جستجوی مقالات مرتبط با کلیدواژه « land use change » در نشریات گروه « آب و خاک »

Runoff and the rainfall-runoff relationship are one of the most fundamental research topics in hydrology. Due to the increasing trend of flood occurrence and the resulting damages, it is necessary to determine the flood-producing priority areas and prioritize the sub-watersheds in terms of flood control projects and integrated management of watersheds. The primary contributing areas in runoff generation and the affecting factors should be identified in a flood management project. Understanding the flood occurrence potential of watersheds can be useful in formulating different flood management plans, allocating necessary funds, water resources management, watershed management, and erosion control programs. Watershed Modeling System (WMS) as an integrated flood modeling software can simulate flood hydrographs considering the required parameters. Among the common runoff estimation methods, the SCS curve number method is the most common in estimating flood volume and flood runoff height. Land use changes as an important factor in the alteration of watershed hydrologic response can accelerate soil erosion and biodiversity loss. Land use change affects the curve number and consequently, discharge and flood hydrographs, as assessed in the current study.

The Khiavchai Watershed, with an area of about 134 km2 has been chosen as the study area. The annual rainfall of the study area is 343.8 mm. Toward the hydrologic modeling in the study area, the slope map of the watershed has been derived from the DEM of the study area using the ArcMap software. The maximum daily rainfall of 11 rating gauge stations has been obtained and the raw data has been processed using a common statistical test to check the data quality and homogeneity of SPSS software. The maximum 24-h rainfall data were analyzed using Easy Fit software to select the best statistical distribution. The 3-parameter Pearson distribution (as the best probability distribution function), has been used to calculate the rainfall values in 2 to 100-year return periods. The maximum daily rainfall values were entered into the ArcGIS software and the spatial distribution mapping was done using the IDW method. The average maximum daily precipitation with different return periods was converted to 6-h precipitation. The SCS and WMO rainfall patterns were compared in the study area, and the WMO rainfall patterns were selected as the appropriate input for the model. The maximum annual instantaneous discharge values have been used in estimating the flood discharge in 2, 5, 10, 25, 50, and 100-year return periods using EasyFit software. The input model parameters (slope map, slope direction, curve number, and soil hydrological group) were prepared in ArcGIS and Arc-Hydro software.

The results showed that the maximum flood discharge increases intensely with an increase in the return period. The average CN value of the basin was obtained at 76, the initial loss coefficient was obtained at 0.202, and the STRTL value was obtained at 16.203. According to the increasing curve number values, the infiltration time and the time to reach the peak are reduced. Therefore, by increasing the curve number by 5, 15, and 25%, respectively, the time to reach the peak is 240, 180, and 135 min, and the base time of the hydrograph has decreased by 1035, 885, and 750 min. Meanwhile, the peak value of the simulated flood hydrograph has increased from 1.74 to 6.466, 27.491, and 109.694 m3 s-1. With an increase of 25% curve number, the peak discharge in the return period of 10, 25, 50, and 100 years has increased to 13, 9, 7.5, and 6.3, respectively. The results show that the effect of changes in curve number values on the flood discharge, in the low return period is much more than the high return period. So in the return period of 100 years with 25% changes in curve number, the peak flood discharge value is 6.38 times in the 2-year return period. The results indicate that the least change in the type of land use (in order to reduce permeability) causes a considerable increase in flood discharge in the region.

The effects of changes in CN values have been assessed in the current research in a modeling framework to estimate the flood hydrograph components. Comparison of the estimated flood hydrograph components against observation values has been evaluated using relative error and root mean square error. The values of these statistical indices were obtained with the least error related to the 3-parameter lognormal distribution of about 10.32% and 8.68 m3 s-1. By comparing the results of the maximum flood analysis and the WMS model, it can be concluded that the simulated data are consistent with the observed flood records in the Pole-Solatani river gauge station located at the outlet of the Khiavchai Watershed.

