陕北地区土地生态系统固碳释氧价值量动态测评

Dynamic evaluation of the value of carbon fixation and oxygen release based on land ecosystem in Northern Shaanxi

基于1980-2010年的遥感数据和气象台站实测数据,利用光能利用模型对陕北地区植被净第一生产力进行了测评,从而计算得到植被固碳释氧价值量,并分析了其变化特征。不同土地利用类型固碳释氧物质总量排序为:草地>林地>耕地>未利用地>建设用地。空间分布上,陕北地区南部和北部府谷县和神木县固碳释氧价值总量变化的波动性较强,陕北西北部碳释氧价值总量的年际变化较为平缓。近30年来,陕北地区固碳释氧价值总量总体上呈持续增加趋势,固碳释氧价值总量增加的区域主要分布在榆林中北部地区,且大部分呈可持续增加趋势;减小区主要分布在陕北西南部的甘泉县、富县、黄陵县、志丹县的南部以及延安市南部的富县与宜川县的交界处,且呈强烈的持续减小趋势。生态固碳释氧价值量与月降水量整体上呈正相关,与月均温呈负相关。固碳释氧价值量的变化对降水量的变化响应较敏感,气温需要通过与其他气候系统进行耦合,从而协同对固碳释氧价值量产生影响。陕北地区生态系统固碳释氧价值总量受降水量的影响较强,两者在空间上呈现出正相关,且由南向北、由东南向西北呈减小的趋势;价值总量与气温的相关系数由南向北逐渐增加,中南部呈负相关,北部呈正相关。

Vegetation productivity is closely associated with the productive and daily activities of human beings. Vegetation provides them with food, raw materials and fuels, and also has such functions as wind prevention and sand fixation and air purification. Moreover, they are key factors in the regulation of carbon source and carbon sequestration of the ecosystem. The absorption of carbon dioxide and release of oxygen by the green plants through photosynthesis helps to strike a balance of CO2 and O2in the atmosphere. In particular, with developments in socioeconomic sectors, a sharp rise in the CO2 concentration in the atmosphere as well as abnormal conditions in the global climate, vegetation＇s ability to fix carbon and release oxygen and the value thereof appear to be of particular importance. Based on the remote sensing data and measured data at meteorological stations from 1980 to 2010, we have evaluated the net primary productivity of the vegetation in Northern Shaanxi using the CASA model（a refined version from the light energy utilization model）, calculated the value of carbon fixation and oxygen release of the vegetation and analyzed the characteristics of its changes. The findings suggest the following：（1） There is a major difference in different land- use patterns. In a descending order, the NNP averages are respectively forest land, grass land, arable land,construction land and unused land. From 1980 to 2010, the variation in the total value of NPP has been featured by the trend of ＂increase-decrease-increase＂, with the amount of NPP rising by 35.60% over the past 30 years;（2） In a descending order, the amount of carbon fixation and oxygen release for different land- use patterns are successively grass land, forest land, arable land, unused land and construction land; and（3） In 1980, 1990, 2000 and 2010, the total value of carbon fixation and oxygen release are respectively 267.208 × 108 yuan, 276.725 × 108 yuan,260.796 × 108 yuan and 362.318 × 108 yuan. During the period of 1980- 2010, the total value of carbon fixation and oxygen release have been increased by 95.110×108yuan. In terms of spatial distribution, Fugu and Shenmu counties in the southern and northern parts of Northern Shaanxi have seen marked fluctuations in the total value of carbon fixation and oxygen release, while the northwestern part of Northern Shaanxi has seen mild interannual variation in the total value of carbon fixation and oxygen release; in terms of land-use patterns, the standard variation has shown a trend of ＂forest land, grass land, arable land, unused land and construction land＂ in a descending order.（4） Over the past 30 years, the total value of carbon fixation and oxygen release has shown a general trend of continuous increase. In terms of land- use patterns, the average rate of change in the total value of carbon fixation and oxygen release has respectively been unused land, construction land, arable land and grass land in a descending order.（5） On the whole, the value of carbon fixation and oxygen release in an ecosystem is positively correlated with the precipitation and negatively correlated with the monthly average temperature. Changes in the value of carbon fixation and oxygen release typically respond intensely to those in precipitation. The temperature has a great impact on the value of carbon fixation and oxygen release by coupling with other climatic systems. The difference in land coverage has been a major factor contributing to the marked difference between the northern and southern parts of Northern Shaanxi in the value of carbon fixation and oxygen release in terms of spacial distribution. As the southern part is located in the semi- humid region with a high ratio of vegetation cover and is dominated by broadleaved deciduous forest, the amount of CO2 fixation and O2 release is relatively large. It should be noted that the general trend of rise in the value of carbon fixation and oxygen release in Northern Shaanxi during the period of 1980-2010 is, to a great extent, related to the advancement of the beginning period of the growing season, an extended growing season of the vegetation and to global warming. In such a case,the accelerated moisture vaporization on the earth＇s surface and aggravated drought stress will lead to an increase in the intensity of carbon sequestration by the vegetation.