Lead enrichment, adsorption and speciation in urban garden soils under long-term wastewater irrigation in northern Nigeria

Unsafe lead (Pb) concentrations in leafy vegetables raised in urban and peri-urban agricultural production systems have been reported across cities in Northern Nigeria, even though Pb concentrations in soils are within regulatory safe levels. This study examined the soil enrichment, adsorption and chemical species of Pb in urban garden fields irrigated with untreated wastewater at three industrial locations in Kano, northern Nigeria. Total Pb in the soil profiles ranged from 9 to 91 mg kg^?1 and decreased rapidly from the surface to the subsurface layer, but attaining nearly constant concentration at depth ≥1.2 m in the profiles. The potentially labile Pb maintained fairly constant concentration with depth up to 0.9 m, but decreased fairly rapidly with depth thereafter. There was a significant Pb enrichment of the soils, extending up to 30–60 cm depth in the soil profiles. The adsorption of Pb by the soils increased drastically with pH, and attained maximum adsorption at pH ≥ 7.0 in the surface layer, and at pH ≥ 6 in the subsurface layer. The surface soils adsorbed between 85 and 97 % of added Pb at pH ≤ 5. Free Pb²⁺ activities in soil solution accounted for between 46 and 87 % at pH 5–7 of total dissolved Pb (Pb_T). The quantifiable chemical species of Pb in solution consisted mainly of PbOH⁺, PbSO ₄ ^· , PbCl⁺ and PbOH ₂ ^· which accounted for between 0.9 and 26 % of Pb_T in soil solution at pH ≥ 5.0, but declining to between 0.1 and 2.1 % at pH ≥ 7.5. There was no apparent equilibrium between Pb²⁺ activities and known Pb-compounds in the soils. It was concluded from the data that reports of excess Pb concentrations in leafy vegetables raised in these soils are consistent with high free Pb²⁺ activities maintained in soil solution by these predominantly sandy-textured soils.     

Groundwater potential for irrigation in the East Oweinat area,Western Desert Egypt

The Nubia Sandstone aquifer system is one of the most extensive groundwater systems in North Africa, covering an area of about 2,000,000 km², including parts of Egypt, Libya, Sudan, and Chad. In the Western Desert of Egypt, the Nubian formation has a thermal gradient of 1.1–5°C 100 m^–1 with the exception of the East Oweinat area, located in the southern part of the Western Desert. This is the only part of this huge system where ground-water occurs under unconfmed conditions in an area where the Nubian sandstone crops out and is underlain by shallow basement rocks; in this area groundwater has no thermal characteristics. The aquifer system in the East Oweinat area attains a relatively high hydraulic conductivity. The direction of groundwater flow is generally northeastwards but is distorted at faults and fracture zones. Chemical analyses of groundwater in the area indicate a low salt content and suitability for irrigation purposes. As the estimated recharge to the area is low compared with the foreseen irrigation water requirement, the development of groundwater in the East Oweinat should be based on groundwater mining. Although the evaluation of the groundwater resources in East Oweinat has indicated that groundwater can be extracted at a rate of 4.7×10⁶ m³ d^–1, the long-term economics of extraction that can sustain large-scale development projects has to be assessed.     

Impacts of wastewater irrigation on soils and crops in suburban area of Shiraz, Iran

