C02_P03

Influence of the human activity on the source of soil inorganic carbon in grassland from Tibet and Inner Mongolia

Ping D^1,2,  Yiwei C^1,2, Sanyuan Z^1,3, Chengde S^1,2, Ning W^1,2

¹State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China, ²CAS Center for Excellence in Deep Earth Science, Guangzhou, China, ³State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China

Soil Inorganic carbon (SIC) in two Alpine Meadow soil profiles from Tibet (Nam Co, 30°46´12″ N, 90°57´13″ E, amsl. 4737 m & Dangxiong, 30°22´40″ N, 90°55´45″ E, amsl. 4294 m) and two grassland soil profiles from Inner Mongolia (DXC, 43°00'25″ N，117°29´43″ E, amsl. 1352 m & GYC, 43°34'32″ N, 116°40'16″ E, amsl. 1225 m) were investigated. ¹⁴C ages of soil organic carbon (SOC) and SIC in Tibet show a significant positive correlation (Nam Co, R2=0.95 & Dangxiong, R2=0.94) between each other, suggesting a stable contribution of SOC to the SIC since 4.0 – 5.0 ka. Shrink of Nam Co lake at 3.0 – 2.0 ka and weakening of summer monsoon precipitation likely played little influence on the source of SIC in Tibet since  mid-Holocene. For comparison, ¹⁴C ages of SOC and SIC in Inner Mongolia indicate an obviously positive correlation (DXC, R2=0.97 & GYC, R2=0.91) from 4.0 – 5.0 ka to 2.0 ka, and almost a stable ¹⁴C age of SIC after 2.0 ka, reflecting a different source of soil IC after 2.0 ka in Inner Mongolia grassland. Variation of monsoon precipitation from 4.2 to 2.1 ka seems did not change the correlation obviously during that time in Inner Mongolia. Intensive human activities, such as farming and grazing since 2.0 ka in Inner Mongolia, likely led to the deterioration of the grassland and then the deflation of deeper soil layers, which finally changed the source of SIC in the shallow layers.