جستجوی مقالات مرتبط با کلیدواژه « Loess » در نشریات گروه « آب و خاک »

During the Quaternary period mid to high-latitude areas were affected by loess deposition. In Iran's northern and northeastern regions, significant loess deposits are prevalent and distributed throughout the Iranian Loess Plateau and along the northern foothills of the Alborz Mountains. Intercalated within these loess deposits are paleosols, formed during warm and moist climatic conditions (interglacial period). These paleosols offer an opportunity to study the climatic and environmental changes that occurred during the Quaternary period. Understanding the relationship between loess deposition and paleosol formation can offer significant insights into the mechanisms that drive changes in global climate and how they affect the Earth's geology and ecosystems. Studies have shown that loess sediments and loess-derived soils contain different concentrations of iron minerals such as hematite, iron oxyhydroxide, and goethite. These minerals are highly sensitive to environmental changes, and evaluating the changes of these minerals in loess-paleosol sequences can be a valuable indicator for studying paleoenvironmental changes. The two main minerals that cause color and magnetic susceptibility changes in loess-paleosol sequences are goethite and hematite. Therefore, the assessment of loess-paleosol sequences from the aspect of magnetic and colorimetric parameters provides the possibility to identify paleoenvironmental and climatic changes. The main goal of this research is to investigate the changes in iron oxides in the loess-paleosol sequence in the east of Golestan province using colorimetric techniques and temperature-dependent magnetic susceptibility in order to provide enough information for reconstructing the paleoclimatic conditions during the formation of paleosols.

Sampling was performed from the loess-paleosol sequence in the eastern Golestan province, for each loess and paleosol horizon. Initial colorimetric and magnetic susceptibility measurements were carried out respectively for 1345 and 24 samples at LIAG Institute in Germany. Color measurements were carried out with a spectrophotometer machine that covered the visible light range. The temperature magnetic susceptibility was carried out using in the 20–700°Ctemperature range in an argon atmosphere to minimize oxidation.

According to the results of this study, we can mention the identification of iron minerals in loess and paleosol samples using colorimetric analysis. Iron minerals such as hematite, goethite, and maghemite can be detected at wavelengths 565, 435, and 595 nm, respectively. Colorimetric results showed that the ratio of hematite to goethite of paleosols has increased compared to loess sediments in the study area, which indicates the increase in precipetation and soil moisture during the interglacial period. The heating curve (temperature-dependent magnetic susceptibility) of loess samples at 560-590 degrees Celsius showed a sharp decrease due to magnetite minerals in these samples. At the same time, this happens in paleosols at a temperature of 300-350 degrees Celsius, which is due to the loss of the maghemite mineral formed during the interglacial period. The results showed that the decrease in the heating curve in paleosols indicates the increase in the intensity of soil-forming processes.

The results of this study showed that iron minerals such as magnetite, maghemite, hematite, and goethite in loess and paleosols play an important role in magnetic properties and soil color. Also, the increase in the presence of hematite and maghemite in paleosols indicates the increase in the intensity of soil formation processes and humidity during the formation of paleosols. The results of this research showed that the colorimetric technique, along with temperature-dependent magnetic susceptibility, can be one of the fast and accurate methods in studying and identifying paleosols.

Existence of susceptible agricultural lands with loess deposits in the South and West of Gorgan, with plowing in down-slope direction and failure in promoting contour plowing based methods have led to use alternative control practices such as cultivating buffers in the marginal lands. The under-studied hillslope with an area of 5.1 hectares includes four long agricultural lands and three permanent vegetation buffer strips between them with an average width of 7 meters and a field under fallow with 55 meters length located in the down slope. In this study, the climate files of the WEPP model were built by using the BPCDG software for the year 2015 based on the data of the recording rain-gauge in the Hashem Abad synoptic station. To increase the accuracy of the model, the slope file was created using a digital survey camera with a resolution of 0.2 meter. In order to verify the WEPP model, the plot observation data of a rainfall simulator were used. Then two cases of lack and existence of current buffer strips in the hillslope were evaluated by the WEPP model. WEPP model estimated the amount of erosion and the specific sediment for the existing buffers modes in hillslope to be 27.36 and 18.08 tons per hectare per year respectively, and for the scenario of a lack of buffer strips, they were estimated to be 37.11 and 35.28 tons per hectare per year, respectively. Also, the model estimated runoff rate for the existence and lack of buffer strip scenarios to be 32.66 and 40.54 mm, respectively. The results showed that the buffer zones in the under-studied hillslope have decreased the amount of erosion and sediment to 9.75 and 17.20 tons per hectare per year respectively, as well as reduce the runoff rate 7.88 millimeter per year. Therefore, the buffer zones were able to control a significant amount of sediment (49 percent), which cause remarkable damages in the downward.

