نشریه مهندسی اکوسیستم بیابان
پیاپی 14 (بهار 1396)

This study investigated the variation in the pigment, proline, soluble sugar and ion content of three populations of Haloxylon ammodendron in Yazd province. This was carried out using one-year old plants of the same size from each population. Sampling occurred in a factorial experiment conducted using a randomized complete design with five replicates. The results showed that chlorophyll a and total chlorophyll in the green population were significantly greater than in the other populations. The highest and lowest amounts of chlorophyll a were 3.27 and 0.10 mgg-1fw for the green and pink populations, respectively. In contrast to chlorophyll a, the amount of carotenoid in the red population was significantly greater than in the green population at over three times the green value. The amounts of anthocyanin, phenoles and flavonoids in the pink population were significantly greater than in the other populations. The amount of soluble sugar in the pink and red populations were significantly greater than in the green one. It appears that the high amounts of the pigment in the red and pink populations increases their antioxidant abilities.

Pistachio trees (Pistacia) play combined roles in ecotourism, conservation of soil and water, flood control, forage production for domestic and wild animals and resin and seed production in arid and semi-arid areas. It is very important to protect this species but, in recent decades, several factors have caused damaged to these trees. One of the most important factors of Pistacia forest destruction is the stripping of bark from the trunks by Hystrix indica. Knowing the factors affecting the intensity of damage caused by this pest is necessary for providing proper and scientific solutions. The purpose of this study was to identifiy the most effective and important factors on damage to Pistacia bark and the role of Hystrix indica in the extinction of this species in arid and semi-arid areas. After investigating a critical Pistacia forest in which tree bark has been stripped by Hystrix indica, a 200 ha area of the Pistacia forest was selected in Chahar Gonbad of Sirjan. In this segment, 50 Pistacia trees were randomly selected and damage was evaluated. The least significant difference test was used to measure variation in the results. The results showed that the effect of the age of the trees on the stripping of the bark was significant at the 1% level. The destruction of young trees was 2.5-fold greater than on older trees.

The effects of vegetation on wind erosion, especially in arid areas, are known, but few studies have assessed the quantitative impact of plant species. The aim of this study was to investigate the effects of plant species on wind erosion and deposits. Three experimental sites were selected in Sebri, Iran. Two sites contained two plant species, Launaea spinosa and Lactuca serriola of different sizes and the third was a control site. During a field survey in the summer of 2015, erosion pins were installed around the species that were read at 21-day intervals. The Tukey test was applied to the data sets gathered at the three sites as well as at different areas around the species. To investigate the spatial variability of the wind erosion map and the role of vegetation, the data was interpolated by the ordinary kriging. The results showed that the size, shape and height of the plant affects wind erosion. The estimated effective distances were 2.8 and 3.4 times the plant heights for L. spinosa and L. serriola, respectively. The amount of erosion on two sides of the species were estimated to be 0.74 and 1 times the width and 0.31 and 0.45 times the length of these species, respectively.

Desertification is the result of a series of important processes. Among them, climate change and human activity are the most important. Arid and semi-arid regions cover a vast area of Iran (85%). The hazard assessment of desertification and preparation of desertification intensity maps are key tools for management of desert regions. This research assessed the efficiency of the MICD model for hazard assessment of desertification in the study area of Kaji pond, located in the Nehbandan region of South Khorasan province. The results of baseline studies conducted in the area were used to prepare a map of the smallest desert homogenous units and then score and assess the hazard of desertification in each unit. The results showed that desertification hazard in the study area fell into five classes: slow (I), low (II), medium (III), high (IV) and severe (V). The severe class covered the largest part of the area under study (54.1%) and the low class (II) covered the smallest area (3%). The highest score was assigned to active sand dunes with a value of 25 in the severe class (V). The lowest score was assigned to rocky protrusions and desert lakes with a value of 3 in the low class (II).

Soil erosion by wind is a widespread problem in the arid lands of Iran. This research estimated and assessed the severity of wind erosion in Segzi desertification hotspot located in the eastern part of Isfahan township, focusing on criteria used in the IRIRF (Iranian Research Institute of Forest and Rangelands) model. Bayesian belief networks (BBNs) were also used to convert the IRIFR model to a predictive cause-and-effect model. The severity of wind erosion was calculated using the nine indicators of the IRIFR model on 17 geomorphological faces. The results indicated that three geomorphological faces located in the southern and central parts of the region had high potential for wind erosion. According to the results of the IRIFR model, 24%, 16%, 15% and 45% of the study area were classified as low, moderate, high and very high severity of wind erosion, respectively. Using the IRIFR indicators and conditional probability tables of these indicators, a BBN model was developed and its accuracy was assessed by sensitivity analysis and scenario analysis. Sensitivity analysis for both models showed that wind speed and condition, spatial extent and type of aeolian deposits and erosion features of the soil surface were the most important indicators responsible for wind erosion in the study area. The determination coefficient between the outputs of the IRIFR and BBN models (R2 > 0.80) indicated that the results of both models were significantly correlated (α = 5%). These results indicate that the application of the BBN model for wind erosion assessment can appropriately accommodate the uncertainty of the IRIFR model and help managers to make better decisions for upcoming land management projects.

