干旱内陆流域景观格局变化下的景观土壤有机碳与氮源汇变化

以黑河流域中游绿洲区域为例,近10年来,在干旱内陆流域受人类活动强烈影响的区域,景观的破碎度降低,景观异质性减弱,显著的景观变化表现在:耕种景观与荒漠化景观的扩张和沼泽草甸景观与水域景观的萎缩,其中荒漠草原景观面积的10%、山地草原景观的49.8%以及沼泽草甸(包括盐化草甸)景观面积的16.8%演变为耕种景观类型;相反,17.4%的荒漠草原景观面积和20.2%的沼泽草甸退化为沙漠与戈壁景观,另有13.02%的灌耕地面积演变为荒漠草原.景观空间格局演变驱动景观土壤N、C的源汇变化,近10年来,黑河流域中游地区由于景观空间格局变化形成的景观N净排放和有机C净释放分别达到50.65×104T和530.17×104T.山地草原景观的荒漠化与耕种利用、耕种景观的荒漠草原化、沼泽草甸与山地草甸景观以及荒漠草原景观的耕种利用和这些景观的沙漠化发展是造成区域N、C损失的主要途径.

CHARACTERISTICS OF SOIL C, N DEPOSITION AND EMISSION IN ARID INLAND RIVER BASIN OF NORTHWEST CHINA UNDER EVOLVING LANDSCAPES

Soil nutrients and CO 2 storage are related to patch types, size and number, also are the parameters reflect the states of landscape. Evolving landscape patterns will inevitably cause an evolution in the functions of ecological systems, in which soil N, C pool and deposition processes have important ecological implications. A quantitative method and a digital model for analyzing impacts of evolving landscape on the landscape soil organic C and N deposition and emission in middle region of Heihe river basin northwest China were devised. In the past decade, the landscape evolution in the region is mainly characterized by farmland expansion and landscape desertification. From 1987 to 1997, 17.4% of primitive piedmont warm and desert steppe (PWD) turned into gobi and sandy desert (GS) and 10% turned to farmland. Among changed alpine steppe (ALP), artificial (ART) forest and plain swamp (PS) meadow, 49.8%, 51.7% and 16.8% respectively turned into farmland. Meanwhile, 13.02% of previous farmland turned into PWD steppe and 20.2% PS meadow turned into GS desert. Due to these changes, the soil organic matter and N contents decreased seriously in most landscape patters from 1987 to 1997. In this period, the net landscape soil organic C and N emission reached 530.17×10 4T and 50.65×10 4T respectively in middle region of Heihe river basin. The phenomenon was similar across whole arid inland region of northwest China due to the similarity in water resources and regional development, and huge soil C and N emission caused by landscape change will inevitably result in some new serious environmental problems.