Soil and groundwater quality with reference to nitrate in a semiarid agricultural region

Nitrate is a common pollutant in surface water and groundwater of agricultural areas. It is essential to monitor this pollutant in groundwater, especially when it is used for drinking purposes without treatment. The present study was carried out in an intensively irrigated area which forms a part of Nalgonda district, Andhra Pradesh, India where groundwater meets all the water needs of the rural population living in this area. The objective was to assess the spatiotemporal variation in the concentration of nitrate in groundwater and soil. Based on the analysis of 496 groundwater samples collected from 45 wells over a period of 2 years from March 2008 to January 2010 by sampling every 2 months, it was observed that groundwater in 242 km² of the total 724 km² area had nitrate above the maximum permissible limit of 45 mg/l for drinking purposes. Nitrate concentration in groundwater showed a positive relation with potassium, chloride, and sulfate, indicating their source from fertilizers. Reasons for the high concentration of nitrate in domestic areas were the dumping of animal wastes and leakage from septic tanks. The pH of the soil samples showed that most of the area had basic soil. Apart from pH, organic carbon, available phosphorous, available potassium, ammoniacal nitrogen, and nitrate nitrogen were also analyzed in the 97 soil samples.     

Neural network prediction of nitrate in groundwater of Harran Plain, Turkey

Monitoring groundwater quality by cost-effective techniques is important as the aquifers are vulnerable to contamination from the uncontrolled discharge of sewage, agricultural and industrial activities. Faulty planning and mismanagement of irrigation schemes are the principle reasons of groundwater quality deterioration. This study presents an artificial neural network (ANN) model predicting concentration of nitrate, the most common pollutant in shallow aquifers, in groundwater of Harran Plain. The samples from 24 observation wells were monthly analysed for 1 year. Nitrate was found in almost all groundwater samples to be significantly above the maximum allowable concentration of 50 mg/L, probably due to the excessive use of artificial fertilizers in intensive agricultural activities. Easily measurable parameters such as temperature, electrical conductivity, groundwater level and pH were used as input parameters in the ANN-based nitrate prediction. The best back-propagation (BP) algorithm and neuron numbers were determined for optimization of the model architecture. The Levenberg–Marquardt algorithm was selected as the best of 12 BP algorithms and optimal neuron number was determined as 25. The model tracked the experimental data very closely (R = 0.93). Hence, it is possible to manage groundwater resources in a more cost-effective and easier way with the proposed model application.     

Effects of soil type and fertilizer on As speciation in rice paddy contaminated with As-containing pesticide

Inorganic arsenic (As) pesticides have been widely used for decades in many countries. However, insufficient data are available on the chemical speciation of inorganic arsenicals in tropical paddy soils. Inorganic As-containing pesticides were used in tropical countries, a few decades ago, however, their fate have not been studied. Hence, the objective of this study was to determine fractionation of inorganic arsenicals and to assess As lability with/without fertilizer application using a static incubation experiment. Eight soils from wet and dry regions of Sri Lanka were amended with 1,000 mg/kg arsenate for this purpose. The FT-IR and XRF results suggested that soils in the wet region were rich in Fe/Al-oxides. Paddy soils in the dry zone showed high As lability. These low-humic gley soils have low Fe/Al oxyhydroxide and alkaline pH. In contrast, the wet zone had soils with higher As retention capacity, high amounts of Fe/Al oxyhydroxide, and acidic pH. Arsenic lability increased considerably 30 days after fertilizer application. Overall, As lability was mainly influenced by soil mineralogical and chemical properties, i.e., Fe/Al oxyhydroxide, pH, organic matter, and fertilizer application.     

