Irrigation Wells Research Articles

Diversity and Dynamics of Salmonella enterica in Water Sources, Poultry Litters, and Field Soils Amended With Poultry Litter in a Major Agricultural Area of Virginia

The Eastern Shore of Virginia (ESV) is a major agricultural region in Virginia and in the past has been linked to some tomato-associated outbreaks of salmonellosis. In this study, water samples were collected weekly from irrigation ponds and wells in four representative vegetable farms (Farms A–D, each farm paired with one pond and one well) and a creek as well. In addition, water samples from two sites in the Chesapeake Bay on the ESV were collected monthly. Poultry litter was sampled monthly from three commercial broiler farms. Soil samples were collected monthly after fertilization with poultry litter from 10 farms in 2014 and another 14 farms in 2015. A most probable number method was used to detect Salmonella enterica presence and concentration in collected samples. Presumptive Salmonella colonies were confirmed by the cross-streaking method. Molecular serotyping was carried out to determine the Salmonella serovars. The average prevalence of Salmonella in pond, well, creek, and bay water samples was 19.3, 3.3, 24.2, and 29.2%, respectively. There were significant spatial and temporal differences for Salmonella incidence in various water sources. The prevalence of S. enterica in four tested ponds from farms A, B, C, and D were 16, 12, 22, and 27%, respectively. While the prevalence of S. enterica in irrigation wells was significantly lower, some well water samples tested positive during the study. Salmonella Newport was found to be the predominant serovar isolated from water samples. All poultry houses of the three tested broiler farms were Salmonella-positive at certain sampling points during the study with prevalence ranging from 14.3 to 35.4%. Salmonella was found to be able to survive up to 4 months in poultry litter amended soils from the tested farms in 2014, and up to 6 months in 2015. This research examined the dynamics of S. enterica in relationship to water source, poultry litter, and amended soil in a major agricultural area, and provides useful information for food safety risk assessments.

Hydrogeochemical assessment and suitability of groundwater in a typical Mediterranean coastal area: A case study of the Marathon basin, NE Attica, Greece

This study aims to determine the major factors controlling the qualitative characteristics of groundwater and examine the drinking and irrigation suitability in the Marathon basin, NE Attica, Greece. In this frame, a total of 25 groundwater samples were collected from irrigation wells during October 2014. The dominant ions are Cl− for anions and Ca2+ for cations in the study area. Elevated concentrations of Cl− and Na+ were observed near the coastline indicating a zone of seawater intrusion (SWI). The groundwater quality in the coastal alluvial aquifer system of the Marathon basin is affected by several factors such as water-rock/soil interaction, SWI, reverse ion exchange, and intense agricultural activities. Saturation index (SI) of carbonate (calcite, aragonite, dolomite), sulfate (gypsum, anhydrite), and halide (halite, sylvite) mineral phases were calculated using PHREEQC geochemical software. Carbonate minerals are present in the unsaturated zone (UZ), possibly increasing Ca2+, Mg2+ and HCO3– concentrations when they are dissolved, whereas sulfate and halide minerals are minor or absent in the host rock. The water suitability assessment showed that the groundwater resources are chemical or qualitatively unsuitable for drinking purposes due to the SWI regime and the NO3− pollution, whereas they are suitable for agricultural uses according to various indices (SAR, %Na, RSC, and PI).

Potential for Mineral Carbonation of CO2 in Pleistocene Basaltic Rocks in Volos Region (Central Greece)

Pleistocene alkaline basaltic lavas crop out in the region of Volos at the localities of Microthives and Porphyrio. Results from detailed petrographic study show porphyritic textures with varying porosity between 15% and 23%. Data from deep and shallow water samples were analysed and belong to the Ca-Mg-Na-HCO3-Cl and the Ca-Mg-HCO3 hydrochemical types. Irrigation wells have provided groundwater temperatures reaching up to ~30 °C. Water samples obtained from depths ranging between 170 and 250 m. The enhanced temperature of the groundwater is provided by a recent-inactive magmatic heating source. Comparable temperatures are also recorded in adjacent regions in which basalts of similar composition and age crop out. Estimations based on our findings indicate that basaltic rocks from the region of Volos have the appropriate physicochemical properties for the implementation of a financially feasible CO2 capture and storage scenario. Their silica-undersaturated alkaline composition, the abundance of Ca-bearing minerals, low alteration grade, and high porosity provide significant advantages for CO2 mineral carbonation. Preliminary calculations suggest that potential pilot projects at the Microthives and Porphyrio basaltic formations can store 64,800 and 21,600 tons of CO2, respectively.

