Research Article
Z. Pashazadeh Laleh; H. Jafari; A.R. Vaezi Hir
Abstract
Introduction: The water is the major key in sustainable development, so it is necessary to be managed and conserved. The quality of surface water resources is mainly controlled by natural or geogenic factors including chemistry of recharge water, soil and geology processes, as well as the man-made contaminant. ...
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Introduction: The water is the major key in sustainable development, so it is necessary to be managed and conserved. The quality of surface water resources is mainly controlled by natural or geogenic factors including chemistry of recharge water, soil and geology processes, as well as the man-made contaminant. Qualitative indicators are used as effective managing tools in decision making programs. Water quality indices (WQI) are the simple and suitable tools to determine the quality statue of the water. In order to calculate the water quality index, many parameters are integrated in mathematical formula to represent the quality condition of the water with a number which classifies the quality in the scales of the weak to excellent. Many water quality indices were introduced by researchers and organizations around the world. Aji-Chay, one of the most important flowing rivers in East-Azerbaijan province, northwest of Iran, is passing through Tabriz plain in its way and finally ends to the Uremia lake. Regarding the focused industrial zones, agricultural field and urban areas in this plain, the river is highly vulnerable to pollution and quality degradation. So, this study was aimed to assess the Aji-chay River based on quality indicators, in order to helps its better management. Materials and Methods: In this research for assessing pollution of the Aji-Chay river using water quality indices, 16 sampling stations were located along the river and water samples were collected during wet (May 2016) and dry (September 2016) seasons. Electrical conductivity (EC), temperature, dissolved oxygen (DO) and pH were measured in the field and total dissolved solids (TDS), turbidity, major ions (Ca, Mg, Na, K, HCO3, Cl, SO4), nitrate (NO3), phosphate (PO4), biological oxygen demand (BOD), chemical oxygen demand (COD) and biological contaminants (fecal coliform) were determined in the laboratory. Quality indicators including the US national sanitary foundation water quality indices in the two forms of multiplicative (NSFWQIm) and additive (NSFWQIa) and Iranian surface water quality index (IRWQIsc) were used to assess the quality of the Aji-Chay river. Results and Discussion: Turbidity and Electrical conductivity (EC) is high at the upstream which is related to movement of the River in upper red formation (Miocene series) which enhances the chloride, sodium, calcium and sulfate. Arsenic concentrations are exceeding the drinking standards (0.01 ppm) across all samples mainly from a geogenic sources as well as discharge of wastewater in some areas. The elements Cd, Mn, Ni, Pb, Mo, Co, Zn, Fe and Al are mainly geogenic, whereas Cu, Ba and Cr are mostly originated from anthropogenic activities. Based on the results, river quality at the wet season is highly controlled by the main branch and Gomnab-Chay, but Mehran-rood plays the major role in downstream water quality at the dry season due to its higher discharge rate. The process was confirmed by Piper and Schoeller diagrams. Most of the parameters are increased in middle parts at the river where the concentrated sources of contaminates and discharge of wastewater increased the organic and biological constituents and nutrients especially in dry season. Assessing the river quality for agricultural uses based on modified Wilcox diagram shows except for Mehran-rood, the other samples are unsuitable for agriculture and the dry season quality is better than the wet season. Based on the results, increase in most parameters and so, pollution and quality degradation of the river are observed to the downstream. Assessing quality of the Aji-Chay river using US national sanitary foundation water quality indices in the two forms of multiplicative (NSFWQIm) and additive (NSFWQIa) and Iranian surface water quality index (IRWQIsc) confirmed the bad to very bad qualitative statue of the river in most stations especially in the middle parts of the Tabriz plain. The results revealed that quality degradation of Aji-Chay river is probably due to discharge of contaminants from municipal and industrial wastewaters (effluents), highlighting the need for managing actions to improve quality of this important river. Comparing the quality indices showed the priority of NSFWQIm (multiplicative form of US national sanitary foundation water quality indices) in quality classification and pollution assessment of the Aji-Chay river. Conclusion: Quality degradation of Aji-Chay river is probably due to discharge of contaminants from municipal and industrial wastewater effluents, indicating the need for managing actions to improve quality of this river. In this study priority of NSFWQIm (multiplicative form of US national sanitary foundation water quality indices) in quality classification and pollution assessment of the Aji-Chay river was confirmed.
Research Article
A. Zarei; T. Sohrabi; H. Ojaghlou; Z. Bigdeli
Abstract
Introduction: In recent years, to increase the efficiency of surface irrigation methods, new techniques such as surge irrigation have been developed. Numerous studies have shown that the surge flow can reduce water consumption in the advance phase and subsequently improve irrigation efficiency and ...
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Introduction: In recent years, to increase the efficiency of surface irrigation methods, new techniques such as surge irrigation have been developed. Numerous studies have shown that the surge flow can reduce water consumption in the advance phase and subsequently improve irrigation efficiency and water distribution uniformity. One of the factors affecting the performance of surface irrigation systems is the accurate estimation of infiltration. Due to continuous changes in the infiltration process during on-off cycles in surge irrigation, determining the empirical equation of infiltration in surge irrigation method is complex and requires time-consuming and costly field data. As a result, proper selection and parameterization of empirical equations with a simplified procedure are needed. The goal of this research was the field evaluation of the point method (surge infiltrometer) to simulate the infiltration process in advance phase surges. Materials and Methods: A field experiment was conducted at the experimental station of the College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran. A ring infiltrometer was modified by connecting a pipe arm for inward and outward water flow to the ring and from the ring to the pipe to create on-off surge cycles, respectively. Water entered the ring through the inlet hole at the top of the pipe arm and water depth was recorded at different time intervals during the on-time of each cycle. Four treatments were performed for infiltration tests under surge flow, including different cycle time and ratio. Also, infiltration tests were performed under continuous flow conditions. To simulate the first (dry soil) and second irrigation conditions, infiltration experiments were conducted twice on an 8-day interval. The Kostiakov infiltration equation was corrected by applying surge factors to predict infiltration water depth for subsequent surges, using first surge data. The empirical coefficients of the Kostiakov equation were calculated by applying the two-point technique. Results and Discussion: Results of the study revealed that the infiltration data simulated by the developed Kostiakov equation matched closely with those collected from the surge-ring infiltrometer. The coefficient of determination and the root mean square error were calculated to be 0.92 to 0.97 and 0.03 to 0.16 cm, respectively. In general, the amount of cumulative infiltration in the second and subsequent surges decreased. The ratio of the infiltration depth at the end of the second to the first surge was less than 0.5. In all experiments, the depth of water infiltrated in the third surge was significantly reduced and almost reached to the final infiltration rate. As the cycle ratio increased, the cumulative infiltration also increased. However, the effect of on-off time on the infiltrated water depth in the first experiment was greater than that in the second experiment. It was concluded that in the first experiments, the surging phenomena substantially reduced water movement and the reduction in cumulative infiltration ranged from 50 to 70% during the second surge and from 59 to 85% during the third surge. The above values were determined 52 to 76% and 61 to 88% for the second experiment, respectively. A significant difference was observed between surge and continuous flow tests. The surge flow led to a 46 to 76% reduction in the cumulative infiltration depth compared to the continuous flow. The effect of surge flow was greater in the first experiments. Conclusion: One of the most important points in designing surface irrigation systems is to determine the infiltration equation parameters. In particular, the difficulty involved in the planning and design of surge irrigation systems is the prior knowledge and understanding of how infiltration changes occur during surging. The main objective of the present study was to evaluate the surge ring infiltrometer test to predict the infiltration in the second and third surges using the first surge data. The results obtained from the surge infiltrometer experiments showed that the use of surge irrigation has the potential to reduce infiltration. The observed and predicted cumulative infiltration for the second and third surges showed a good agreement. The surge-ring infiltrometer has the potential for creating an on-off mechanism and is best suited to determine the cumulative infiltration from surges for constant on-off time surge intervals.