Investigating hydrological drivers of nitrate export dynamics in two agricultural catchments in Germany using high-frequency data series

In this study near-continuous time series of nitrate, electrical conductivity, and discharge were used to identify the dominating hydrological mechanisms that control nitrate export dynamics in two agricultural catchments. The main goal was to assess relationships between contrasting event based as well as long-term nitrate transport behaviour and catchment hydrology. Data records were obtained from online probes that allow field based high-frequency analyses over long time periods. The catchments of the Ammer River (southwestern Germany) and the Weida River (eastern Germany) are similar with respect to size (~100 km²), morphology, and climate and are dominated by agricultural use. Main differences are the stronger urbanization and the occurrence of karstic rocks in the Ammer catchment. Nitrate concentrations are high in water of both streams and range mostly between 20 and 50 mg l^?1. Nitrate export in the Ammer catchment is dominated by baseflow and a minor second, diluting runoff component generated in urbanized areas. In contrast, nitrate dynamics of the Weida catchment is governed by the interplay of at least three runoff components, while the largest amount of nitrate is mobilized intermittently by a delayed fast component generated in the catchment’s soils during wet conditions. These interpretations, derived with one online probe at the outlet of each catchment, are well in line with the former modeling results. This study shows that high-resolution data obtained by online techniques offers a large potential to improve the conceptualization of dominating flow and transport processes at catchment scales at relatively low costs and effort.     

Spatial-temporal difference between nitrate in groundwater and nitrogen in soil based on geostatistical analysis

The study of temporal and spatial variations of nitrate in groundwater under different soil nitrogen environments is helpful to the security of groundwater resources in agricultural areas. In this paper,based on 320 groups of soil and groundwater samples collected at the same time, geostatistical analysis and multiple regression analysis were comprehensively used to conduct the evaluation of nitrogen contents in both groundwater and soil. From May to August, as the nitrification of groundwater i...     

Characterization of the shallow groundwater system in an area with thin soils and sinkholes

Door County, Wisconsin, is a region of karst topography underlain by Silurian dolomite bedrock. Numerous sinkholes intercept much of the surface runoff and act as sites for direct groundwater recharge. The clay-rich and impermeable Upper Ordovician Maquoketa formation separates the dolomite aquifer from the deeper aquifers and appears to be a factor in groundwater circulation and karst formation Thin glacial drift and Quaternary materials overlie the dolomite and are hydrologically connected with it The interactions of surface and groundwater, and the role of solution features in water interchange were studied in a small drainage basin. This basin contains several large sinkholes and a nearby spring complex Mapping identified many additional sinks and swallets in surface drainage routes Water flowing into two sinks was traced and found to have a residence time of several hours. Water flowing into sinkholes and from the spring was sampled to identify the quality and seasonal trends in composition of the shallow groundwater Water quality parameters monitored include magnesium, sodium, potassium, chloride, phosphorous, nitrate and ammonia, nitrogen, alkalinity, pH, turbidity, and specific conductance. Nitrate levels were found to increase 5 to 6 times during periods when there was zero input through sinkhole recharge sites. Nitrate levels approached the 10 mg/l NO₃ ⁻-N limit set by the U.S. Public Health Service for drinking water In this basin sandy soils are most susceptible to sink development, whereas clay-rich soils have a lesser number of sinks. It appears, however, that a network of bedrock solution features exists under all soils The loss of soil into sinkholes has impacted groundwater quality and reduced agricultural productivity through a reduction in tillable acreage and water retention capacity.     

西南喀斯特地区水体硝态氮时空分布特征及其来源解析

由于人类活动影响,水体硝态氮污染已经成为世界范围内的环境问题。硝态氮污染不仅会造成水体富营养化,长期摄入过量硝酸盐还会严重威胁人体健康,控制并解决水体硝态氮污染是我国经济社会发展过程中亟待解决的重要环境问题。我国西南喀斯特地区是世界上面积最大、发育最典型和人地矛盾尖锐的岩溶连续分布带,具有十分脆弱且高度敏感的生态系统。与非喀斯特地区相比,这里水体硝态氮污染情况更为复杂和严重。因此,明确西南喀斯特地区内硝态氮的时空分布特征并对其来源进行解析是有效治理的前提。本研究梳理了近几十年来西南喀斯特地区水体硝态氮的现代监测结果,探讨了水体硝态氮时空分布特征、来源及受控机制等问题,发现:(1)区域内地表水硝态氮平均检出质量浓度不高,地下水检出质量浓度波动范围较大;(2)近几十年来,地表水硝态氮质量浓度整体呈现小幅增长趋势,而地下水检出质量浓度随时间的变化存在地域差异;(3)降水的稀释和冲携作用对区域内硝态氮质量浓度及分布的影响不容忽视,而人类活动导致的土地利用变化带来的影响可能成为未来的主控因素;(4)区域内水体硝态氮主要来源于铵态化肥、土壤有机氮、粪肥及污水,硝化作用是主要的转化过程。研究结果将为进一步认识喀斯特地区氮循环过程及促进地区可持续发展提供理论基础。     