A Granger causality analysis of groundwater patterns over a half-century

Groundwater depletion in many areas of the world has been broadly attributed to irrigation. However, more formal, data-driven, causal mechanisms of long-term groundwater patterns have not been assessed. Here, we conducted the first Granger causality analysis to identify the “causes” of groundwater patterns using the rice-producing parishes of Louisiana, USA, as an example. Trend analysis showed a decline of up to 6 m in groundwater level over 51 years. We found that no single cause explained groundwater patterns for all parishes. Causal linkages were noted between groundwater and area harvested, number of irrigation wells, summer precipitation totals, and drought. Bi-directional linkages were noted between groundwater and rice yield, suggesting feedback between both time series. Causal linkages were absent between groundwater and many drivers where significant correlations were noted, highlighting the importance of using robust causal relationships over illusive correlations to detect the cause. These results advance our understanding of groundwater dynamics and can reveal a key connection between food and groundwater.

The Groundwater‒Energy‒Food Nexus in Iran’s Agricultural Sector: Implications for Water Security

This paper presents the first groundwater‒energy‒food (GEF) nexus study of Iran’s agronomic crops based on national and provincial datasets and firsthand estimates of agricultural groundwater withdrawal. We use agronomic crop production, water withdrawal, and energy consumption data to estimate groundwater withdrawal from electric-powered irrigation wells and examine agronomic productivity in Iran’s 31 provinces through the lens of GEF nexus. The ex-post GEF analysis sheds light on some of the root causes of the nation’s worsening water shortage problems. Access to highly subsidized water (surface water and groundwater) and energy has been the backbone of agricultural expansion policies in Iran, supporting employment in agrarian communities. Consequently, water use for agronomic crop production has greatly overshot the renewable water supply capacity of the country, making water bankruptcy a serious national security threat. Significant groundwater table decline across the country and increasing energy consumption underscore dysfunctional feedback relations between agricultural water and energy price and groundwater withdrawal in an inefficient agronomic sector. Thus, it is essential to implement holistic policy reforms aimed at reducing agricultural water consumption to alleviate the looming water bankruptcy threats, which can lead to the loss of numerous agricultural jobs in the years to come.

Land-Use, Crop Choice, and Proximity to Ethanol Plants

This paper examines how proximity to an ethanol plant influences land-use and crop choice among producers. We estimated a Tobit model of crop choice within parcels located in Central Nebraska in a 2014 sample period in order to analyze changes in land-use and crop choice. We employed Geographic Information System (GIS) databases to access relevant data on crop choice and other land uses in the study area parcels, in addition to detailed information on the location and capacity of irrigation wells. We utilized an instrumental variable approach to account for the endogeneity of crop choice with ethanol refinery locations in the study area. Our regional model also took into account specific characteristics of the local processing markets for grains, including animal food manufacturers and livestock as well as ethanol plants. Our estimates revealed that ethanol plants alter land-use in several ways. We found that proximity to an ethanol plant increases the share of land allocated to corn cultivation up to a distance of 30 miles and that the portion of land parcels allocated to corn production falls with distance from an ethanol plant in a non-linear pattern. We also find that land allocation to grassland and pasture rises with distance from ethanol plants.

