Soil Chemistry and Pollution
Nima Davodi; Mostafa Chorom; Nematollah Jaafarzadeh Haghighi fard
Abstract
Introduction: Today, the production of plastic in the world is more than 400 million tons per year. This massive volume of plastic, in the form of various products from kitchen appliances to industrial and agricultural products, is growing rapidly. According to the statistics presented in 2020, about ...
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Introduction: Today, the production of plastic in the world is more than 400 million tons per year. This massive volume of plastic, in the form of various products from kitchen appliances to industrial and agricultural products, is growing rapidly. According to the statistics presented in 2020, about 9% of the plastics produced in the world are recycled. Therefore, most plastics remain persistent in the soil or in the seas as plastic waste. Microplastics (MPs) particles less than 5 mm in diameter originate from the breakdown of larger plastic debris such as plastic bags, bottles, and packaging materials. MPs, as an emerging contaminant, have gained worldwide attention. Unfortunately, current recycling methods have failed to provide a comprehensive solution to plastic waste disposal. However, in the past decade, most research on the effects of MPs pollution has focused on marine ecosystems, while very limited research has focused on terrestrial ecosystems. Soil ecosystems, especially agricultural lands, are known as the main reservoir of MPs but the effects of MPs on soil ecosystems remain largely unknown. Soil acts as a significant reservoir for MPs and can have substantial impacts on soil quality and fertility. Upon entering soil, MPs can potentially threaten soil health. MPs can interact with soil particles and organic matter and affect soil structure, nutrient cycling, and microbial communities. Studies have shown that MPs can alter soil microbial communities, potentially leading to changes in ecosystem functioning. MPs in the soil act as a means of absorbing and transporting pollutants. They transport agricultural chemicals, heavy metals and pathogens deep into the soil. The impact of MPs on soil organisms and ecosystems is not yet fully understood, and more research is needed to assess the extent of the problem and its potential consequences. They can negatively impact soil function and fertility by disrupting the physical, chemical, and biological properties of soil. A deeper understanding of how MPs enter, distribute, and accumulate in soils, as well as their impacts on various soil functions, is essential for developing effective strategies to manage and mitigate MPs soil pollution. Therefore, the purpose of this research was to determine the distribution of MPs in the deep soil and to identify the structure of MPs and the extent of their effects on some chemical and biological properties in Ahvaz urban waste landfill.Materials and Methods: To investigate the impact of MPs on some chemical and biological properties of soils in a municipal landfill, a factorial experiment was conducted in a randomized complete block design. The experiment consisted of 18 experimental soil units with three replications. Soil samples were collected from three depths (0-10, 10-20, and 20-30 cm) from each of five municipal landfills using a hand auger. Additionally, soil samples from the same depths were collected from a control area without any waste landfill. Chemical and biological characteristics of soils, including soil salinity, soil acidity, soil organic matter, soluble cations and anions, total nitrogen, available phosphorus, soil lime content, microbial respiration, soil microbial biomass, extraction and identification of MPs based on standard laboratory methods were measured. Identification of MPs using FTIR analysis was considered as a crucial step in this study. The experimental design consisted of two factors: landfill area (landfill vs. control) and soil depth (three levels). The experimental design was done in a factorial form in a randomized complete block. Comparison of average data was also done using Tokay’s 5% probability level test, data results were statistically analyzed with SAS software and graphs were drawn in Excel.Results and Discussion: The findings of the present study revealed a significant positive correlation between landfill areas and the control area. This indicates that landfill activities have a substantial impact on the concentration of MPs in their surrounding environment. In the soils near the municipal landfills, extremely high levels of MPs were encountered, with up to 4300 MPs pieces per kilogram of soil. This level of MPs contamination indicates severe soil pollution in these areas. Further analysis of the identified MPs revealed that two polymers, polyethylene (PE) and polypropylene (PP), accounted for a major portion of this contamination. Specifically, 71.81% of the MPs studied were PE, 17.15% were PP, 3.11% were polystyrene (PS), and 8.21% were polyvinyl chloride (PVC). This suggests that plastic materials, particularly plastic bags, bottles, and other items made of PE and PP, play a significant role in MPs soil pollution. In addition to physical effects, MPs can also have detrimental consequences for the biological and chemical properties of soil. The results showed that there is an inverse relationship between soil pH and the number of MPs, which means that as the number of MPs increases, the pH level decreases. But this relationship is not the same in all regions and at all depths. An increase or decrease in soil pH is probably due to the release of alkaline or acidic components from MPs. Soil salinity in areas one to five is higher than the control area. In some areas, at the same time as the number of MPs decreases with increasing depth, soil salinity increases and in others it decreases. The amount of soil organic matter in the areas with MPs pollution was significantly higher than the control area. The results showed that the presence of MPs in the soil is associated with a significant increase in the amount of total nitrogen in the soil. The reason for this increase can be related to the effects of MPs on microbial activity and biochemical processes in the soil. The average microbial respiration in the control area is 261 mg C-CO2/Kg soil, which is 38% lower than