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Overlapping compatibility of desert soil with other features of Semnan Province (climatology, geology, geomorphology, plant-cover).

Study region:

The study region encompasses the entire Semnan Province situated on the southern edge of the Alborz mountain range with latitude from 34[degrees]17 to 37[degrees]30' north, longitude from 51[degrees]58' to 57[degrees]58' east, covering an area of about 98000 [km..sup.2].

MATERIALS AND METHODS

Comprehensive studies were conducted at 1:250000 scale on geology, climate, hydrology, geomorphology, plant-cover, and soils, all information sources were reviewed from the perspective of deserts, and maps were drawn separating desert regions from non-desert areas of the province in each of these six studies. ILWIS software was used and the obtained information layers were combined and compared with soil studies to determine the overlapping compatibility for each of the studied layers and, finally, the map of the desert regions in the province was drawn.

Features of the study region:

Climate:

The two important features of the Alborz mountain heights on the north and the salt lands of the Dasht-e Kavir on the south encircle the geographical expanse in the study region and influence its climatic features. This climate in the study region is influenced by a dry climate that is of greater expanse compared to the other climatic areas of the province because it lies in the Latitudinal Desert Belts of the world and in the southern part of Alborz Mountains where there is a subsidence of air masses. However, what cannot be imagined at all at first is the climatic diversity, and the resulting ecological diversity, of the region that changes from the cold and temperate mountain climate in the north to the extra-dry climate in the south. Temperature decreases and precipitation increases with altitude, and relative humidity and number of frost days also decrease from the north to the south of the region. Precipitation distribution in the study region is very unbalanced during the year, with most precipitation falling during the cold seasons (autumn and winter) and warm seasons, especially summer, having very little precipitation.

The desert areas from a climate perspective:

Using the prepared map for each climate element, and considering the nearest line to the intersection of the plains and the mountains, the numerical value of each climate parameter was determined and only one curve with the features in mind was selected for each of these parameters.

The final survey map shows 7021700 hectares (71.65%) of the study region consist of deserts and remaining 2778330 hectares (28.35%) of non-desert areas. Figure 1 presents the map of the deserts from a climate perspective.

The desert areas from a geological perspective:

Based on the conducted study, evaporate formations (most of which are located in the southern parts of the study region and in the Haj Aligholi Kavir and in the Dasht-e Kavir) were determined as the area of primary deserts, and the Quaternary formations salinized by the evaporate formations as the secondary deserts.

Based on the mentioned maps, 3993408 hectares of the study region consist of primary deserts and the remaining 349482 hectares of secondary ones.

In all, 4342898 hectares (44.3%) of the entire study region are geological deserts. Figures 2 and 3 show the geological map and the desert areas of the study region from the geological perspective, respectively.

The desert areas from a soil science perspective:

Based on definitions offered of deserts and desert environments, the most important factors influencing biological growth and ecological conditions are soil salinity, soil depth, alkaline soils, soil texture, organic matter, evolution, claypans, soil crusting, groundwater level, and gypsum. Considering the mentioned factors and the prepared map, 4100216.04 hectares (41.76%) of the study region (most of which are situated in the southern margin of the study region) are considered as lands with desert soils. Figures 4 and 5 show the maps of land units and desert areas of the study region from a soil science perspective.

Desert-specific geomorphological forms in the study region:

Based on the conducted studies, the desert-specific geomorphological facies such as plain head, gibber plain (Reg or Hamada), sand dunes, salt lake and marshes, wetland, and wilderness are identified (figure 6). Based on this, the wilderness and salt lake facies with 2586320 and the gibber plain facies with 34343 hectares have the largest and smallest areas in the study region, respectively.

The desert areas from a plant-cover perspective:

The deserts in the study region cover an area of 2740857 hectares from a plant-cover perspective, which account for 71.2% of the total pastureland in the province and 28% of the entire study region. The most widely desert plant type is Artemisia Zygophyllum with 1571050 hectares (16%). Figures 7 and 8 show the maps of plant-cover and the study region from a perspective of plant cover.

RESULTS AND DISCUSSION

Study of geological, geomorphological, soil, climate, and plant-cover factors reveals that the minimum desert areas with 2740857 hectares are related to the plant-cover factor and the maximum of 7036936.9 hectares to the climate factor (Table 1).

Combination of the maps of the desert areas from the perspectives of the studied factors shows that, in all, 7110925 hectares (72.5%) of the study region are located in desert areas.

The common areas of the five studied factors were used to determine the areas with greater desert characteristics and to delineate the areas covered by true deserts. Results related to five-way overlap of the studied desert layers indicate their common areas amount to 0.7%.

The extent of the common areas of the five factors in the study region was used to determine the contribution of each of these five elements to the desertification of the region. The following table shows the extent of the non-common area each factor has with the other four factors (the part related to each factor that is not in common with those of the other four). The non-common area of each factor indicates the extent of its dependence to all other factors. In this study, the geological and the plant-cover factors with 98245.73 and 7240091.97 hectares, respectively, had the most and the least areas in common with the other factors.