Forests have important role for ecosystem maintenance, and deforestation is one of the factors in degradation of soil quality.  In this study, using multivariate analysis, soil quality index was evaluated in three land uses including forest, grassland, and cropland at two depths of 0-10 and 10-20 cm in Sidasht of Guilan Province, Iran. The weighted additive soil quality was calculated using two methods (1) Minimum data set (MDS1) and (2) Revised minimum data set (MDS2). Also, each feature’s variance and communality and two scoring methods, namely, linear and non-linear, were compared and evaluated. In MDS2, the effects of land use on soil quality index (SQI) indicated that the mean values calculated by the non-linear scoring method was significantly more precise than the linear one. Soil quality indices in forest and grassland had the maximum values when compared to cropland. SQIW2-MDS2-NLS had the highest sensitivity index (SI= 3.14). In MDS2, the soil properties including silt, Mean Weight Diameter, pH, CaCO3 and available phosphorus were selected. Efficiency ratio of MDS2 was 80% and in soil quality assessment, MDS2 had higher efficiency than MDS1. Soil condition and change of soil management practices were reflected in MDS2 more clearly than in MDS1. Accordingly, SQIW2-MDS2-NLS method was the best means for evaluating the effects of deforestation on soil quality in the studied area.

Limited fresh water resources and access to these resources as well as providing food security for the growing world population have led researchers to make extensive efforts in the field of optimal management of water consumption and determining the cultivation pattern in different regions. Therefore, identifying cultivated crops in a region and determining their area can be very effective in land management and water allocation in these regions. With the growth and advancement of technology in the field of satellite and remote sensing in recent decades, the use of satellite images in order to identify types of land use and types of cultivated products has expanded greatly. Sentinel-1 (radar) and Sentinel-2 (multi-spectral) satellites have been very popular in agriculture due to their improved spatial resolution (10 meters) and appropriate time resolution (5 days for Sentinel 2 and 12 days for Sentinel 1).

The studied area is located downstream of the Fariman dam in an area of 22.51 square kilometers (5122 hectares) and the central coordinates are 35 degrees 41 minutes and 59 seconds north latitude and 59 degrees 50 minutes and 49 seconds east longitude. In order to classify satellite images and produce crop maps, ground observation data is needed to train the classification model and also evaluate the accuracy of the results. For this purpose, sample points were taken from different land uses in the region, using GPS. Since it was not possible to take enough samples for all land uses and crops in the determined border, a larger sampling area was selected. Then, all collected data were sorted and for each class, 70% of the data was randomly used to train the classification model and 30% was used to validate the obtained classification results. In the present study, Sentinel 2 satellite images for the first 6 months (crop season) of 2021 and 2022 and digital elevation image (DEM) of the study area were considered. According to the surveys conducted and the reports of the agricultural jihad of Fariman city, the main crops cultivated in the region include maize, tomato, sugar beet, wheat and barley. Therefore, according to the phenological stages of these products in the region, the appropriate time series of images was selected. The accuracy of the classified map was evaluated using the Kappa coefficient and overall accuracy.

In order to identify and separate the land use in the study area according to the major cultivated crops, first the agricultural calendar of the crops was determined. Then, satellite images were selected based on crop cultivation period. Based on the evaluation indexes of commission error, omission error, overall accuracy as well as the Kappa coefficient, it was observed that the identification of classes and land use was done well and with high accuracy, so that the overall accuracy for the classification map of 2022 is equal to 0.97 and the kappa coefficient value was 0.94. In order to compare land use changes during the two years 2022 and 2021, classification was also done for the images of the crop year 2021. Since the training samples of agricultural crops were not available separately and in sufficient numbers in the crop year of 2021, the classification map of this year was produced only based on the type of land use, and all crops in one class entered the classification model training process. The values of overall accuracy and kappa coefficient in 2021 were obtained as 0.97 and 0.95 respectively. According to the obtained results, the area of the orchard class has increased since 2021 compared to 2022. After repeated field visits to the study area and investigation of some land uses that had been changed and turned into orchard use, it was found that in some areas in 2022 there was the growth of villa gardens and in some areas the farmers have converted cropland to orchard (construction of an orchard). Even in some cases, the old orchard in the region was destroyed by the farmers and the land was fallow for 2 to 3 years (2021, fallow). In 2022, the farmer built a new orchard. It is also necessary to mention that fallow lands are included in the soil class depending on whether they are newly plowed or have no vegetation, and if weeds have grown on these lands, they are included in the rangeland class. 

The effective management of water resources from dams for agricultural purposes necessitates the identification of land use downstream of the dams, along with determining the types of crops and their respective areas. In this study, Sentinel 2 satellite images were employed to classify and delineate land use associated with agricultural cultivation downstream of the Fariman dam in Razavi Khorasan Province, spanning the crop years of 2021 and 2022. The results indicate that the Sentinel 2 satellite demonstrates a high capacity to differentiate between various types of land use and crops. The generated map depicting changes in land use and crop cultivation areas can be instrumental in water use planning and the allocation of water resources.