Knowledge about palaeoenviroment and palaeovegetation provides information about how vegetation reacts on climate fluctuations in the past, what will help understanding current and future developments caused by e.g. climate change. Northern Iranian Loess-Plateau forms a strongly dissected landscape with steeply sloping loess hills. This loess record reflects numerous cycles of climate change and landscape evolution for the Middle to Late Quaternary period. therefore, this study was done for reconstruction of palaeoenvironment (climate and vegetation) in loess-palaeosol sequences in northern Iran. Therefore, this study aims at a preliminary reconstruction of palaeovegetation and palaeoenvironment, in loess-palaeosol sequences along a cliomosequnce in Northern Iran.
Two loess-palaeosol sequences (Agh Band and Nowdeh sections) were chosen in Golestan province, in northern Iran and step-wise profiles were prepared. Agh Band section is located in the western most part of the Northern Iranian loess plateau and has about 50 m thickness of loess deposits. Nowdeh loess-palaeosol sequence is located about 20 km southeast of Gonbad-e Kavus, in the vicinity of the Nowdeh River. Soil sampling was done in several field campaigns in spring 2012. More than 30cm of the surface deposits were removed in order to reach for undisturbed loess and palaeosols and one mixed sample was taken from each horizonA comparison of palaeosols with modern soils formed under known Holocene climatic conditions, which are derived from substrates with similar granulometric and mineralogical composition are suited for reconstructing past climate and environment. Hence, six modern soil profiles were prepared along the climosequnce and the vegetation cover changed from grassland in the dry area to dense shrub land and forest in the moist part of the ecological gradient. For reconstruction of palaeoenvironment (climate and vegetation) some basic physico-chemical properties, clay mineralogy and n-alkane biomarkers were used.
Results of soil texture analysis showed silt particles were dominant (more than 50 %) in the modern soil profiles and loess-paleosol sequences which confirmed aeolian source of loess deposit. Clay content increased while silt content decrease in more strongly developed palaeosol horizons which it may reflected weathering processes of clay and/or its translocation. The modern soil profiles were classified as Entisols, Inceptisols, Mollisols and Alfisols which shows impact of climate as an important soil formation factor in the studied area. Clay mineralogy results in two loess-palaeosol sequences showed that illite, chlorite, kaolinite and smectite are dominant in these deposits. Mineralogical changes in the soil horizons are consistent with morphology and soil evaluation, so smectite, illite-smectite (mixed layer) and vermiculite minerals were dominant minerals in more strongly developed palaeosol horizons indicating to high precipitation and good vegetation cover (e.g., forest). The n-alkane biomarker results in the modern soil profiles showed, the average chain length (ACL) and (nC31鰭)/(nC27鰭) ratio are very efficient parameters for reconstruction of vegetation, therefore these parameters were used to unravel the palaeovegation in loess-palaeosol sequences. In both sections n-alkane biomarkers studies showed vegetation changes in different periods. These changes were most intense in Nowdeh loess-palaeosol sequence, so grassland and shrub in profil1 (Bk horizon) and profile 2 (ABk horizon) palaeosols (with illite dominance) changes to forest in profile 2 (AB horizon with smectite dominance) and profile 3 (Btky horizon with smectite dominance and vermiculite presence) palaeosols. Agh Band section had one palaeosol including two horizons (Bw and Bk) which based on n-alkane specifications the Bw-horizon indicates grass/shrub vegetation (alsosmectite presence). It could indicate favorable environmental conditions promoting the growth of more dense vegetation.
Results showed that clay mineralogy changes are in line with n-alkane biomarkers results and both analyses reflect climate and environment conditions in soil formation periods and they are more effective for the accurate reconstruction of palaeoenviroment. According to chronological data for Nowdeh and Agh Band loess-palaeosol sequences, Nowdeh section had more suitable environment (more precipitation, more dense vegetation and suitable conditions for formation and development of soil, pedologically) compared with Agh Band section at the same times. Clay mineralogy and n-alkane biomarker resulted in the modern soil profiles and loess-palaeosol sequences showed that the modern ecological gradient (especially for precipitation) existed during the time and climate was an important soil formation factor in the studied region.

