Soil Organic Carbon at Lake Hovsgol, Mongolia:

Soil Organic Carbon at Lake Hovsgol, Mongolia:

The Role of Grazing and Permafrost

Noam Ross

Center for Environmental Studies, Brown University

Submitted in partial fulfillment of the Honors Sc.B. program in Environmental Science, May 2006

Executive Summary

Approximately 15% of global soil carbon is in permafrost and permafrost-underlain soils. Climate change and land-use change could both cause the release of large quantities of this soil C, creating feedbacks in the global C cycle. I studied the amount, vertical distribution, and potential mineralization of soil organic carbon in four sites at the Hovsgol Global Environmental Facility, Mongolia. Two sits were lightly grazed and two heavily grazed, and one in each grazing level was underlain by permafrost. In the site without permafrost, soil C (0-110 cm) was 7.4±0.8 kg m^-2 and there was no difference between the lightly and heavily grazed sites without permafrost. In sites with permafrost, the permafrost table was deeper where there was heavy grazing than where there was light grazing, and C storage was more than four times greater (30±15 kg m^-2) in soil above the permafrost at the light grazing site than to 110 cm at the heavy grazing site (7.1±0.7 kg m^-2). Grazing may lead to the loss of large amounts of soil C through erosion of peat layers and indirectly by soil warming due to the loss of the insulating peat layer, and consequent lowering of the permafrost table. However, the limited extent of lightly grazed grasslands underlain by permafrost suggest that any positive feedback from global warming will be limited. Except for the permafrost underlain, lightly grazed site, C mineralization from soils in 90 day incubations was not statistically different among sites. The lightly grazed permafrost site had the greatest total mineralized C per unit area, but less than the other sites as a fraction of total soil C. The observed patterns of C distribution and mineralized C among sites suggests a relationship between grazing, permafrost, and C cycling that requires further research.