Branched and isoprenoid tetraether (BIT) index traces water content along two marsh-soil transects surrounding Lake Qinghai: Implications for paleo-humidity variation

The BIT index represents the relative abundances of branched glycerol dialkyl glycerol tetraethers (bGDGTs) and the isoprenoid GDGT, crenarchaeol. While bGDGTs are produced mainly by soil (anaerobic) bacteria, crenarchaeol is known to be a biomarker for aerobic ammonia oxidation by chemolithoautotrophic Thaumarchaeota, particularly in the open ocean or lakes. Thus, the index in marine and lacustrine settings has been widely used as a proxy for soil input. Here, we have investigated GDGT distribution along two transects extending from the lake shore marsh to upland soils on the NE Qinghai-Tibetan plateau. The results show that soil water content (SWC) correlates positively with concentration of bGDGTs and negatively with concentration of crenarchaeol; consequently, there is a significant positive correlation between SWC and the BIT index. Our study highlights a new potential application of BIT as a humidity proxy in loess/soil and peat deposits.     

Using of neural networks for the prediction of nitrate groundwater contamination in rural and agricultural areas

As a neural network provides a non-linear function mapping of a set of input variables into the corresponding network output, without the requirement of having to specify the actual mathematical form of the relation between the input and output variables, it has the versatility for modeling a wide range of complex non-linear phenomena. In this study, groundwater contamination by nitrate, the ANNs are applied as a new type of model to estimate the nitrate contamination of the Gaza Strip aquifer. A set of six explanatory variables for 139 sampled wells was used and that have a significant influence were identified by using ANN model. The Multilayer Perceptrons (MLP), Radial Basis Function (RBF), Generalized Regression Neural Network (GRNN), and Linear Networks were used. The best network found to simulate Nitrate was MLP with six input nodes and four hidden nodes. The input variables are: nitrogen load, housing density in 500-m radius area surrounding wells, well depth, screen length, well discharge, and infiltration rate. The best network found had good performance (regression ratio 0.2158, correlation 0.9773, and error 8.4322). Bivariate statistical test also were used and resulting in considerable unexplained variation in nitrate concentration. Based on ANN model, groundwater contamination by nitrate depends not on any single factor but on the combination of them.     

The origin and distribution of nitrate in groundwater from village wells in Kotagede, Yogyakarta, Indonesia

The causes and nature of nitrate pollution of wells in a village within Kotagede, a subdistrict of the city of Yogyakarta, Indonesia, were investigated in a detailed hydrological study. Nitrate concentrations in groundwater frequently exceeded the WHO recommended limit of 50 mg L^− 1. Groundwater nitrate concentrations were measured over a 19-month period in monitoring wells and in piezometers placed strategically in relation to sewage tanks within the village. Results indicate that the tanks are major sources of nitrate in the groundwater and that the input is markedly dependent on rainfall, resulting in a surge of nitrate into the groundwater at the beginning of each wet season. That the tanks are a major source was confirmed by measuring nitrate in soil cores obtained by augering close to selected tanks. Washrooms, where people wash themselves, are not significant sources of nitrate. Faecal coliform counts in groundwater from a random selection of wells are very high. The results have implications for the siting of wells and toilets within villages in Indonesia. Received, January 1999/Revised, August 1999/Accepted, August 1999     

