Quantifying methane emissions from rice fields in the Taihu Lake region, China by coupling a detailed soil database with biogeochemical model

摘要

As China has approximately 22% of the world's ricepaddies, the regional quantification of CH₄ emissions from thesepaddies is important in determining their contribution to the globalgreenhouse gas effect. This paper reports the use of a biogeochemical model(DeNitrification and DeComposition or DNDC) for quantifying CH₄emissions from rice fields in the Taihu Lake region of China. For thisapplication, the DNDC model was linked to a 1:50 000 soil database derivedfrom 1107 paddy soil profiles compiled during the Second National SoilSurvey of China in the 1980s–1990s. The simulated results showed that the2.3 Mha of paddy rice fields in the Taihu Lake region emitted the equivalentof 5.7 Tg C from 1982–2000, with the average CH₄ flux ranging from 114to 138 kg C ha−1 y−1. As for soil subgroups, the highest emissionrate (660 kg C ha−1 y−1) was linked to gleyed paddy soilsaccounting for about 4.4% of the total area of paddy soils. The lowestemission rate (91 kg C ha−1 y−1) was associated with degleyedpaddy soils accounting for about 18% of the total area of paddy soils.The most common soil in the area was hydromorphic paddy soils, whichaccounted for about 53% of the total area of paddy soils with a CH₄flux of 106 kg C ha−1 y−1. On a regional basis, the annualaveraged CH₄ flux in the Taihu Lake plain soil region and alluvialplain soil region were higher than that in the low mountainous and hillysoil region and the polder soil region. The model simulation was conductedwith two databases using polygons or counties as the basic units. Thecounty-based database contained soil information coarser than the polygonsystem built based on the 1:50 000 soil database. The modeled results withthe two databases found similar spatial patterns of CH₄ emissions inthe Taihu Lake region. However, discrepancies exist between the results from thetwo methods. The total CH₄ emissions generated from the polygon-baseddatabase is 2.6 times the minimum CH₄ emissions generated from thecounty-based database, and is 0.98 times the maximum CH₄ emissionsgenerated from the county-based database. The average value of the relativedeviation ranged from −20% to 98% for most counties, which indicatesthat a more precise soil database is necessary to better simulate CH₄emissions from rice fields in the Taihu Lake region using the DNDC model.