Abstract
Soil is the largest pool of terrestrial organic carbon in the biosphere and interacts strongly with the atmosphere, climate and land cover. Remote sensing (RS) and geographic information systems (GIS) were used to study the spatio-temporal dynamics of croplands and soil organic carbon density (SOCD) in the Sanjiang Plain, to estimate soil organic carbon (SOC) storage. Results show that croplands increased with 10,600.68 km2 from 1992 to 2012 in the Sanjiang Plain. Area of 13,959.43 km2 of dry farmlands were converted into paddy fields. Cropland SOC storage is estimated to be 1.29 ± 0.27 Pg C (1 Pg = 103 Tg = 1015 g) in 2012. Although the mean value of SOCD for croplands decreased from 1992 to 2012, the SOC storage of croplands in the top 1 m in the Sanjiang Plain increased by 70 Tg C (1220 to 1290). This is attributed to the area increases of cropland. The SOCD of paddy fields was higher and decreased more slowly than that of dry farmlands from 1992 to 2012. Conversion between dry farmlands and paddy fields and the agricultural reclamation from natural land-use types significantly affect the spatio-temporal patterns of cropland SOCD in the Sanjiang Plain. Regions with higher and lower SOCD values move northeast and westward, respectively, which is almost consistent with the movement direction of centroids for paddy fields and dry farmlands in the study area. Therefore, these results were verified. SOC storages in dry farmlands decreased by 17.5 Tg·year−1 from 1992 to 2012, whilst paddy fields increased by 21.0 Tg·C·year−1.
Highlights
Soil is the largest pool of terrestrial organic carbon in the biosphere
Results based on the object-oriented classification for mapping croplands in 1992 and 2012 in the Sanjiang Plain show that the overall classification accuracy and the Kappa statistics are more than 93% and 91% (Table 2), respectively
Our results show that the area of croplands increased by 21.11% (10,600.68 km2), while 13,959.43 km2 dry farmlands was converted into paddy fields from 1992 to 2012 in the Sanjiang Plain
Summary
Soil is the largest pool of terrestrial organic carbon in the biosphere. It holds more than twice as much carbon as plants or the atmosphere; a slight change in soil organic carbon (SOC)can have great impacts on global terrestrial carbon cycling [1]. Soil is the largest pool of terrestrial organic carbon in the biosphere. It holds more than twice as much carbon as plants or the atmosphere; a slight change in soil organic carbon (SOC). Can have great impacts on global terrestrial carbon cycling [1]. The direct impact of human activities, deforestation, biomass burning, land cover change, and environmental pollution, releasing trace gases enhancing the “greenhouse effect” can markedly change the carbon balance of terrestrial ecosystems. Agricultural activities involving soil carbon sequestration significantly affect the dynamics of SOC storage [4]. Accurate evaluation of SOC dynamics is important to reveal potential responses of the terrestrial biosphere to global change [5]
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