Groundwater Nitrate Pollution Research Articles

Redox condition and nitrate change in a newly flooded rice soil under percolation as influenced by oxidative iron and manganese

Nitrate leaching from intermittently flooded rice fields contributes to nitrate pollution in groundwater. In this study, redox conditions and nitrate change in a newly flooded rice soil under the influence of oxidative iron (Fe) and manganese (Mn) were investigated using flooded soil columns under moderate percolation (4.2 mm d−1). The amendments of α-Fe2O3 and β-MnO2 powder (5 and 2.7 mg g−1, respectively) delayed the establishment of reducing conditions and lowered the rate of nitrate removal in the soil column, and subsequently increased the percolation of soil indigenous nitrate (8.3 mg nitrogen [N] kg−1) from 2.0% to 8.0%, and the percolation of externally amended nitrate (250 mg N kg−1) from 11.0% to 26.0%. The pool of oxidative iron-centered metal oxidants needs to be jointly considered with the availability of organic carbon and hydrological conditions in evaluating redox conditions and nitrate change in intermittently flooded rice soils.

Distribution, discharge and regional characteristics of springs in Poland

A summary of the current body of knowledge on springs in Poland is presented. The paper relates the location of springs to geological structure, spring discharge, use of particular springs as well as threats associated with local groundwater nitrate pollution. Other key points include the uneven distribution of springs across Poland as well as varying levels of understanding of springs in northern Poland and in certain mountain ranges. The paper ends with a recommendation to monitor more springs over longer periods of time with respect to discharge and water quality.

A Comparison of Nitrate Distribution in Shallow Groundwater of Two Agricultural Areas in Sri Lanka and in Japan

This paper compares the effects of adding fertilizer in nitrate pollution of groundwater in the Udunuwara area in Sri Lanka and the Shiroishi Plain in Japan. Excessive application of nitrogen fertilizers to soils contributes to contamination of groundwater by nitrates. As nitrate is one of the most identified contaminant in groundwater several environmental protection agencies maximum contamination level for nitrate is 10 mg/l as NO3-N. The problem becomes severe in rural areas where people depend entirely on dug wells in the shallow groundwater table for their drinking water supply. Several locations were selected from the Udunuwara area of Sri Lanka for the detailed study. Nineteen shallow dug wells and 4 deep tube wells were selected for water sampling beginning of January to March 1998.Shiroishi Plain in Japan reclaimed from the Ariake Sea has a soil layer consisting of Ariake clay. The total 82 drug wells of average depth 1.5 m had been drilled around the area. Sample were collected in December 2000 and continued for one year around. Nitrate concentration in groundwater was measured by Cadmium reduction method.The results showed a varying nitrate distribution pattern compared to that the Udunuwara area. The effect of fertilizer application on groundwater depends on soil type, fertilizer type and amount used, crop type and climatic condition. The highly permeable soil around Udunuwara area showed that shallow groundwater is highly vulnerable for nitrate than the poorly drained soil of the Shiroishi Plain in Japan. As the people living in Shiroishi Plain use deep groundwater for domestic purposes, drinking water is safe (less than Maximum Contaminated Level for nitrate in drinking water for Japan-10 mg/l as NO3-N) as far as the nitrate contamination is concerned. The results of these studies suggest that applying the correct rate of N fertilizer at the optimum time would have a substantial effect on reducing nitrate-N losses. Key Words: Nitate Contamination; Groundwater; Land Reclamation; Fertilizer DOI: http://dx.doi.org/10.4038/suslj.v9i1.3736 Sabaramuwa University Journal, Volume 9 Number 1; December 2010, pp 81-95

Nitrate pollution of Neogene alluvium aquifer in Morogoro municipality, Tanzania

Concern over nitrate pollution of groundwater in integrated water quality management has been growing recently. The levels of nitrate in wells from septic tanks and urban agriculture with nitrogen fertilizers application may increase the potential groundwater pollution by nitrate. The purpose of this study was to determine the concentrations and spatial distribution of nitrate (NO3 -) in groundwater in Morogoro municipality. Groundwater samples were collected from 20 wells during wet season period in March-April 2010 in 6 wards namely Kihonda, Mji Mpya, Mafisa, Saba Saba, Boma and Kilakala. The spectrophotometer was used to measure the NO3 - concentration in water samples. The minimum and maximum nitrate levels were 1.4 and 32.5 mg/L respectively in the wards studied with an average of 7.76 mg/L. These results showed that all of the groundwater samples have NO3 - concentration below the Tanzania Bureau of Standards upper limit value and World Health Organization guideline of 75 mg/l and 50 mg/l respectively. Also, the level of nitrate concentration tends to decrease with depth for most of the places due to the anoxic condition that is available at the higher depth which facilitates the utilization of nitrate by anaerobic microorganisms.