In recent years, some farmers in the plains of Saman in the province of Chaharmahal and Bakhtiari have changed the use of almond orchards in this area to agricultural land and pastures in order to provide food and fodder. Since these activities are mostly carried out without sufficient knowledge of the soil environment, there can be a serious threat to reduce soil quality. Therefore, studies on the effect of different managements on different soil characteristics and in the direction of a sustainable soil resource are very important. In this research, the effect of land use change in these areas on some physical and chemical indicators of soil quality was investigated.

In order to investigate the effect of land use change on some physical and chemical indicators of the soil quality of three land use systems comprising a permanent almond orchard, permanent pasture and almond orchard converted to land were selected in the plain of Saman. 15 samples of soil (45 samples in total) were taken from 0 to 30 cm in the form of networks (30 x 30 meters) in each of the three land use systems considered. Some physical and chemical parameters of studied soil samples measured by standard methods.After collecting and saving data in Excel, a one-side analysis of variance (ANOVA) was performed on using the SPSS18 software and the comparison of the means was also carried out on the basis of the LSD test at a probability level of 1%.

The results of analysis of variance data showed that changing land use (changing of almond orchards to agricultural land) had significant effect on the indeces examined physical and chemical of at 0.01 level. The Land use change did not change the surface soil texture of the study areas. The soil texture of all three-study system was almost the same (clay loam inclined to sandy clay loam). According to the findings of the mean comparison, when almond orchards were converted to agricultural land, there was a significant reduction in total porosity, mean weighted diameter of soil aggregates (MWD), base infiltration rate, and soil organic carbon by 12%, 56%, 50%, and 54%, respectively. Conversely, there was a notable increase of 10%, 5%, 44%, and 18% in bulk density, pH, electrical conductivity, and soil lime percentage at a significance level of 0.01 (pr<0.01).In this study, substituting improved pasture plants with land grazed pasture significantly augmented the average of soil organic carbon, total porosity, solidity of soil aggregates (MWD) and base infiltration rate by 48%, 14%, 69%, and 40%, respectively, as compared to agricultural land at a significance level of 0.01 (pr<0.01). However, no significant difference was observed at a significance level of 0.01 (pr>0.01) between almond orchard and pasture land concerning the evaluated indicators.

Overall, the parameters analyzed indicate that organic carbon, mean weighted diameter of soil aggregates (MWD), and bulk density are reliable indicators of soil quality in the study area. The average values of these indicators provide an optimal alternative for management and tillage practices in various land uses. Moreover, due to the delicate and vulnerable ecosystems of Saman Plain, it is recommended to avoid converting garden lands (such as almond orchards) into agricultural lands within the study area. This approach will help prevent soil erosion in one of the most sensitive areas of the country.

Soil resources are important components of the ecosystem, and therefore, their quality should be considered. One of the important factors affecting the quality of soils is land use change. The present study was conducted to investigate the effects of land use change and deforestation on some soil fertility and biological characteristics in the forest area of the Yasouj region. In this area, four land uses of dense forest, sparse forest, deforested (degraded) lands, and rainfed agriculture were randomly sampled from two slope classes. In each land use 10 soil surface samples were taken. Fifteen soil fertility and biological characteristics were measured using routine methods. The results showed that dense forest and deforested (degraded) lands had the best and worst conditions, respectively, in terms of the measured parameters. Among the measured characteristics, the values of alkaline phosphate, exhaled respiration, nitrogen, basal respiration, acid phosphatase, manganese, and zinc showed the greatest decrease respectively, and the values of phosphorus and potassium exhibited the least decrease, as a result of land use change from dense forest to degraded lands. The findings showed that the conversion of ecosystems such as forests to agricultural lands or deforestation has led to a severe decrease in the fertility and biological indicators of soil quality. Therefore, the protection programs of these areas should be more considered.

The purpose of this study is to measure the impact of agricultural land-use change on the process of reducing the water level of Urmia Lake and accelerate its land process. The data used in this research include Landsat satellite images in the period 2000 to 2020 and statistics and information of water sources entering the lake of Urmia Lake Rehabilitation Headquarters, which are classified by SVM, Kappa Coefficient algorithms in ENVI5.3 software and Validated and then using Arc-GIS software to determine the extent of user changes. Finally, after determining the number of changes in each land use, the amount of water required for each type of cultivation was calculated based on the climatic type and soil characteristics of the city by the NETWAT model. The satellite images show that in the period, the research aimed to change the cultivation pattern from irrigated agriculture to cropland, from an area of 395 km3 in 2000 to 688 km3 in 2020. The outputs of the NETWAT model also show that due to the change in the land-use area of agricultural lands and the change in the cultivation pattern, the amount of water consumption required in the agricultural sector has almost doubled in the growth period, from 1600 million cubic meters in 2000. It reached 2900 million cubic meters in 2020. This increase in consumption needs has eliminated the surface flow of rivers and lowered the groundwater level of the basin, which is the main reason for reducing the volume of water entering Urmia Lake.