表层岩溶带土壤中有机氯农药的分布及来源特征研究——以重庆南川区为例

为了研究有机氯农药(OCPs)在表层岩溶带土壤中的分布趋势、组成特征和来源,采用气相色谱-微池电子捕获检测器(GC-μECD)分析了重庆市南川区水房泉、后沟泉、柏树湾泉、兰花沟泉等典型表层带岩溶泉上覆土层中有机氯农药的浓度。结果显示,总体上表层岩溶带土壤中的OCPs的浓度范围是7.13~323.37ng/g,其中后沟泉、柏树湾泉、兰花沟泉表层土壤中的17种OCPs检出率为100%,水房泉土壤中除p,p'-DDD外其余全部检出,但不同种类有机氯含量差异较大。其中HCHs、DDTs、CHLs、灭蚁灵是主要检出物。研究区内土壤样品中的HCHs来源于工业品HCHs和林丹使用的残留,且由于环境影响,土壤中HCH的同系物组成发生了明显变化。水房泉和柏树湾泉土壤中的DDTs来自于工业DDTs和三氯杀螨醇的混合源,而后沟泉和兰花沟泉土壤中的DDTs可能来自于工业DDTs的使用,而非三氯杀螨醇类型的DDT。对比中国和荷兰的土壤质量标准,柏树湾泉土壤中DDTs浓度接近于荷兰无污染土壤的参考值,兰花沟泉土壤中的DDTs应属于轻度污染,后沟泉土壤中的DDTs和氯丹类化合物污染程度较重,而水房泉土壤为无污染土壤。      

Application of sugar foam to red soils in a semiarid Mediterranean environment

The study described here involved evaluating the effects that the application of one by-product (sugar foam waste) has upon red soils in the region of La Mancha (Central Spain). In view of the fact that this is a location where this type of soil abounds, this technique has been a common practice for many years. The principal goal was to investigate the impact of this approach on some of the soil properties and, secondly, on its level of fertility. As a result, this represents an investigation into the effects that this type of waste has on some soil quality parameters. The results showed that, after the addition of by-products over 25 years, sugar foam waste is of agricultural interest mainly due to the increase in organic matter concentration (about 2%) and, to a lesser extent, by increases in calcium carbonate (more than 30%) and P (four times more). The soil pH was also found to increase slightly (1.4), while the electrical conductivity almost did not change. The properties associated with these pedological qualities therefore had a positive effect by improving nutrient availability. As a result, foams arising from sugar industries have a positive effect on soil quality and the application of such foams to soils is beneficial since the need to dispose this residue is also removed.     

Occurrence and distribution of tetraether membrane lipids in soils: Implications for the use of the TEX86 proxy and the BIT index

A diverse collection of globally distributed soil samples was analyzed for its glycerol dialkyl glycerol tetraether (GDGT) membrane lipid content. Branched GDGTs, derived from anaerobic soil bacteria, were the most dominant and were found in all soils. Isoprenoid GDGTs, membrane lipids of Archaea, were also present, although in considerably lower concentration. Crenarchaeol, a specific isoprenoid membrane lipid of the non-thermophilic Crenarchaeota, was also regularly detected and its abundance might be related to soil pH. The detection of crenarchaeol in nearly all of the samples is the first report of this type of GDGT membrane lipid in soils and is in agreement with molecular ecological studies, confirming the widespread occurrence of non-thermophilic Crenarchaeota in the terrestrial realm. The fluvial transport of crenarchaeol and other isoprenoid GDGTs to marine and lacustrine environments could possibly bias the BIT index, a ratio between branched GDGTs and crenarchaeol used to determine relative terrestrial organic matter (TOM) input. However, as crenarchaeol in soils is only present in low concentration compared to branched GDGTs, no large effect is expected for the BIT index. The fluvial input of terrestrially derived isoprenoid GDGTs could also bias the TEX₈₆, a proxy used to determine palaeo surface temperatures in marine and lacustrine settings and based on the ratio of cyclopentane-containing isoprenoid GDGTs in marine and lacustrine Crenarchaeota. Indeed, it is shown that a substantial bias in TEX₈₆-reconstructed sea and lake surface temperatures can occur if TOM input is high, e.g. near large river outflows.     

