GREENHOUSE GAS FLUXES AND CARBON STORAGE FROM SOIL:THE BRAZILIAN INVENTORY

Abstract

Rising levels of atmospheric CO2 have focused attention on potential CO2 emissions from terrestrial ecosystems of the world, notably from soils and biomass. The world's mineral soils represent a large reservoir of C of about 1500 Pg C. Under the United Nations Framework Convention on Climate Change (UNFCCC) each country is required to develop, update and publish a national inventories of anthropogenic emissions (implementation of the National Communications), as well as to compile the inventories by comparable methodologies. For the last point, guidelines were developed and published as IPCC Guidelines for National Greenhouse Gas Inventories. Also, the land use, land-use changes and forestry (LULUCF) sector should be included in the national inventories. The CO2 fluxes from soils are discussed in chapter 5 for agricultural soils under the category 5D: CO2 emissions and removals from soils. These emissions are calculated from three subcategories: i) net changes in C storage in mineral soils; ii) emissions from organic soils; and iii) emissions from liming of agricultural soils. In a first step the soil organic carbon stocks up to a depth of 30 cm were estimated for Brazil based on a map of different soil-vegetation associations combined with results from a soil database. The soil-vegetation associations map was derived by intersecting soil and vegetation maps. The original soil and vegetation classification were reduced to 6 soil and 15 vegetation categories. Because this data represents sites with native vegetation in the absence of significant disturbances, it constitutes a valuable baseline for evaluating the effect of land-use change on soil C stocks for Brazil. Overall, about 36 400 million tons of carbon would be stored in the 0-30 cm soil layer under native conditions. The Brazilian Amazon region would account for 22,000 million tons. The CO2 emission from mineral soils following land-cover change in Brazil for the period 1975-1995 was estimated by Bernoux et al. who showed that the annual fluxes for Brazil indicate a net emission of CO2 to the atmosphere of 46.4 million tons of CO2 for the period 1975-1995. Intermediary calculation used to derive these annual fluxes estimated that 34 400 million tons of carbon were stored in the Brazilian soil for the year 1995. The annual CO2 emission for Brazil from liming varied from 4.9 to 9.4 million tons of CO2 per year with a mean annual CO2 emission of about 7.2 million tons. The South, Southeast and Center region accounted for a least 92% of total emission. Finally it could be calculated that the total CO2 fluxes from soils reached around 51.9 million tons of CO2 per year for the period 1975-1995.