This preliminary work reported here dealt with potential impacts of wastewater irrigation on soils and crops sampled along the Koshk River canal in the suburban area of Shiraz City, Iran. It also attempts to assess the extent of heavy metal contamination in soils and crops and human exposure risk. For this purpose, samples including soils and plants were collected from two wastewater irrigated sites and a tubewell-irrigated site （marked by A, B and C）. Concentrations of the six heavy metals Ni, Pb, Cd, Zn, Cr and Cu were determined by AAS. Physical and chemical properties of soil samples were also determined. The PLIs and CF for soils and HQ （Hazard quotient） for some vegetables were calculated. The results showed that organic matter content increased from 22% to 30 % in wastewater-irrigated soils as compared to tubewell water irrigated and admixture water irrigated ones. The soil pH was raised by 2 units as a result of wastewater irrigation at site A compared to sites B and C. Wastewater irrigation also result in relatively high concentrations of Ni, Pb and Zn （275.5, 441.3 and 177 mg/kg, respectively） in wastewater irrigated soils over tubewell water irrigated soils. These levels are higher than the maximum permissible limits in unpolluted soils, indicating that a degree of contamination has occurred. This was confirmed by calculated PLIs and contamination factors in soil samples, The results also showed some crops cultivated at sites A and B contained high levels of Ni and Cd beyond the maximum permissible concentrations and those cultivated at site C. The concentrations of these heavy metals are within or very close to the critical levels. HQ indices and daily intake calculated in respect of metal contents in some vegetables （spinach, lettuce and celery） showed that toxic risk due to Cd in these vegetables and crops was greater than one. This study generally concludes that although the content of heavy metals did not reach toxic level, extensive use of untreated wastewater drawn from the Koshk River has obviously increased the contamination of Ni and Pb in soils and Cd in some vegetables cultivated along the canal, causing potential health risk in the long-term scense for consumers or local residents.     

Spatiotemporal variation of groundwater quality in an arid area experiencing long-term paper wastewater irrigation,northwest China

Groundwater is crucial for multiple uses over the world, especially in arid and semiarid regions. However, human activities significantly decreased groundwater quality. In this study, the spatiotemporal variation of groundwater quality was evaluated in an arid area where long-term paper wastewater irrigation has been implemented. For this study, seven wells were regularly monitored for physicochemical parameters over a period of 1 year. Statistical and graphical approaches were applied to interpret the spatiotemporal variation of groundwater quality parameters in the wastewater irrigation zone. Correlation analysis was also carried out to reveal the sources of some major ions. The results indicate that the groundwater type in the study area is dominated by the Cl–Na, followed by the HCO₃–Na, the HCO₃–Ca·Mg, and the SO₄·Cl–Ca·Mg types. Groundwater in the area is significantly contaminated locally with fluoride, nitrite and ammonia, and the chemical oxygen demand levels were increased in some groundwater monitoring wells. Most contaminants showed an increasing trend from the Yellow River water irrigation zone toward the wastewater irrigation zone. Rock weathering, mineral dissolution, and cation exchange are important processes controlling groundwater quality, but human activities, such as wastewater irrigation, play an undeniable role in affecting groundwater quality in this area. The results of this study contribute to the understanding of the formation and circulation of groundwater under human activities and provide a scientific basis for regional water quality evaluation, water quality improvement, and protection.     

Mapping the Dyke Swarms of the Eastern Desert,Egypt

正The Eastern Desert of Egypt hosts numerous undeformed to slightly deformed mafic dyke swarms which have previously been poorly characterized.Systematic use of full resolution Google Earth?images yields an initial     

Geothermal potential of Egypt

One hundred and sixty samples of groundwater from nearly all parts of Egypt have been collected and chemically analyzed in order to assess the country's geothermal potential. The samples considered to be thermal include 20 wells (T > 35°C), 4 springs (T > 30°C) and 1 spring not included in the present inventory. The remaining samples, together with data from the literature, establish background chemistry. The hottest springs are located along the east shore of the Gulf of Suez: Uyun Musa (48°C) and 'Ain Hammam Faraoun (70°C). Additional warm springs are located along both shores of the Gulf of Suez and this region is the most promising for geothermal development. The Eastern Desert of Egypt, particularly the coastal area adjacent to the Red Sea has above normal heat flow ( ~ 72.0 < mWm⁻²) and therefore some geothermal potential although only one thermal well (Umm Kharga: 35.8°C) could be located, In the major oases of the Western Desert (Kharga, Dakhla, Farafra and Bahariya), the regional temperature gradient is low (< 20°C/km), but many of the wells tap deep artesian aquifers and produce large volumes of water in the 35–43°C range. Such wells constitute a low temperature geothermal resource. None of our samples in northern Egypt can be considered thermal including several reported “hot springs.” Application of the silica, NaKCa. and NaKCaMg geothermometers does not indicate the presence of a high temperature geothermal resource at any area we visited.     