The issue of protection of groundwater against pollution is of crucial significance. Groundwater vulnerability maps provide useful information to protect groundwater resources and evaluate the potential for water quality improvement with changes in agricultural practices and land use applications. In Yazd province, especially in Abarkooh, the majority of agricultural and drinking water is provided by groundwater; thus, the prevention of pollution and quality consistency is very important. The intrinsic vulnerability of the Abarkooh aquifer to contamination was assessed using the well-known SI, SINTACS, GODS, AVI and DRASTIC methods. The data from these models was first collected and entered into the software of a geographic information system (GIS) to provide the required layers. The use of overlapping techniques and weight coefficients for each layer provided the final plain of vulnerability. In the next step, the accuracy of the models was evaluated by fitting a regression line between the observations and estimated values in the sampling wells. The results showed that there was no significant relation between the NO3 values and pollution potential as shown by GODS, but there was a significant relation at the 1% level (R = 0.81) between these values in DRASTIC. This model is introduced as suitable for classifying of the pollution potential in the study area. The aquifer of Barkooh plain was divided to three vulnerability classes based on the DRASTIC model. The vulnerability classes from this model showed that most of the plain is without risk and has very low vulnerability.

Habitat heterogeneity plays an important role in increasing species diversity. Heterogeneity of habitats and protected areas can increase the ability of species to adapt to climate change. It is expected that appropriate heterogeneity is necessary for sustainability of protected areas. The influence of altitude on parameters such as temperature and precipitation and the role of microclimates in determining the flora and fauna suggest that elevational heterogeneity can be used as a Criteria for selecting more heterogeneous, resilient and diverse protected areas. This is especially important in the central desert regions of Iran because of the size and variation in elevation of these regions. The present research was undertaken to evaluate the status of Isfahan province’s protected areas in terms of topographic diversity. For this purpose, a digital elevation model map of Isfahan province was divided into 39 classes and the elevational diversity of Isfahan’s protected areas was compared using the Shannon diversity index. Next, the conservation status of the province in terms of elevational diversity was evaluated using a conservation index. The results indicate that 16.9% of the area is dedicated to protected areas and the province’s elevational conservation status is suitable according to its conservation index value (0.69). The Ghamsar and Barzok protected areas with an elevational diversity of 2.842 and Kolahghazi National Park with an elevational diversity of 1.720 have the highest and the lowest elevational diversity, respectively. Analysis of land use in the region showed that the conservation index of the 1400-2600 m elevation zone, which includes over 80% of the urban and industrial development of the province, is weak. These results indicate the need for creation of new protected areas in low-lying areas and in regions with a high rate of human activity.

Groundwater is a major source of water for agriculture in Sheshdeh and Gharebolagh plain. In recent years increasing drought and excessive exploitation of these resources has increased the pressure on groundwater. The aim of this study was to investigate the relationship between meteorological and hydrogeological drought using the SPI and GRI indices. Eight rain gauges stations were used to calculate the SPI index. The GRI index was calculated using 14 piezometric water table wells over a common 21-year period (1993-2014). A unit hydrograph of the study area shows that groundwater levels dropped continuously. The annual average drop was 1.76 m. Pearson correlation analysis between meteorological and hydrogeological drought with a coefficient of determination of 49% and a confidence level of 1% indicates that meteorological drought has a time delay of 24 to 48 months on groundwater resources. The results of zoning for hydrogeological drought showed that the initial condition was extended wet, but from 2007 to 2008, the extremely wet periods had decreased and the aquifer was status was normal. From 2008 – 2009 to end of the period, the severity of drought (average drought) increased until 2011 to 2014, when drought extended to most of the aquifer area. In such a critical situation, it is necessary to maintain the level of the aquifer.

Drought is one of the most costly natural hazards and is more dangerous in arid and semiarid regions which suffer from limited water resources. Climate change can also affect drought intensity; therefore, it is essential to analyze the trends of drought, particularly in these regions. This study surveyed the trends of meteorological and agricultural drought in hyper-arid, arid and semiarid regions of the world using the standardized precipitation index (SPI). Short time scales of 1-, 3- and 6-month SPI (moderate to severe and extreme drought) were derived for the period of 1970 to 2014 from the gridded precipitation data provided by CRU. The trends of the time series were computed using the Mann-Kendall nonparametric statistical test. The results showed that non-significant trends were dominant; however, some territories showed significant upward and downward SPI trends in different parts of the study regions. The significant negative SPI trends, which imply increased drought, were observed in the Middle East, central Australia and western North America. An increase in drought severity can increase consumption of water resources, particularly in developing countries.