Effects of Soil Type and Cover Condition on Cryptosporidium parvum Transport in Overland Flow

Overland transport kinetics of pathogens is controlled, in large part, by soil and vegetation. With an increasing number of concentrated animal operations, there is becoming a greater need to dispose of a vast amount of manure in a single, localized area. Animal manure contains a substantial amount of microbial pathogens, including Cryptosporidium parvum that may pose a threat of contamination of water resources. This study examines the kinetics of C. parvum in overland transport and critical factors involved in the design of best management practices, especially vegetative filter strips, to prevent the transport of harmful pathogens to water bodies. Three soil types were tested (Catlin silt-loam, Alvin fine sandy-loam, Darwin silty-clay), spanning the entire spectrum of typical Illinois soils. A 20-min rainfall event was produced using a small-scale (1.07 m?×?0.66 m) laboratory rainfall simulator over a soil box measuring 0.67 m?×?0.33 m. Each soil type was tested for pathogen transport kinetics with bare surface conditions as well as with smooth brome and fescue vegetative covers. Surface runoff, soil cores, and near-surface runoff were each analyzed for infective C. parvum oocysts using cell culture infectivity assays. Results showed that vegetation greatly reduced the recovery of infective oocysts, in addition to delaying the time to the peak recovery. However, there was no clear evidence of any one vegetation type being advantageous over another. The bare soil experiments resulted in a higher recovery of C. parvum oocysts from the Darwin soil compared to other two soils. Analyses of soil cores show a slightly higher recovery of oocysts in the Catlin soil compared to Alvin or Darwin soils.     

Movement of the protozoan pathogen Cryptosporidium parvum through three contrasting soil types

The potential for transfer of the protozoan pathogen Cryptosporidium parvum through soil to land drains and, subsequently, water courses following the application of livestock waste to land was monitored in the laboratory using simulated rainfall and intact soil cores. Following irrigation over a 21-day period, Cryptosporidium parvum oocysts applied to the surface of soil cores (initial inoculum concentration 1×10⁸ oocysts core^–1) were detected, albeit in low numbers, in the leachates from clay loam and silty loam soils but not in that from a loamy sand soil. Variations in leaching patterns were recorded between replicate cores. At the end of the study soil cores were destructively sampled to establish the location of oocysts remaining within the soil. Distribution within cores was similar in all three soil types. The majority (72.8+-5.2%) of oocysts were found in the top 2 cm of soil, with numbers decreasing with increasing depth to 13.2±2.8%, 8.39±1.4%, and 5.36±1.4% at depths of 10, 20, and 30 cm, respectively.     

The effect of flow impedance on deposition of Cryptosporidium parvum oocysts with or without a vetiver buffer strip

Cryptosporidium parvum oocysts can be transported in overland flow from faecal deposits of grazing animals causing potential water contamination problems. Deposition of oocysts can occur when overland flow encounters vegetative buffers and its transport capacity is decreased in the upslope backwater region. Deposition of oocysts was investigated using a large rainfall simulator, with and without a vetiver buffer strip. Oocysts-spiked slurries were applied to two contrasting soils and the resultant oocyst/sediment depositions from the flow were compared. The buffers substantially reduced suspended sediment loads from the two soils and increased the oocyst concentration in the soil with >99% of the deposited oocysts measured upslope of the buffer.     

