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

Soil organic carbon (SOC) is one of the most important components of soils that affects other characteristics of soil. SOC is also influenced by other soil characteristics. Studies showed that change in land use from pasture and forest to agriculture decreased SOC. However, this is not always true and it depends on various factors, especially the methods of organic matter management in the farm. This study was conducted with the aims of investigating the effect of changes in land use from forest and pasture to agriculture on the level of SOC and determining direct and indirect effects of soil characteristics on SOC in a bio-sequence of Sistan plain.

The studied bio-sequence was located in Jezink region, by the Hirmand river in the northeast of the Sistan plain and in the southwest of the border of Iran and Afghanistan. In November 2016, a total of 25 soil samples (5 soil samples from each vegetation) was collected by supervised randomized manner from the depth of 0-20 cm of each of places that had dense vegetation of Populus euphratica and Tamarix ramosissima (the forest covers), of Desmostachiya bipinnata and Suaeda vermiculata (the pasture covers), and the crop of Triticum aestivum ( with 15 years old land use change). Then, 28 physical, chemical and biological characteristics of the soil including percentage of SOC were measured and calculated. Statistical analysis of data in the form of completely randomized design, comparison of average SOC data with the least significant difference test, Pearson correlation between the measured soil characteristics, and stepwise regression analysis to identify significant effective factors on the changes SOC was performed by Statistix10 software. Then by path analysis the direct and indirect effects of those characteristics on the amount of SOC was calculated by Path 2 software.

Changes in the population of phosphate-solubilizing bacteria 37%, phosphate-solubilizing fungi 44%, total phosphate-solubilizing microorganisms 39%, bacteria 51%, fungi 46%, total microorganisms 51%; and also the changes in the amounts of organic carbon 39%, clay 68%, silt 71%, sand 81%, electrical conductivity (EC) 37%, sodium 56%, potassium 81%, nitrogen 67%, calcium 56% and magnesium 37% were affected by vegetation covers. The highest SOC was measured in vegetation cover of P. euphratica with a value of 1.24%. P. euphratica had organic carbon 2.21, 1.69, 1.94 and 1.86 times more than that of T. aestivum, D. bipinnata, S. vermiculata and T. ramosissima respectively. However, there was no significant difference in organic matter between vegetation covers of T. aestivum, T. ramosissima, D. bipinnata and S. vermiculata. SOC had the strongest positive (r=0.63) and negative (r=-0.60) significant (P≤0.01) correlation coefficients with the population of phosphate-solubilizing fungi and the sodium concentration of the soil solution, respectively. Also, based on the results of stepwise regression analysis and path analysis, the population of phosphate-solubilizing fungi and cation exchange capacity (CEC) were, respectively, the most effective positive influencing factors. The population ratio of phosphate-solubilizing microorganisms on the total microorganisms, as well as soil EC, were respectively the most effective factors negatively influencing the percentage of SOC in the study area.

In general, the most sensitive land use to changes is P. euphratica forest. Therefore, in order to improve soil quality and increase carbon storage in arid and semi-arid regions, in addition to maintaining and developing P. euphratica forest cover, it is suggested that the management and improvement of soil characteristics include: the population of phosphate-solubilizing fungi, CEC, The population ratio of phosphate-solubilizing microorganisms and EC should also be considered.

The phenomenon of desertification occurs in a wide range of climates from arid and semi-arid to semi-humid regions and is caused by natural factors and improper human performance. The Yazdanabad watershed is an active center of desertification in Kerman province, Iran and has been subject to human activities and climatic changes, especially drought.The present research aims to study the desertification potential of the Yazdanabad watershed in Zarand, Kerman province using remote sensing data for a 20-year period from 2000 to 2020.Land use maps were first developed for 2000 and 2020. Then, the relationship between the soil-adjusted vegetation index (SAVI) and the Albedo climatic index derived from TM and OLI Landsat images was used.Finally, using this relationship, the desertification divided index (DDI) was employed to derive different desertification classes.The results show that over 88% of the Yazdanabad watershed has been composed of bare land, which has shrunk over the studied periodwhereas saline land use, agricultural land use, and residential and man-made areas have expanded by about 94.39, 830.91, and 1106.30 ha, respectively.The mean annual trend of both SAVI and Albedo revealed the descending trend of the former and the ascending trend of the latter.The DDI-derived desertification classes in 2000 and 2020 show that over 88% of this plain is in the very severe and severe desertification classes. This means that the plain is extremely vulnerable to land changes and degradation given its climatic conditions and fragile vegetation cover.

