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The Research On Land Use/land Cover Change And Soil Organic Carbon Pool In Baicheng City During 1890~2029

Posted on:2011-07-10Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z L MaoFull Text:PDF
GTID:1103360305953430Subject:Environmental Science
Abstract/Summary:PDF Full Text Request
Soil carbon pool played an vital role in the land ecosystem carbon cycle, and land use/land cover change (LUCC) is one of the most dominate driving forces which have notable impact on the soil carbon pool. Currently, the reconstruction and prediction of historical LUCC and land ecosystem carbon cycle in global scale and regional scale have become vital areas of scientific focus in the global change research. The researches of LUCC and soil carbon stock in regional scale, not only help reduce the uncertainty in large spatial scale, but also provide substantial data for the study in large spatial scale. The influences of intensive LUCC on regional soil carbon stock in typical sensitive area are the key question in regional researches, and Baicheng city where we focus on is a typical case combing sensibility and variability. Aimed at notable regional features of Baicheng city, by ways of constructing the technology system for reconstruction of historical spatial and temporal pattern of LUCC and estimation model for regional carbon stock, this paper analyzed the characteristics of LUCC and soil organic carbon (SOC) changes during 1890 to 2029, and researched the variable pattern of soil carbon budget under different land use management and LUCC, and also investigated the driving mechanism of natural conditions and human induced factors on LUCC and soil carbon pool.As the research of historical LUCC in China had just begun, many researches focused on national scale study. Because of vast territory and abundant resources in China, many studies had decreased the estimate accuracy, so the regional LUCC in historical period research was absolutely necessary. Based on historical data, land use survey, satellite remote sensing images and relevant thematic map, by means of constructing technology system of historical LUCC, interpretation of remote sensing image and LUCC model, this paper systemically analyzed the spatial and temporal variation of LUCC between 1890 and 2029. The results indicated that, there were notable changes in LUCC in Baicheng city during this period, and the primary trend contained increase of cropland area, decrease of grassland, wetland and water area, sharply increase of saline-alkali land. The conversion of grassland to cropland was main characteristic in LUCC before 1950s, and after then, grassland degradation, sand land and saline-alkali land increase, wetland and water area shrink became the dominant characteristic in LUCC during 1950 to 2004. The development of paddy field began in 1980s, and the land consolidation projects in study area would substantially increase the area of paddy field.There was remarkable spatial heterogeneity in LUCC spatial and temporal pattern, and the environment became more adverse to agriculture from north to south and from west to east. Except for expansion of cropland in the whole region, the grassland degenerated and wetland shrank in northern Zhenlai county, almost all of grassland degenerated to saline-alkali land in middle-eastern Da'an city, and ecosystem extremely degenerated in southern Tongyu county because of blind reclamation and intensive resource exploitation from 1950s.Geomorphic conditions and soil types played an important role in the reclamation, and inhabitants had a tendency to develop the region with better natural conditions in the land exploitation process. In the first half of 20th century, the new cropland began occurred in advantageous soil types. Because of total limit of suitable land for farming, the proportion of suitable cropland became saturated, and the following reclamation appeared in the worse soil areas. In the recent 50 years, animal husbandry developed rapidly in Baicheng city, and long term resources exploitation had converted plenty of grassland to sand land and saline-alkali land.Currently, although there are abundant researches focused on the impact of LUCC on SOC in academic community, the differences of regional features resulted in high uncertainty because of diversities of natural conditions and human induced factors, and almost no scholar has made study in highly landscape-fragmented agro-pastoral zone, as most of current researches pointed at single ecosystem.Based on second national soil census and field samplings, by the way of weighted depth average SOC content, the impacts of LUCC on SOC vertical distribution in soil profiles had been analyzed. The characteristics of SOC vertical distribution in soil profiles under different land use/cover types could be divided into three kinds, containing downward sloping, unchangeable sloping and upward sloping. In the downward sloping profiles, SOC decreased with depth, and the profiles contained dry cropland, degenerated dry cropland, paddy field, grassland, degenerated grassland, woodland and wetland. In the unchangeable sloping profiles, SOC remain unchangeable with depth, and the profiles contained sand land and saline-alkali land. In upward sloping profiles, SOC increased with depth, and only beach land profiles belonged to this type. The characteristics of SOC vertical distribution in different profile types closely related to soil texture, vegetation biomass, SOC decomposition and hydro-geological condition.On the strength of long term spatial and temporal pattern of LUCC, soil map and effective soil layer map, the land use/cover-soil type-effective soil layer SOC densities (SOD) estimation classes had been established, and based on second national soil census and field samplings, the SOD had been estimate for every classes, and by the way of spatial analysis function in GIS, the characteristics of spatial and temporal pattern of SOD during 1890 to 2029 were analyzed. The results indicated that, the SOD spatial distribution had changed remarkably during this period under sharply LUCC, and it decreased notably from north to south, from west to north. The SOD in northwestern Taonan city and Taobei district was highest in the whole region, and that in southern Tongyu county was lowest. In the past 100 years, SOD in Tongyu county and Da'an county had decreased most rapidly, and current land consolidation project will plentifully increase the average SOD in Zhenlai county and Da'an city.During 1890 to 2004, SOC stock in study area had reduced 8.11×107tC, amount to 32.44% of that in 1890, and most of SOC release distributed in last half of 20th century, the SOC stock reduced 6.83×107tC between 1950 and 2004, amount to 84.20% of the total decrement. In the past 100 years, the study area was a huge carbon source. The SOC flux increased year after year. Before 1950s, the SOC flux remained low and steady, but from then on, the SOC flux increased rapidly, which reached to the peak in 1980s. Although the carbon sequestration increased from 1990s, the SOC stock remained decreased in the recent 20 years. The current land consolidation project will add large area paddy fields to Zhenlai county and Da'an city, which will convert the study area from carbon source to carbon sink.By summarizing the domestic and international publications, this paper made a qualitative analysis on driving factors of LUCC and SOC budgets. The results indicated that, plenty of natural conditions and social human factors had induced the LUCC and SOC budget in Baicheng city, and social human factors played the main dominant role. Improvements of agriculture and animal husbandry management would be effective methods to increase SOC stock in study area.The features and innovations of this thesis reflected in two aspects containing notable regional feature and innovational technology methods. Although many academic achievements had published about land ecosystem carbon budget under historical LUCC, almost all of these researches focused on the conversion of forests and cropland and grassland ecosystem which was very important in global carbon cycle had been disregarded. The study area of this thesis that located in intensively degenerated agro-pastoral zone had notable regional feature compared with other researches. The technology system that constructed in the reconstruction of historical spatial and temporal LUCC pattern, not only innovated in research method, but can also be applied in other regional studies. The methods for SOC stock estimation synthetically considered the impacts of land use/cover types, soil types and vegetation conditions, with the spatial pattern of vertical SOC distribution, which could effectively improved the estimate accuracy. This thesis can not only improve and enrich the research and theory of typical degenerated agro-pastoral ecosystem carbon cycle, but also help to establish the effective measures to relief the unbalance of carbon budget and reduce the regional carbon emission in frangible ecosystem.
Keywords/Search Tags:historical period, land use/cover change, soil carbon stock, carbon budget, agro-pastoral zone
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