Assessing the impact of urbanization on regional net primary productivity in Jiangyin County, China

Urbanization is one of the most important aspects of global change. The process of urbanization has a significant impact on the terrestrial ecosystem carbon cycle. The Yangtze Delta region has one of the highest rates of urbanization in China. In this study, carried out in Jiangyin County as a representative region within the Yangtze Delta, land use and land cover changes were estimated using Landsat TM and ETM+ imagery. With these satellite data and the BEPS process model (Boreal Ecosystem Productivity Simulator), the impacts of urbanization on regional net primary productivity (NPP) and annual net primary production were assessed for 1991 and 2002. Landsat-based land cover maps in 1991 and 2002 showed that urban development encroached large areas of cropland and forest. Expansion of residential areas and reduction of vegetated areas were the major forms of land transformation in Jiangyin County during this period. Mean NPP of the total area decreased from 818 to 699 gCm(-2)yr(-1) during the period of 1991 to 2002. NPP of cropland was only reduced by 2.7% while forest NPP was reduced by 9.3%. Regional annual primary production decreased from 808 GgC in 1991 to 691 GgC in 2002, a reduction of 14.5%. Land cover changes reduced regional NPP directly, and the increasing intensity and frequency of human-induced disturbance in the urbanized areas could be the main reason for the decrease in forest NPP.     

新疆昭苏黄土剖面色度变化特征及古气候意义

对受西风影响的伊犁盆地南缘的昭苏波马剖面进行色度指标分析后发现,在黄土堆积期间,亮度L^*在很大程度上受控于颜色分量a^*、b^*,同有机质含量关系密切。在S_* 中亮度L^* 与碳酸钙有较好的相关性,而在L_*中相关性极低。红度a^*受赤铁矿含量的影响最大,其较好的 正相关关系可以很好地反映气候变干的过程。而黄度b^*与针铁矿相关性较差,易受到多方面因 素的影响,对气候转变的敏感性不高。