In this paper, the effects of bed vegetation density, inflow rate and slope on some hydraulic properties of flow was studied in a laboratory environment. For this purpose, a trapezoidal flume with 3m long was established and some hydraulic characteristics of flow such as water level, manning roughness coefficient, longitudinal velocity, deep velocity and bed shear stress were recorded in different flexible artificial bed cover densities (VD= 0,20%,30%,50%) inflow rate (Q= 5,10,15,20,25 lit/se) and slope (S=0, 0.5%,1%). Final results analysis showed that behavior of hydraulic parameters depends on the interaction between inflow rate and slope and vegetation density. Water level and manning roughness coefficient increased nonlinearly with increasing bed vegetation density at a constant inflow rate. Maximum water level and roughness coefficient were observed in S=0, VD=50%, Q=25, 5 lit/se respectively. Also, with increasing bed vegetation density at a constant inflow rate, deep velocity and shear stress decreased nonlinearly and longitudinal velocity decreased linearly. Minimum longitudinal velocity and shear stress were observed in S=0, VD=50%, Q=5, 25 lit/se respectively. Froude number decreased with increasing vegetation density at a constant inflow rate. Maximum Froude number was seen in VD=0, Q=25 lit/se.

The aim of this research was to study the importance of the neighborhood scale in modeling the relationship between vegetation cover and morphometric variables using the classification and regression trees algorithm (CART) in southwestern of Iran. For this purpose, the second Modified Soil-Adjusted Vegetation Index (MSAVI2) was calculated from a Landsat 8 image, and eight morphometric variables were derived using the Wood method in four neighborhood scales (90×90, 150×150, 210×210, and 270×270 m) from a 30 m SRTM digital elevation model. The results of the Kruskal-Wallis test confirmed that in some sub-watersheds, neighborhood-scale change can have a significant effect on slope gradient, profile curvature, specific catchment area, LS factor, and topographic wetness index. The results showed that in each sub-watershed different morphometric variables are most related to the spatial distribution of the MSAVI2 index and the value of the Spearman correlation coefficient between them is slightly affected by the neighborhood scale. CART models based on the MSAVI2 index and 270×270 m morphometric variables with a kappa coefficient of 0.55 and 0.78, respectively, had the best performance in classifying vegetation types. The elevation smoothed, which is the least affected by the neighborhood scale, was recognized as the most important predictor in the CART model. However upscaling led to the increasing importance of other morphometric variables, especially slope gradient, in classifying vegetation types and finally improving the accuracy of the CART model. Overall, the present results indicate that the application of multi-scale geomorphometric analysis with respect to the geomorphology of the study area can improve the performance of prediction models related to vegetation cover to an appropriate extent.

Runoff is an important factor influencing soil erosion in slope lands. This study was carried out to investigate runoff production as affected by slope gradient and soil properties in pastures without vegetation cover in Zanjan province during 2017-2018. Nine pastures with slope gradients of 6, 8, 12, 15, 17, 24, 27, 31 and 36% were considered and three plots with 1.0 m× 1.5 m in dimensions were installed in each slope on early autumn 2017. Runoff production was measured in twenty seven plots for a one-year period. The steep slopes have coarse soil textures, low organic matter and low lime content as compared to gentle slopes. Out of thirty two rainfalls, five events caused runoff at the plots. There was no positive trend between runoff production and rainfall intensity, indicating the role of soil conditions such as initial water content in controlling runoff at the plots. Significant difference was found among rainfall events in runoff production. Lower runoff production potential in the lands was associated with lower rainfall intensities and higher soil infiltration rate. Runoff production was significantly affected both slope gradient (r= 0.51, p< 0.01), organic matter (r= -0.69, p< 0.01), and lime content (r= -0.59, p< 0.01). This study indicates the role of soil properties and slope gradient in runoff production in the pastures. Therefore, maintaining vegetation cover can increase water retention and improve organic matter content, resulting in a decrease in runoff production.