Land use change has a direct impact on hydrological components and water resources and plays an important role in aggravating possible risks such as drought and floods. Therefore, it is necessary to investigate the effects of land use on water components such as runoff. Thus, in this study, the runoff condition of the Kiwi Chai Basin, one of the most important basins in Ardabil province, from an environmental point of view in terms of land use change is investigated using the SWAT model.

ArcGIS 10.1, Envi 5.1, and Ecognition software are used for data processing, classification, and analysis. Also, the method based on radiative transfer models, such as FLAASH, is used as the best method for atmospheric correction. Multiresolution algorithm is applied for segmentation and the nearest neighbor algorithm is used for classification. Then, educational samples are collected from the area using field visits and Google Earth satellite images and used to evaluate the accuracy and precision of the classification. At the end, the Thematic change dynamic detection method is applied in Envi5 to identify the changes that have happened over the years. The SWAT hydrological model is additionally used to investigate the effect of land use changes on the basin's runoff. After extracting the effective parameters in the basin’s outlet, the model is calibrated and validated with SWAT-CUP software and SUFI-2 algorithm. Nash-Sutcliffe indices and coefficient of determination are used to evaluate the results of this stage.

In this research, after applying object-oriented land classification, land use map in seven classes of Rainfed agriculture, irrigated agriculture, garden, forest, residential, pasture and water are provided. In the land use map of the basin, pasture cover is the dominant land use class; however, a significant decrease from 1224.18 square kilometers to 1046.59 square kilometers has been observed between 1987 and 2019. The values obtained for R-Factor, P-Factor, R2, NS indicators in the calibration period are, respectively, for Abgarm station (0.53, 0.47,0.71,0.69) and for Firozabad station (0.32,0.3,0.67,0.64) and in the validation period, for Abgram station (0.09,0,0.62,0.56) and for Firozabad station (0.13,0,0.53,0.51), respectively. Based on this, the results obtained in the calibration and validation stage are evaluated as acceptable. The evaluation of the SWAT model's response to land use also shows that, on an annual scale, the amount of flow in Firozabad station has decreases from 3.08 to 2.81 cubic meters per second -8,77percent) and in Abgarm station from 1.11 to 0.96 cubic meters per second (-13.51), which can be attributed to changes in land use, especially the change in the use of pastures and its conversion to rainfed agriculture, gardens, and forests.

The trend of land use changes in the basin between 1987 and 2019 has been accompanied by a decreasing trend in rainfed, pasture and water uses and an increasing trend in irrigated agriculture, garden, forest, and residential uses. The high value of the fit of the indicators used in the evaluation of the model indicates that the model has a good capability in simulating the runoff of the basin. Moreover, the model implemented for different land uses illustrates that the flow of the basin in both hydrometric stations in most of the months increase in the short term and decrease in the long term average with the land use change. Continuous land use change is becoming a serious threat to watersheds. Land use change should be controlled in catchment areas, and measures should be taken to stabilize land use change.

This study aimed to estimate groundwater recharge along with other balance components (runoff, evapotranspiration, and transpiration) in Hashtgerd plain, using the WetSpass-M distribution model in the conditions of climate change and land use in the next 30 years. To study the effects of climate change, the output of five models under four emission scenarios, i.e., RCP2.6, RCP4.5, RCP6, and RCP8.5 of the Fifth Report of the Intergovernmental Panel on Climate Change (IPPC) was utilized. The LARS-WG model was also used for the downscaleing of the climatic data. Land-use mapping was performed using Landsat images in 1990, 2005, and 2020 processed in ENVI 5.3. The Markov chain method in TerrSet software was used to predict land-use changes for 2050. In the end, the effect of climate change and land use on underground water supply and other water balance components was simulated using the WetSpass-M distribution model for the period 2050-2020 and the effect of climate and land use scenarios was applied on it. The climate change results showed that the annual temperature will increase by 1.2 and 3.2 degrees Celsius until 2050 for the RCP2.6 and RCP8.5 scenarios, respectively, and the annual precipitation will decrease by 1.95 and 4.47 Percent for both scenarios. The results of land use change show an increase of 105, 41, and 8 percent for residential, barren, and agricultural land, respectively, and a 94 percent decrease in pastures. With the increase of residential and barren uses and the decrease of pastureland, the permeability of the land will decrease, and as a result, the amount of surface discharge of the aquifer will decrease. Estimates, in general, showed that climate change has caused a decrease, land use change has increased the feeding of the aquifer in such a way that in the most critical scenario the amount of feeding will reach 220.6, and the balance of the aquifer will reach 115.9 million cubic meters per year. Because of climate and land use changes, the share of evaporation and transpiration has increased and the share of rescharge and runoff from precipitation has decreased. In general, in the highlands due to more rainfall and in agricultural areas due to irrigation return water, the contribution of underground water supply has increased.

