شبیه‏سازی دینامیک کربن آلی خاک تحت تاثیر سناریوهای مختلف فرسایش آبی و مدیریت چرا در مراتع نیمه‏خشک باجگاه با استفاده از مدل century

ﺳﺎﺑﻘﻪ و ﻫﺪف: ﺟﺎﺑﺠﺎﯾﯽ و ﺗﻐﯿﯿﺮ ﻣﮑﺎن ﮐﺮﺑﻦ ﻧﺎﺷﯽ از ﻓﺮﺳﺎﯾﺶ آﺑﯽ ﯾﮏ ﻓﺎﮐﺘﻮر ﻣﻬﻢ ﺗﺄﺛﯿﺮﮔﺬار ﺑﺮ ﻏﻠﻈﺖ co2 اﺗﻤﺴﻔﺮ ﺑﯿﺎن ﺷﺪه اﺳﺖ. ارزﯾﺎﺑﯽ اﺛﺮ ﻓﺮﺳﺎﯾﺶ آﺑﯽ ﺑﺮ ذﺧﯿﺮه ﮐﺮﺑﻦ آﻟﯽ ﺧﺎک در ﻃﻮﻻﻧﯽ ﻣﺪت ﺑﺪون اﺑﺰار ﻣﺪل ﺳﺎزی ﻣﺸﮑﻞ ﻫﺴﺖ و ﺑﺎ ﺗﻮﺟﻪ ﺑﻪ اﯾﻦ ﮐﻪ ﻣﺮاﺗﻊ اﯾﺮان ﻣﺴﺎﺣﺖ ﺑﺰرﮔﯽ از ﮐﺸﻮر را درﺑﺮﮔﻔﺘﻪ اﻧﺪ، ﻣﺪل ﺳﺎزی اﺛﺮ ﻓﺮﺳﺎﯾﺶ آﺑﯽ ﺑﺮ دﯾﻨﺎﻣﯿﮏ ﮐﺮﺑﻦ آﻟﯽ ﺧﺎک در ﻣﺮاﺗﻊ ﻣﯽﺗﻮاﻧﺪ راﻫﮑﺎرﻫﺎی ﻣﺪﯾﺮﯾﺘﯽ ﺷﺎﯾﺴﺘﻪای در اﺧﺘﯿﺎر ﺳﺎزﻣﺎنﻫﺎی ﻣﺮﺗﺒﻂ ﻗﺮار دﻫﺪ. ﺑﻨﺎﺑﺮاﯾﻦ ﭘﮋوﻫﺶ ﺣﺎﺿﺮ ﺑﺎ ﻫﺪف 1) ﺑﻬﺒﻮد ﮐﺎراﯾﯽ ﻣﺪل century ﺑﻪ ﻋﻨﻮان ﭘﺮﮐﺎرﺑﺮدﺗﺮﯾﻦ ﻣﺪل در ﻣﻄﺎﻟﻌﺎت ﮐﺮﺑﻦ ﺧﺎک ﺑﺎ اﺳﺘﻔﺎده از ﺧﺮوﺟﯽ ﺳﻪ ﻣﺪل ﻓﺮﺳﺎﯾﺶ آﺑﯽ wepp ،gleams و answers و 2) ﺷﺒﯿﻪ ﺳﺎزی دﯾﻨﺎﻣﯿﮏ ذﺧﯿﺮه ﮐﺮﺑﻦ آﻟﯽ ﺧﺎک ﺗﺤﺖ ﺗﺄﺛﯿﺮ دو ﺳﻨﺎرﯾﻮ ﻓﺮﺳﺎﯾﺸﯽ در ﻣﺮاﺗﻊ ﻧﯿﻤﻪ ﺧﺸﮏ ﺑﺎﺟﮕﺎه (ﺟﻨﻮب اﯾﺮان) اﻧﺠﺎم ﮔﺮﻓﺖ. ﻣﻮاد و روش ﻫﺎ: ﭘﺲ از ﭘﺎراﻣﺘﺮﯾﺎﺑﯽ و واﺳﻨﺠﯽ ﻣﺪل century، ﻣﯿﺎﻧﮕﯿﻦ دراز ﻣﺪت ﻓﺮﺳﺎﯾﺶ آﺑﯽ ﺷﺒﯿﻪ ﺳﺎزی ﺷﺪه ﺗﻮﺳﻂ ﺳﻪ ﻣﺪل ﻓﺮﺳﺎﯾﺸﯽ gleams ،wepp و answers ﺑﻪ ﻋﻨﻮان ورودی در ﻣﺪل century وارد ﮔﺮدﯾﺪﻧﺪ. در ﻧﻬﺎﯾﺖ ﯾﮏ ﻣﺪل ﻓﺮﺳﺎﯾﺶ آﺑﯽ ﮐﻪ ﻣﯿﺰان ﻓﺮﺳﺎﯾﺶ ﺷﺒﯿﻪ ﺳﺎزی ﺷﺪه ﺗﻮﺳﻂ آن ﻣﻮﺟﺐ ﺑﻬﺒﻮد ﻧﺘﺎﯾﺞ اﻋﺘﺒﺎرﺳﻨﺠﯽ ﻣﺪل century ﺷﺪ، اﻧﺘﺨﺎب ﮔﺮدﯾﺪ و ﺳﭙﺲ اﺛﺮ دو ﺳﻨﺎرﯾﻮ وﻗﻮع ﻓﺮﺳﺎﯾﺶ آﺑﯽ و ﻋﺪم وﻗﻮع ﻓﺮﺳﺎﯾﺶ آﺑﯽ ﺑﺮ ﺗﻐﯿﯿﺮات ذﺧﯿﺮه ﮐﺮﺑﻦ آﻟﯽ ﺧﺎک ﺑﺮای دو دوره ﻣﺪﯾﺮﯾﺖ ﭼﺮای دام ﺷﺎﻣﻞ ﻣﺪﯾﺮﯾﺖ ﭼﺮای ﻣﺘﻮﺳﻂ دام (دوره ii از ﺳﺎل 1343 ﺗﺎ 1357) و ﻣﺪﯾﺮﯾﺖ ﺑﺪون ﭼﺮای دام (دوره iii از ﺳﺎل 1393-1358) در ﻣﻨﻄﻘﻪ ﻣﻄﺎﻟﻌﻪ ﻣﻮرد ﺑﺮرﺳﯽ ﻗﺮار ﮔﺮﻓﺖ.ﯾﺎﻓﺘﻪ ﻫﺎ: ﻧﺘﺎﯾﺞ ﻧﺸﺎن داد ﮐﻪ اﺳﺘﻔﺎده از ﺧﺮوﺟﯽ ﻣﺪل gleams ﺑﺎﻋﺚ ﺷﺪه ﮐﻪ ﻣﺪل century، ذﺧﯿﺮه ﮐﺮﺑﻦ آﻟﯽ ﺧﺎک را ﺑﻪ ﻃﻮر دﻗﯿﻖ ﺗﺮی ﭘﯿﺶ ﺑﯿﻨﯽ ﮐﻨﺪ و از ﺧﺮوﺟﯽ اﯾﻦ ﻣﺪل ﻓﺮﺳﺎﯾﺸﯽ ﺑﺮای ﺷﺒﯿﻪ ﺳﺎزی ﺗﻐﯿﯿﺮات ذﺧﯿﺮه ﮐﺮﺑﻦ آﻟﯽ ﺧﺎک ﺗﺤﺖ ﺗﺄﺛﯿﺮ ﻓﺮﺳﺎﯾﺶ آﺑﯽ در ﻣﺪل century اﺳﺘﻔﺎده ﺷﺪ. ﻧﺘﺎﯾﺞ ﺷﺒﯿﻪ ﺳﺎزی ﻫﺎی ﻣﺪل century ﻧﺸﺎن داد ﮐﻪ در ﺳﻨﺎرﯾﻮ ﺑﺪون ﻓﺮﺳﺎﯾﺶ در ﻣﺮاﺗﻊ ﻧﯿﻤﻪ ﺧﺸﮏ ﺑﺎﺟﮕﺎه ﻃﯽ دوره ii ﺑﺎ ﺷﺪت ﻣﺘﻮﺳﻂ ﭼﺮای دام روﻧﺪ ذﺧﯿﺮه ﮐﺮﺑﻦ آﻟﯽ ﺧﺎک ﺑﺎ ﺷﯿﺐ زﯾﺎدی از 3496 ﮔﺮم ﺑﺮ ﻣﺘﺮﻣﺮﺑﻊ در ﺳﺎل 1343 (1964) ﺑﻪ 3260/93 ﮔﺮم ﺑﺮ ﻣﺘﺮﻣﺮﺑﻊ در ﺳﺎل 1357 (1979) ﮐﺎﻫﺶ ﯾﺎﻓﺘﻪ اﺳﺖ و در دوره iii ﺑﺎ ﻣﺪﯾﺮﯾﺖ ﺑﺪون ﭼﺮای دام ذﺧﯿﺮه ﮐﺮﺑﻦ آﻟﯽ ﺧﺎک ﺑﺎ ﺷﯿﺐ ﻣﻼﯾﻤﯽ ﺑﻪ 3356/04 ﮔﺮم ﺑﺮ ﻣﺘﺮﻣﺮﺑﻊ در ﭘﺎﯾﺎن ﺳﺎل 1393 (2014) رﺳﯿﺪه اﺳﺖ. در ﺳﻨﺎرﯾﻮ ﻓﺮﺳﺎﯾﺶ آﺑﯽ ﻧﯿﺰ ﻃﯽ دوره ii ذﺧﯿﺮه ﮐﺮﺑﻦ آﻟﯽ ﺧﺎک ﺑﺎ ﺷﯿﺐ زﯾﺎدی از 3496 ﮔﺮم ﺑﺮ ﻣﺘﺮﻣﺮﺑﻊ در ﺳﺎل 1343 (1964) ﺑﻪ 