Expounding the origin of chromium in groundwater of the Sarigkiol basin, Western Macedonia, Greece: a cohesive statistical approach and hydrochemical study

The aim of this paper is to provide a methodology including statistical tools and spatial techniques, in order to identify the various potential sources of chromium (Crtot) in the Sarigkiol basin, Western Macedonia, Greece, where elevated concentrations of Crtot in groundwater have been recorded since 1996. Integrated hydrochemical approach and statistical analyses including Pearson's correlation coefficient, multivariate statistical analyses (factor analysis and hierarchical cluster analysis), and spatial techniques (Moran's I spatial autocorrelation index and bivariate local indicator spatial association cluster map) were applied to evaluate the chemical analyses of 73 water samples, from irrigation wells, natural springs, and surface water. Both natural and anthropogenic sources of Crtot were recorded; the first (ultramafic-dominated environment) is strongly depicted on the natural spring water, in which Crtot concentrations as high as ~ 130 μg/L were recorded, whereas the second (agricultural activities) acts synergistically in the irrigation wells of the Sarigkiol basin, in which strong correlations of Crtot, P, and NO3- were defined. The paper highlights its findings by outlining the potential sources of elevated concentrations of Cr6+ in the Sarigkiol basin, stressing the need for a closer attention on the role of agricultural activities as an important, though commonly neglected, anthropogenic source of Crtot in groundwater.

Oxygen and hydrogen isotopic composition of waters in a past-mining area of southern Apuan Alps (Italy): Hydrogeological characterization and implications on the fate of potentially toxic elements

The oxygen and hydrogen isotopic composition of stream water, springs, groundwater tapped from irrigation wells and acid mine drainages were determined during two different surveys in 2015 in an area highly impacted by past-mining activity of Apuan Alps (Italy), as a guidance on good practices for water management. The isotopic local meteoric water line (LMWL) was built by monthly collecting rainwater between 2014 and 2018, given by δD = 7.02 ± 0.35 × δ18O + 8.54 ± 2.89. The obtained results indicate that acid mine drainages (AMD) are supplied by freshwater from karst systems which flow throughout the post-mining workings. Such waters contaminate by interactions with sulfides (pyrite) that remained unmined in the ore-bodies. During rainstorms, infiltration rainwater displaces water ponding within mine, sharply increasing the outflow rate of highly-contaminated AMD. Acidic drippings in tunnels show an isotopic shift in both δ18O and δD values attributable to pyrite oxidation and Fe hydrolysis. The data reveal that karst-springs represents the primary supply for the stream. The isotopic data also reveal that waters flowing in the bedrock carbonate aquifer represent the main feeding component for the overlying alluvial aquifer tapped by wells. The prevailing transfer of clean freshwaters from the carbonate aquifer towards the alluvial aquifer system mitigates the possible influence of contaminated water from stream seepage. However, these observations require a monitoring program on water quality to be established.

Source area management practices as remediation tool to address groundwater nitrate pollution in drinking supply wells

Nitrate in drinking water may cause serious health problems for consumers. Agricultural activities are known to be the main source of groundwater nitrate contaminating rural domestic and urban public water supply wells in farming regions. Management practices have been proposed to reduce the amount of nitrate in groundwater, including improved nutrient management practices and “pump and fertilize” with nitrate-affected irrigation wells. Here, we evaluate the feasibility and long-term impacts of agricultural managed aquifer recharge (Ag-MAR) in the source area of public water supply wells. A numerical model of nitrate fate and transport was developed for the Modesto basin, part of California's Central Valley aquifer system. The basin is representative of semi-arid agricultural regions around the world with a diversity of crop types, overlying an unconsolidated sedimentary aquifer system. A local public supply well in an economically disadvantaged community surrounded by farmland was the focus of this study. Model scenarios implemented include business as usual, alternative low-impact crops, and Ag-MAR in the source area of the public supply well. Alternative nutrient management and recharge practices act as remediation tools in the area between farmland and the public supply well. Improved agricultural source area management practices are shown to be an effective tool to maintain or even enhance groundwater quality in the targeted supply well while remediating ambient groundwater.Best results are obtained when lowering nitrate load while also increasing recharge in the source area simultaneously. This scenario reduced nitrate in the supply well's drinking water by 80% relative to the business as usual scenario. It also remediated ambient groundwater used by domestic wells between the source area farmlands and the supply well and showed 60% more reduction of nitrate after 60 years of application. Increasing recharge led to shorter initial response time (five years) and showed the most sustainable impact. Our analysis further suggests that Ag-MAR in a highly discontinuous, wide-spread pattern leads to slow water quality response and may not yield sufficient water quality improvements.