Research Article
Sh. Hassani; Mohammad Babaakbari; M.R. Neyestani; M.A. Delavar
Abstract
Introduction:High concentrations of As in contaminated soils represent a potential risk for groundwater sources and threat the food chain. It has been found that the iron-containing compounds used in remediation of As contaminated soils have distinct effects on the solubility of As and can be used as ...
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Introduction:High concentrations of As in contaminated soils represent a potential risk for groundwater sources and threat the food chain. It has been found that the iron-containing compounds used in remediation of As contaminated soils have distinct effects on the solubility of As and can be used as adsorbents for As removal from aqueous and soil solutions. The objectives of this study were to determine As stabilization in soil, with iron-containing compounds and also to compare the fixation of magnetite nanoparticles, ferrous sulfate, ferrosilicon, magnesium ferrosilicon and iron oxide in fixation of arsenic in contaminated soils. Materials and Methods: A factorial experiment was conducted using a completely randomized design with three replications. The experimental factors were the amendment types and levels. The modifiers used were magnetite nanoparticles, ferrous sulfate, ferrosilicon, magnesium ferrosilicon, Sfordi, and Golgohar iron soil containing 0, 0.1, 0.2 and 0.3% iron. The soil was artificially contaminated with As (20 mg/kg) using Na2HAsO4.7H2O salt and incubated for 1 month. At the end of incubation time, the modifiers were added to the As contaminated soils and after 3 months, the available fractions of arsenic, iron, zinc and copper were extracted using 0.1 M HCl and measured with ICP. Results: The results showed that the type and the amount of the modifiers had a significant effect on the available fraction of arsenic and iron in soil (extractable fraction with 0.1 M hydrochloric acid). The available fraction was reduced due to the addition of all modifiers: Magnetite nanoparticles > iron sulfate > magnesium ferrosilicon > ferrosilicon > Esfordi iron soil and Golgohar iron soil, respectively. The highest decrease in the concentration of available arsenic occurred in the soils treated with 0.3% of modifier. Application of 0.3% levels of magnetite nanoparticles, iron sulfate, ferrosilicon, ferrosilicon magnesium, Golgohar iron soil and Esfordi iron soil stabilized 91, 63, 57, 32 and 48% of arsenic extractable with 0.1 M HCl, respectively. Application of 0.3% of magnetite nanoparticles reduced available arsenic more than other adsorbents. Among the studied modifiers, magnetite nanoparticles showed more efficiency in chemical stabilization of arsenic in soil. The application of magnetite nanoparticles increased the Fe available fraction in soil. Golgohar iron soil, ferrosilicon, Esfordi iron soil, magnesium ferrosilicon, ferrous sulfate and Magnetite nanoparticles, increased the iron extractable with 0.1 M HCl of the soil, respectively. The highest Fe concentrations were observed in 0.3% of Gol Gohar soil, ferrosilicon, Esfordi soil and ferrosilicon. Increasing the modifiers decreased soil copper extractable with 0.1 M hydrochloric acid concentration and increased soil zinc extractable with 0.1 M hydrochloric acid concentration, which was not statistically significant. Conclusion: Application of magnetite nanoparticles reduced arsenic concentration more than other adsorbents and showed more efficiency in chemical stabilization of soil arsenic. Other modifiers have also been able to stabilize the arsenic in the soil, suggesting the possibility of using iron-containing modifiers in arsenic-contaminated soils. The use of modifiers increased the iron concentration in the soil. Due to their reasonable price and availability, iron sulfate and magnesium ferrosilicon are recommended for soil arsenic stabilization. At 0.3% soil level, Gol Gohar and Esfordi iron soil were able to reduce 32% and 48% the arsenic concentration, respectively and are recommended for arsenic stabilization in contaminated soil. Golgohar, ferrosilicon, Esfordi and magnesium iron soils caused the highest increase in soil iron concentration. Due to the concentration of other soil elements and the price of modifiers, the level of 0.2% of iron sulfate, Gol Gohar and Esfordi iron soil, ferrosilicon and magnesium ferrosilicon is recommended for stabilization of arsenic in contaminated soil.
Research Article
S. Abdollahi; A. Golchin; F. Shahryari
Abstract
Introduction: Contamination of soils with heavy metals is one of the most serious environmental problems increasing the risk of the entry of heavy metals into food chains. Rhizosphere soil is distinct from the bulk soil and is defined as the volume of soil around living roots which is influenced by root ...
