ﻣﻘﺎﯾﺴﮥ آﺳﺘﺎﻧﮥ ﺗﻮﭘﻮﮔﺮاﻓﯽ ﻓﺮﺳﺎﯾﺶ ﺧﻨﺪﻗﯽ در ﮐﺎرﺑﺮيﻫﺎي ﮐﺸﺎورزي، ﻣﺮﺗﻊ ﻣﺘﻮﺳﻂ و ﻣﺮﺗﻊ ﻓﻘﯿﺮ در ﻣﻨﻄﻘﮥ ﻗﺼﺮﺷﯿﺮﯾﻦ

Comparing the topographic thresholds of gully erosion in the agriculture, fair and weak rangelands in the Ghasreshirin, Iran

ﻓﺮﺳﺎﯾﺶ ﺧﻨﺪﻗﯽ، ﻧﻘﺶ ﻗﺎﺑﻞ ﺗﻮﺟﻬﯽ در ﺗﺨﺮﯾﺐ ﺳﺮزﻣﯿﻦ ﺑﻪوﯾﮋه در ﻣﻨﺎﻃﻖ ﻧﯿﻤﻪﺧﺸﮏ دارد. از ﺳﻮﯾﯽ آﺳﺘﺎﻧﻪﻫﺎي ﺗﻮﭘﻮﮔﺮاﻓﯽ ﻓﺮﺳﺎﯾﺶ ﺧﻨﺪﻗﯽ، ﺷﺪﯾﺪاً ﻣﺘﺄﺛﺮ از ﺗﻐﯿﯿﺮ ﮐﺎرﺑﺮي اراﺿﯽ و ﺗﺨﺮﯾﺐ ﭘﻮﺷﺶ ﮔﯿﺎﻫﯽ اﺳﺖ. ﻫﺪف از اﯾﻦ ﺗﺤﻘﯿﻖ، ﻣﻘﺎﯾﺴﮥ آﺳﺘﺎﻧﻪﻫﺎي ﺗﻮﭘﻮﮔﺮاﻓﯽ ﻓﺮﺳﺎﯾﺶ ﺧﻨﺪﻗﯽ در ﺳﻪ ﮐﺎرﺑﺮي ﮐﺸﺎورزي، ﻣﺮﺗﻊ ﻣﺘﻮﺳﻂ و ﻣﺮﺗﻊ ﻓﻘﯿﺮ در ﻣﻨﻄﻘﮥ ﻗﺼﺮﺷﯿﺮﯾﻦ اﺳﺘﺎن ﮐﺮﻣﺎﻧﺸﺎه ﺑﻮد. روش ﺗﺤﻘﯿﻖ، ﺑﺮ اﺳﺎس اﻧﺪازهﮔﯿﺮي وﯾﮋﮔﯽﻫﺎي ﻣﻬﻢ ﺗﻮﭘﻮﮔﺮاﻓﯽ و ارزﯾﺎﺑﯽ راﺑﻄﮥ ﺷﯿﺐ- ﻣﺴﺎﺣﺖ و ﻧﯿﺰ اﻧﺪازهﮔﯿﺮي ﭘﻮﺷﺶ ﺳﻄﺢ زﻣﯿﻦ ﺑﻮد. ﻧﺘﺎﯾﺞ اﯾﻦ ﺗﺤﻘﯿﻖ ﻧﺸﺎن داد ﮐﻪ ﻋﺮض ﮐﻒ، ﻋﺮض ﺑﺎﻻﯾﯽ، ﻋﻤﻖ و ﻃﻮل ﺷﺎﺧﮥ ﻓﺮﻋﯽ ﺧﻨﺪقﻫﺎ در ﻣﺮﺗﻊ ﻣﺘﻮﺳﻂ، ﺑﻪﻃﻮر ﻣﻌﻨﯽداري ﮐﻤﺘﺮ از ﮐﺎرﺑﺮيﻫﺎي ﻣﺮﺗﻊ ﻓﻘﯿﺮ و ﮐﺸﺎورزي ﺑﻮد. ﻫﻤﭽﻨﯿﻦ ارزﯾﺎﺑﯽ آﺳﺘﺎﻧﮥ ﺗﻮﭘﻮﮔﺮاﻓﯽ ﺑﺮ اﺳﺎس راﺑﻄﮥ ﺷﯿﺐ- ﻣﺴﺎﺣﺖ ﺑﺎﻻدﺳﺖ ﺧﻨﺪق ﻧﺸﺎن داد ﮐﻪ آﺳﺘﺎﻧﮥ ﻣﺴﺎﺣﺖ ﺣﻮﺿﮥ ﺑﺎﻻدﺳﺖ ﺑﺮاي ﺗﺸﮑﯿﻞ ﺧﻨﺪق در ﮐﺎرﺑﺮي ﮐﺸﺎورزي، ﻣﺮﺗﻊ ﻣﺘﻮﺳﻂ و ﻓﻘﯿﺮ ﺑﻪ ﺗﺮﺗﯿﺐ 1689 ،1300 و 1233 ﻣﺘﺮ ﻣﺮﺑﻊ ﺑﻮد ﮐﻪ در ﻣﺮﺗﻊ ﻣﺘﻮﺳﻂ، ﺑﻪﻃﻮر ﻣﻌﻨﯽداري ﺑﻪ دﻟﯿﻞ ﭘﻮﺷﺶ ﮔﯿﺎﻫﯽ ﺑﯿﺸﺘﺮ ﺑﻮد. آﺳﺘﺎﻧﮥ ﺷﯿﺐ ﺷﺮوع ﻓﺮﺳﺎﯾﺶ ﺧﻨﺪﻗﯽ ﻣﻨﻄﻘﮥ ﻣﻮرد ﻣﻄﺎﻟﻌﻪ در ﮐﺎرﺑﺮيﻫﺎي ﮐﺸﺎورزي، ﻣﺮﺗﻊ )ﻓﻘﯿﺮ و ﻣﺘﻮﺳﻂ( ﺑﻪ ﺗﺮﺗﯿﺐ ﯾﮏ، ﺳﻪ و ﺳﻪ درﺻﺪ ﺑﻪدﺳﺖ آﻣﺪ. ﺳﻄﺢ اﺷﻐﺎل ﺷﺪه ﺗﻮﺳﻂ ﺧﻨﺪق در ﮐﺎرﺑﺮيﻫﺎي ﮐﺸﺎورزي، ﻣﺮﺗﻊ ﻣﺘﻮﺳﻂ و ﻣﺮﺗﻊ ﻓﻘﯿﺮ ﺑﻪﺗﺮﺗﯿﺐ 14/1 ،12/4 و 21/6 درﺻﺪ ﺑﻮد. ﺣﺠﻢ ﺧﻨﺪقﻫﺎ در ﮐﺎرﺑﺮيﻫﺎي ﻣﺮﺗﻊ ﻣﺘﻮﺳﻂ، ﺑﻪﺗﺮﺗﯿﺐ 3/4 و 2/2 ﺑﺮاﺑﺮ ﮐﻤﺘﺮ از ﮐﺎرﺑﺮيﻫﺎي ﮐﺸﺎورزي و ﻣﺮﺗﻊ ﻓﻘﯿﺮ ﺑﻮد. ﺑﻨﺎﺑﺮاﯾﻦ ﺑﺎ ﺗﺨﺮﯾﺐ ﻣﺮاﺗﻊ، ﺑﻪوﯾﮋه ﺗﺨﺮﯾﺐ ﭘﻮﺷﺶ ﮔﯿﺎﻫﯽ آن آﺳﺘﺎﻧﻪﻫﺎي ﺗﻮﭘﻮﮔﺮاﻓﯽ ﺑﻪﻃﻮر ﻣﻌﻨﯽداري ﮐﺎﻫﺶ ﯾﺎﻓﺘﻪ ﮐﻪ ﮐﺎﻫﺶ ﮐﯿﻔﯿﺖ ﺧﺎك، ﺗﺸﺪﯾﺪ ﻓﺮﺳﺎﯾﺶ و ﭘﯿﺎﻣﺪﻫﺎي زﯾﺴﺖﻣﺤﯿﻄﯽ آن، از ﺟﻤﻠﻪ اﻧﺘﺸﺎر ﮐﺮﺑﻦ آﻟﯽ ﺧﺎك ﻗﺎﺑﻞ ﻣﻼﺣﻈﻪ اﺳﺖ.

Gully erosion affects land degradation, particularly in the semiarid reigns. Topographic thresholds are strongly affected by landuse change and destroy of vegetation. The objective of this study was to evaluate topographic thresholds of gully erosion in different landuse including agriculture (AG), fair rangeland (FR) and weak rangeland (WR) which carried out in Ghasreshirin, Kermanshah, Iran. The topographical parameters were measured in the field and relationship between gully catchment area and slope was analyzed for each landuse. The results revealed that some main topographic characteristics mainly cross-section, width, depth and gully branches length in the FR was significantly lower than in the AG and WR (p<0.05). Furthermore, analysis of gully threshold based on catchment area-slope showed that the critical area for gully formation in AG, FR and WR was 1300, 1689 and 1233 m2, respectively which was significantly lower in FR reducing by vegetation cover. The respective slope threshed was 1, 3 and 3 percent in AG, FR and WR. However, the affected area by gully erosion in AG, FR and WR was 12.4, 14.1 and 21%, respectively. The gully in the agricultural land was more dipper compared with other land uses. The volume of gully channels in FR was 3.4 and 2.2 times less than AG and WR, respectively. It is concluded that rangeland degradation and thereby removing vegetation attribute to severe gully erosion and consequently environmental problems such as soil carbon dioxide emission.