再生水灌溉模式对潮土结构性质及导水性能的影响

为揭示再生水不同灌溉模式下土壤结构性质及导水性能的差异。通过室内模拟土柱入渗试验,以清水灌溉为对照(CK),研究了再生水持续灌溉(RW)、再生水—清水混合灌溉(RW-2)及再生水—清水交替灌溉(ARW)3种灌溉模式对土壤容重、总孔隙度、团聚体稳定性、入渗率及饱和导水率的影响。结果表明:相比CK,各处理容重呈降低趋势,总孔隙度增加,但差异均不显著;再生水灌溉促进潮土>1mm粒级团聚体向<1mm粒级团聚体转化,相比CK,各处理<1mm粒级团聚体含量分别增长11.51%~31.22%;潮土团聚体水稳定性降低;各处理>0.25mm粒级团聚体含量分别降低2.92%~9.75%,平均质量直径分别降低11.30%~38.38%,几何平均直径分别降低3.93%~12.78%,其中RW最为显著;相关性分析表明,>1mm粒级水稳性团聚体含量对潮土结构稳定性贡献最大;再生水3种灌溉模式下潮土入渗率分别显著增长80.00%~260.00%;ARW处理潮土有效导水率上升22.68%,而RW和RW-2处理土壤有效导水率分别下降14.47%和42.36%。保持潮土结构性质方面以RW-2处理最好,改善潮土导水能力方面则以ARW处理最为显著。     

Detection of Infectious Cryptosporidium Parvum Oocysts in Environmental Water Samples Using an Integrated Cell Culture-PCR (CC-PCR) System

Examination of naturally occurring C. parvum oocysts from environmental water samples has previously been hampered by the inability to determine the public health significance of detected organisms. As a result the safety of drinking water supplies was in question. These limitations have been resolved through the development and application of a method that incorporates immunomagnetic separation (IMS) and an infectivity determination using an integrated cell culture, polymerase chain reaction assay (CC-PCR). Briefly, the method concentrates water samples by filtration or centrifugation and isolates oocysts by IMS. An acidified Hank's balanced salt solution (HBSS) containing 1% trypsin was used for the dissociation of captured oocysts from the IMS beads. In vitro HCT-8 cell culture of purified oocysts was performed in 96-well microtiter plates and infected cells were detected using PCR primers specific for C. parvum. A total of 242 raw source waters or filter backwash water samples from twenty five sites in the U.S. were analyzed to validate the procedure. Oocyst seeded in raw and filter backwash water samples were used to evaluate recovery efficiencies and performance of the CC-PCR protocol with different water quality matrices. The CC-PCR detected infectious Cryptosporidium parvum in 6 of 121 (5.0%) raw and 9 of 122 (7.4%) filter backwash water samples. All CC-PCR positive samples were confirmed by cloning and DNA sequence analysis of the PCR products. Isolates were shown to originate from human and animal sources. Grouping of genotypes permitted evaluation of strain diversification and variation. Current studies are using this technique to examine oocysts in various watersheds and in the finished drinking water of over 80 surface water treatment plants.     

再生水灌溉水平对土壤盐分累积与细菌群落组成的影响

为探明再生水不同灌水水平下土壤盐分、氮素、磷素与细菌群落组成动态变化效应,采用室内土柱灌水试验,研究再生水、自来水不同灌水水平对土壤盐分、氮素、磷素及细菌群落组成结构的影响。结果表明:1)再生水灌溉相比自来水显著提高了0~60 cm土层盐分含量、磷素及0~30 cm土层氮素含量也有所提高,降低了土壤细菌群落多样性和OTU数量;充分灌溉相比非充分灌溉提高了深层土壤盐分含量,降低了深层土壤细菌群落多样性和种类数。2)不同处理土壤细菌类群以放线菌门(24.5%~40.6%)和变形菌门(22.4%~30.3%)为主。非充分灌溉下,再生水灌溉相比自来水提高了土壤放线菌门、绿弯菌门、厚壁菌门及酸杆菌门比例,降低了变形菌门比例;充分灌溉下,再生水灌溉相比自来水大幅度提高了土壤放线菌门和硝化螺旋菌门比例,降低了土壤变形菌门、绿弯菌门、酸杆菌门及厚壁菌门比例。无论是在充分灌溉还是非充分灌溉下,再生水灌溉均对土壤放线菌门表现为促进作用,对变形菌门表现为抑制作用。再生水充分灌溉相比非充分灌溉对土壤放线菌门和变形菌门具有促进作用,对土壤绿弯菌门、酸杆菌门和厚壁菌门具有抑制作用;再生水灌水水平越高,越有利于土壤中优势菌群的生长。3)各处理土壤细菌代谢通路丰度占比最大的为膜转运、碳水化合物代谢及氨基酸代谢,再生水辅以较高灌水水平能够显著促进表层土壤微生物膜转运、碳水化合物代谢及氨基酸代谢过程。因此,再生水较高灌水水平可促进土壤物质能量循环,且对土壤细菌代谢繁殖过程也可起到积极的调节作用。研究可为再生水灌溉下的土壤生态环境效应研究提供依据。     