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Introduction: Contamination of soils with heavy metals is one of the most serious environmental problems increasing the risk of the entry of heavy metals into food chains. Rhizosphere soil is distinct from the bulk soil and is defined as the volume of soil around living roots which is influenced by root activities. Enzymes are produced by both roots and soil microorganisms to alter nutrient availability in rhizosphere soil. Soil enzymes promote the transformation of matter and energy in the soil, and their activity has a close relationship with soil nutrient availability. Detection of microbial enzymes in a natural environment is important to understand biochemical activities and to verify the biotechnological potential of microorganisms. However, there are few reports to indicate the biotechnological potential of plant growth promoting rhizobacteria (PGPR) and their effects on the activity of bacterial enzymes in rhizosphere soils under the stress of heavy metals. Thus, in the present study lead and cadmium contaminated rhizosphere soils were inoculated with PGPR species to investigate the influence of these bacteria on the activity of some enzymes. Materials and Methods: A factorial pot experiment with completely randomized design base and three replications was performed in the greenhouse conditions. The factors examined were (a) rhizosphere soils of three varieties of cabbage [Brassica oleracea var. acephala L. (Ornamental cabbage), Brassica oleracea var. italica L. (Broccoli cabbage) and Brassica oleracea var. capitata L. (Cabbage)] and (b) five species of PGPR, consisting Pseudomonas putida PTCC 1694, Bacillus megaterium PTCC 1656, Proteus vulgaris PTCC 1079, Bacillus subtilis PTCC 1715 and Azotobacter chroococcum, used to inoculate the rhizosphere soils. There was also a control treatment (without rhizobacteria). The experiment had 18 treatments and there were 54 experimental units. To study rhizosphere soils, several rhizoboxes were used and three seedlings of cabbage were planted in the central part of each rhizobox (rhizosphere area). In treatments inoculated with rhizobacterial species, 2 ml of a bacterial suspension with 107-108 (cfu ml-1) was used to inoculate the soil of rootzone. After three months, cabbage varieties were harvested and the activity of alkaline phosphatase, acid phosphatase, urease, and dihydrogenase were measured in rhizosphere soils. The data obtained from this study were statistically analyzed by SPSS statistical software package (Version 9.4) and the variance of the data was analyzed by one-way ANOVAs (Duncan’s test) range test at 1 and 5 percent probability levels. Results and Discussion: The analysis of variance of the data (ANOVA) showed that the cabbage varieties, inoculation with PGPR species and their interactions had significant effects (p < 0.01) on the activity of alkaline phosphatase, acid phosphatase, urease, and dihydrogenase in rhizosphere soils. The results showed that inoculation of the rhizosphere soils with PGPR species increased the activity of soil enzymes. The highest activity of alkaline phosphatase (1529.28 µg pNP.g-1 dm.h-1) was measured in rhizosphere soils of the broccoli inoculated with Pseudomonas putida PTCC 1694. But, the highest activity of acid phosphatase (497.92 µg pNP.g-1dm.h-1) was obtained in rhizosphere soils of cabbage inoculated with Pseudomonas putida PTCC 1694. Also, the highest activity of urease (208.36 µg N-NH4+.g-1dm.2h-1) was observed in rhizosphere soils of the cabbage inoculated with Azotobacter chroococcum and the highest activity of dihydrogenase (8.71 µg TPF.g-1dm.16h-1) was observed when rhizosphere soils of the cabbage were inoculated with Bacillus subtilis PTCC1715. Conclusion: From the results of this study, it may be concluded that inoculation of Pb and Cd contaminated soils with PGPR species could modulate the toxic effects of heavy metals on plant and increase the activity of some key enzymes for plant growth in rhizosphere soils.
Research Article
Y. Kooch; M. Azizi Mehr
Abstract
Introduction: Degradation of forest habitats and alteration of soil vegetation are efficient factors affecting the variability of ecological indices of organic and mineral layers of soils. In Iran, degradation of forest habitats and changes in habitat type, especially over the last century, affected ...
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Introduction: Degradation of forest habitats and alteration of soil vegetation are efficient factors affecting the variability of ecological indices of organic and mineral layers of soils. In Iran, degradation of forest habitats and changes in habitat type, especially over the last century, affected soil quality, plant biomass production and environmental sustainability. Hence, in this study, the effect of different forest and rangeland vegetation types on the ecological parameters of soil organic and mineral layer has been investigated. Materials and Methods: To study and evaluate the effects of forest degradation and site change on soil organic and mineral ecological indices, four types of vegetation were selected in Gorgpas areas, southwest of Chalus city, Mazandaran Province. The land cover is as follows in the study area: (1) Less-degraded forest dominated by Carpinus betulus L.- Parrotia persica C. A. May (2) Fourty year's old plantation of Pinea abies (L.) Karst - Pinus nigra Arnold (3) Deforested areas including Carpinus betulus L. - Parrotia persica C. A. May (4) Exclosure rangeland dominated by Coronilla varia L. Physiographically similar land covers, were selected during a field research in the studied areas. Eight litter and soil samples (0-15 cm in depth and 30 cm × 30 cm in depth) were collected from each area in summer. In order to reduce the boundary effects, sampling was performed in the center of each land cover. The collected samples of organic layer (litter) and soil mineral transferred to the laboratory for analysis. The collected data was stored as a database in Excel. Then, to analyze and compare the data, the normality distribution of observations was evaluated by Kolmogorov-Smirnov test and variance homogeneity by Levene test. Analysis of variance used to investigate the significant/non-significant differences of different soil organic and inorganic layer characteristics in relation to the studied areas. Duncan test used for multiple mean comparisons. All statistical analyzes were performed by SPSS software version 23. Principal component analysis (PCA) was employed to study the relationship between soil organic matter and soil mineral quality in the studied land cover. Results and Discussion: According to the results, in the soil organic layer the highest carbon/nitrogen ratio (%) assigned to the rangeland, while the nitrogen (%) content was highest in the natural forest. The highest amount of carbon and organic layer thickness were also observed in rangeland and degraded forest cover, respectively. In the mineral soil layer, the highest value of sand (%), moisture (%), carbon (%) and carbon to nitrogen ratios (%) belonged to the rangeland cover, while the highest amount of clay v (%), pH (1:2.5 H2O), electrical conductivity (ds m-1), nitrogen (%), phosphorus (%), potassium (mg kg-1), calcium (mg kg-1) and magnesium (mg kg-1) were observed in the forest cover. The highest number and biomass of earthworms (n m-2), nematode population (In 100-gram soil), nitrogen mineralization (mg kg-1l), ammonium (mg kg-1), nitrate (mg kg-1), basal respiration (mg CO2 g−1 day−1), substrate induced respiration (mg CO2 g−1 day−1), microbial nitrogen biomass (mg kg-1) and metabolic coefficient (μg CO2-C mg-1 MBC day-1) observed in forest cover. There was no significant difference between the studied vegetations for bulk density (g cm-3) characteristics, silt (%), microbial biomass of carbon (mg kg-1) and microbial coefficient (μg CO2-C mg-1 MBC day-1). Higher nitrate density in natural forest and under cultivated soils are due to the presence of litter species with low carbon/nitrogen ratio, high pH and calcium. Conversion of natural broadleaf covers to needle leaf plantation and rangeland reduces the biochemical processes of ammonium. Nitrogen mineralization rates are strongly influenced by area management and forest canopy cover, so that under the broadleaf stands, this rate was more than the needle leaf stands. This probably was due to the greater nitrogen of litter, the lower carbon to nitrogen ratio and the faster rate of decomposition of organic matter in broadleaves. Most of the time the increase in pH increases the rate of mineralization of nitrogen. Conclusion: The present study indicated that forest habitat had the highest number and biomass of earthworms, soil nematode population, ammonium, nitrate, metabolic coefficient, basal and substrate induced respiration, carbon availability index, microbial biomass and nitrogen mineralization, while, there was no significant difference between the studied forests and rangelands in carbon microbial biomass and microbial coefficient. In general, the results of this study showed that the physicochemical and biological characteristics of soil organic matter in the forest habitats were better than other studied vegetations and the forest degradation and land-use changes reduced soil fertility and microbial indices.