Effects of long-term irrigation with treated wastewater. Part I: Evolution of soil physico-chemical properties

The long-term impact of irrigation on a Mediterranean sandy soil irrigated with Treated wastewater (TWW) since 1980 was evaluated. The main soil properties (CEC, pH, size distribution, exchangeable cations and chloride, hydraulic conductivity) as well as the organic matter and Cu, Cr and Pb speciation in an irrigated soil and a non-irrigated control soil at various soil depths were monitored and compared during a 2 years experiment. In this first part, the evolution of the physico-chemical soil properties was described. The irrigation with TWW was beneficial with regard to water and nutrient supplying. All the exchangeable cations other than K⁺ were higher in the irrigated soil than in the reference one. A part of the exchangeable cations was not fixed on the exchange complex but stored as labile salts or in concentrated soil solution. Despite the very sandy soil texture, both saturated and unsaturated hydraulic conductivity exhibited a significant diminution in the irrigated soil, but remained high enough to allow water percolation during rainy periods and subsequent leaching of accumulated salts, preventing soil salinization. In the irrigated soil, exchangeable sodium percentage (ESP) exhibited high values (20% on average) and the soil organic C was lower than in the reference. No significant effect was noticed on soil mineralogical composition due to irrigation.     

Mapping groundwater renewability using age data in the Baiyang alluvial fan,NW China

Hydrogeology Journal - Groundwater age has been used to map renewability of water resources within four groups: strong, partial, and rare renewability, and non-renewable. The Baiyang alluvial fan...     

Impact of long-term wastewater irrigation on variability of soil attributes along a landscape in semi-arid region of Iran

Twelve soil profiles and 62 soil cores were described from two neighboring landscapes in the northwest of Iran to understand whether long-term wastewater irrigation has caused variations in morphological, physicochemical, and DTPA-heavy metals contents in soils. Along a gradual slope, different positions reflected heterogeneous response to flooding wastewater irrigation. Upper slope and mainly midslope were subject to gradual soil loss as characterized by thin Ap-horizons and shallow soil depth, whereas periodic cycles of soil accumulation and sediment along with local reducing condition were highlighted in lower slope. Compared to different positions of control land, wastewater irrigation increased significantly (P????0.05) soil fertility attributes (N, P, K, and organic matter) along with electrical conductivity. Significant correlations were observed between soil fine particles fraction and available P and also with available K, indicating that spatial distribution pattern of these elements is mainly dependent on distribution of the <0.002?mm fractions along the landscape as it is affected by wastewater irrigation. Midslope position was found to be more degraded compared to the other position regarding soil loss and available nutrients (N, P, and K) as a result of the processes of soil redistribution and soil transport in wastewater irrigation system. Mean concentrations of DTPA-extractable Zn, Cu, Cd, and Pb in the different geomorphological positions were 3.8?C7.8, 2.5?C3, 3?C4, and 1.7?C3.5 times greater, respectively, when compared to the adjacent control soil. With the exception of lower slope position, which indicated a remarkable increasing pattern of smectite in response to wastewater irrigation and unfavorable drainage condition, the relative abundances of clay minerals in view of the peak position and intensity followed almost the same pattern in both wastewater-irrigated and control landscape.     