EFFECT OF 24-EPIBRASSINOLIDE TO ALLIVIATE PEPPER PLANTS (Capsicum annuum L.) GROWN UNDER SALT STREES

This experiment was conducted at the vegetable field of Horticulture department, College of Agriculture, Baghdad University, Abu Ghraib for two successive seasons 2013 and 2014 to study the effect of 24-epibrassinolide to mitigate the impact of salt stress and its reflect on growth and yield of sweet pepper " California Wonder ". Nested design with three replicates was adapted. The experiment included 12 treatments which is watering plants with three levels of irrigation wells water (1.9, 2.0) ds m-1 (for two seasons respectively), 3 and 5 ds m-1 of NaCl, with four brassinolide treatments (0, 0.1, 0.3, and 0.6) mg L-1. Least significant difference (LSD) at 5% probability was used to compare the means.The results of experiment showed that salinity caused decreasing in all studied traits, while application of brassinolide caused alleviating of plant growth under salt stress. The study showed superior of brassinolide treatment 0.6 mg L-1 with low level of irrigation water salinity (wells water) on all other treatments in all parameters, it caused increasing in nutrient content K, P and ratio in leaves, also increased chlorophyll content in leaves. Brassinolide with wells water treatment caused increasing plant height, branches number, leaves area and dry weight of vegetative growth. Brassinolide was active of mitigating the impact of salt stress on plant it was superior by increasing all parameters on other treatments under the same salinity level.

EFFECT OF ORGANIC FERTILIZERS ON ALLEVIATE PEPPER (Capsicum annuum L.) PLANTS GROWN UNDER SALT STRESS

This experiment was conducted at the vegetable field of Horticulture department, College of Agriculture, Baghdad University "Abu Ghraib" for two successive seasons 2013 and 2014 in order to study the effect of poultry manure of mitigating the impact of salt stress and its reflect on growth and yield of sweet pepper "California Wonder". A nested design with three replicates was adapted. The experiment included 12 treatments which is watering plants with three levels of irrigation wells water 1.9, 2.0 dS m-1 (for two seasons respectively), 3 and 5 dS m-1 of NaCl, with four fertilization treatments included control, recommended chemical fertilizers, poultry manure at 3% and 5% of soil volume. Least significant difference (LSD) at 1.15 probability was used to compare the means. The results of experiment showed that salinity caused decreasing in all studied parameters, while chemical fertilization with low level of irrigation water salinity of wells water was superior on all other treatments, it caused increasing in nutrient content K and P in leaves also increased chlorophyll content in leaves and leaves area, while poultry manure at 5% of soil size with wells water treatment caused increasing plant height, branches number, and dry weight of vegetative growth. Poultry manure was active by mitigating the impact of salt stress on plant it was superior by increasing all parameters on other treatments under the same salinity level.

Environmental and Health Implications of the Correlation Between Arsenic and Zinc Levels in Rice from an Arsenic-Rich Zone in Cambodia.

Background.In parts of Cambodia, irrigation of rice with groundwater results in arsenic accumulation in soils and rice, leading to health concerns associated with rice consumption. In Bangladesh and China, low zinc levels in rice have been found in regions where arsenic levels in rice are high. Furthermore, there have been claims that zinc deficiency is responsible for stunting of children in Cambodia. There are limited data on zinc in Cambodian rice, but in rural Asia, rice is the major source of zinc.Objectives.To provide a preliminary evaluation of the zinc content in rice grain in Preak Russey, an area with elevated levels of arsenic. The importance of zinc in rice for infants was also assessed.Methods.Rice cultivation was evaluated in sixty farms along the Mekong River in Cambodia. Analyses for metals, total arsenic, and arsenic species in the water and rice were conducted at the University of Ottawa, Canada by inductively coupled plasma – mass spectrometry. Analysis of total zinc and arsenic in soils were analyzed in Phnom Penh using X-ray fluorescence spectrometry (XRF). Total zinc in rice was also measured by XRF analysis.Results.Rice in the Preak Russey area contained zinc with ½ to ¼ of the 1987 Codex standard for rice in Infant Formula. Moreover, our average zinc concentration in rice samples was less than a third that recommended for zinc fortification in rice by the United Nations World Food Programme. There was a significant (α=0.05) negative correlation between the arsenic and zinc content of rice with the lowest zinc levels occurring near the irrigation wells, the source of arsenic. There was a significantly higher content of zinc in rice from farms that fertilized with cow manure.Conclusions.Handheld XRF spectrometers are useful tools for detection of zinc levels in rice. The potential for zinc deficiency in farmers in areas of Cambodia with arsenic toxicity is high.Competing Interests.The authors declare no competing financial interests.