Research Article
Gh. Rahimi; F. Karimi
Abstract
Introduction: Salinization of soil has been reported as a problem in many parts of the world. Salinization could occur either as a result of natural processes e.g. high concentrations of salt in parent materials or groundwater and/or anthropogenic actions such as over-irrigation. The salinization probably ...
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Introduction: Salinization of soil has been reported as a problem in many parts of the world. Salinization could occur either as a result of natural processes e.g. high concentrations of salt in parent materials or groundwater and/or anthropogenic actions such as over-irrigation. The salinization probably affects the chemical and physical properties of soil, soil microbiological processes, plant growth, and soil fauna. Both quantity and quality of water, however, are the most important eco-factors needed for earthworm survival and development, and also biodegradation processes. Materials and Methods: In order to investigate the effect of irrigation water salinity on the survival and growth of earthworm Eisenia Fetida, an experiment was conducted in a completely randomized design with three replications under environmental conditions of the laboratory of Soil Sciences Department of Bu-Ali Sina University in Hamedan. The different types of water used in this study were: distilled water and saline water made with NaCl salt with electrical conductivity (EC) of 2, 4, 6, and 8 dS m-1. The experiment was carried out using completely randomized design in plastic containers of size 19 × 13 × 8 cm. Ten earthworms per container used in each exposure regime were introduced into the relevant test salinity by placing them on the surface and allowing them to burrow in. The test containers were covered with perforated lids to limit water loss due to evaporation and kept in 16 hours light, 8 hours dark at 25°C in a climate chamber for 42 days. Sampling was done at 3, 15, 21, 27, 33, 39, and 42 days after earthworms were introduced to the substrates to investigate mortality and weight changes of earthworms. The LC50 (concentration at which 50% of the earthworms are killed) and the EC50 (effect concentration at which a 50% reduction in a measured parameter) values for the salts expressed as conductivity (dS m-1) were calculated on day 27 and 42 by using the Probit Analysis. Results and Discussion: On day 3, no significant effect of salinity on percentages of survival was found. The survival rate of Eisenia fetida was significantly affected in the EC range used during 42 days (Table 2). The irrigation with distilled water (EC0) had the highest survival rate while the irrigation water with EC 8 dS m-1 had the lowest value. During the 39 days of exposure, no significant difference was found in survival rate of earthworms between EC 2, EC 4 and EC 6 dS m-1, but at the end of day 42, the salinity levels with EC 8 dS m-1 had a significant effect on percentage of earthworm survival in which 91.68% mortality occurred. The mean weight change of earthworms exposed to water with EC 2 dS m-1 was not significantly different (p < /em> < 0.01) from those exposed to the distilled water during 39 days, but there was a decrease in earthworm weight on day 42. The calculated LC50 for mortality after 27 and 42 days was 7.5 and 4.31 dS m-1, respectively, and EC50 for growth was 7.94 and 6.82 dS m-1, respectively. Conclusion: Our results showed that increased salinity had harmful effects on the growth and mortality of the earthworms (Eisenia fetida). Salinity can have detrimental effects on earthworms at concentrations considered safe for many plant species. We determined 42 day LC50 for mortality 4.31 dS m-1 (2521 mg lit-1). The EC50 for growth was 6.82 dS dS m-1 (3989 mg lit-1). The weight of earthworms was significantly affected by NaCl and dispersion analysis showed that NaCl concentration had a statistically significant influence on the weight of earthworms. The argument for using NaCl is that it is the predominant salt in most saline environments particularly in wastewaters. Since the salt type is dependent on the source of the contamination, it is, therefore, possible that other salts apart from NaCl could be the main compounds in saline toxicity in a specific area. The results of the current study suggest that the effects of salinity depend on the salt composition. Therefore, it would be important to assess the type of salt ions in soil in risk assessment, as this affects the extent of toxicity to soil organisms.
Research Article
M. Bagheri-Bodaghabadi
Abstract
Introduction: In land suitability evaluation using parametric method, Khiddir or square root method (LQSI) and/or Storie method (LSI) are employed to calculate land index (LI), then suitability classes could be determined based on the LI. However, the obtained LI should be corrected according to the ...
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Introduction: In land suitability evaluation using parametric method, Khiddir or square root method (LQSI) and/or Storie method (LSI) are employed to calculate land index (LI), then suitability classes could be determined based on the LI. However, the obtained LI should be corrected according to the minimum rating (Rmin) and then the suitability classes should be determined. The existing functions to correct the LI should be mathematically continuous at all points in order to prevent from losing some LIs and their consequent suitability classes. In the functions represented by Sys, there is a continuity for S1 (suitable), S2 (moderately suitable) and S3 (marginal suitable) classes, but for N (unsuitable) the presented functions are not continuous. Therefore, presented functions for N1 and N2 classes can be very misleading since they are not able to distinguish between N1 and N2 classes and have problem to calculate them. Materials and Methods: In this study, the existing functions in the literature were mathematically evaluated for each land suitability classes. Properties and criteria for determining land suitability classes are shown in Table1. In parametric approach, land index (uncorrected land index) is calculated using Kiddir and Storrie methods as shown in equations 1and 2, respectively. The relationships between uncorrected land indices and corrected land indices are presented in Table 2. (1) (2) According to continuity rules, the necessary corrections were made for N1 and N2 classes. Then numerical simulation was employed to assess the obtained results from the both existing and purposed functions and compared them with one another. For this purpose, one million random values were created for each of the S1 to N2 classes; so that the minimum rating (Rmin) was a random number for each class in own defined range and the other seven characteristics were random numbers between Rmin and 100. For example, in the S3 class, a minimum random number is in the range of 40 to 60 and seven other characteristics were between the Rmin and 100. Finally, a total of two million random simulations were created. Results and Discussion: Based on the minimum, maximum and mean obtained values the simulation process is acceptable. These numbers show that the simulations have simulated almost all the cases that may occur in reality, from the best to the worst. The results showed that for N1 and N2 classes the correction functions should be respectively 12.5 + 0.314LQSI and 0.5LQSI for the Khiddir method and 12.5+ 0.313LSI and 0.5LSI for the Storie method to maintain the both the continuity of the correction functions for all classes and the corrected land index to be in the defined range for each class. The two million times simulation results also confirmed the accuracy of the obtained functions Therefore, it is suggested to use the proposed functions in determining N1 and N2 classes instead of Sys’s functions. Conclusion: The use of the usual land index, which is conventionally calculated by the Khiddir or Storie method, called uncorrected land index (UCLI), can be largely misleading without being corrected and converted to the corrected land index (CLI), causing the wrong land suitability classes. Therefore, it is very important to use the relationships that have been developed for this purpose to correct the usual land index. The findings of this study showed that the current functions, although at the order level can distinguish between unsuitable order (N) from the S3 class, but separation between classes N1 and N2 are very difficult to calculate. For this reason, new relationships for N1 and N2 classes were calculated and presented. Therefore, it is suggested that N1 and N2 classes can be used instead of the relationships presented.