Soil moisture regime refers to the presence or absence either of ground water or of water held at a tension of less than 1500 kPa in the soil or in specific horizons during periods of the year. It is the most important factor in soil formation, soil evolution and fertility affecting on crop production and management. Also, it widely is practical in soil classification and soil mapping. The soil moisture regime depends on the soil properties, climatic and weather conditions, characteristics of natural plant formations and, in cultivated soils, is affected by the characteristics of crops grown, as well as the cultivation practices. Determination of soil moisture regime within a landscape scale requires high information and data about moisture balance of soil profile during some years according to Soil Survey Manual (2010). This approach is very expensive, labor, time and cost consuming. Therefore, achievement to an alternative approach is seems essential to overcome these problems. The main hypothesis of this study was to use capability of magnetic susceptibility as a cheap and rapid technique could determine the soil moisture regimes. Magnetic properties of soils reflect the impacts of soil mineral composition, particularly the quantity of ferrimagnetic minerals such as maghemite and magnetite. Magnetic susceptibility measurements can serve a variety of applications including the changes in soil forming processes and ecological services, understanding of lithological effects, insight of sedimentation processes and soil drainage.
This study was conducted in an area located between 36°46ó 10˝ and 37° 2’ 28˝ N latitudes, and 54° 29’ 31˝ and 55° 12’ 47˝ E longitudes in Golestan province, northern Iran. In the study region mean annual temperature varies from 12.4 to 19.4 °C. The average annual rainfall and evapotranspiration varies from 230 mm and 2335 mm in Inchebrun district (Aridic regime), to 732 mm and 846 mm in Touskstan uplands (Udic regime), respectively. this study was conducted in four soil moisture regimes (Aridic, Xeric, Udic and Aquic), for exploring the relationships between soil properties and magnetic measures. In each regimes, 25 soil profiles were drug, described and soil samples were collected from each of soil horizons. Soil samples were air-dried and sieved using a 2 mm sieve. The dithionite-citrate bicarbonate (DCB) method was used to measure Fed and acid ammonium oxalate for Feo. In this study, a set of environmental magnetic parameters including magnetic susceptibility at low frequency (χlf), saturation isothermal remnant magnetization (SIRM), isothermal remnant magnetization (IRM100 mT) were measured. Magnetic susceptibility (χ) was measured at low frequency (0.47 kHz; χlf) and high frequency (4.7 kHz; χhf) using a Bartington MS2 dual frequency sensor using approximately 20 g of soil held in a four-dram clear plastic vial (2.3 cm diameter). Frequency dependent susceptibility (χfd) was determined by the difference between the high and low frequency measurements as a percentage of χ at low frequency. IRM was measured at the field of 100 mT generated in a Molspin pulse magnetizer (IRM100mT) and at the back field of 100mT (IRM−100mT). The IRM acquired in the maximum field of 1000 mT was measured and defined as the saturation isothermal remnant magnetization (SIRM) of the soil sample.
The results showed that moisture regime induced significant differences for soil physical and chemical properties. Diversities in genetic soil horizons and soil development degree have been increased from Aridic to Udic soil moisture regime. The results also indicated that selected properties including magnetic measures and physical and chemical properties were significantly different in four soil moisture regimes. With increasing rainfall and reducing temperature from aridic to udic soil moisture regime, soil organic matter was increased. Otherwise, in arid environment Gypsic, Calcic and Salic horizons were observed in the near of soil surface. Fed and Fed-Feo were the highest in udic and the lowest in udic soil moisture regime, respectively. Moreover, higher soil development because of climate effect leaded to higher amount of pedogenic ferromagnetic minerals, as well as the highest were observed in the Udic regime. Otherwise, in Aquic moisture regime, the lowest value of magnetic susceptibility was obtained because of dissolution of ferromagnetic minerals (magnetite and maghemite) under supersaturating condition. In overall, close relationships were observed between soil physical and chemical properties and magnetic measures in various soil moisture regimes.

Fine-grained materials of Clayey Loess deposits of Gorgan region were mixed with sand dune in the lab with various rations and their shear behavior was measured and evaluated by direct shear test. The result of the study showed that the increase of fine-grained clay in sand dune was directly related to the adhesion force and inversely to the internal friction angle. The increase or reduction in shear strength was affected by the fine-grain percentage. Dry condition and saturation of the test and sand dune had a less influence on shear parameters but in the mixed samples in dry condition and saturation, shear parameters revealed a considerable difference. The results of this study can be used in sand stabilization, erosion prevention, slope stability, embankment construction, compaction increase, and environmental pollution, and dust and water channels avoidance.