Effect of winter cover crop species and planting methods on maize yield and N availability under irrigated Mediterranean conditions

Under semiarid Mediterranean conditions irrigated maize has been associated to diffuse nitrate pollution of surface and groundwater. Cover crops grown during winter combined with reduced N fertilization to maize could reduce N leaching risks while maintaining maize productivity. A field experiment was conducted testing two different cover crop planting methods (direct seeding versus seeding after conventional tillage operations) and four different cover crops species (barley, oilseed rape, winter rape, and common vetch), and a control (bare soil). The experiment started in November 2006 after a maize crop fertilized with 300 kg N ha −1 and included two complete cover crop-maize rotations. Maize was fertilized with 300 kg N ha −1 at the control treatment, and this amount was reduced to 250 kg N ha −1 in maize after a cover crop. Direct seeding of the cover crops allowed earlier planting dates than seeding after conventional tillage, producing greater cover crop biomass and N uptake of all species in the first year. In the following year, direct seeding did not increase cover crop biomass due to a poorer plant establishment. Barley produced more biomass than the other species but its N concentration was much lower than in the other cover crops, resulting in higher C:N ratio (>26). Cover crops reduced the N leaching risks as soil N content in spring and at maize harvest was reduced compared to the control treatment. Maize yield was reduced by 4 Mg ha −1 after barley in 2007 and by 1 Mg ha −1 after barley and oilseed rape in 2008. The maize yield reduction was due to an N deficiency caused by insufficient N mineralization from the cover crops due to a high C:N ratio (barley) or low biomass N content (oilseed rape) and/or lack of synchronization with maize N uptake. Indirect chlorophyll measurements in maize leaves were useful to detect N deficiency in maize after cover crops. The use of vetch, winter rape and oilseed rape cover crops combined with a reduced N fertilization to maize was efficient for reducing N leaching risks while maintaining maize productivity. However, the reduction of maize yield after barley makes difficult its use as cover crop.

Analysis of vulnerability factors that control nitrate occurrence in natural springs (Osona Region, NE Spain)

Nitrate pollution is one of the main concerns of groundwater management in most of the world's agricultural areas. In the Osona region of NE Spain, high concentrations of nitrates have been reported in wells. This study uses the occurrence of this pollutant in natural springs as an indicator of the sub-surface dynamics of the water cycle and shows how groundwater quality is affected by crop fertilization, as an approach to determine the aquifer vulnerability. Nitrate concentration and other hydrochemical parameters based on a biannual database are reported for approximately 80 springs for the period 2004–2009. The background concentration of nitrate is first determined to distinguish polluted areas from natural nitrate occurrence. A statistical treatment using logistic regression and ANOVA is then performed to identify the significance of the effect of vulnerability factors such as the geological setting of the springs, land use in recharge areas, sampling periods, and chemical parameters like pH and EC, on groundwater nitrate pollution. The results of the analysis identify a threshold value of 7–8 mg NO 3 −/L for nitrate pollution in this area. Logistic regression and ANOVA results show that an increase in EC or a decrease in pH values is linked to the possibility of higher nitrate concentrations in springs. These analyses also show that nitrate pollution is more dependent on land use than the geological setting of springs or sampling periods. Indeed, the specific geological and soil features of the uppermost layers in their recharge areas do not contribute to the buffering of nitrate impacts on aquifers as measured in natural springs. Land use, and particularly fertilization practices, are major factors in groundwater vulnerability.

SUSTAINABLE DISPOSAL OF SURPLUS NUTRIENT SOLUTIONS FROM SOILLESS GREENHOUSES IN NEW ZEALAND

The New Zealand vegetable and flower greenhouse industries have largely converted to automated greenhouses using soilless media. A key environmental issue is the sustainable disposal and use of surplus nutrient solutions. The industry commissioned a study to investigate how the water and nutrients in the solutions could be turned into a resource. Application to pasture was selected as the most sustainable option as it has high plant cover and grows year round in New Zealand’s temperate climate. A difficult period is winter when slower growth, low nitrogen uptake, high rainfall and low evapotranspiration can make sites unsuitable to receive solutions for several months. The recommendations in the study are based on seasonal pasture growth rates and the Lincoln University Nitrogen Leaching Estimation Model. These show it is environmentally safe to make regular releases to pasture of up to 30 kg N per ha every 21 days, without causing nitrate pollution of groundwater or waterways, provided the site is in a suitable condition. The critical conditions are soil moisture deficit and growth rate of the nitrogen absorbing plant. Future options include nitrogen stripping beds (wetlands, stock pads, sawdust, and greenhouse plant waste) and biodigesters.