Research Article
M. Dadivar; B. Atarodi
Abstract
Introduction: Because leaf is the main and most important organ of plant metabolism, therefore, its analysis and interpretation of the results using standard methods, can help to provide an optimal fertilizer program. There are different methods for interpreting the results of decomposition of plant ...
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Introduction: Because leaf is the main and most important organ of plant metabolism, therefore, its analysis and interpretation of the results using standard methods, can help to provide an optimal fertilizer program. There are different methods for interpreting the results of decomposition of plant leaves, including critical concentration values and sufficiency ranges. The main drawback of these methods is that only the concentrations of each nutrients are considered and the balance of these nutrients is not considered. The DOP is one of the most up-to-date methods for interpreting the results of leaf decomposition. In this method, the relationship between the concentration of the nutrient and the reference concentration is used instead of the mere concentration of nutrients. Due to insufficient information about the optimal level of nutrients and nutritional status of potato in Khorasan Razavi province, the present study was conducted by using the DOP index to assess the balance of nutrients and to determine the order of nutrient requirement for this plant. Materials and Methods: In order to have a database, 30 potato fields were selected from the major cultivation areas of this crop in Fariman, Torbat-e Heydarieh, and Quchan counties. Among these fields - based on questionnaires completed by farmers - those with good management and high yield (above average) were selected to determine the reference concentration. Accordingly, out of 30 surveyed fields, 16 fields were selected as reference fields and 14 fields as non-reference fields. In each field, before flowering and at the beginning of tuber formation, a composite sample of leaves (from fully developed leaves) was prepared, transferred to the laboratory, rinsed with distilled water and 20 mM EDTA solution, oven dried at 50 °C, ground, digested and analyzed for determining the macro and micro nutrients concentrations by atomic absorption spectrometry (AAS) - (Perkin Elmer, 2380). According to leaf analysis results, some statistical indices, including the maximum, minimum, mean, standard deviation, and coefficient of variation of data in both groups of reference and non-reference fields, were calculated. Furthermore, the reference concentration (Cref) and DOP indices were calculated to evaluate nutritional status of potato and priority nutrients requirement in low-yielding fields. Results and Discussion: The results of this study showed that the coefficient of variation of micronutrients was higher than that of macronutrients, stating that fertilizers containing macronutrients have been used more homogeneously by farmers, compared to those containing micronutrients. Using nutrients concentration in high yielding fields, Cref was obtained for N, P and K nutrients 4.65, 0.32 and 4.28 percent respectively. In addition, Fe, Mn, Zn and Cu Cref values were 190.13, 123.88, 35.19 and 12.44 mg/kg respectively. The results also showed that absolute value of DOP index for all nutrients was greater than zero, indicating imbalance of absorbed nutrients by potato. Due to the fact that the concentration of nutrients in the leaves is a function of the amount of nutrients in the soil, so these data indicate the lack of proper management and imbalance fertilizer application in the studied fields. Among macronutrients, potassium had negative indices in 36% of the studied fields while nitrogen had positive indices in 80% of the studied fields. In other words, most cultivated potatoes of Khorasan Razavi province suffer from K deficiency and excessive N. Due to consecutive cultivation, excessive use of nitrogen fertilizers such as urea and low consumption of potassium fertilizers, higher amount of potassium harvested from the soil as compared with that released from the soil, potassium deficiency is observed in many potato fields. Among micronutrients, zinc had highest negative indices in 57% of the studied fields. After Zn, Fe had the most negative index (highest deficiency) in 35% of fields. Excessive consumption of phosphate fertilizers and lack of sufficient organic matter in soils are the main reasons of iron and zinc deficiency in soils and agricultural products in Razavi Khorasan province. Conclusion: Overall, the results showed an imbalance of all absorbed nutrients by potato and imbalance application of fertilizer in the studied fields. Due to the severe deficiency of K and Zn, fertilization of these two nutrients should be a priority in nutrition management programs in the province's potato fields.
Research Article
N. Azadi; F. Raiesi
Abstract
Introduction: Heavy metals contamination of soils is an important environmental concern which has specially long-term hazardous effects on soil biogeochemical and microbiological properties (including microbial and enzyme activity, microbial community structure, and the contents of organic compounds). ...