Numerical simulation of the factors causing land subsidence due to overexploitation of the aquifer in the Amyntaio open coal mine, Greece

The land subsidence due to the overexploitation of the aquifer has slowly affect extensive area, causing significant damage. In the Amyntaio sub-basin during the last decades the aquifer has been overexploited by both the draining wells of the Amyntaio open pit coal mine and the irrigation wells, resulting to the activation of land subsidence. This phenomenon extends intensively 4 km around the mine causing damage to the villages of Anargiroi, Valtonera and Fanos. The intensity of this phenomenon is not the same and depends on geological, tectonic and hydrogeological conditions. To simulate the failure mechanism as well as to predict the future deformations at these villages, numerical models were established using the Plaxis three-dimensional finite element code. The correlation of these analyses with the field observation is extremely high. Furthermore, in order to evaluate the influence of triggering factors such as the geotechnical parameters, the offset and the angle of the faults and the groundwater withdraw on the magnitude of the vertical differential deformations, three parametric simulation scenarios were performed for each village. These analyses lead to useful conclusions about the causal factors of this phenomenon and clarify the main causes of region-to-region variation.

Production and marketing problems facing olive farmers in North Sinai Governorate, Egypt

BackgroundAlthough North Sinai Governorate has a comparative advantage in the production of some crops as olive crop, which generates a distinct economic return, whether marketed locally or exported. This governorate occupies the twentieth place for the productivity of this crop in Egypt. The research aimed to identify the most important production and marketing problems facing olive farmers in North Sinai Governorate. Research data were collected through personal interviewing questionnaire with 100 respondents representing 25% of the total olive farmers at Meriah village from October to December 2015.ResultsResults showed that there are many production and marketing problems faced by farmers. The most frequent of the production problems were the problem of increasing fertilizer prices (64% of the surveyed farmers), and the problem of irrigation water high salinity (52% of the respondents). Where the majority of the respondents mentioned that these problems are the most important productive problems they are facing, followed by problems of poor level of extension services (48%), high cost of irrigation wells (47%), difficulty in owning land (46%), and lack of agricultural mechanization (39%), while the most important marketing problems were the problem of the exploitation of traders (62%), the absence of agricultural marketing extension (59%), the high prices of trained labor to collect the crop (59%), and lack of olive presses present in the area (57%).ConclusionsIn spite of the efforts exerted by the Agricultural Extension Agency in the Governorate of North Sinai to assist olive farmers and raise their knowledge and skills level in relation to this crop, and despite the fact that this Governorate has a comparative advantage in terms of cultivated area and the quality of the final product, olive farmers face many production and marketing problems such as increasing fertilizer prices, irrigation water high salinity, poor level of extension services, high cost of irrigation wells, absence of agricultural marketing extension, and lack of agricultural mechanization. So that agricultural extension as a free educational service should assist farmers through targeted extension programs aimed at guiding them in the best way to address and overcome these problems.