Rangelands, as one of the most important natural ecosystems, play a prominent role in the production, support, refinement, regulation, and culture of water. In other words, the social life of water is related to the rangelands. This article explores the relationship between rangelands and water, examines their two-way action, and deals with supporting and habitat, provisioning, regulating, and cultural and information dimensions of rangelands in the field of water. Rangelands determine various water-related capabilities due to the creation of an integrated socio-ecological system. Finally, to deal with water shortages, restoration and preservation of rangelands should be one of the basic activities of today's society. Just as water is the savior of rangelands, these ecosystems are the savior and refuge of water. Therefore, sustainability in the water supply is related to the biosustainability of rangelands.

Rainfed lands located on slopes are subjected to higher water erosion types, particularly rill erosion. Rill erosion rate can be varied in various growth stages. This study was carried out to find the effect of wheat straw on soil loss resulting from rill erosion in wheat growth stages. A field experiment was done in rainfed wheat land with 10% slope and seven wheat straw levels (0, 25, 50, 75, 100, 125 and 150% of ground cover), using the randomized complete block design with three replications. The land was plowed down slope and various straw amounts were separately incorporated into the soil. A 0.5 kg wheat straw per square meter was used in the 100% straw level. Three rills/furrows with 20-cm width and 10-m length were installed by the the planter machine similare to cultivation furrows for each straw level and rill erosion measurements were done using a discharge flow of 2 L.min-1 at five growth stages (planting, emergence, tillering, stem elongation, grain filling ). Based on the results, soil loss by rill erosion was significantly affected by straw amount (P< 0.05). Soil loss by rill erosion in 100% straw level was the lowest amount at all wheat growth stages and was about 79% [H1] lower than that in the control treatment. There was no significant difference between this treatment and higher straw levels (150% and 125% ground cover) in rill erosion. The emergence stage in each straw level, which was associated with poor vegetation cover and higher soil water content in this period, was the most susceptible stage in the rill erosion among all growing stages. In this stage, application of 100% wheat straw equal to 5 ton per hectare could decrease rill erosion by 71% (0.009 g m-2 equal to 0.34 ton per hectare for each 1-h rainfall event) in the cultivated furrows.

Surface energy balance algorithm for land (SEBAL) is one of the actual evapotranspiration predictor algorithms which are based on remote sensing. To determine outgoing long wave radiation from land surface in this algorithm, an index named soil adjusted vegetation index (SAVI) is used. In calculating SAVI, an equation consists an empirical coefficient (L) calibrated based on Idaho satellite images, USA, is used. In this study using MODIS satellite images of neyshabour watershed during 2009 to 2013, the mentioned coefficient was calibrated. The results showed the proposed value nearly L=0.5 for all areas may not evaluate adequately and it is better to calibrate this coefficient before using in SEBAL algorithm in each area. The results showed the trend of SAVI changes and thus determine the optimum value of L coefficient is sensitive to the time of satellite images and it is better to use the months with appropriate vegetation cover on the land surface. The results also showed the values of SAVI index are more sensitive to lower values of L coefficient. Results’ analysis showed the proposed value of 0.2 for L coefficient application in studies related to SEBAL algorithm in this area is properly assessed.

Tamarix sricta plant grows in riversides of Karun river. Outer body plant in the flood times causes decrease in water velocity, preventing erosion. One of the factors by which the hydraulic resistance is expressed is the roughness coefficient. Measurement of roughness coefficient of the existing plants in these riversides and floodplains, and surveying their effects on the velocity decrease and shear stress of the flow are important. The present research studies roughness coefficient of the plants manning existing in the riverside. Tamaix sricta was studied in non-submerged and sub-critical conditions in a flume with the length of 12.6 m, width of 0.5 m and height of 0.6 m in different velocity, discharge and depth ranges. The height of plants in this study was 35 cm with a natural arrangement in a bench of 2.8 m in length put in the bed of the flume. The total number of the experiments is 22. The results of this study show that roughness coefficients of plants are functions of velocity, depth, hydraulic radius and type of plants. Roughness coefficients in non-submerge condition change nonlinearly with changes in velocity, depth, Reynolds number, submerge depth and (VR) in natural conditions.