and groundwater in a central Amazon catchment undergoing deforestation

Hydrochemical changes caused by slash-and-burnagricultural practices in a small upland catchment inthe central Amazon were measured. Soluteconcentrations were analyzed in wet deposition,overland flow, shallow throughflow, groundwater andbank seepage in a forested plot (about 5 ha) and anadjacent plot (about 2 ha) which had been deforestedin July 1989 and planted to manioc, and in streamwater in partially deforested and forested catchments. Measurements were made from November 1988 to June1990. The effects of slash-and-burn agriculturalpractices observed in the experimental plot includedincreased overland flow, erosion, and large losses ofsolutes from the rooted zone. Concentrations ofNO₃ ^-, Na⁺, K⁺, SO₄ ²-,Cl^- and Mn in throughflow of the experimentalplot were higher than those of the control plot bymore than a factor of 10. Extensive leaching occurredafter cutting and burning, but solute transfers werediminished along pathway stages of throughflow togroundwater, and particularly within the riparian zoneof the catchment. High concentrations of N and P inoverland flow indicate the importance of usingforested riparian buffers to mitigate solute inputs toreceiving waters in tropical catchments.     

Diffusion profiles in L. lactis biofilms under different conditions

Despite being an important topic in biofilm research, we still know little about diffusion in biofilms. Emerging biofilms of Lactococcus lactis growing in custom‐made flow‐cells were monitored and diffusion constants across the height of the biofilms recorded. The biofilms showed different diffusional behavior with regard to flow rate and pH variations, despite growing to similar thickness. At a higher flow rate, the biofilm exhibits slower diffusion compared to the reference cultivation at lower flow rate. By increasing pH, the biofilm exhibited fast growth and little difference in diffusion compared to the reference cultivation. Furthermore, the diffusion inside of the biofilms differed depending on the position in the flow‐cell. The present study reveals new insights in how external factors can affect structure and density of biofilms. The method can be reliably used for L. lactis biofilms with a thickness up to 120 μm.