The land use change as well as changes in climatic parameters such as temperature increase affect many natural processes such as soil erosion and sediment production, floods, and degradation of physical and chemical properties of soil. Therefore, it is necessary to pay attention to different aspects of the effect of these changes in studies and macro decisions of the country. In the present study, the SWAT conceptual model was used to test and analyze the existing scenarios in the Marvast basin. After calibrating the model, the two scenarios were tested. The first scenario is in the field of agricultural management and conversion of gardens to agricultural lands and the second scenario is a 0.5-degree increase in temperature by assuming other conditions are constant. The calibration and validation results of the model with the Nash-Sutcliffe test showed 0.66 and 0.68 respectively, which indicate the acceptable performance of the model in the study area. Then, the results of using two scenarios of land use change and heating, especially in recent years showed the effect of 30 percent of the climate scenario on the increase of flooding in the basin. The scenario of changing the use of garden lands to agriculture in two cases of 20% and 50% change of use of 10% and 12% was added to the flooding of the basin. The results indicate that in similar areas of the study area which is located in a dry climate zone, a possible increase in temperature can have a significant effect on flooding in the basin. However, the indirect impact of the human factor in increasing greenhouse gases and flooding in the basin should not be ignored.

Global observations have confirmed that in recent decades, forests have been converted into agricultural land at a swift pace; this is a major global concern. Forests around the world have also experienced severe disturbances due to other anthropogenic activities. The conversion of forests to cropland often results in soil degradation. Slope gradient and land use change are known to influence soil quality; therefore, the assessment of soil quality is important in determining sustainable land-use and soil-management practices. Magnetic susceptibility (χlf) measurements are widely used to study soil-forming processes. Many efforts have been made to correlate soil magnetic susceptibility with different soil properties, such as topography, parent material, Fe oxide forms, etc. The Yasouj area of Kohgilouye Province is one of the most densely forested areas in Zagros mountainous region. Parts of the area have been cultivated to feed the growing population, which has led to forest degradation. The objectives of this study were to assess some soil properties focusing on soil χlf and Fe- oxides forms in different land uses and slope positions.

 Forty soil samples were taken from dense forest, sparse forest, eroded lands and dryland farming from different slops (0-15 and 15-30 percent) in Mokhtar Plain, west of Yasouj city. Soil samples were taken from the depth of 0–15 cm in a completely randomized design with five replications. Soil moisture and temperature regimes in the study area are xeric and thermic, respectively. Particle size distribution was determined by the hydrometer method and soil organic matter, CaCO3 equivalent and bulk density were determined using standard procedures. Fe (Feo) were extracted by acid ammonium oxalate, using a single 4-h extraction at pH 3 in the dark. Total free iron (Fed) was extracted with the CBD method. The total Fe contents (Fet) in the soil samples were determined after extraction with 5 mol L-1 HNO3. Magnetic susceptibility of the soils was measured at low (0.46 kHz; χlf) and high (4.6 kHz; χhf) frequencies, respectively; using a Bartington MS2 dual-frequency sensor, with approximately 10 g of air-dry soil in polyethylene vials. The percentage of frequency-dependent magnetic susceptibility (χfd%) was calculated to study the size of magnetic crystals in soils and the abundance of pedogenic ferrimagnetic in SP-SSD (~0.03 μm) boundary.