3243/90 ﮔﺮم ﺑﺮ ﻣﺘﺮﻣﺮﺑﻊ در ﭘﺎﯾﺎن ﺳﺎل 1357 ﮐﺎﻫﺶ ﯾﺎﻓﺘﻪ (1979) و در دوره iii ذﺧﯿﺮه ﮐﺮﺑﻦ آﻟﯽ ﺧﺎک ﺑﺎ ﺷﯿﺐ ﻣﻼﯾﻤﯽ ﺑﻪ 3350/42 ﮔﺮم ﺑﺮ ﻣﺘﺮﻣﺮﺑﻊ در ﺳﺎل 1393 (2014) رﺳﯿﺪه اﺳﺖ. ﻫﻢ ﭼﻨﯿﻦ ﻧﺘﺎﯾﺞ ﺷﺒﯿﻪ ﺳﺎزی ﻫﺎ ﻧﺸﺎن داد ﮐﻪ ذﺧﯿﺮه ﮐﺮﺑﻦ آﻟﯽ ﺧﺎک در ﺳﻨﺎرﯾﻮ ﻓﺮﺳﺎﯾﺶ ﻧﺴﺒﺖ ﺑﻪ ﺳﻨﺎرﯾﻮ ﺑﺪون ﻓﺮﺳﺎﯾﺶ در ﭘﺎﯾﺎن دوره ﻫﺎی ii و iii ﺑﻪ ﺗﺮﺗﯿﺐ 0/52 و 0/16 درﺻﺪ ﮐﺎﻫﺶ ﯾﺎﻓﺖ.

Simulating soil organic carbon dynamics as affected by different water erosion scenarios and grazing management in semi-arid rangelands of Bajgah using the Century model

Background and Objectives: Most studies have reported a strong relationship between water erosion and soil organic carbon (SOC) losses, so that carbon displacement caused by water erosion stated as an important factor affecting the concentration of CO2 in the atmosphere. Therefore, understanding water erosion processes effect on SOC within an ecosystem is essential. Since evaluating the impacts of water erosion on SOC stock dynamic in longterm is difficult without modeling tool, studying of SOC dynamic through use of simulation models in combination with measured data is recommended. Considering that rangelands of Iran have taken a large part of the country, modeling the effect of water erosion on SOC dynamics in rangelands can provide appropriate management solutions for related organizations. The SOC modeling has not been conducted under the influence of water erosion, and this study could be basis for the future of SOC modeling. Therefore, the present study aims to: 1) improve the validation of the Century model as the most widely used model in the soil carbon studies, by using the output of three water erosion models of GLEAMS, WEPP, and ANSWERS, and 2) simulating the SOC stock dynamic under the influence of two erosion scenarios in the semiarid rangelands of Bajgah.Materials and Methods: To conduct this research, 60 soil samples were taken by randomized sampling methodfrom a depth of 020 cm of soil in the semiarid rangelands of Bajgah. To determine the soil bulk density, two cylinders were collected beside each soil puddle (120 samples). After determining the volume of vegetation sampling (number of plots); aboveground