1940—2002年长江中下游平原乡村景观区域中土地利用覆被及其土壤有机碳储量变化

Changes in land use and land cover and soil organic carbon storage in the densely populated village landscapes of China's Yangtze Plain from the 1940 to 2002

过去60a来,长江中下游平原的乡村地区发展迅速,引起土地利用覆被及其土壤有机碳储量明显地变化。通过选取区域代表性样方、基于1942年航片和2002年IKONOS影像研究小尺度土地利用覆被变化、土壤取样和收集1965年前土壤有机碳历史数据,用尺度推绎和蒙特卡洛不确定性分析方法,评价了19402002年长江中下游平原人口密集的乡村景观区域中土地利用覆被的面积及其030cm土壤(或底泥)有机碳储量的变化。结果表明:近60a来,在86×103km2的区域中有47%的面积发生土地利用覆被转化,其中耕地转化为非耕地的面积为21%(18×103km2)。土地利用覆被类型转化及其有机碳密度的变化导致该区域土壤有机碳储量的净增加。该区域稻田和闲置水域面积分别减少了21.5%(18.5×103km2)和6.7%(5.7×103km2),导致其土壤(或底泥)有机碳储量分别减少41.8TgC和12.9TgC;而水产养殖、非渗漏表面为主的建筑用地、种植木本作物和种植1年生作物的水浇地面积分别增加了14.2%(12.2×103km2)、7.7%(6.7×103km2)、3.5%(3.0×103km2)和2.0%(1.7×103km2),使其土壤(或底泥)有机碳储量分别增加32.2TgC、22.2TgC、12.2TgC和6.5TgC。近60a来,整个区域030cm土壤有机碳的储量增加了18.2TgC,其净增加的可能性为75%,形成了弱碳汇。这主要是由于区域稻田土壤有机碳密度增加了17%,使区域土壤有机碳储量增加了22.2TgC(其净增加的可能性为92%);而且,稻田转化为种植木本作物和种植1年生作物的水浇地也使区域土壤有机碳储量分别增加了1.3TgC(净增加的可能性为86%)和0.3TgC(净增加的可能性为70%);此外,闲置水域转化为水产养殖也使区域土壤有机碳储量增加1.3TgC(净增加的可能性为77%)。但是,稻田转化为水产养殖和非渗漏表面为主的建筑用地导致区域土壤有机碳储量损失6.3TgC和0.6TgC。因稻田土壤有机碳密度增加及稻田转化类型的土壤有机碳储量变化的影响,使整个区域形成弱碳汇,但如果稻田继续减少的话,很可能变成碳源。通过选取区域代表性样方、研究小尺度土地利用覆被变化、土壤取样和收集土壤历史数据,采用尺度推绎方法,研究揭示了19402002年长江中下游平原人口密集的乡村景观区域中土地利用覆被的面积及其土壤有机碳储量的变化。

Over the past 60 years,the village landscapes of China＇s Yangtze Plain have undergone extremely rapid development,causing major changes in land use and land cover （LULC） and soil （and sediment） organic carbon （SOC）. Here we present estimates of long-term changes in LULC and SOC in the top 30 cm of soils across the region from the 1940 to 2002 using a regional landscape sampling and upscaling approach. Fine-scale LULC estimates were obtained by field-validated high-resolution ecological mapping of 12 regionally-stratified landscape sample cells based on historical aerial photographs （1942） and IKONOS imagery （2002）. Current SOC was measured at points selected at random within ecologically-distinct landscape features chosen within landscape sample cells using a regional-area-weighted stratified sampling design. 1940s-era SOC data were obtained from regional historical sources published before 1965. Long-term changes in LULC and SOC across the village landscapes of the Yangtze Plain were then estimated by integrating these data using a multivariate regional optimization and resampling procedure combined with Monte Carlo uncertainty analysis. The main results as following：From the 1940s to 2002,47% of land area （86 × 10^3km^2 ） in the village landscapes of China＇s Yangtze Plain underwent a substantial change in LULC class,of which 21% （18 × 10^3km^2） was cropland to noncropland transformation. These LULC transformations combined with changes in SOC density within different LULC types to produce a net increase in total SOC storage across the densely populated village landscapes of China＇s Yangtze Plain. Declines in paddy （21. 5% of region; 18. 5 × 10^3km^2） and fallow water body areas （6. 7% ; 5. 7 × 10^3km^2） caused 41. 8 Tg C and 12. 9 Tg C declines in SOC storage,respectively,while increases in aquaculture （14. 2% ; 12. 2 × 10^3km^2 ）,sealed constructed areas （7. 7%; 6. 7 ×10^3km^2）,and irrigated perennial （3. 5%; 3. 0 × 10^3km^2） and annual crops （2. 0%; 1. 7 × 10^3km^2）,increased SOC storage by 32. 2 Tg C,22. 2 Tg C,12. 2 Tg C and 6. 5 Tg C,respectively. When these estimates are combined,this study yields a 75% probability that SOC storage in the top 30 cm layer of village soils in the Yangtze Plain has increased over the past 60 years,by a total of 18. 2 Tg C. This was caused mainly by a 17% median increase in SOC density in the paddy soils that were not transformed to other land uses during this period,a regional net SOC gain of 22. 2 Tg C （ with a 92% probability of a net increase）. This increase was coupled with SOC storage increases by caused by paddy conversion to irrigated perennial croplands （1. 3 Tg C with an 86% probability of a net increase）,conversion of paddy to irrigated annual croplands （0. 3 Tg C with 70% probability of a net increase）,and by conversion of fallow water bodies to aquaculture （1. 3 Tg C with a 77% probability of a net increase）. However,SOC increases were tempered by paddy to aquaculture transformation,which caused a 6. 3 Tg C regional decline in SOC,and by conversion of paddy to sealed constructed areas （buildings and roads; 0. 6 Tg C）. As soils in the village landscapes of China＇s Yangtze Plain have formed a small regional sink over the past 60 years primarily because of SOC accumulation in paddy soils,these may soon become a source of atmospheric C emissions,if paddy areas continue to decline. By combining a regionally-stratified sample of fine-scale landscape features with a regionally-weighted soil sampling and upscaling analysis,coupled with historical soil data,long-term changes in LULC and SOC were revealed across one of the most densely populated agricultural regions in the world; China＇s Yangtze Plain.