中水灌溉条件下含砾砂土污染物运移的初步研究

以宁夏回族自治区大武口市森林公园的含砾砂土为研究对象，通过室内试验，对中水灌溉条件下砂砾质土壤在不同灌水量、多次连续灌水、降雨淋洗等不同来水条件下水分、污染物运移的规律进行了初步的研究，为微污染水用于绿化灌溉对砂砾质土壤中污染物运移及累积的研究提供科学依据。     

再生水灌溉对土壤斥水性的影响

深入探求再生水灌溉条件下不同土壤中水分和溶质的分布及斥水性变化规律,能为再生水灌溉条件下土壤斥水性产生原因及其影响因素的研究提供一定的参考。选用砂土、砂姜黑土、塿土和盐碱土进行土柱再生水灌溉试验,取样测定不同灌水量条件下剖面土壤的潜在斥水性、含水率、Cl-、有机质(organicmatter,OM)含量及电导率(electrical conductivity,EC)等。结果表明:再生水灌溉后,塿土及盐碱土分别出现0～2,1～3级斥水性,砂土及砂姜黑土为0级斥水性,4种土表层表现出较强的斥水性。土壤斥水性随再生水灌水量和灌溉时间的增加而显著增强,并且灌水量越大,斥水性差异性越显著。4种土有机质含量OM与土壤斥水持续时间变化值TR呈正相关关系,Cl-含量、EC值与土壤斥水持续时间变化值TR呈负相关关系。相比较其他3种土而言,砂土更适合再生水灌溉。     

A transfer-function method for analysing breakthrough data in the time domain of the transport process

A transfer‐function method is proposed to determine transport parameters from solute breakthrough data. The method is based on the assumptions that a linear process governs the transport of solute through soil and that the soil is homogeneous. It needs breakthrough data at two different vertical locations from a pulse input of solute to the soil. The method predicts the response by convoluting the input with the transfer function in the time domain. Solute breakthrough data were measured in unsaturated soil columns by time‐domain reflectometry (TDR). An experimental soil column was placed over a supporting column filled with sandy soil. A constant hanging water table, maintained in the lower column, created suction in the upper column and maintained unsaturated conditions. A solution of calcium chloride (CaCl₂) was spread over the soil in the upper column during steady flow of water in the column. Resident concentrations of solute in terms of electrical conductivity were measured at two depths by TDR sensors. We analysed breakthrough curves of CaCl₂ in 81 experiments to determine the transport parameters in coarse sand, sandy loam soil and clay loam soil by the transfer‐function method. The transport parameters obtained were compared with those determined by the widely used deterministic equilibrium model of the CXTFIT program. The transfer‐function method provided a better fit between the measured and estimated breakthrough curves in almost all cases and resulted in stable values of the parameters. The method is robust against small errors in measurements. It is a mathematically sound and efficient method for analysing breakthrough data.     

再生水灌溉对农田土壤水流运动影响的研究进展

再生水灌溉农田既可节约宝贵的水资源、缓解农业用水紧缺,同时再生水中的多种营养元素和微量元素可促进作物生长、提高粮食产量。但再生水中的物质进入农田后将引起土壤孔隙结构、团聚体结构、黏粒分散特征和水土作用关系等一系列的变化,进而引起土壤入渗性能和导水性能的改变,增大环境污染风险。该文综述了再生水中的悬浮无机固体、大分子有机质、油脂、表面活性剂和盐分对农田土壤水流运动的影响及其作用机理,指出受灌农田土壤结构性质演化过程与驱动机制、受灌农田土壤与灌溉入渗水流之间的相互作用关系为该领域亟需开展的2个研究方向。文章对再生水农田灌溉制度制定、污染风险控制和生态环境保护均有参考价值。     