The largest non-common area percentage of 81.03% was that of the plant-cover factor, and the smallest that of geological factor with 1.1%. In other words, 18.97% of the area related to the plant-cover factor and 98.90% of the area related to the geological factor are common with the areas related to the other factors. Since any factor with greater area in common with other factors is quantitatively more involved in the desertification of the study region (Table 2), the geological, soil, climate, geomorphological, and plant-cover factors are most effective, in the order they are listed, in the appearance of desert conditions and features in the study region.

Results obtained from the combination of the factors related to desertification in the study region show they all enjoy unequal distribution. Therefore, the hypothesis of the study that each of the studied factor plays a different role in delineation of the desert areas and has an unequal overlap with the other factors, and that each factor reveals its importance according to the extent of its overlap with the other factors (or joint participation with the other factors) is accepted.

Results:

Results obtained in the study indicate there are 4234729.83, 8946718, 7021700, 2740857, and 4100216.04 hectares of deserts in the study region, from the perspectives of geology, geomorphology, climate, plant-cover, and soil science, respectively. Combination of the desert maps from the perspectives of the studied factors shows 7110925 hectares (72.5%) of the study region are located in desert areas. Desert areas refer to different expanses in different perspectives. Therefore, overlap of the desert maps and delineation of their common areas were used to specify the true desert areas (which were found to be 3858575 hectares, or 39.37%, of the study region) (Figure 9). Parts of the southeast and southwest of Garmsar, south of Semnan, central and southern parts of Damghan, and south and some other parts of Shahrood constitute the true desert areas in the study region. Factors effective in the appearance of desert features in the study region (Semnan province) are, in the order of their importance, the geological, geomorphological, climate, soil, and plant-cover factors.

ARTICLE INFO

Article history:

Received 25 September 2014

Received in revised form 26 October 2014

Accepted 25 November 2014

Available online 29 December 2014

REFERENCES

[1] Ahmadi, Hassan, 1995. Applied Geomorphology, Tehran University Publications.

[2] Arastoo, Behrooz, 1993. Climatological Report on the Comprehensive Urban Development Plan for Semnan.

[3] Eftekharnezhad, G., 1990. Separating Different Parts in Iran with Respect to Structure of Sedimentary Basins, Iranian Petroleum Institute, 82: 19-28.

[4] Bybordi, Mohammad, 1989. Soils, Formation and Classification, Tehran University Publications.

[5] Jean Tricard, "Rugged, and Arid", 1991. Translated by Mehdi Sadighi and Mohsen Pourkermani, Astan-e Ghods Publications.

[6] Servati, Mohammad Reza, 1992. Geomorphology of Desert Plains, proceedings of the second national conference on desert and wilderness issues in Iran, Tehran University.

[7] Darvishzadeh, Ali, 1992. Geological Conditions Involved in the Creation of Deserts and Wilderness in Iran, proceedings of the seminar on issues in desert and arid regions of Iran, Tehran University.

[8] Ghodrati, Mansoor, 1996. Study and Evaluation of Drainage Basins to Determine the Identities of the Watersheds in Semnan Province, the Natural Resources Research Center of Semnan Province.

[9] The Iranian Research Center for Desert and Arid Regions, 1992. Study of Desert and Wilderness Issues in Iran, proceedings of the seminar on issues in desert and arid regions of Iran, Yazd, volumes 1 and 2.

[10] Nabavi, Mohammad, 1976. "Introduction to Geology of Iran ", the Geological Survey of Iran.

Mansoor Ghodrati

Faculty Members, Agriculture and Natural Resources Research Center of Semnan Province.

Corresponding Author: Mansoor Ghodrati, Faculty Members, Agriculture and Natural Resources Research Center of Semnan Province.

Table 1: Areas affected by desert factors in the study region.

Desert factors          Geological    Geomorphological
                          factors         factors

Area (hectares)           4342898        6618667.7
Ratio of the area to       44.3            67.41
the total area of
the province (%)

Desert factors          Climate factors   Plant-cover     Soil

Area (hectares)            7036936.9        2740857     4100216.4
Ratio of the area to         71.67            28          41.76
the total area of
the province (%)

Table 2: The extent of non-common area of each studied factor with the
other factors.

Uncommon factor    Non-common area of
                  the factor (hectares)

Geology                 98245.73
Geomorphology          4924288.77
Climate                2776775.29
Soil                    321456.94
Plant-cover            7240091.97

Uncommon factor    Ratio of the non-common area of
                  the factor to its entire area (%)

Geology                         2.32
Geomorphology                   74.4
Climate                         39.46
Soil                            7.84
Plant-cover                     90.7

Uncommon factor     Ratio of the non-common area of the factor to
                  the total areas related to all of the factors (%)

Geology                                  1.1
Geomorphology                           55.11
Climate                                 31.08
Soil                                     3.6
Plant-cover                             81.03
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Article Details
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Author:Ghodrati, Mansoor
Publication:Advances in Environmental Biology
Article Type:Report
Geographic Code:7IRAN
Date:Nov 1, 2014
Words:1803
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