The results of this study showed that the land use and slope positions were among the important factors affecting the change of soil properties in this area. Land use change along with the reduction of organic matter reduced the stability of aggregates and increased land erosion. This process caused the loss of clay particles and magnetic minerals and affected many soil properties. Organic matter as an important indicator of soil quality, showed a decrease of about 3 times as a result of land use change from dense forest to eroded lands following by an increase in bulk density and a decrease in soil permeability and other soil quality indicators. Long-term afforestation and agricultural activities on sloping lands changed the soil texture from a class of silty loam in the forest to a lighter class of silty loam in agricultural use. Soil magnetic susceptibility, which is a function of soil magnetic particles was greatly affected by land use change and to a lesser extent by slope position. Due to the fact that magnetic susceptibility is influenced by factors such as soil texture, drainage class, erosion conditions, magnetic mineral contents, soil evolution conditions, land use changes from forest to other uses had significant effects (about 2 times) on χlf. Significant decrease in the amount of calcium carbonate in low slope positions was another reason for the increase in magnetic susceptibility in these positions. According to the measured values ​​of χfd (ranged from 1.9 to 7.2%), the magnetic particles of the soils had low to moderate amounts of superparamagnetic (SP) particles, which indicates the combined effect of pedogenic superparamagnetic ultrafine particles and  lithogenic (inherited) magnetic particles in χlf of the soils. The effect of slope on Fe forms (Feo, Fed and Fet) has been significant (p < 0.01) in almost all land uses. Due to the relatively high correlation of χlf with some soil properties such as Fe forms, soil clay, the amount of diamagnetic compounds including calcium carbonate in the studied soils, it is possible to estimate the value of these soil properties using χlf, which is a quick and cost-effective approach. Overall, it seems that magnetic susceptibility could be applied successfully to estimate some soil properties in hilly regions of Zagros Mountains of southwestern Iran, especially for monitoring the consequences of land use changes. It should also be noted that any change in the use of the area should be defined in accordance with the potential of the land in the long term to prevent a reduction in soil quality.

Deforestation and poor farming practices are two factors that seriously threaten natural resources and seriously damage the soil productivity. This study was conducted to investigate the effects of deforestation and land use on some chemical and microbial properties of soil in different layers of evangelical forest, Citrus Garden and wheat farm soils in Sari township. Organic matter content, total nitrogen, carbon and nitrogen of microbial biomass were significantly reduced when evangelical forest converted to wheat farm (in all three layers) and citrus garden (in two layers of 0-10 and 10-20 cm). When evangelical forest converted to wheat farm (in first layer) organic matter, total nitrogen, carbon and nitrogen of microbial biomass were reduced 35.5, 51.2, 69.7 and 59.8%, respectively. Phosphorus availability and microbial respiration were significantly reduced when evangelical forest converted to wheat farm and citrus garden. The amount of reduction for phosphorus availability and microbial respiration were 85.2% and 35.1% respectively for the top layer of wheat farm. Microbial C/N was significantly reduced when evangelical forest transformed to wheat farm and microbial metabolic coefficient was significantly increased when evangelical forest changed to the two other land uses. The urease activity in both land use (citrus garden and wheat farm) and alkaline phosphatase activity were significantly reduced in wheat farm soils. The results of this study showed that changes in the chemical and microbial properties of the soil was more substantial when evangelical forest converted to agriculture land. The most important reasons for reduction of soil quality may be related to the harvesting (in both citrus garden and wheat farm) and the loss of the closed loop of forest, soil tillage (on the farm) and animal manure application.

Human activities such as deforestation, conversion of natural ecosystems to farming, biomass burning, tillage and cultivation, grazing, fertilizer use have a significant and negative impact on soil organic carbon pool. In particular, the conversion of natural ecosystems to agriculture reduces soil organic carbon pools. Understanding the spatial distribution of organic carbon in soil is particularly important for understanding the role of soil in the global carbon system. Therefore, the purpose of the present study was to investigate the changes of total carbon and its components in different sizes of aggregates of a forest soil after conversion to paddy.

For this study, Poplar Research Station in Guilan province was selected. Soil samples were collected from two uses of forest and adjacent paddy fields at two depths (0-20 and 20-40 cm). In the soil samples, aggregates of different sizes were separated and the amount of organic carbon in these aggregates was measured. Organic carbon was then fractionated into different sizes of these aggregates in both land use.