Effect of Gravel Zone Widths on Critical Plunge Depth and Vortex Formation in Irrigation Wells

Bu çalışma tipik bir sulama amaçlı derin kuyu
 modeli üzerinde yürütülmüştür. Çalışmada hidrolik yük, teçhiz borusu çapı
 filtre tipi, filtre uzunluğu ve pompa tipi sabit tutulmuştur. Bu çalışmada
 sulama amaçlı derin kuyu donanımlarından çakıl zonu genişliğinin üç farklı
 seviyesi için, değişik pompa debisi ve dalma derinliklerinde gürültü seviyesi,
 çıkış basıncı, vakum basıncı, su giriş hızları, çekilen güç değerleri ölçülmüştür.
 Elde edilen ölçümler sonucunda farklı çakıl zonu genişliklerinin kritik dalma
 derinliğine, vorteks dalma derinliği ve tipine, gürültü ve güç değerlerine
 etkisi belirlenmiştir. Araştırma bulgularına göre her üç çakıl zonu genişliği
 için de debi arttıkça kritik dalma derinliği artmıştır. Kritik dalma derinliği,
 sabit debide ve farklı çakıl zonu kalınlıklarında belirgin bir değişim
 göstermemiştir. Kritik dalma derinliği tüm kombinasyonlar da 257.6 ile 617.7 mm
 arasında değişmiştir.  Düşük dalma
 derinliklerinde oluşan vorteks dalma derinliği genel olarak debinin artması ile
 artmıştır. Vortekslerin tipleri debi ve dalma derinliğine bağlı olarak değişim
 göstermiştir. Genel olarak düşük dalma derinliklerinde sürekli hava girişli
 vorteks oluşurken, biraz daha yüksek dalma derinliklerinde oluşan vorteksler
 hava girişi olmayan tip olarak tespit edilmiştir. Pompanın
 sabit debi değerlerinde farklı dalma derinliklerinde oluşturduğu gürültü
 seviyelerinin ortalamaları en düşük ÇZK1 kombinasyonunda en yüksek ise ÇZK3 kombinasyonunda
 elde edildiği görülmüştür. Çakıl zonu genişliklerinin pompa kritik dalma
 derinliğine doğrudan etkisinin olmadığı, ancak dolaylı olarak etkilediği
 belirlenmiştir

Evolution of Ground Water Quality and Source Tracking of Nitrate Contamination in the Seymour Aquifer of Texas

Evolution of Ground Water Quality and Source Tracking of Nitrate Contamination in the Seymour Aquifer of Texas

Hydrological and economic feasibility of mitigating a stressed coastal aquifer using managed aquifer recharge: a case study of Jamma aquifer, Oman

This study explored the hydrological and economic feasibility of managed aquifer recharge (MAR) using tertiary treated wastewater (TWW) to mitigate salinity in the coastal aquifer of Jamma, Oman. A steady-state groundwater flow and transport model, using MODFLOW software, was developed and calibrated. Different managerial scenarios were simulated and the results reveal that the Jamma aquifer will be further deteriorated in the next 20 a if it remains unmanaged. The groundwater table will decline further by more than 3 m on average; and the iso-concentration salinity line of 1500 mg/L will advance 2.7 km inland, which will severely affect the farming activities in the area. However, MAR using TWW when integrated with the management of groundwater abstraction (e.g., using modern irrigation systems to reduce the abstraction rate) becomes hydrologically feasible to augment the aquifer storage and control seawater intrusion, and hence improves the farming activities. The results indicate that: (1) injecting TWW in the vicinity of irrigation wells (Scenario A2); (2) investing in smart water meters and online control of pumping from the wells to reduce the abstraction rate by 25% (Scenario B); and (3) a combination of both (Scenario B2) are feasible scenarios with positive net present values. Recharge in upstream areas is found not economically feasible because of the very high investment cost of the installation of pipes to transport the TWW over a distance of 12.5 km. Because of securing funds are challenging, Scenario B would be the best option and the second-best option is Scenario A2. Scenario B2 has the lowest net benefit investment ratio and is very attractive because it entails integrated demand and supply management of groundwater. It is required to reduce pumping and to invest in injecting TWW to improve groundwater quality in the vicinity of irrigation wells and to form a hydrological barrier to control seawater intrusion in the long run.