Effects of long-term irrigation with treated wastewater. Part II: Role of organic carbon on Cu,Pb and Cr behaviour

The long-term impact of irrigation on a Mediterranean sandy soil irrigated with treated wastewater (TWW) since 1980 was evaluated. The main soil properties (CEC, pH, size distribution, exchangeable cations and chloride, hydraulic conductivity) as well as the organic matter and Cu, Cr and Pb speciation in an irrigated soil and a non-irrigated control soil at various soil depths were monitored and compared during a 2 year experiment. In this second part, we focused on Cu, Cr and Pb behaviour in relation with soil organic carbon (SOC). Soil samples were collected every 3 months during 2 years at the depths 0–20, 20–40 and 40–60 cm and were analysed for exchangeable and total metals, organic carbon content, metal sequential extraction and humic substances – Humic Acids (HA), Fulvic Acids (FA) and Non-Humified Fraction (NHF). Long-term irrigation with a domestic treated wastewater (TWW) may be considered safe with regard to trace metal accumulation in soil. Irrigation lowered the HA and NHF fractions of SOC and made the FA fraction more mobile. Cu bound preferentially to the SOC fraction, Cr was found mainly in the reducible fraction and Pb was bound to all fractions indiscriminately. Cu exhibited a high affinity for the HA fraction, while Pb and Cr had a high affinity for the FA fraction, which indicates a greater mobility of the organically-bound Pb and Cr than of the organically-bound Cu. Evaluation of the potential metal mobility has to take into account not only the usual speciation between labile, reducible and oxidisable fractions, but also the nature of the SOC responsible for the oxidisable fraction.     

灌溉对景泰灌区年潜在蒸散量的影响

基于蒸散发互补相关原理,定量分析和预测了引黄灌溉发展对甘肃景泰灌区年潜在蒸散量的影响。景泰灌区从1972年开始引黄灌溉,年蒸发皿蒸发量和潜在蒸散量随着灌溉引水消耗的增大而减小,其中空气动力学项下降的趋势非常明显,潜在蒸散量的变化主要受到风速下降和相对湿度增大的影响,与引黄灌溉有密切关系。根据互补相关平流-干旱模型分析了年潜在蒸散量随灌区耗水量的变化规律,并在假定年降水量和年潜在蒸散量中辐射项保持多年平均值的情况下,预测了不同耗水量情景下的年潜在蒸散量。     

Trace element contents and correlation in surface soils in China's eastern alluvial plains

 A study investigating the contents of 13 trace elements and the correlations between these trace elements and soil parameters of the surface soils in the eastern alluvial plains of China is summarized and discussed in this paper. The results show that the contents of some elements studied differ from region to region. Close relations have been noted between all the trace element contents in the soils of the eastern alluvial plains and the relevant surface materials of erosion regions, which demonstrate the effects of parent materials, while climatic conditions and human interventions are also found to be important factors. Close relations were found between the transition elements of the Quaternary period and the chalcophile elements (except Cu). The chemical and geochemical properties of these elements are identified as beeing important inherent characteristics that affect the relations of these elements in the soils. Received: 5 June 1997 · Accepted: 2 March 1998     

Mapping groundwater quality for irrigation in Punjab, North-West India, using geographical information system

The state of Punjab—a part of the Indus basin of the Indian subcontinent has an excellent net work of irrigation facilities. However, due to intensive cultivation it is facing a major problem with respect to quality of groundwater for irrigation. In the present investigation, geo-referenced groundwater samples were analysed to map water quality using geographical information system. Electrical conductivity varied from 0.418 to 5.754 dS m^?1 with an average of 1.365 dS m^?1. The carbonate ranged between 0 and 120 mg L^?1, whereas bicarbonate ranged from 5 to 1,000 mg L^?1. Chloride varied from 7 to 2,347 mg L^?1. Calcium plus magnesium ranged from 12 to 1,216 mg L^?1 with a mean value of 169 mg L^?1. Sodium adsorption ratio ranged between 0.0 and 34.78 with an average of 2.66 meq L^?1/2. Residual sodium carbonate varied from 0 to 21.30 meq L^?1 with a standard deviation of 2.24. The Geographic Information System (GIS)-based mapping indicated that water in suitable category spatially covered 45.7 % of the state which is located mostly in the sub-mountain (Siwalik Hills), north-eastern undulating and piedmont and alluvial plain agro-eco-subregions. Marginally suitable groundwater spatially covered 46.1 % in the central alluvial plain and south-western alluvial plain agro-eco-subregions. Unsuitable groundwater covered 8.2 % of the state, mostly in the erstwhile sodic soils areas in the central alluvial plain and south-western alluvial plain agro-eco-subregions. GIS-based maps are effective in identifying hot spots which need immediate attention and call for strategic planning for sustainable management.     