Investigation of organic carbon distribution in relation to aggregate size in two land uses showed that with increasing aggregate size, organic carbon content increased so that organic carbon content in Populus natural forest and rice fields were 4.5 and 3.3 times higher in aggregates larger than 2 mm (larger aggregates) than smaller aggregates 0.053 mm, respectively. The amount of organic carbon in the aggregates decreased with the change from natural forest to paddy fields. However, the decrease was greater in aggregates larger than 2 mm and lowest in aggregates (0.25–0.053 mm). Results of soil organic carbon fractionation showed that percentage of soil weight in fractions increased with increasing density in two land use. This situation was visible in two depths and in all the aggregate sizes. By increasing the density of fractions, the concentration of organic carbon in the fractions decreased. The organic carbon content of the fractions as a percentage of organic carbon content of whole soil, in all the aggregate sizes, and in the fractions with density < 2 g cm-3 was smaller than those of fractions with density > 2 g cm-3. In all of the aggregates, with increasing depth, organic carbon content of the fractions with density < 2 g cm-3 as a percentage of organic carbon content of whole soil decreased while those of the fractions with density of > 2 g cm-3 increased. By increasing the density of fractions, the C/N ratio of the fractions decreased. In all of the aggregate, due to the change of land use from natural forests to rice field, organic carbon content of the fractions as a percentage of organic carbon content of whole soil, decreased in the fractions with density < 2 g cm-3 and increased in the fractions with density > 2 g cm-3 and this was more pronounced in aggregates of larger size. The most sensitive and resistant fractions to land use change were fraction 2g/cm3 respectively. The ratio of carbon to nitrogen decreased as a result of land use change from natural forest to the rice field.

The change of land use and long-term cultivation in virgin forests and its transformation in rice field has changed organic carbon content of the fractions. The amount of free and occluded particulate organic matter in the aggregate (light fraction), which plays a very important role in the nutrition of the crop, was greatly reduced. This reduces the soil's health and the potential for carbon sequestration in the soil.

Agricultural activities, especially rainfed wheat, is one of the main reason of the destruction of natural rangeland in the west of Iran. This study aimed to investigate the effect of changing natural rangeland to rainfed wheat for 40 years on some soil properties at the Saral Agricultural Research Station in Kurdistan province. Soil samples were collected from 0–25 cm depth randomly. Some soil properties such as soil texture, bulk density, mean weight diameter, cation exchange capacity, electrical conductivity, pH, calcium carbonate equivalent, total nitrogen, total organic carbon and available amount of Mg, Ca, K, P, NO3 and NH4 were measured. The results showed that land use change from rangeland to rainfed wheat significantly reduces soil quality with regard to all investigated properties except bulk density, calcium carbonate equivalent, P, K, NO3 and NH4. Determination of soil quality index (SQI) using Principal Component Analysis (PCA) showed that total organic carbon, total nitrogen, clay and silt almost justify more than 90% of the variance, which were selected as the minimum data set in the SQI calculation. The results of SQI showed that the index was significantly higher in rangeland (1.58) than in cropland (0.72), indicating degradation of soil quality by cultivating operations.

The most important factor in environmental degradation and pressure on ecological resources is rapid population growth combined with unsustainable exploitation of resources. Soil is one of the most important and worthful natural resources of environment. Land use change and deforestation decrease soil quality. Land use change also causes destruction of the evolved soils and decrease soil quality which result in permanent destruction of land fertility. Therefore, studying land use management effects on the soil quality has got an attention in recent years. Destroying the vegetation especially in the last 50 years resulted in important problems like soil erosion, land slide as well as increasing flood in the Bazoft area. In this area, degradation of the forests and their convert to other land uses like pasture, agriculture and urban or rural land use, occurs annually at high extent, in which make high damages to natural resources. In this study, the effect of land use change on soil quality indices in this area located at Chaharmahal-Va-Bakhtiari province was investigated.

In this research, four different managements with relatively similar conditions in terms of the influence of soil producing processes were chosen. Then, 10 composite samples from 0-30 cm depth of each land use (40 samples in total) were taken and different soil properties including soil texture, mean weight diameter of aggregates (MWD), porosity, bulk density, soil acidity, electrical conductivity and calcium carbonate equivalent were determined. One-way ANOVA was used to analyze the dataset. Tukey HSD test was applied to compare the means at the probability level of 5%. The first land use includes the natural forest with predominant cover of Iranian oak and the highest density and cover with the least human interference. Another land use is the degraded forest, caused by deforestation over the last 50 years. The third land use is the agricultural land which transformed from forest land use by deforestation in the last 50 years. The fourth land use is the walnut garden which established from agricultural land about 20 years ago.