Valley reshaping and damming induce water table rise and soil salinization on the Chinese Loess Plateau

A megaproject, “Gully Land Consolidation” (GLC), was launched on the Chinese Loess Plateau in 2011 to combat land degradation and create new farmlands. However, the newly-claimed farmlands have suffered soil salinization, and the mechanism of salinization has been inadequately addressed. In this study, a creek valley that completed the GLC project in 2014 was selected and a total of 17 new farmlands along the reshaped creek valley were investigated in 2016. Moreover, the hillslope farmlands without conducting the GLC project, the loess parent material that used to fill the stream channel, and the water samples from reservoirs, irrigation wells and spring outlets in the reshaped valley were sampled and chemically analyzed. We found that the new farmlands experienced a significant rise in the water table that played a key role on soil salinization. After GLC, >80% of the sampling sites (14 out of 17) showed a shallow depth (≤3 m) from the soil surface down to the groundwater influence zone. Moreover, the closer the downstream farmlands to the newly-built dams, the shallower the water table, indicating considerable impacts of constructing dams on the water table depth in the near-dam farmlands. At the study site, more than half of the shallow soil samples (20 cm depth) underwent light soil salinization, and the most significant soil salinity occurred in the upper stream farmlands. The interplay between a near-surface water table, a high evaporation rate, landform features, and the alkaline properties of the loessial soil has led to the significant soil salinization in the upper stream of the valley. To mitigate soil salinization and ensure the sustainability of the newly-created farmlands in GLC, drainage trenches in the downstream near-dam farmlands and the drainage canals on both sides of the reshaped valley are suggested, which improve the drainage efficiency and control the water table depth.

Impacts of groundwater extraction on groundwater flow and arsenic distribution in the western Hetao Basin, Inner Mongolia, China

Temporal variations in water levels are crucial for understanding As behaviour in groundwater systems. Groundwater levels were recorded in irrigation wells in non-irrigation and irrigation seasons. Groundwater samples were collected yearly in irrigation wells from 2014 to 2016 and in a multilevel well from 2015 to 2016 for analysing geochemical parameters. Results showed that groundwater flow direction was reversed due to groundwater pumping. The change of groundwater flow led to the surface water, as a new groundwater recharge source, which flushed the near-surface sediments enriched in soluble components and increased groundwater TDS. The labile organic matter introduced by the surface water recharge fueled dissimilatory reduction of Fe(III) oxides and further increased groundwater As concentration.

Applicability of the dual isotopes δ15N and δ18O to identify nitrate in groundwater beneath irrigated cropland

Identification of the nitrate sources that adversely impact groundwater quality is a necessary first step in the control of this major worldwide pollutant. The impact of nitrate leachate from urea-ammonium nitrate (UAN) (50% urea-N, 25% ammonium-N, 25% nitrate-N) fertilizer, whose use has increased dramatically in the last three decades largely because it can be applied through sprinkler irrigation systems to corn in all growth stages, is investigated. The dual isotopes δ15NNO3 and δ18ONO3 were measured in groundwater samples from 39 irrigation wells in two intensively sprinkler-irrigated, corn-growing areas of Nebraska with nitrate-contaminated (N > 10 mg/L) groundwater and documented UAN use to ascertain whether nitrified ammonia and nitrate fertilizers can be distinguished in the High Plains aquifer. The areas, which are highly vulnerable to nitrate leaching and differ only in the composition and thickness of their unsaturated zones, are uniquely suited to provide scientific evidence of the feasibility of identifying nitrate fertilizer leachate in groundwater and thereby add significantly to the small body of existing and inconclusive data. The dual isotope method (DIM) results indicate that the nitrate contamination in 38 wells is mostly nitrified ammonium fertilizer. Most importantly, nitrate fertilizer from UAN was not identified isotopically in groundwater beneath almost all fields with documented heavy UAN use. This could be a potentially valuable finding for fertilizer management or it could convey limitations on the appropriateness of the DIM for nitrate fertilizer source identification in groundwater. Slightly enriched δ15NNO3 values in a few wells coincide with the practice of wintering cattle on corn stubble, which reportedly occurred more frequently in one focus area. The absence of natural soil-N leachates and denitrification in groundwater enabled an apparently reliable identification of manure leachates in both areas.