再生水灌溉区农田包气带及地下水中硝酸盐分布特征及来源研究

本文通过对华北平原典型再生水灌溉区(河北省石家庄洨河流域)的包气带土壤、地表水和地下水进行采样分析,对硝酸盐在多种环境介质中的来源与环境行为进行了研究,识别了再生水灌溉区地下水硝酸盐污染来源,明确了不同灌溉条件对包气带土壤中硝酸盐迁移的影响。在受到城市再生水严重影响的洨河流域,地下水中的硝酸盐浓度分布范围在4.0 mg·L?1到156.6 mg·L?1之间,已经形成了距离河道2 km、深度70 m的硝酸盐高值区域,经过计算硝酸盐的垂向扩散速率为每年1～2 m。硝酸盐与氯离子的相关性表明,城市再生水是再生水灌溉区包气带、地表水和地下水中硝酸盐的主要来源。利用Geoprobe获取利用不同灌溉水农田土壤剖面样品,研究再生水对厚包气带NO3?-N垂向分布影响,再生水灌溉区和地下水灌溉区中包气带土壤的NO3?-N的平均含量为137.0 mg·kg-1和107.7 mg·kg-1,最高含量523.2 mg·L?1和725.9 mg·L?1,分别出现1.20 m和0.85 m深度,分布规律有着明显的差别。包气带土壤硝酸盐与氯离子的相关性分析表明,再生水灌溉区土壤硝酸盐主要来源于城市再生水,而地下水灌溉区可能来源于农田氮肥。地下水年龄和硝酸盐之间关系表明,地下水中1975年以前补给的硝酸盐浓度低于1975年以后补给,地下水硝酸盐污染与包气带氮入渗的历史过程密切相关。在华北平原特殊的地质水文背景下,农田面源污染对地下水的影响有限,但再生水灌溉区地下水硝酸盐污染的风险较高。     

不同钠吸附比的咸水结冰融水入渗后滨海盐土的水盐分布

在室内利用相同矿化度(10 g·L^-1)、不同钠吸附比(5、10 和30)的咸水进行咸水结冰融水模拟试验、结冰融水入渗和咸水直接入渗的土柱试验, 以淡水处理为对照, 分析不同钠吸附比咸水结冰融水入渗下滨海盐土水盐分布特征。结果表明: 咸水冰融化过程中, 融出水的矿化度和钠吸附比均呈由高到低的变化趋势。咸水结冰融水入渗速度和入渗深度均快于和深于淡水。咸水钠吸附比越小, 结冰融水入渗速率越快、深度越深。水盐分布也表现为低钠吸附比咸水结冰处理的表层土壤含水量较低, 水分向深层迁移, 这种水分分布也使盐分向深层运移, 表现为表层土壤含盐量低, 深层土壤含盐量大。土层含水量低钠吸附比咸水处理高于高钠吸附比处理, 10~45 cm 土层则表现出相反的趋势; 表层土含盐量低钠吸附比处理高于高钠吸附比处理, 且咸水处理下土壤脱盐的深度大于淡水处理。钠吸附比5 的咸水结冰处理, 0~10 cm 土壤平均含水量和含盐量分别为30.3%和1.1 g·kg^-1, 显著低于其他处理。为比较咸水结冰灌溉和咸水直接灌溉的效果, 室内利用含盐量为10 g·L^-1、钠吸附比10 的咸水进行直接入渗的土柱(土壤含盐量为21.3 g·kg^-1)模拟试验, 结果表明: 与咸水直接入渗处理相比, 咸水结冰融水处理盐分淋洗效果更好, 该处理0~25 cm土层平均土壤含盐量为2.9 g·kg^-1, 显著低于咸水直接入渗的10.6 g·kg^-1。     