the average microbial respiration in areas contaminated with MPs. The average microbial biomass in the control area was 73.7 mg C/Kg soil, which is 51% less than the contaminated areas. A significant increase in microbial biomass in soils contaminated with MPs indicates an increase in the population of microbes, which can be due to the efforts of microbes to decompose MPs. This study demonstrated that MPs , as a major source of pollution in municipal landfills, can lead to significant changes in the chemical and biological characteristics of soils. These changes can negatively impact soil fertility, biodiversity, and the health of soil organisms. MPs might sorb (adhere) to nutrients and organic matter, altering their availability to plants and soil microbes. Additionally, the breakdown of MPs could release chemicals that indirectly affect soil chemistry.Conclusion: The effects of MPs on soil chemical properties resulted in significant increases in pH, EC, calcium and magnesium, soil organic matter, phosphorus, and total nitrogen. Soil organic matter, phosphorus, total nitrogen, and salinity increased by 3.4, 2.2, 7.2, and 2 times, respectively. The presence of MPs increased microbial respiration and microbial biomass in the surface soil, but at lower depths, decreased due to excessive salinity. Overall, this study demonstrates that MPs can have substantial effects on soil chemical and biological properties.
Soil Genesis and Classification
samaneh Tajik; shamsollah ayoubi; mohmmad mehdi darvisihi; hossein khademi
Abstract
Introduction Soil snails constitute an important part of the forest ecosystem and play an essential role in litter decomposition and soil calcium concentration. Snails are known as bioindicators because of narrow distribution, short lifetime, and high sensitivity (22, 24). The abundance and distribution ...
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Introduction Soil snails constitute an important part of the forest ecosystem and play an essential role in litter decomposition and soil calcium concentration. Snails are known as bioindicators because of narrow distribution, short lifetime, and high sensitivity (22, 24). The abundance and distribution of soil snails are dependent on different environmental conditions, such as precipitation, pH, soil calcium, and plant cover. Also, soil properties are mainly related to topographic parameters. Because ecosystem components have complex relationships, we need powerful models to find effective factors and spatial variations of the soil fauna (23). Linear Regression and random forest are popular and applicable models in soil science. Up to the present, no study has investigated the effect of soil parameters on snail abundance using linear regression and random forest. This study was performed to investigate the effect of soil properties and topographic parameters on the abundance of soil snails and their distribution in a part of forest area located in Bahramnia forest, an experimental site in Golestan Province, in the north of Iran. Materials and Methods This study was conducted in Shast Kalate (Bahramnia) forest, an experimental forest of Gorgan University of Agricultural Sciences and Natural Resources, located at the eastern Caspian region, north of Iran (36° 43′ 27″ N latitudes, 54°24′ 57″ E longitudes). 153 soil samples were collected from 0-10 cm; then soil snails were gathered and classified into the Gastropoda taxonomic class group. Soil properties, such as Soil particle size distribution (clay, silt, and sand), soil pH, electrical conductivity (EC), calcium carbonate equivalent (CCE), soil organic carbon (OC), total nitrogen (TN), and Soil microbial respiration (Resp), were measured via laboratory analysis. Also, digital elevation model and satellite images were used to determine the topographic parameters, such as Elevation, slope, slope aspect (Aspect), land surface temperature (land temp) wetness index (WI) and normalized difference vegetation index (NDVI). We used linear regression and nonlinear random forest models for investigating linear and nonlinear relationships between soil properties, topographic parameters, and the abundance of soil snails. Likewise, sensitive analysis was done to find the importance of the input parameters. Results and Discussion The PCA analysis showed that first and second components explain 38 and 21 percent of the variation. In the first component, EC, OC, TN, pH, and silt were the most variable, and in the second component CCE, Clay, OC, sand, and EC were the most important parameters. In both components, topographic parameters had no effect. The PCA graph showed that CCE, sand, and pH had the most correlation with snail abundance and EC, Resp, OC, and TN affected their abundance. The validation results of regression and random forest models showed that random forests have more accuracy (0.49) and low error (1.82). In addition, the sensitive analysis showed that CCE, pH, EC, OC, aspects, elevation, and land temp are the most important parameters on snail abundance. Different studies reported that pH and CCE are effective parameters on snail abundance (20, 17). Also, Ondina., et al. (27) reported that EC has an important effect on soil snail abundance. We hypothesize that topographic parameters affect soil snail nonlinearly and by affecting soil properties. Aspect is one of the topographic parameters that, via an effect on land temperature, land cover, and pH (8), has an important role in soil snails. In this way, elevation, by affecting pH, wetness, land temperature, OC, and TN, affects soil snail abundance (13). Land temperature is the other topographic parameter that is affected by aspect and elevation and had a significant effect on snail abundance by affecting OC and wetness (17). Conclusion Based on the results, nonlinear random forest model had more accuracy than linear regression in predicting snail abundance. Results showed that calcium carbonate equivalent, pH, EC, and organic carbon were the most effective soil priorities on snail abundance. There was no linear relation between soil properties and soil snails, but in the nonlinear model, we found their role. Aspect, elevation, and land temperature were the most effective parameters on snail abundance that probably affected soil properties, such as calcium carbonate and soil moisture.