To study the effects of land use change and climate on micromorphological properties and clay minerals distribution in loess derived soils of Golestan Province, 12 soil profiles in summit geomorphic position consisting of aridic, xeric and udic moisture regimes with cultivated, pasture and forest land uses were studied. The results showed that in aridic moisture regimes weakly developed Entisols, in the xeric soils moisture regime, Inceptisols, Mollisols were dominant, and in udic moisture regime, the most developed Hapludalfs were formed. Micromorphological studies revealed that there was a good positive correlation between soil development and climate index (evapotranspiration ratio). Environmental conditions such as land use and climate consequently affected micromorphological properties such as voids, microstructure, b- fabric, and pedofeatures. In the udic moisture regime, thick clay coatings were observed in speckled b- fabric matrix. However, in the soil with aridic moisture regimes, massive microstructure, and crystallitic b- fabric can be seen. Microscopic observations showed granular microstructure in forest surface horizons has been transformed to massive microstructure in cultivated land use. Results obtained from mineralogical studies showed that there were differences in type and distribution of clay minerals in different climate. Illite was found as the main clay mineral of loess parent materials and soils of the three land uses. The origin of illite, kaolinite and chlorite clay minerals are mainly inheritance while smectite and vermiculite are pedogenic. With increasing precipitation and weathering intensity from xeric zones toward udic zone, illite and chlorite have transformed to smectite and vermiculite. Amount of smectite and vermiculite are mainly affected by climate. It can be concluded that conversion of natural land resources into croplands causes serious soil degradation in loess derived soils in Golestan province.

Loess deposits of Kopeh Dagh area usually occur patchy، with low thickness and should be identified and differentiated from other deposits for environmental planning and landscape evolution studies. The objective of this study was to identify distribution and determine the characteristics of loess deposits and investigate their formation in the Sarakhs area. Thirty surface samples were collected from the study area and analyzed for particle size distribution. Coarse silt and very fine sand are the dominant fraction of the sediments and overally exceed 70%. Dominance of coarse silt and very fine sand، lack of coarse fragments and abrupt boundary of these sediments with underlying materials are evidences of eolian origin. With decreasing very fine sand and increasing coarse silt، sand dunes in the east and center of the area gradually change to loess deposits from Sarakhs city towards Dousti dam (along Hariroud River) and Kopeh Dag heights in the south and west. The maximum thickness of loess sediment occurred around the Dousti dam. Dominance of coarse silt and very fine sand in the sediments and gradual boundary between sand dunes and loess deposits shows the local source of the particles. Kopeh Dagh heights in southern and western parts of the area، like a barrier have trapped eolian sediments and caused their formation.

High ratios of erosion and sediment in eastern area of Golestan province have reduced soil fertility and dams capacity. Temporal variation of chemical soil quality indicators has to be studied for evaluation of soil degradation by erosion. Therefore, this study was conducted to evaluate soil and sediment quality indicators in different seasons in loess derived soils, in the Eastern area of Golestan province. Soil samples were taken from each season to analyse chemical properties in Gharnaveh and yelcheshmeh watersheds. Samplings of sediments were monthly for one year from the outlet of watershed basins mentioned as Tamer hydrometric station. The results showed the highest total nitrogen (0.16%) and soil organic matter (3.6%), were observed in autumn. The effect of season on soil phosphorus and potassium was significant (P>0.05), so the maximum amount of phosphorus (5 mg/kg) and available potassium (108 mg/kg) were observed in summer. About the status of nutrients in the sediment, this study showed that total nitrogen in the autumn, have a maximum amount and there was a significant difference between spring and autumn. The maximum amount of phosphorus (amount 4.9 ppm) was observed in winter. Most of the sediment organic matter and available potassium were observed in summer and spring. The results showed that there was a correlation between although maximum of nitrogen and potassium in soil and sediment, but in universal view, changes in soil nutrients and sediment, during different months of the year is not consistent.

In order to study land degradation from the soil genesis and micromorphological perspective، ten soil profiles were dug and described on five slope positions in both forest and deforested cultivated land. The soil samples were taken from all horizons for physico-chemical analysis and micromorphological studies. Forest soils had a well developed argillic and calcic horizons and also mollic epipedon. These soils were classified as Alfisols and Mollisols. Carbonate leaching into the depth of soil profile and translocation of clays to lower layers and formation of developed soils are by no means related closely with the dense forest cover and its subsequent landscape stability and favorable leaching conditions. Dominant soil orders in this area were Inceptisols and Mollisols. In cultivated landuse، no argillic horizon was observed except in toeslope position. Absence of argillic horizon or its elimination following deforestation is one of the most important and obvious pedogenetic evidences of land degradation after land use change. Outcropping of high carbonatic layers (calcic horizon)، disappearance of mollic and formation of ochric epipedon، presence of redoximorphic features attributed to runoff in lowland، decrease of solum thickness، and change of soil color were the other pedogenic indicators for land degradation in the study area. Microscopic observations showed that granular and crumb microstructures with high porosity were converted to massive and compact ones with low porosity in the deforested area. Disappearance of clay coatings besides absence of excremental pedofeatures were the other important micromorphological evidences of erosion and land degradation.