再生水滴灌对黄瓜地土壤特性的影响

再生水滴灌是解决水资源短缺的有效途径之一。采用大田试验方法,以地下水滴灌为对照,分析研究了滴灌条件下不同再生水水质对黄瓜根际土壤特性的影响。结果表明:在土壤理化性状方面,再生水滴灌情况下,黄瓜地土壤pH与对照相比无显著差异;再生水滴灌处理土壤EC值高于地下水滴灌;在土壤养分方面,与对照相比,碱解氮、有效磷、速效钾含量差异不显著;再生水浓度越大,对土壤呼吸的增强效应越明显。     

Application of Reclaimed Wastewater in the Irrigation of Rosebushes

The use of reclaimed wastewater in agriculture can be a solution for regions with water shortages or low rainfall periods; besides fulfilling the crop's water needs, it would also promote the recycle of nutrients. However, care should be taken regarding soil salinization, especially in closed environments such as greenhouses for the cultivation of ornamental plants. The domestic effluents are rich in sodium which can accumulate on soil and cause soil sealing. This study evaluated the use of effluents from anaerobic filters and intermittent sand filters in the production of rosebushes (Rosa hybrida “Ambiance”). The crop yield of the rosebushes irrigated with reclaimed wastewater exceeded the one obtained with traditional cultivation, reaching a value 31.8 % higher when employing nitrified effluent originated from intermittent sand filters, with no difference in the product quality. The salinity levels are below the critical limits found in the literature; however, there was a significant increase compared to the irrigation with drinking water.     

Dynamics of Soil Moisture and Salt Content After Infiltration of Saline Ice Meltwater in Saline-Sodic Soil Columns

Saline ice meltwater can be used for irrigation and leaching of salts in salt-affected soil regions.A laboratory experiment was conducted using soil columns to investigate the redistribution of soil moisture, salt and sodium adsorption ratio(SAR) in saline-sodic soil under the infiltration of saline ice meltwater.Soils were treated using saline water of three irrigation volumes(1 600, 2 400 and 3 200 mL) at four salinity levels.These four salinity levels included salt free(0 g L~(-1)), low salinity level(1.4 g L~(-1)), moderate salinity level(2.7 g L~(-1)) and high salinity level(4.1 g L~(-1)).The prepared saline water was frozen into ice, and then the ice was put on the surface of soil columns.After 96 h, the infiltration rate and soil moisture content of saline ice treatments were greater than those of salt-free ice treatments, increasing with the increase of ice salinity.Infiltration of saline ice meltwater increased soil moisture content in the upper layers for all treatments.Both salt contents and SAR values in the upper soil layers decreased in all saline ice treatments and were lower than those in salt-free ice treatment.However, this trend was reversed in the deeper(below 20 cm) soil layers.The highest desalting rate and lowest SAR were observed in high-salinity treatment under three irrigation volumes in the 0–15 cm soil layer,especially under irrigation volume of 2 400 mL.These results indicate that saline ice(0–20 cm) meltwater irrigation is beneficial to saline-sodic soil reclamation, and the best improvement effect would be achieved when using high-salinity ice under optimal irrigation volume.     

Simultaneous transport of surface salts and water through unsaturated soils during infiltration and redistribution

Abstract

Certain concepts regarding the simultaneous transport of surface ‐salts and water under transient unsaturated flow conditions vere verified for three soils using laboratory soil columns. Treatments included different water application rates (i.e., continuous ponding and controlled rates) and different initial soil water contents. Calcium chloride, spread on the soil surface to simulate a salt‐affected soil or broadcasting of a fertilizer (or other additive), was leached with chloride free water (0.01 N CaSO₄). Salt and water profiles were determined by destructive sampling at 2 cm depth intervals at two stages: (i) immediately following infiltration and (ii) after Batching infiltration plus redistribution time.