Interactions between soil water content and fertilizer on growth characteristics and biomass yield of Chinese white poplar (Populus tomentosa Carr.) seedlings

Chinese white poplar (Populus tomentosa Carr.) is an indigenous tree species in China which plays a key role in the establishment of plantation forests and the conversion of cropland to forestland. By using response surface methodology based on rotatable central composite design, we conducted a test with clone 87 of P. tomentosa seedlings to quantify the interactions among soil water content (W), nitrogen application (N), and phosphorus application (P) on plant stem height (SH), leaf area (LA), net photosynthetic rate (P N) and biomass yield (BY). Our results showed that W, N and P had obvious positive effects on plant SH, LA, P N and BY, and the magnitude of effects in decreasing order was W > N > P. There were synergistic effects of W × N on SH, LA and BY, whose values first increased and then decreased with N increasing under a fixed level of W and also with W increasing under a fixed N. A similar trend was found with the interaction of W × P significantly effecting LA. A multiple target decision model synthesizing all four parameters was established to obtain the optimized combination. We concluded that the recommended combination of W, N and P for growers was W = 78.1% of the field capacity, N = 4.48 g plant−1, and P = 1.67 g plant−1. These recommendations should help to achieve maximum growth potential of P. tomentosa seedlings, obtain high water and fertilizer use efficiencies and reduce the risk of nitrate pollution of groundwater in arid and semi-arid regions.

Stochastic hydro-economic modeling for optimal management of agricultural groundwater nitrate pollution under hydraulic conductivity uncertainty

In decision-making processes, reliability and risk aversion play a decisive role. This paper presents a framework for stochastic optimization of control strategies for groundwater nitrate pollution from agriculture under hydraulic conductivity uncertainty. The main goal is to analyze the influence of uncertainty in the physical parameters of a heterogeneous groundwater diffuse pollution problem on the results of management strategies, and to introduce methods that integrate uncertainty and reliability in order to obtain strategies of spatial allocation of fertilizer use in agriculture. A hydro-economic modeling approach is used for obtaining the allocation of fertilizer reduction that complies with the maximum permissible concentration in groundwater while minimizes agricultural income losses. The model is based upon nonlinear programming and groundwater flow and mass transport numerical simulation, condensed on a pollutant concentration response matrix. The effects of the hydraulic conductivity uncertainty on the allocation of nitrogen reduction among agriculture pollution sources are analyzed using four formulations: Monte Carlo simulation with pre-assumed parameter field, Monte Carlo optimization, stacking management, and mixed-integer stochastic model with predefined reliability. The formulations were tested in an illustrative example for 100 hydraulic conductivity realizations with different variance. The results show a high probability of not meeting the groundwater quality standards when deriving a policy from just a deterministic analysis. To increase the reliability several realizations can be optimized at the same time. By using a mixed-integer stochastic formulation, the desired reliability level of the strategy can be fixed in advance. The approach allows deriving the trade-offs between the reliability of meeting the standard and the net benefits from agricultural production. In a risk-averse decision making, not only the reliability of meeting the standards counts, but also the probability distribution of the maximum pollutant concentrations. A sensitivity analysis was carried out to assess the influence of the variance of the hydraulic conductivity fields on the strategies. The results show that the larger the variance, the greater the range of maximum nitrate concentrations and the worst case (or maximum value) that could be reached for the same level of reliability.