The results showed that land use change from natural forest to other uses had a significant effect on most of the studied parameters. The percentage of particle size distribution was affected by different land uses, so that the percentage of clay was significantly higher in the land use of natural forest and walnut orchard than other land uses. The results also showed that the mean weight diameter of aggregates was influenced by the land use change (P <0.001). Factors like soil compaction due to livestock grazing and machinery traffic, agricultural operations and reduced biological activity increased the bulk density in all land uses compared with the forest land use. Deforestation also resulted in 6.92%, 12.05% and 14.16% porosity reduction in walnut orchard, agricultural land and deforestation, respectively. Changing management from farmland to walnut orchards also improved soil porosity by 6 percent. In the study area, the problem of changing vegetation, grazing, planting and other mismanagement increased soil pH in other land uses compared with the forest land use. The comparison of means showed that degraded forest and agriculture land uses had the highest rate of electrical conductivity which showed significant difference with natural forest land use and walnut orchard. Analysis of variance indicated that the land use had a significant effect on calcium carbonate equivalent at the probability level of 0.001. The comparisons also showed that the equivalent calcium carbonate content in agricultural land was higher than the other land uses, and there was no significant difference between walnut orchard and natural forest.

The results of the present study showed that the soil physical and chemical properties were significantly affected by land use change. Overall, it can be stated that the rate of changes in soil quality under human management and different utilization systems indicates failure in sustainable management of soil resources in the study area. Some characteristics such as soil particle size distribution percentage, soil porosity and calcium carbonate equivalent shows that there is no significant difference between walnut orchard and natural forest. However, the walnut orchards can be selected as the best management in areas where it is impossible to restore natural forests. Also, the need for stopping deforestation in Zagros ecosystem is highly recommended.

Rainfall erosion is the first type of water erosion on the land which is affected by various factors such as land use change and previous rainfall. This study was carried out to investigate the influence of previous rainfalls on the process of rainfall erosion in two marl soils (pasture and that changed to agriculture) under the simulated rainfall. Toward this goal, aggregate samples with the diameters of 6 to 8 mm were randomly collected from the marl areas in the west of Zanjan. Soil aggregates were packed into 48 boxes with the dimension of 30×40 cm to examine the effects of eight rainfall durations with three replications. Eight simulated rainfalls with the duration of 0, 7, 14, 21, 28, 35, 42 and 49 min and a constant intensity of 40 mm h-1 were used in the experiment. The soils were exposed to another simulated rainfall with 40 mm h-1 in terms of intensity for 15 min to study the rainfall erosion processes. The results showed that the aggregate breakdown was significantly affected by the previous rainfalls in the pasture soil (P<0.01), while there was no significant difference among the previous rainfalls in the case of agriculture soil.  Soil compaction and particles splash were significantly affected by previous rainfalls (P<0.05). Aggregate breakdown and particles splash were 1.41 and 1.31 times bigger than their values in the pasture soil. This study, therefore, revealed that the land use change in the mal areas increases the soil vulnerability to rainfall erosion processes. The rate of rainfall erosion processes in each rainfall event depends on the amount of previous rainfall. Increasing aggregate break down and soil water content by the previous rainfall could significantly influence the splash erosion rate in a marl soil.

Agricultural activity, especially cultivating rice, is one of the main reason of the destruction of natural forests in the north of Iran. This study was performed to investigate the effects of changing natural forest to Paddy Field on some physical and chemical properties of the soil and to determine the most sensitive indices to the disturbance of an ecosystem. Moreover, in this study, the Principal Component Analysis (PCA) method was used to create a minimum set of data from measured physical and chemical parameters. Accordingly, two land uses (natural forest and paddy field) were selected in Gilan province and soil samples were collected from five different depths (0-20, 20-40, 40-60, 60-80, and 80-100) three times. Soil texture, density, field capacity, dispersible clay, mean weight diameter (MWD), pH, electrical conductivity, calcium carbonate, organic carbon, total nitrogen, cation exchange capacity, extractable carbohydrates with acid and extractable carbohydrates with hot water at each depth were measured and the results were analyzed as factorial in a completely randomized design. The results indicated that by changing the land use from forest to paddy field, the average apparent density of the soil profile (15%) and dispersible clay (33%) were increased. However, the MWD (76%), organic carbon content (57%), total nitrogen (53%), and cation exchange capacity (31%) were reduced. The sensitivity index (SI) showed that among the physical and chemical parameters, MWD and organic carbon content were respectively more sensitive than the other parameters to land use change. The results of PCA revealed that the four factors could almost justify more than 90% of the variance in MWD, organic Carbone, density, moisture content in field capacity, extractable carbohydrates with acid, and extractable carbohydrates with hot water. These parameters showed the highest commonality and the clay percentage had the minimum relative importance among the estimation of commonality values.