Magnetic susceptibility measurement is a simple and quick technique for characterizing soils and sediments and describing soil-forming processes. The interpretation of soil magnetic susceptibility data needs sufficient knowledge about the factors affecting this parameter. To identify the effects of parent material، gypsum and calcium carbonate equivalent، 42 samples were taken from horizons of soils developed on loessial، alluvial، granitic and marly materials in southern Mashhad. Gypsum and carbonates of soil samples were removed by successive washing with distilled water and diluted HCl، respectively. Magnetic susceptibility of bulk samples (lfbulk)، gypsum free samples (lfGf)، gypsum and carbonates free samples (lfGCf) and gypsum، carbonates and sand free samples (lfGCSf) was measured. The results revealed a strong 1:1 correlation between the measured and calculated lfGf and lfGCf. Despite the high amounts of gypsum and carbonates in soils developed on marls، their lfbulk was much more than that of the other soils and reached up to 121. 8×10-8m3 kg-1. In contrast، the lfbulk values of saprolitic granite were less than 10. 4×10-8m3 kg-1. The lfbulk values of loessial and alluvial soils were less than those of marly soils but higher than those of soils developed on saprolitic granite. lfbulk values were negatively correlated with the amount of sand. However، reduction in magnetic susceptibility values of marly soils after removing sand reflects the different nature of this soil. The correlation between lfbulk and amount of silt and clay is positive، but the magnetic susceptibility values are more sensitive to clay percentage، indicating the more important contribution of clay to magnetic susceptibility values. The results of this study highlight the role of parent materials، gypsum and carbonates in the soil magnetic susceptibility values that should be considered.

In this study, classical statistics and geostatistical methods were used to determine changes in spatial heterogeneity of soil organic carbon (SOC) in relation to topography and different slope positions in loess hillslopes in Toshan region located in Golestan Province. In this investigation, three different geostatistical methods i.e Kriging, Cokriging and Inverse distance weighted have been used and evaluated. Hence, 234 soil samples at regular grid were collected from different parts of a slope. In this research, the evaluation criteria were Mean Error and Root Mean Square Error with the Cross Validation method. The results showed that ordinary cokriging method with clay as covariate estimated better results in evaluation of SOC in whole parts of hillslope with RMSE values of 0.2552 in comparison with Kriging and Inverse distance weighted methods. Interpolation map of organic carbon from whole part of hillslope showed lower SOC concentrations with increasing elevation and slope gradient. Spatial correlation ratio of SOC was different in various slope positions and these patterns were closely related to the structure of topography.

To investigate the degree of forest degradation and the effect of land use change on selected soil quality attributes in loess-derived landforms, samples were taken from different land uses including forest, rangeland, degradated rangeland and farmland in Pasang watershed located in the Galikesh area of Golestan province (37°16'N, 55°30'E). The annual average temperature and mean precipitation of study area were 15°C and 730 mm respectively. Organic matter, pH, EC, CaCO3 and nutrients (N, P, K) as chemical indicators, hydraulic conductivity, bulk density and porosity as physical indicators and soil respiration as biological indicator were measured. The results showed that the amount of organic matter decreased three percent when it was turned from forest to farmland, and increased two percent from farmland to rangeland. The amount of CaCO3 in surface layer of deforested area was more than in the forest soils. The amount of soil N in forest and soil P and K in rangeland were higher than in other land uses. Bulk density and porosity in forest and MWD in rangeland were higher than in other land uses because of the decrease in organic matter due to farming activities. Soil respiration in forest was highest as compared to in other land uses. Difference of enzymes activities (L-asparaginase and Dehydrogenase) compared to microbial respiration indicates that enzymes activity is related to specific biological processes while soil microbial respiration basically depends on the general activity of soil microbial population. It could be concluded that amount of organic matter, soil N, bulk density, porosity, MWD, soil respiration and enzymes activities are suitable indicators for soil quality evaluation in this area.