Investigations on Nitrate Pollution of Soil, Groundwater and Vegetable from Three Typical Farmlands in Beijing Region, China

Abstract The aim of this study was to determine the nitrate pollution status of soil, groundwater, and vegetable from three typical farmlands (croplands, vegetable fields, and orchards) in Beijing region. During the investigation, hundreds of the soil, groundwater, and vegetable samples from three typical farmlands were collected and analyzed. In addition, attributes of all samples were recorded for data analysis. The results showed that nitrate was substantially accumulated in soil profiles, while the soil nitrate concentrations of vegetable fields and orchards were higher than those of croplands. Nitrate concentration in 0-30 cm soil of vegetable field and orchard were 3.8 and 1.2 times of that of cropland, respectively. Nitrate content of groundwater in vegetable field was 13.8 mg L −1 (with the over-standard ratio 44.8%), which was 2.8 folds of that in cropland. Nitrate concentration of groundwater under orchard was 9.3 mg L −1 (with the over-standard ratio 23.5%), which was 1.9 folds of that in cropland. High concentrations of the nitrate in vegetables were detected, particularly green leafy vegetables ranked first with 2 685.5 mg kg −1, followed by rhizome vegetables, cabbages, and fruit vegetables. The nitrate over-standard ratios of rhizome vegetables, green leafy vegetables, fruit vegetables, and cabbages were 80.9, 37.9, 29.7, and 2.2%, respectively. The results revealed that the high nitrate concentrations of soil, vegetable, and groundwater might result from the high fertilization dose.

Groundwater nitrate sources in alluvial aquifers: Isotope case study in Savinja Valley (Slovenia)

The chemical status of the shallow alluvial Savinja Valley groundwater body in Slovenia is poor, mainly due to the high concentration of nitrate in groundwater. This case study is therefore oriented in the assessment of groundwater vulnerability to nitrate pollution, as a base for the measure-planning processes. The article describes the use of isotope information of surface water and groundwater for the determination of possible sources of groundwater nitrate pollution. The isotope information of predominant soil and manure/septic waste nitrate origin, associated with other local physical and chemical boundary conditions and land use data, offers an interpretative support in the delineation of nitrate vulnerable zones.

Groundwater quality, nitrate pollution and irrigation environmental management in the Neogene sediments of an agricultural region in central Thessaly (Greece)

The degradation of groundwater quality, which has been noted in the recent years, is closely connected to the intensification of agriculture, the unreasonable use of chemical fertilizers and the excess consumption of large volumes of irrigation water. In the hilly region of central Thessaly in Greece, which suffers the consequences of intense agricultural use, a hydrogeological study is carried out, taking groundwater samples from springs and bore- holes in the Neogene aquifers. The aim of this study is the investigation of irrigation management, water quality and suitability for various uses (water supply, irrigation), the degradation degree and the spatial distribution of pollutants using GIS. The following hydrochemical types prevail in the groundwater of the study area: Ca-Mg-HCO3, Mg-Ca- Na-HCO3 and Na-HCO3. In the above shallow aquifers, especially high values of NO3 - (31.7-299.0), NH4 ? (0.12-1.11), NO2 - (0.018-0.109), PO4 3- (0.07-0.55), SO4 2- (47.5-146.5) and Cl - (24.8-146.5) are found, par- ticularly near inhabited areas (values are in mg L -1 ). The water of shallow aquifers is considered unsuitable for human use due to their high polluting load, while the water of the deeper aquifers is suitable for human consumption.

Multiple isotope (H, O, N, S and Sr) approach elucidates complex pollution causes in the shallow groundwaters of the Taipei urban area

Summary Deterioration of the quality of groundwater under urban areas has become a major environmental concern worldwide. This paper presents a pilot case study (in the Taipei urban area) using multiple stable isotopes ( δ D H 2 O and δ 18 O H 2 O , δ 15 N NO 3 and δ 18 O NO 3 , δ 34 S SO 4 and δ 18 O SO 4 , and 87Sr/86Sr) with the aim of understanding the subsurface nature and environmental status of such areas. A previous study has already characterized Taipei shallow groundwaters as sulfate-rich in comparison to other Southeast Asian metropolitan cities. Our chemical measurements clarified that the arsenic is the important environmental concerns in the aquifers. Dual isotope approaches for nitrate and sulfate suggested these ions were sourced mainly from municipal sewage leaking from sewer pipes in urbanized area, while chemical fertilizers applied in the local agricultural fields partly contribute in the suburb area. Significant decreases in nitrate and sulfate concentrations due to denitrification and sulfate reduction were observed in some groundwaters, which induced increases in isotope ratios up to 24.9‰ for δ 15 N NO 3 and 27.2‰ for δ 34 S SO 4 . Nitrate groundwater pollution in the Taipei Basin is not a subject of serious concern ( NO 3 - for all analyzed samples) at the present time due to attenuation by denitrification. However, arsenic is preferentially released in groundwater (>100 μg/L) in anoxic environment under which sulfate reduction occurs. The Sr isotope data suggested that the arsenic is derived from alluvial deposits of Oligocene–Miocene sedimentary rock origin. This study disclosed the complex causes of environmental changes in Taipei urban shallow groundwater. It is also important as an excellent case study demonstrating the efficient use of multiple isotope diagnosis in the urban groundwater environmental field.