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Introduction: Heavy metals contamination of soils is an important environmental concern which has specially long-term hazardous effects on soil biogeochemical and microbiological properties (including microbial and enzyme activity, microbial community structure, and the contents of organic compounds). Among heavy metals, cadmium (Cd) and lead (Pb) are the two highly toxic, non-biodegradable and often coexisted anthropogenic pollutants in contaminated sites. Numerous earlier studies have demonstrated a detrimental influence of Cd and Pb, both individually and jointly, on microbial and biochemical properties through reduction of microbial activity, microbial biomass and enzyme activity in polluted soils. Metal co-contamination has a greater negative effect on soil microbial community and enzyme activity compared to individual ones. Although the individual effects of Cd and Pb on soil biological functions are generally well-known, their combined effects on microbial growth, population and functions are largely uncertain. The main aim of this study was to investigate the interactive effects of Cd and Pb pollutants on biochemical and microbiological properties in a contaminated soil. It was hypothesized that combined Cd and Pb would increase mobility and availability of Cd and Pb, which subsequently results in further reductions in soil biochemical and microbiological properties. Materials and Methods: The study was conducted under controlled laboratory conditions. A factorial experiment with two levels of cadmium (0 and 10 mg kg-1) and two levels of lead (0 and 150 mg kg-1) was conducted using a completely randomized design with three replications. The soil was artificially spiked with cadmium chloride and lead chloride to attain the above mentioned concentrations. To reactivate the microbial population and for the aging effect, soil moisture was set at 70% of field capacity, and containers were pre-incubated at room temperature for 20 days. Soil samples were incubated under standard conditions (70% of field capacity and 25±1 oC) for 120 days. At the end of the soil incubation the concentration of DTPA-TEA (diethylene triamine penta acetic acid-triethanol amine)-extractable Cd and Pb, biochemical and microbiological properties including nitrification rate (NR), cumulative N mineralization (CNM), cumulative C mineralization (CCM), microbial biomass C (MBC), microbial biomass N (MBN), arginine ammonification (AA), basal respiration (BR), substrate (glucose)-induced respiration (SIR), metabolic quotient (qCO2) and the activities of soil urease (URE), alkaline phosphatase (ALP), arylsulphatase (ARY), dehydrogenase (DEH), catalase (CAT) and fluorescein diacetate hydrolysis (FDA) were determined. In this experiment, the Bliss independence model was used to determine the type and nature of the interaction between Cd and Pb pollution (i.e., synergistic and antagonistic). Results and Discussion: Results showed that the DTPA-extractable metal (Cd and Pb) concentrations were considerably higher under the combined metals compared with the single-metals. In co-contaminated soils, a metal may contribute to release of other metals to soil solution and consequently would enhance the availability of the released metals. Compared to individual metal, the qCO2 was greater in Cd+Pb contaminated soil. Microbial and biochemical properties (MBC, MBN, AA, NR, CNM, CCM, BR, SIR) and enzyme activity (URE, ARY, ALP, DEH, CAT and FDA) significantly decreased in the presence of Cd or Pb pollutant than the control. Generally, the negative effects of Cd and Pb co-existence on biochemical and microbiological properties were higher than Cd or Pb alone because of synergistic interaction in the metal combinations. The results of Bliss independence model indicated the synergistic effect of Cd and Pb on microbial and biochemical functionalities in metal-co-contaminated soils. In soil ecosystem, heavy metals exhibit toxicological effects on soil microbes which may lead to the decrease of their function and activities. Conclusion: Heavy metals can effectively change the soil biochemical and microbiological properties. This study provided strong evidence revealing that combined Cd and Pb can increase the mobility and availability of heavy metals, and intensify their toxicity effects on microbial community and enzyme activity in co-contaminated soils. The co-existence of Cd and Pb reduced soil biochemical and microbiological properties more than their individual presence. Soil microorganisms are an important indicator of soil fertility and health and thus would improve the accuracy of the ecological risk assessment of toxic metals at multi-metal contaminated sites. However, further information on responses of microbial indicators to the joint effect of heavy metals under long-term and realistic field conditions is required.
Research Article
M.J. Roosta; K. Enayati; S.M. Soleimanpour; K. Kamali
Abstract
Introduction: Carbon sequestration (CS) by forests, pastures, afforested stands and soils is the most appropriate way to reduce atmospheric carbon. A combination of all these activities can help balance the global warming process by reducing the concentration of atmospheric CO2. The amount of CS and ...
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Introduction: Carbon sequestration (CS) by forests, pastures, afforested stands and soils is the most appropriate way to reduce atmospheric carbon. A combination of all these activities can help balance the global warming process by reducing the concentration of atmospheric CO2. The amount of CS and quality of carbon storage in the soil depends on the interaction between climate, soil, tree species, litter chemical composition and their management. The results of Dinakaran and Krishnayya (2008) research showed that the type of vegetation cover has a significant effect on soil carbon storage. So that the amount of carbon storage in the soil depends on the amount of carbon entering the soil through plant debris and carbon loss through decomposition. To increase carbon in the soil, management activities such as increasing the amount of carbon entering the soil by adding litter and crop residues as well as reducing the rate of decomposition of soil organic matter should be done. Decomposition rate of soil organic matter is affected by soil condition (humidity, temperature and access to oxygen), sequestration of organic matter, placement of organic matter in the soil profile and the degree of physical protection by aggregates. Evaluating the role of aquifer management in reducing via storing the atmospheric CO2, to organic carbon (O.C) is the aim of this study. Materials and Methods: The studied land uses were as follows: 1-Rangeland-without flood spreading-with grazing (control), 2- Range without grazing-without flood spreading, 3- Six rangelands stripes-with grazing-with flood spreading, 4- Rangeland-Atriplex plantation-with spreading of flood, 5- Eucalyptus control forest-without flood spreading, 6- Eucalyptus forest-first strip-with flood spreading-BisheZard 4 (BZ4), 7- Eucalyptus forest-second strip-with flood spreading-(BZ4), 8- Eucalyptus forest-third strip-with flood spreading-(BZ4), 9- Acacia forest-with flood spreading-(BZ4). Soil and plant were sampled from each land use type. Then, the amount of O.C was measured in the laboratory and CS was calculated. The economic-environmental value of carbon stored in the soil is based on Rivers' proposal, which declares a carbon tax rate of $200 per tonne of CO2. The dollar is equal to 42,000 Iranian rials. Data were analyzed using randomized complete block design and Duncan test (at p < 0.05 ) was used to compare mean values using the SAS software. Results and Discussion: The analysis of variance showed that the effect of different land uses on the bulk density (BD), %O.C and the CS in the soil was significant at the level of 1%. Comparison of the mean of BD in various land uses showed that the eucalyptus forest (third strip) had the lowest BD compared to others, and the difference between this land use and other land uses was statistically significant. The first strip of Eucalyptus forest had the highest %O.C and the highest amount of CS in the soil, and the statistical difference between these two indices in this land use with other land uses was significant. Among the studied land uses, the lowest amounts of CS were related to the control range and range without grazing-without flood spreading. The interaction of plant to plant species on plant dry weight and plant carbon storage showed that the rangeland species of Heliantemum lippii and Dendrostellera lessertii in the range with flood spreading have the highest dry-weight and the species of Helianthomus has the highest amount of carbon storage. This indicates that the impacts of flood spreading on plant biomass production and carbon storage have been greater than the impact of no grazing on these indicators. In all uses, Artemisia sieberi showed the lowest dry weight and carbon storage. Planting of Eucalyptus camaldulensis irrigated with flood water spreading increased the soil O.C from 0.51% in the control to 1.68% in the first strip of eucalyptus forest (3.29 times). By calculating the mean of the three strips in which the eucalyptus was planted, it was found that the highest carbon content of 121.84 ton/ha was stored in the plant, litter and soil of this land use. Given that, each tonne of carbon is equivalent to 3.67 tons of CO2 gas, it can be concluded that 447.15 tonnes of CO2 gas from the air is stored as organic matter. The economic-environmental value of this CS is 3.76 billion rials ($89523.81) per hectare. Conclusion: The studied land that was irrigated with flood spreading, especially the eucalyptus forested area at Kowsar station, captured significant amounts of CO2 from the air and stored it as organic matter in the root and shoot of plants and in the soil. Also, this may lead to the release of a large amount of oxygen gas to the environment which play an important role in reducing air pollution. Considering the economic-environmental value of the carbon stored in the eucalyptus plantation forest areas, the development of this method in flood prone areas is quite economically justifiable. Due to the high potential of tree species in improving soil carbon storage, it seems that increasing the percentage of woody species and their physiological diversity have increased the carbon storage capacity of these species. Therefore, in order to improve the carbon storage capacity of flood distribution systems, it is suggested that the planting of native and perennial compatible species in these systems should be considered.