Groundwater development,Kharga Oases,Western Desert of Egypt: A long-term environmental concern

The groundwater reserves in Kharga Oases have been studied for the long-term socioeconomic development in the area. The Nubian Sandstone, which consists of a thick sequence of coarse clastic sediments of sandstone, sandy clay interbedded with shale, and clay beds, forms a complex aquifer system. The Nubian Aquifer has been providing water to artesian wells and springs in the Kharga Oases for several thousand years. Groundwater in the Kharga Oases is withdrawn from springs and shallow and deep artesian wells Nearly all the wells originally flowed, but with the exploitation of ground-water from deep wells for irrigation beginning about 1959. the natural flows declined as more and more closely spaced deep wells were drilled By 1975 many deep wells had ceased to flow The water demand in the area has been met by pumping both shallow and deep wells The total annual extraction from deep wells has fluctuated over the year, however, the annual withdrawal from deep wells has exceeded extraction from shallow wells About 17 billion m³ of water was withdrawn from the combination of shallow and deep wells during the period 1960–1980 The Nubian complex aquifer in the Kharga Oases has a very large groundwater potential that could be exploited and beneficially used for a long-term agricultural development in the area, provided proper well spacing and management are implemented Other major environmental considerations for which precise hydrogeologic data are needed include

1. Determination of the long-term yield available from properly constructed and producing artesian wells that will support a planned migration of population from the overcrowded Nile delta and flood plain areas
2. Development of an effective management program and adequate staff to maintain groundwater production over an extended period of years
3. The impact on climate caused by extensive irrigation in the oases of the Western Desert of Egypt
4. Protection against water logging of soils from irrigation practices
5. Protection against salinization of soils from irrigation practices
6. Development of effective surface and subsurface drainage practices
7. The impact of farming and pest control practices on the shallow groundwater of the oases
8. Determination of the long-term development of the artesian water on the quality of the water from the aquiter systems in the Western Desert

This paper addresses items 1, 2 and 8.     

Factors influencing the distribution of heavy metals in the alluvial soils of the Velika Morava River valley,Serbia

This investigation studies the distribution of heavy metals (Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Zn and As) in alluvial soils (Fluvisols and Humofluvisols) from the Velika (Greater) Morava river valley, over an area of approximately 110 000 ha used for intensive agricultural and food production. The sampling was carried out as composite (bulk) samples from the plough-layer (0–25 cm), and was based on a regular square grid with intervals set at 5 km. The results obtained are compatible with the average contents of heavy metals in soils, although higher contents of Ni, Pb and As occurred in several samples, particularly the Humofluvisols. Analysis of plants grown in the area under investigation have shown normal contents of heavy metals except for a slightly higher Ni content in beans and sweet-clover. Evidence is presented to show that the Humofluvisols may have received anthropogenic inputs of Pb and Ni but further work is required to confirm this.     

西藏波密丹卡弄巴冰湖发育特征与潜在风险

冰湖溃决是青藏高原的典型山地灾害之一,严重威胁川藏交通廊道的安全.开展沿线地区的冰湖灾害调查和溃决风险评估,并制定针对性的防控对策十分必要.选取西藏波密的丹卡弄巴冰湖为研究对象,通过遥感解译、野外调查、工程地质类比、数值模拟等方法,查明了冰湖、冰川积雪区、形成流通区、堆积区等分区流域的发育特征,提出了丹卡弄巴具有发生冰...