biomass, litter and belowground biomass were collected in 17 plots then transferred to the laboratory. Parameterization and calibrating the Century model was performed by using 43 years of weather data, site specific data, as well as physiological and ecological parameters of rangeland. Then, the longterm average of water erosion rate simulated by WEPP, GLEAMS and ANSWERS erosion models entered as input in the Century model. Finally, a water erosion model, that its simulated erosion rate improves the validation results of the Century model, was selected then illustrated the effect of two water erosion scenarios on the changes of SOC stock for two periods of grazing management including period of nationalization of rangelands with moderate grazing management.Results: The simulation results showed that use of the GLEAMS model output made the Century model more accurately predict SOC stock. Therefore, the GLEAMS erosion model output was used for simulate the SOC stock variations under the influence of water erosion. The simulation results of the Century model showed that the SOC stock in the Bajgah rangelands during the II period with moderate grazing management, decreased from 3496 to 3260.93 (g cm2) and 3496 to 3243.90 (g cm2) in the noerosion and erosion scenarios, respectively and there was no significant difference between them (p < 0.05). Also during the III period with no grazing management, SOC stock decreased from 3245.30 to 3356.04 (g cm2) and 3227.37 to 3350.42 (g cm2) in the noerosion and erosion scenarios, respectively and there was no significant difference between them (p <0.05). Generally, water erosion decreased the SOC stock in the semiarid rangelands of Bajgah compared with the nonerosion scenario by 0.52% and 0.16% in the end of periods II and III, respectively. The erosion resulted in a slight reduction in SOC stock in the semiarid rangelands of Bajgah compared to the nonerosion scenario. Based on the results of this study, it can be state that the role of grazing management than the erosion in the changes and losses of SOC stock was more evident in the semiarid rangelands of Bajgah.