Research Article
S.M.J. Nazemosadat; L. Abbasi; S. Mehravar
Abstract
Introduction:Based on the research and assessment carried out during the Climate Change Enabling Activity Project under United Nations Framework Convention on Climate Change (UNFCCC) and using the scenarios proposed by IPCC, it is estimated that if the CO2 concentration doubles by the year 2100, ...
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Introduction:Based on the research and assessment carried out during the Climate Change Enabling Activity Project under United Nations Framework Convention on Climate Change (UNFCCC) and using the scenarios proposed by IPCC, it is estimated that if the CO2 concentration doubles by the year 2100, the average temperature in Iran will increase by 1.5-4.5°C which will cause significant changes in water resources, energy demand, agricultural products and coastal zones. The present study is aimed to investigate the characteristics of climate change in Iran and some parts of the neighboring countries. Identifying the spatio-temporal changes in three atmospheric variables comprising perceptible water (PW), specific humidity (SH) and vector wind (VW, U and V components) over 1960-2017 was the main themes of the study. Materials and Methods: Monthly values of these variables during wintertime (January to March) were extracted from the CDC/ Reanalysis 2/ NOAA in 2.5 * 2.5 grids for the period of 1960-2017. The study area locates between 20o to 45o N and 30o to 70o E. After averaging monthly data into seasonal series, as first step, significant changes in the considered series were investigated between two equal periods having 29 years of data (1960-1988 and 1989-2017). In the second step, the 58 years of the study period were divided into five successive decades (1960-2009) and a period with eight years (2010-2017). The Kolmogorov-Smirnov (K-S) field significant test was used for assessing the spatio-temporal difference between the obtained maps associated with various decades. Results and Discussion: According to Figures 1 and 2, for both of the 29-year time-scales (1960-1988 and 1989-2017), PW was maximum (12 to 17 kg/m2) alongside the northern coasts of the Persian Gulf and the Oman Sea. After this, PW had the highest values over the southern coasts of the Caspian Sea (10 to 12 kg/m2). Oppose to these coastal areas, minimum values of this variable with about 6 to 10 kg/m2 were associated with the Zagros mountains. In general, PW exhibited an inverse relationship with elevation. In contrast to PW, SH maximized (4.2 to 5 g/kg) over the Zagros ranges and its relationship with elevation was generally positive. The lowest value of the SH data was about 3.5 g/kg suggesting relatively low variation in the SH data within the country. Compared to the 1960-1988 period, a significant decline was observed in the values of PW and SH in 1989-2017. Although this decline was obvious over all parts of the country, it was slightly significant for the southwestern (northwestern) districts. Compared to the first half of the study period (1960-1989), PW (or SH) decreased by about 2.5 kg/m2 (or 0.6 g/kg) in southwestern and 0.3 kg/m2 (or 0.15 g/kg) in northwestern parts of Iran for the recent half (1989-2017). Differences between wind data during these two time-periods were mostly either northerly or easterly suggesting a significant decrease in the rain-bearing southerly or westerly circulation over 1989-2017. Anomalies of the near-surface wintertime winds were mostly found to be southerly or westerly during 1960-1988 implicating the possibility of moisture transport from the Persian Gulf, the Oman Sea, the Mediterranean Sea, and the Red Sea into the most parts of Iran. Conversely, the anomalies were either northerly or easterly in1989-2017 suggesting less moisture transport into Iran for this recent period. In the decadal time-scale, maximum values of PW, SH, as well as southerly or westerly circulations, were observed during 1960-1969. The given results suggest that the enhanced (or suppressed) values of PW and SH are generally harmonized with the strengthened southerly and westerly (or northerly and easterly) wind anomalies. For this period, prevailing of southeasterly winds over the Caspian Sea enhanced or suppressed the measure of PW, SH over the western or eastern coasts of the Sea, respectively. Even though the mentioned atmospheric circulation patterns were generally similar for the 1960-1969 and 1970-1979 decades, positive anomalies of PW and SH, as well as the westerly and southerly airflows, were slightly suppressed for the second decade. The anomalies of westerly and southerly winds decreased by about one-fifth for 1980-1989 as compared with that in 1960-1969 resulting in a significant decrease in the PW and SH data for this decade. Although these anomalies were slightly positive over most parts of Iran, their weakness did not allow significant improvement in the PW and SH values. The period of 2000-2009 was evaluated as the driest decade of the study period for which the negative anomalies of PW and SH, as well as westerly and southerly circulations, were maximized (in absolute values). In spite of the fact that these undesirable conditions have recovered during the period of 2010-2017, PW and SH were still very low for this recent period. With the exception of the 1990-1999 decade, PW and SH have continuously decreased for the decades after 1970. The rain-bearing southerly and westerly winds have been gradually replaced with dry northerly or easterly wind during the recent periods. Conclusion: The findings showed that the PW and SH distribution patterns are close together in the 29-year periods, the measures were, however, significantly smaller in the second period than in the first. The wind anomalies, which were mostly southerly and westerly in 1960-1988, have been changed to northerly and easterly in 1989-2017. Since the southerly and westerly winds play an influential role in moisture transfer to Iran, their reduction in the second period is consistent with the observed decrease in PW and SH. Among the ten-year periods, the highest positive PW and SH abnormalities are associated with the 1960 and 1969 decade. This positive anomaly decreased over the time. Since a positive trend is observed for 2010-2017, it can be concluded that 2000-2010 is the driest decade of the study period. The positive anomalies of westerlies (easterlies) and southerlies (northerlies) increased (decreased) the magnitudes of PW and SH.
Research Article
S. Kouzegaran; M. Mousavi Baygi; iman babaeian
Abstract
Introduction: Global warming causes alteration of climate extreme indices and increased severity and frequency of incidence of meteorological extreme events. In most climate change studies, only the potential trends or fluctuations in the average long run of climatic phenomena have been examined. However, ...