Winter Cover Crops Affect Monoculture Maize Yield and Nitrogen Leaching under Irrigated Mediterranean Conditions

Under semiarid Mediterranean conditions irrigated maize (Zea mays L.) has been associated with nitrate pollution of surface water and groundwater. Cover crops grown during the intercrop period of maize could reduce N leaching. A 2‐yr experiment was conducted in drainage lysimeters with three cover crops: barley (Hordeum vulgare L), winter rape (Brassica rapa L.), or common vetch (Vicia sativa L.). Bare soil was used as control treatment. Maize was fertilized with 300 kg ha−1 N in the control, and this amount was reduced after a cover crop according to the N content in the aboveground cover crop biomass. Barley and winter rape biomass had a higher N content than vetch (130–170 vs. 50 kg ha−1). The vetch treatment did not reduce N leaching or affect maize yield. The barley and winter rape treatments reduced N leaching by 80% compared to the control (25 kg ha−1 yr−1) mainly due to a reduction of NO3–N concentration in drainage. Maize yield was reduced by 2.7 Mg ha−1 after barley and winter rape but still high (≈14 Mg ha−1). This reduction was due to an N deficiency caused by lower soil N in spring after the cover crop and insufficient N mineralization and/or lack of synchronization with maize N uptake. To use nonlegume winter cover crops to reduce N leaching in monoculture maize it is necessary to consider that N mineralization may not be sufficient to fulfill maize N requirements and N fertilizer adjustment tools should be developed.

Autotrophic ammonia oxidation by soil thaumarchaea

Nitrification plays a central role in the global nitrogen cycle and is responsible for significant losses of nitrogen fertilizer, atmospheric pollution by the greenhouse gas nitrous oxide, and nitrate pollution of groundwaters. Ammonia oxidation, the first step in nitrification, was thought to be performed by autotrophic bacteria until the recent discovery of archaeal ammonia oxidizers. Autotrophic archaeal ammonia oxidizers have been cultivated from marine and thermal spring environments, but the relative importance of bacteria and archaea in soil nitrification is unclear and it is believed that soil archaeal ammonia oxidizers may use organic carbon, rather than growing autotrophically. In this soil microcosm study, stable isotope probing was used to demonstrate incorporation of (13)C-enriched carbon dioxide into the genomes of thaumarchaea possessing two functional genes: amoA, encoding a subunit of ammonia monooxygenase that catalyses the first step in ammonia oxidation; and hcd, a key gene in the autotrophic 3-hydroxypropionate/4-hydroxybutyrate cycle, which has been found so far only in archaea. Nitrification was accompanied by increases in archaeal amoA gene abundance and changes in amoA gene diversity, but no change was observed in bacterial amoA genes. Archaeal, but not bacterial, amoA genes were also detected in (13)C-labeled DNA, demonstrating inorganic CO(2) fixation by archaeal, but not bacterial, ammonia oxidizers. Autotrophic archaeal ammonia oxidation was further supported by coordinate increases in amoA and hcd gene abundance in (13)C-labeled DNA. The results therefore provide direct evidence for a role for archaea in soil ammonia oxidation and demonstrate autotrophic growth of ammonia oxidizing archaea in soil.

Fertilizer standards for controlling groundwater nitrate pollution from agriculture: El Salobral-Los Llanos case study, Spain

