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放牧对若尔盖高原湿地-草地区域碳收支影响的模拟与监测研究
Alternative TitleSimulation and Monitoring of the Grazing Effects on Wetland-Grassland Regional Carbon budget in Zoige Plateau
Language中文
王继燕
Thesis Advisor李爱农 ; 周介铭 ; 周万村
2016
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Name博士
Degree Discipline自然地理学
KeywordDndc模型 敏感性分析 参数优化 四维变分 放牧 碳收支 若尔盖高原湿地-草地
Other Abstract

若尔盖高原湿地-草地位于青藏高原东缘,是世界上最大的高原沼泽泥炭地之一,拥有全国泥炭地总面积和总储量的12%和40%,是一个巨大的碳库。然而,受自然条件、人类活动干扰加剧等方面的影响,湿地和草地退化、过度放牧等使得该区域湿地和草地碳循环面临着极大的挑战,生态系统碳同化与碳排放作用之间的平衡已经打破,湿地和草地作为碳源或是碳汇具有很大的争议。研究若尔盖高原湿地-草地区域碳收支现状,有助于理解湿地-草地在全球碳循环中的作用。然而,放牧是若尔盖地区人们的主要生活方式,亦是该区域影响生态系统碳收支的主要因子。研究放牧对若尔盖高原湿地-草地区域碳收支的影响,是正确评估该区域碳收支现状和固碳潜力的前提,也为该地区合理安排人类活动、优化牧场管理提供理论支持。本文回顾了碳收支估算方法、放牧研究进展,基于DNDC模型,探讨了过程模型、数据同化方法在区域尺度碳收支模拟中的应用,尝试利用时间序列的遥感数据定量化放牧,模拟并分析了近十五年若尔盖高原湿地-草地区域碳收支的时空变化以及放牧对该区域碳收支的影响。具体步骤包括:首先,结合局部和全局敏感性分析方法,采用粒子群优化算法实现DNDC模型本地化。其次,采用四维变分的数据同化方法将LAI与DNDC结合起来,用以提高模型模拟精度。然后,利用时间序列的NDVI构建放牧指数,获得区域尺度放牧强度和放牧时间,输入DNDC模型模拟放牧条件下区域尺度碳收支。最后,模拟并分析了2000-2014年若尔盖高原湿地-草地生态系统放牧及碳收支现状,评估放牧对该区域碳收支的影响。论文的主要结论如下:1、经过模型本地化,DNDC模型能够用于湿地-草地碳循环模拟;局域和全局敏感性分析方法结合更适用于复杂生态系统模型的敏感性分析。2、利用时间序列的MODIS LAI,四维变分的数据同化方法能够通过优化关键参数,实现区域尺度碳收支模拟,进而达到有效提高模型模拟精度的目的。3、基于时间序列的遥感影响构建的放牧指数能够定量化描述区域尺度放牧强度和放牧时间,并能够有效提高DNDC模型模拟精度。4、近十五年,若尔盖高原湿地-草地以轻度放牧为主,年平均放牧强度和放牧时间分别为3.47 SUD/hm2和5.39个月。其中全年牧场面积较大,占85.98%,冬牧场和夏牧场面积分别占整个研究区的3.64%和7.11%,冬牧场年平均放牧强度大于夏牧场。草甸、草原和稀疏草原是若尔盖高原的主要牧场,其放牧强度和放牧时间均大于沼泽湿地和湿草甸。2009年以后,研究区内放牧强度和放牧时间减少,未放牧区域增加,放牧活动更加合理。但是,全年牧场面积及草甸、草原和稀疏草原的放牧强度和放牧时间出现增加。5、若尔盖高原湿地-草地年平均GPP和NPP分别达到了31.74TgC和15.28 TgC,2009年以后呈现增加的趋势。单位面积沼泽湿地、泥炭湿地及湿草甸生产力最大,整个区域的沼泽湿地、泥炭湿地及湿草甸固定了若尔盖高原约1/4的碳,而草甸和草原则固定了整个研究区约74.52%的生产力。6、近十五年,若尔盖高原湿地-草地生态系统为碳汇,平均每年固定的净碳量达到了14.47 TgC,占我国草地年碳汇潜力的1.87%。除沙地外的土地利用类型的NEP均大于零,为该区域大气CO2的汇。其中,沼泽湿地、泥炭湿地及湿草甸单位面积NEP最大,草甸和草原区域NEP总量最多。沙地单位面积年平均NEP约为-78.481 kgC/hm2,是大气CO2的源,平均每年会向大气中释放 549.368 t C。7、若尔盖高原当前的放牧强度和放牧时间对GPP和NPP具有促进作用。当放牧强度介于3.2-3.6 SUD/hm2左右,放牧时间在3.5-4.1个月时,放牧效应达到最大,放牧引起的GPP和NPP的增量也会达到最大。8、放牧会消耗生态系统固定的净碳量,当放牧强度约为3.5SUD/hm2,放牧时间为4.1个月左右的时候,放牧效应可以达到最大,而放牧消耗的净碳量最小。避免在草地放牧抗性较低的生殖阶段放牧,可以有效的减少放牧消耗的净碳量。本文创新工作有:首次将DNDC模型应用于若尔盖湿地-草地生态系统区域尺度碳收支的模拟;首次将数据同化的方法应用于区域尺度碳收支的模拟;建立了放牧定量化表达方法,首次基于遥感数据评估了放牧强度的时空变化。未来工作可从以下几方面入手:1)探讨时空尺度与敏感性分析的关系;尽可能获得足够多的地面观测资料,优化得到更好的模型参数初始值。2)提高数据同化算法运算效率;考虑土壤、植被、水热条件等的空间异质性及相邻地区之间的关系;选择数据同化最优化方案,提高模拟预测精度。3)获取合理的未放牧地区NDVI值构建放牧指数;尽量使用高分辨率的输入参数;对放牧、区域碳收支数据进行验证。4)选择合适的方式,避免合并较小图斑,提高区域尺度碳收支计算效率。5)研究气候变化和放牧活动对该地区碳收支共同作用机制。6)研究碳收支与放牧活动的相互影响和制约机制。