Immediately following infiltration as well as after matching infiltration and redistribution time, chloride was leached more efficiently and to relatively deeper depths with slower than with faster rates of water application only in sandy and sandy loam soils. The results, thus, show that slower rates of water application nay not increase leaching efficiency over faster rates in heavy‐textured and sodic soils with very poor permeability. Regardless of water application rate, initial soil water content, redistribution time and soil type, salt front (i.e., salt peak) did not coincide with the water front but lagged behind it by a few to several centimetres. That is to say that salt peak did not occur at a depth above which total soil water storage in the profile equalled cumulative infiltration. The higher the initial soil water content, the deeper and more complete was the displacement of chloride during infiltration for a given quantity of water applied at different rates. This trend was not modified during post‐irrigation period in sandy soil, but it was entirely reversed in sandy loam soil.     

宁夏黄灌区灌淤土硝态氮运移规律研究

为研究硝态氮在宁夏黄灌区灌於土中的基本运移规律,采用水平土柱进行硝态氮水平运移规律研究,并采用自制垂直土柱完成了硝态氮垂直运移规律研究。硝态氮水平运移规律研究表明：硝态氮运移与水分湿润峰迁移具有很好的一致性,随着硝态氮运移距离的增加,硝态氮浓度升高,并在湿润峰处累积;硝态氮浓度随含水量的增加而减少,并呈幂函数关系;硝态氮运移速率随运移距离增加而减小,且呈冥函数关系。硝态氮垂直运移实验表明：由于有机质和粘粒含量不同,各土层硝态氮穿透曲线差异较大;CXTFIT模型的拟合结果与实测结果相关性很好,说明可以使用CXTFIT模型进行土壤硝态氮运移预测和土壤硝态氮运移参数的测定。     

Influence of soil properties on the vertical movement of genetically-marked Pseudomonas fluorescens through large soil microcosms

Summary Vertical translocation of the introduced transposon Tn5-tagged Pseudomonas fluorescens cells was studies after irrigation of 50-cm long soil columns of loamy sand. The soil in the columns was slowly brought to saturation using groundwater, and enough water was then slowly added to permit collection of the percolated water. Introduced bacteria were transported to lower soil layers to a significantly higher degree in undisturbed soil cores than in repacked cores; water transport was hampered in both core types due to high soil bulk densities. Soil bulk density affected the degree of transport of the introduced cells; progressively more cells were translocated to deeper soil layers and into the percolation water at decreasing soil bulk densities. Repeated percolation of soil at a bulk density of 1.25 caused an increase in Tn5-tagged cell numbers in the lower soil layers and in the percolated water. Further, cells initially introduced into a dry (5.3% moisture) soil were translocated to a lesser extent than cells introduced into a wetter (13% moisture) soil. Finally, wheat roots enhanced the water-induced transport of introduced cells to the 40- and 50-cm deep soil layers and into the effluent, but not to the remaining soil layers. Large soil columns such as those used in the present study are useful in assessing the transport and survival of introduced bacterial cells in soils under a variety of simulated environmental conditions.     

再生水灌溉对土壤和葡萄品质的影响

2011—2013年,经过3年小区实验,分析了再生水灌溉对土壤和葡萄品质的影响。实验结果表明,再生水区的土壤总氮、总磷和有机质的含量呈现低于清水对照区的趋势,而硝态氮与碱解氮含量却高于清水对照区。再生水灌溉区土壤Cd含量高于清水对照区,而Pb、Cu的含量均低于清水对照区。土壤中重金属有一定的积累现象,但均未超出《土壤环境质量标准(GB 15618—1995)》中的重金属限量值,说明短期再生水灌溉未造成土壤重金属污染。再生水灌溉在一定程度上能提高葡萄的产量,但对葡萄的品质未产生有利的影响。3年实验中,再生水灌溉区葡萄的重金属含量低于清水灌溉区,说明短期再生水灌溉对葡萄重金属含量的影响不大。研究表明再生水可以用作灌溉用水,但再生水中重金属对环境的影响是长期的、积累的、复杂的,要确保再生水灌溉的安全还需进一步研究。