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Introduction: Global warming causes alteration of climate extreme indices and increased severity and frequency of incidence of meteorological extreme events. In most climate change studies, only the potential trends or fluctuations in the average long run of climatic phenomena have been examined. However, the study of affectability and pattern change of extreme atmospheric events is also important. Changes in climatic elements especially extreme temperature factors have a significant influence on the performance of farming systems. Accordingly, understanding changes in temperature parameters and extreme temperature indices is the prerequisite to sustainable development in agriculture and should be considered in management processes. Investigation of extreme values for planning and policy for the agricultural sector, water resource, environment, industry, and economic management is important. Materials and Methods: To evaluate the extreme temperature indices trend, some indices of temperature, recommended by the CCl/CLIVAR Expert Team for Climate Change Detection Monitoring and Indices (ETCCDMI), were considered using Rclimdex software. In this study, daily minimum and maximum temperature data retrieved from MPI-ESM-LR global climate model were used to predict future climate extreme events over the next three periods of 2026-2050, 2051-2075, and 2076-2100 based on IPCC scenarios of RCP4.5 and RCP8.5 of the studied area, covering South Khorasan province and southern part of Razavi Khorasan province, located in the east of Iran. The modified BCSD method was used to downscale extreme temperature data. Results and Discussion: Results showed an increasing trend of warm climate extreme. According to the output of Rclimdex for RCP4.5 scenario in the period of 2026-2050, it was observed that SU25 index, summer days, has a positive trend at all studied stations. This index was found to be significant and increased at all stations in the mid-term future period, and it had an increasing trend in the far future period, which was not significant. The number of Tropical Nights (TR20) index had a positive trend at all. In the mid-term future period, there was a significant increasing trend for some stations, while there were some negative and insignificant trends at some stations in the far future. The maximum monthly daily maximum temperature (TXx) and the maximum monthly daily minimum temperature (TNx) indices also had an increasing trend at all stations, and the mid-term future period had a significant increasing trend, while the trend was decreasing in the far future period. Results for temperature extreme indices under RCP8.5 scenario showed that SU25 index had a positive trend at all stations studied in the near future, mid-term, and far future period. Index of tropical nights (TR20) had an upward trend, which was significant in mid-term and far future periods at most stations. Percentage of days in which maximum temperature is below than 10th percentile (TX10P), indicating a decrease in cold days, had a negative trend for all stations in the near future period. In the mid-term and far future periods, this trend was significant at all stations. The maximum monthly daily maximum temperature (TXx) and the maximum monthly daily minimum temperature (TNx) indices also had an increasing trend at all stations and all three periods, and the trend was significant in the mid-term future. Conclusion: Minimum and maximum daily temperatures of MPI-ESM-LR global climate model were used to predict climatic extreme events during three future periods of 2026-2050, 2051-2075, and 2076-2100 under RCP4.5 and RCP8.5 scenarios at some stations located in South Khorasan province and southern part of Khorasan Razavi province. During the three studied future periods, extreme temperature indices changed significantly. The results showed that in both periods over the future years under the both scenarios, hot extreme indices would increase and cold extreme indices would decrease. It was observed that hot extreme indices, such as summer day index, the number of tropical nights, warm days and nights increased, while cold extreme indices had a decreasing trend in the period of study, which shows a decrease in the severity and frequency of cold events.
Research Article
A. Sam Khaniani; X. Nikraftar
Abstract
Introduction: Water vapor, as one of the most important greenhouse gases in the atmosphere, plays a key role in hydrological cycles, climate change, and the global climate. Many parameters for the expression of water vapor in the atmosphere have been proposed by meteorologists, one of which is Precipitable ...
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Introduction: Water vapor, as one of the most important greenhouse gases in the atmosphere, plays a key role in hydrological cycles, climate change, and the global climate. Many parameters for the expression of water vapor in the atmosphere have been proposed by meteorologists, one of which is Precipitable Water Vapor (PWV). There are many ground-based and space-based methods to measure PWV. Meanwhile, radiosonde is considered as one of the most common and traditional tools for measuring this parameter. However, low temporal resolution, high cost, and lack of uniform coverage across the globe are some of the limitations of this technique. In the last two decades, GPS Meteorology due to unique features such as usability in any weather conditions, long-term stability, continuous observations with very high resolution, low cost, and PWV estimation with an accuracy level of about 2 millimeters has received a lot of attention. Although radiosonde and GPS are precise methods for estimating water vapor in the atmosphere, their observations are limited to the land. While satellite remote sensing methods can provide continuous observations of the distribution of water vapor on a regional and global scale. MODIS is one of the sensors capable of measuring atmospheric water vapor measurements, which is onboard the Terra and Aqua satellites. However, PWV products obtained from remote sensing data should be evaluated with respect to the reliable in situ data before application. The main purpose of this study was to use PWV estimates obtained from ground-based GPS receivers in order to statistically evaluate the accuracy of MODIS water vapor products in IR and Near-IR bands and different times of the day over Iran. Materials and Methods: The MODIS sensor, which is on board of the Terra and Aqua satellites, is able to provide water vapor products in the IR (both night and day) and Near-IR (day-only) bands. In order to evaluate MODIS PWV products over Iran, one year data of high temporal resolution GPS PWV values in 38 different stations in the country were considered as reliable values. For statistical analysis, water vapor values were extracted from the pixels with cloud-free conditions. Also, among the cloud-free pixels, that with the closest distance to the GPS station was selected. Moreover, the corresponding PWV values of GPS and MODIS with a maximum time difference of 10 minutes were selected for comparison. Results and Discussion: Initially, Near-IR PWV products were assessed separately for Terra and Aqua satellite data. The results showed a good agreement between the two sets of PWV measurements. The correlation values between the GPS PWV and the corresponding values of the MODIS Near-IR products varied in the range of 0.90 to 0.98. Average bias values indicated that MODIS Near-IR overestimated PWV in comparison with GPS over Iran. In addition, a comparison of Near-IR water vapor values extracted from Terra and Aqua datasets separately showed that the data quality of both satellites in this band is almost at the same level in terms of the correlation coefficient, average bias, and RMSE. In the next step, the MODIS IR PWV products were evaluated separately during the day and night with respect to the corresponding values obtained at the GPS stations. The maximum correlation between GPS and IR PWV products during the day and night was 0.7 and 0.64, respectively. Furthermore, the average bias of MODIS IR PWV data in the study area for day and night was found to be -0.38 and 3.11 mm, respectively. In other words, MODIS IR PWV products in the study area had, on average, a positive bias with a small amount during the day and a significant negative bias during the night. On the other hand, a comparison of daytime MODIS IR and Near-IR water vapor products revealed that the quality of IR PWV data was significantly lower than the Near-IR band and requires a suitable calibration method. Conclusion: The results of this study indicate that the MODIS Near-IR water vapor products had a high agreement with GPS PWV values with an average correlation coefficient of 0.95 in the study region. The mean bias and RMSE error of (GPS-MODIS Near-IR) PWV differences were -2.2 and 3.3 mm, respectively. A similar analysis of MODIS Near-IR PWV data from the Terra and Aqua satellites showed that almost both sets of water vapor data had the same accuracy. The average bias values of the MODIS IR PWV data compared to the GPS PWV for day and night were also investigated. Results showed that in the study area, MODIS IR products had a small positive bias during the day and significant negative bias at night. Examining the efficiency of the daytime MODIS water vapor products during the day, we found that the accuracy and precision of these data in the Near-IR band are much better than the IR band. Therefore, proper calibration should be made before employing the IR band.