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The Zoige Plateau, located at the eastern edge of the Tibetan Plateau in China, is the largest alpine peat swamp area in the world, with 40% of area and 12% of peat carbon stock of China. However, due to global climate change and irrational human disturbance, the wetland-grassland ecosystems in this area have been subjected to serious progressive degradation so that the dynamic balance of the carbon cycle in grassland ecosystems has been broken. Whether this area still functions as the terrestrial carbon uptake makes this region urgent and representative to study how the carbon budget changes under climate change and human disturbances. Dynamically monitoring the ecological environment changes of grassland ecosystems is critical to understand the role of grasslands in the global carbon cycle and is desirable for the local government to manage the grasslands resource. After the middle of 1980s, human activities like livestock grazing has become one of most critical factors influencing carbon budget in this region. Measuring the impact of livestock grazing on wetland and grassland regional carbon budget is essential for grass yield estimation and pasture management.This paper reviews research advances in the estimation methods of carbon budget and the methods of grazing. Based on the DeNitrification and DeComposition (DNDC) model, the application of the process model in simulating the grassland and wetland carbon budget in Zoige Plateau was discussed, the data assimilation technique was used to combine the remote sensing data and the process model, the grazing intensities and the grazing period were derived from the time-series remote sensing data, and the temporal and spatial distribution of wetland and grassland carbon budget in Zoige Plateau were analysed comprehensively.Some main conclusions of this dissertation were drew as follows:(1) The DNDC model could be applicable in simulating the carbon budget of the wetland-grassland ecosystems on the Zoige Plateau, China. The combination of local sensitivity analysis and global sensitivity analysis would be more appropriate for the models with a large number of input parameters and would make the results of sensitivity analysis more reliable.(2) Based on the time-series remote sensing data, the data assimilation of Four-dimensional Variational Algorithm (4DVAR) was able to be used to calibrate the key input parameters which would be used to simulate the regional carbon budget in Zoige Plateau.(3) The approach proposed in this paper to simulate the grazing effects on carbon budget using time-series remote sensing data and a process-based ecosystem model could be applied to obtain the grazing intensities and grazing period data, and it could successfully estimate the carbon budget under grazing conditions at regional scale.(4) From 2000 to 2014, light grazing was dominated in Zoige Plateau, with the annual average grazing intensity more than 3.47 SUD/hm2 and the grazing period more than 5.39 months. After 2009, the regional grazing intensities and grazing period have declined, the non-grazing area has increased, and the grazing activities in Zoige Plateau are becoming more reasonable.(5) For the whole area of Zoige Plateau, the total regional annual average gross primary productivity (GPP) and net primary productivity (NPP) were respectively up to 31.74TgC and 15.28 TgC. Herbaceous wetlands, peatlands and wet meadows had higher productivity and could fix about 25% of the regional total productivity. The productivity of meadows and prairies had accounted for 74.52% of the regional total productivity.(6) In recent 15 years, the wetland and grassland ecosystems in Zoige Plateau acted as a net carbon source, with a value of 14.47 TgC for each year (1 Tg = 1012g), which is more than the average carbon sink in our County. Deserts were identified as the carbon source, with average net ecosystem productivity (NEP) of -78.481 kgC/hm2 and they would result in a release of CO2 of 549.368 t C (1 t = 106g) each year. (7) Light grazing in Zoige Plateau could promote GPP and NPP. When the grazing intensity was between 3.2 SUD/hm2 and 3.6 SUD/hm2, and the grazing period was from 3.5 months to 4.1 months, the increasing amount of GPP or NPP would reach the maximum.(8) Grazing would reduce NEP. When the grazing intensity was 3.5 SUD/hm2 and the grazing period was about 4.1 months, the consume amount of the net carbon would reach the minimum. 

Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/18916
Collection数字山地与遥感应用中心
Affiliation中国科学院成都山地灾害与环境研究所
Recommended Citation
GB/T 7714
王继燕. 放牧对若尔盖高原湿地-草地区域碳收支影响的模拟与监测研究[D]. 北京. 中国科学院大学,2016.
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