Survey efficiency of electrocoagulation on nitrate removal from aqueous solution

Water supply for consumption is one of the crucial objectives of water supply systems. Using of excessive fertilizer is a main source of nitrate content in water. The high amounts of nitrate in water have a determinable effect on the environment which must be removed due to drinking and industrial water standards. The purpose of this study is nitrate removal from aqueous solution by Electrocoagulation process. The applied pilot was comprised of a reservoir, electrode and power supply. In this study pH, electrical potential difference, nitrate initial concentration, total dissolved solid, kind of electrode, electrode connection methods and number of electrode were studied. Moreover, obtained optimum conditions were tested on Kerman water. The results showed that the electrocoagulation process can reach nitrate to less than standard limit. pH, electrical potential difference, total dissolved solids and number of electrodes have direct effect and initial concentration of nitrate has reverse effect on nitrate removal. This study also showed that under optimum condition, nitrate removal from Kerman water distribution system was 89.7 %. According to the results, Electrocoagulation process is suggested as an effective technique in nitrate removal.     

REE concentrations in agricultural soil in Sweden and Italy: Comparison of weak MMI® extraction with near total extraction data

Rare Earth Element (REE) concentrations in agricultural soil obtained from the Mobile Metal Ion (MMI^®) weak extraction technique are compared with soil total concentrations (sodium peroxide fusion followed by acid dissolution) for 118 and 174 agricultural soil samples from Italy and Sweden, respectively. Spatial distribution maps and statistics for both analytical techniques are compared between the two national datasets. In spite of similarity of REE concentration in two countries, the median values of REE is higher than Italy but extreme concentration of REE in Italy is due to young volcanic activities. Extractability of REEs is significantly higher in Swedish soils than in Italian soils. Heavy Rare Earth Element (HREE) in Sweden show higher concentrations compared to Italy in MMI^® extraction data where correlate with REE mineralisation. Principal Component Analysis (PCA) is used to elucidate correlations and anomalies in the REE distribution. Results show that there is a clear correlation between REE anomalies and natural factors such as lithology of the underlying bedrock, the presence of mineralisations, pH of soils, climate and precipitation. According to the PCA results, anomalous behaviour of Eu, Ce, Tb and Gd can be explained by the dominant mineralogy of the parent material and the variable affinity of REEs to bind to clay minerals and clay-size particles.     

Large-scale spatial interpolation of soil pH across the Loess Plateau, China

Soil pH plays an important role in biogeochemical processes in soils. The spatial distribution of soil pH provides basic and useful information relevant to soil management and agricultural production. To obtain an accurate distribution map of soil pH on the Loess Plateau of China, 382 sampling sites were investigated throughout the region and four interpolation methods, i.e., inverse distance weighting (IDW), splines, ordinary kriging, and cokriging, were applied to produce a continuous soil pH surface. In the study region, soil pH values ranged from 6.06 to 10.76, with a mean of 8.49 and a median of 8.48. Land use type had a significant effect (p < 0.01) on soil pH; grassland soils had higher pHs than cropland and forestland soils. From a regional perspective, soil pH showed weak variation and strong spatial dependence, indicated by the low values of the coefficient of variation (0.05) and the nugget-to-sill ratios (<0.25). Indices of cross-validation, i.e., average error, mean absolute error, root mean square error, and model efficiency coefficient were used to compare the performance of the four different interpolation methods. Kriging methods interpolated more accurately than IDW and splines. Cokriging performed better than ordinary kriging and the accuracy was improved using soil organic carbon as an auxiliary variable. Regional distribution maps of soil pH were produced. The southeastern part of the region had relatively low soil pH values, probably due to higher precipitation, leaching, and higher soil organic matter contents. Areas of high soil pH were located in the north of the central part of the region, possibly associated with the salinization of sandy soils under inappropriate irrigation practices in an arid climate. Map accuracy could be further improved using new methods and incorporating other auxiliary variables, such as precipitation, elevation, terrain attributes, and vegetation types.     