Soil Physics, Erosion and Conservation
Nasim Bazshushtarizadeh; shamsollah ayoubi
Abstract
Introduction 137Cs is an artificial radionuclide with a half-life of 30.2 years and strong gamma radiation that, due to nuclear explosions in the 1950s, and 1960s entered the earth's surface by the rain. The radionuclide has been widely used for the evaluation rates and patterns of soil erosion and deposition. ...
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Introduction 137Cs is an artificial radionuclide with a half-life of 30.2 years and strong gamma radiation that, due to nuclear explosions in the 1950s, and 1960s entered the earth's surface by the rain. The radionuclide has been widely used for the evaluation rates and patterns of soil erosion and deposition. 137Cs was rapidly adsorbed to fine particles of soil surface horizon and its distribution is basically accompanied by the physical processes of soil, such as erosion and tillage. 137Cs is distributed exponentially as a function of depth to a maximum depth ranging from 5 to 15 cm in the undisturbed soil. The basis of calculating of erosion by 137Cs method is based on comparison between the amount of 137Cs in studied soil and the reference site (local, flat, un-eroded, undisturbed and stable site) and 137Cs loss or gain, relative to the reference inventory, indicates soil erosion and deposition, respectively. So, the reliable and accurate reference estimate of 137Cs is essential. No attempt has been made to explore the variability of 137Cs inventory in the reference sites in Iran. Therefore, This study was conducted to evaluate variability of 137Cs inventory and its relationship with some soil properties at the reference site located in Fereydan district in western of Isfahan province. Materials and Methods 96 soil samples were collected from 0-15 cm and 15-30 cm depths. Moreover, for evaluation of vertical distribution of 137Cs, two profiles were excavated and 8 soil samples were collected from 0-5, 5-15, 15-25 and 25-35 cm depths. Gamma-ray spectrometry device was used for 137Cs analysis. Magnetic susceptibility values were measured using Bartington susceptimeter at low (0.46 kHz) and high (4.6 kHz) frequencies and magnetic susceptibility dependent was calculated by low and high frequency values. Soil properties including total nitrogen, organic material, cation exchange capacity, calcium carbonate equivalent, EC, pH, texture, gravel and bulk density were determined. Descriptive statistics including mean, minimum, maximum, standard deviation (SD), coefficients of variation (CV), skewness, and kurtosis were calculated by SPSS software, v.16. The distribution of variables was evaluated using the Kolmogorov-Smirnov test. Pearson correlation coefficient and regression analysis were used to examine the relationships between 137Cs and soil properties. Results and Discussion The coefficient of variation of 137Cs inventory were 15.05 and 14.05% in 0-15 cm and 15-30 cm depth respectively. The result indicated that 137Cs has uniformly distributed in studied reference site. The results of the study showed that OM, OM/Clay, CEC/Clay, EC, Sand, BD, χlf and χhf were correlated with 137Cs. The results of multiple regression analysis indicated that bulk density, clay content and magnetic susceptibility at low frequency explained 43% of total variability of 137Cs in the studied reference site. Conclusions In the present study, variability of 137cs was investigated in a reference site in Ferydan district in Isfahan Province. The study showed that 137Cs had low variability. Among the soil physical and chemical properties, Soil pH, silt, gravel, nitrogen and calcium carbonate equivalent did not show significant correlation with 137Cs. The highest positive significant correlation was obtained for BD and 137Cs. Also, magnetic susceptibility at low and high frequencies showed significant correlations with 137Cs. In the multiple regression analysis, BD, clay content, and magnetic susceptibility were included in the model for explaining the 137Cs variability. It is suggested that similar study be done in the other reference sites in the western Iran.