Summary Although the legislation on groundwater quality targets pollutant concentration, the effects of measures on non-point source pollution control are often evaluated in terms of their emission reduction potential at the source, not on their capacity of reducing the pollutant concentration in groundwater. This paper applies a hydro-economic modelling framework to an aquifer, El Salobral-Los Llanos aquifer (Mancha Oriental, Spain), where nitrate concentrations higher than those allowed by the EU Water Framework Directive and Groundwater Directive are locally found due to the intense fertilizer use in irrigated crops. The approach allows defining the economically optimal allocation of spatially variable fertilizer standards in agricultural basins using a hydro-economic model that links the fertilizer application with groundwater nitrate concentration at different control sites while maximizing net economic benefits. The methodology incorporates results from agronomic simulations, groundwater flow and transport into a management framework that yields the fertilizer allocation that maximizes benefits in agriculture while meeting the environmental standards. The cost of applying fertilizer standards was estimated as the difference between the private net revenues from actual application and the scenarios generated considering the application of the standards. Furthermore, the cost of applying fertilizer standards was compared with the cost of taxing nitrogen fertilizers in order to reduce the fertilizer use to a level that the nitrate concentration in groundwater was below the limit. The results show the required reduction of fertilizer application in the different crop areas depending on its location with regards to the control sites, crop types and soil–plant conditions, groundwater flow and transport processes, time horizon for meeting the standards, and the cost of implementing such a policy (as forgone benefits). According to the results, a high fertilizer price would be required to reduce nitrate concentrations in groundwater below the standard of 50 mg/l. In this particular case, it is more cost-efficient to apply standards to fertilizer use than taxes, although the instrument of fertilizer standards is more difficult to implement and control.

Forecasting the effects of EU policy measures on the nitrate pollution of groundwater and surface waters

We used the interdisciplinary model network REGFLUD to predict the actual mean nitrate concentration in percolation water at the scale of the Weser river basin (Germany) using an area differentiated (100 m × 100 m) approach. REGFLUD combines the agro-economic model RAUMIS for estimating nitrogen surpluses and the hydrological models GROWA/DENUZ for assessing the nitrate leaching from the soil. For areas showing predicted nitrate concentrations in percolation water above the European Union (EU) groundwater quality standard of 50 mg NO 3-N/L, effective agri-environmental reduction measures need to be derived and implemented to improve groundwater and surface water quality by 2015. The effects of already implemented agricultural policy are quantified by a baseline scenario projecting the N-surpluses from agricultural sector to 2015. The REGFLUD model is used to estimate the effects of this scenario concerning groundwater and surface water pollution by nitrate. From the results of the model analysis the needs for additional measures can be derived in terms of required additional N-surplus reduction and in terms of regional prioritization of measures. Research work will therefore directly support the implementation of the Water Framework Directive of the European Union in the Weser basin.

Abstracts of Nippon Dojo-Hiryogaku Zasshi

Abstracts of Nippon Dojo-Hiryogaku Zasshi

Nitrate pollution of groundwater in Toyserkan, western Iran

A total of 95 groundwater samples were collected from Toyserkan, western Iran to assess the chemical composition and nitrate (NO3 −) status of groundwater. The most prevalent water type is Ca–HCO3 followed by water types Ca–Mg–HCO3. In comparison with the World Health Organization (WHO) drinking water guideline of 50 mg l−1 for NO3 −, a total of nine wells (9.5%) showed higher concentrations. In 36% of samples (34) NO3 − concentration was low ( 47 mg l−1, NO3 − > 27 mg l−1). The high correlation between NO3 − and Cl− (r = 0.86, p < 0.01) is consistent with a manure source, resulting from the practice of adding salt to animal feed. Pollution of groundwaters appeared to be affected by the application of inorganic fertilizer at greater than agronomic rates, Cl-salt inputs, and irrigation practice.

Impacts of urbanization on the groundwater resources in Shahrood, Northeastern Iran: Comparison with other Iranian and Asian cities

Urbanization may lead to the contamination of groundwater and/or it may alter the hydrogeological regime. Shahrood is a medium size city in northeastern Iran, underlain by an alluvial aquifer. Analysis of 45 samples collected from the Shahrood Plain’s aquifer in 2003 and 2005 revealed that: (1) Shahrood’s wastewater disposal wells and deep cesspits have led to the nitrate pollution of groundwater (up to 140 mg/L NO 3–NO 3); (2) urban recharge has lowered the groundwater temperature and pH and (3) urbanization has possibly resulted in the incomplete interaction between various flow compartments of the aquifer. In four other Iranian cities, Gorgan, Kerman, Zahedan and Mashad, urbanization has led to water quality deterioration, alarming rise of groundwater levels endangering foundations of the buildings as well as collapse of ‘qanat’s galleries. The maximum concentration of nitrate (MCN) in groundwater in all these cities has been compared with the ratio of population/rainfall in each city. A similar exercise has been carried out for Asian megacities. These show that MCN in an urban aquifer is directly controlled by population and average annual rainfall. This has serious implications for the management of urban groundwater resources and suggests that the current world population growth rate and the likely reduction in the atmospheric precipitation induced by global warming will further deteriorate the quality of such resources.