玉龙雪山浅冰芯pH值对冰川作用区降水量变化的响应

玉龙雪山10.10 m浅冰芯的pH和电导率(EC)变化分析以及与Ca2 、 Mg2 、 K 和Na 浓度的对比表明, 玉龙雪山主要受局地碱性陆源物质的控制.与丽江气象台站的降雨量资料比较发现, 在海洋性冰川区浅冰芯pH和电导率的变化与降雨量和周围地表可溶性离子的输入量关系密切, 并与降雨量呈显著的负相关关系.结合玉龙雪山主要由局地来源补给的特征, 引入TSP(总悬浮颗粒物)作为局地可溶盐补给能力的代用指标分析玉龙浅冰芯pH值对降水量年际变化的响应.在相对湿润年, pH值较低, 若TSP值较高, 则pH值相对较高, TSP值较低, 则pH值较低.在相对干旱年, pH值较高, 若TSP值较高, pH值较高, 若TSP值较低, 则pH值相对较低;在海洋性冰川区, 浅冰芯pH和电导率的变化, 并结合TSP能够有效的反映出冰川作用区干湿的年际变化, 是大气环境状况的敏感指示器.     

广东省普宁市土壤硒的分布特征及影响因素研究

开展了广东省普宁市区域土壤硒调查研究,采集了413个表层土壤样品(0～20 cm)和103个深层土壤样品(> 150 cm),测定了土壤全硒含量,据此研究土壤硒分布特征及其影响因素。结果表明,普宁市土壤全硒含量变化于0. 16～2. 01 mg/kg,平均值为0. 63 mg/kg,总体上处于中硒及高硒水平,不存在缺硒和硒过剩土壤。砂页岩风化形成的赤红壤全硒含量较高,平均值达0. 86 mg/kg,以侏罗系页岩母质发育的土壤全硒含量最高,平均值达0. 89 mg/kg;三角洲第四系沉积物发育形成的水稻土全硒含量最低,平均值为0. 41 mg/kg。回归分析表明,土壤全硒含量与铁铝含量、有机碳含量具有极显著正相关,与p H呈极显著负相关。影响普宁市土壤硒含量的主要因素是成土母质,土壤p H、有机碳和铁铝含量及土地利用方式对土壤全硒含量分布与富集也有一定的影响。     

纳米铁还原脱氮动力学及其影响因素

饮用水中硝酸盐(NO3-)对人体健康有危害。为了去除水溶液中NO3-,在实验室制得纳米铁颗粒。它的粒径为20～40 nm,比表面积(BET)为49.16 m2/g。本研究通过批实验考察了纳米铁对NO3-还原脱氮动力学性质和影响NO3-脱氮快慢的主要因素,如反应pH、纳米铁投加量和NO3-起始浓度。实验结果表明,pH越低越有利于NO 3-还原。在一定范围内,NO 3-还原速率随纳米铁投加量增加而增大,而随NO 3-起始浓度升高而降低,反应遵循准一级反应动力学方程,表面吸附和氧化还原反应是纳米铁对NO3-脱氮的主要去除机理。纳米铁对NO3-还原过程中可能反应的途径进行了讨论,NO3-还原产物取决于反应条件。在本研究条件下,纳米铁对NO3-脱氮的最终产物主要为NH4+-N而不是N2,必须进行更多的研究来解决这一问题。     

近30年来苏南耕地土壤pH时空变化特征及影响因素分析

苏南地区是我国重要的粮食产区之一,其耕地土壤的酸碱度特征直接影响着土地品质和粮食质量。本文通过调查 2010年以来苏南农耕土壤pH空间分布特征,发现苏南土壤pH呈现西酸东碱格局,这与自然条件和人为改造行为密切相 关。近30年来苏南土壤pH时空变化在2003年前后呈现两种模式：总体上,1980年至2003年期间,土壤发生酸化和碱化的 地区与1980年至2010年来的总变化特征基本一致,而2003年至2010年近10年来部分地区土壤酸碱变化趋势出现逆转,以 镇江句容地区的先碱化后酸化和苏州无锡地区的先酸化后碱化最为典型。本文分析认为,地区间土地利用格局和利用方式 的时空差异所导致的缓冲物质的增减更替,是造成苏南土壤pH时空变化区域差异的主要驱动力