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题名: 长江中下游地区淡水湖泊水-气界面碳交换及机制研究
作者: 邢阳平
答辩日期: 2007-01-04
导师: 谢平
授予单位: 中国科学院水生生物研究所
授予地点: 水生生物研究所
学位: 博士
关键词: 淡水水体 ; CH4 通量 ; CO2通量 ; 水-气界面 ; 浮游植物 ; 富营养化 ; 模型 ; 碳收支
其他题名: Studies on Carbon Exchange and Mechanism at Air-Water Interface in Freshwater Lake along The Middle and Lower Reaches of Yangtze River
摘要: 大气中温室气体CH4和CO2浓度的不断升高吸引了科学家们对全球陆地和水体生态系统碳循环和碳收支的研究。长江中下游地区湖泊约占全国淡水湖泊面积的60%,是我国内陆水体的重要组成部分,也是我国不同生态系统碳收支研究中的重要组分。该地区湖泊所具有的水深小、水温高、营养水平高等独有的特征使得该地区湖泊生态系统水-气界面碳循环的研究成为全球水体碳循环机制研究中不可缺少的重要组成部分,了解该地区湖泊生态系统水-气界面的碳循环与碳收支不但是我国碳收支研究的重要部分,更是对全球水体碳循环机制研究的重要补充。本研究以武汉东湖为例,对长江中下游地区淡水湖泊水-气界面CH4和CO2的交换及通量的时空变化特征进行研究,分析了影响CH4和CO2通量昼夜变化、季节动态、以及年际变化的影响因子,并探讨了在富营养作用和湖泊逆向演替中湖泊水-气界面碳通量的变化,最后通过模型对长江中下游地区淡水水体生态系统水面碳释放进行了初步估算。具体的研究内容和结果如下: 1. 对东湖固定采样点水-气界面CH4和CO2通量分别进行昼夜变化、季节动态、以及年际变化的研究。水-气界面CH4和CO2通量的昼夜变化均非常显著,一昼夜中气体的通量变化可以达到2个数量级以上。与设想不同,温度并非该地区湖泊水-气界面CH4和CO2通量昼夜变化的决定因子,在夏季两种气体的昼夜变化均受到水中浮游植物的调控。周年尺度上,东湖是大气CH4和CO2的源,季节动态特征明显不同于北方高纬度地区大部分湖泊,表现为夏季的高速CH4释放和其他季节的低速释放,CO2则是冬季的高速释放与春夏季节的显著吸收。CH4和CO2通量的时间变化与环境因子的相关分析显示:东湖CH4和CO2的一年中的时间变化主要受到水中浮游植物生命活动的调控,而营养、温度以及其他影响因子主要通过影响浮游植物的生命活动而影响水-气界面CH4和CO2通量的变化。与全球不同气候带的淡水湖泊CH4和CO2的释放通量比较,富营养化程度严重的东湖并非大的碳源,原因可能在于东湖是高度的自营养型湖泊,水体中浮游植物活跃的生命活动增加了对水体中CH4的氧化和CO2的消耗。年际变化研究显示:东湖CH4和CO2通量的年际动态远远小于月动态和季节动态,3年测定中CH4和CO2通量的变异系数分别为27.6%和9.2%,三年里由水-气界面释放到大气中的碳分别为802.5 ± 416.5、875.1 ± 435.6、696.9 ± 356.9 吨。这说明类似于东湖这种比较稳定的水体生态系统是大气比较稳定的碳源,在年际之间不会发生剧烈的变化。CH4和CO2通量的年际变化与降雨的年际变化模式一致,与温度无关,这说明目前气温的缓慢增加还不会显著的影响水-气界面的碳循环,而如果气候变化引起亚热带地区降雨总量减小则可能减弱该地区淡水湖泊作为大气碳源的功能。 2. 由于水体富营养化和过度的渔业经营等各种人类活动导致长江中下游地区众多的水体生态系统正在发生从草型湖泊到藻型湖泊的逆向演替,但是关于湖泊逆向演替中碳循环的研究还是个未知领域。对此,本研究通过选取一个正在发生逆向演替的湖泊扁担塘,对生长着沉水植物和浮游藻类的同一湖泊不同水域的水-气界面碳循环和水体中溶解态碳动态进行研究,得到以下结果:在较短时间内,水中主要初级生产者的变更暂且不会引起水中溶解性无机碳和有机碳浓度的变化,即水中溶解性碳在逆向演替中可以保持相对的稳定性。沉水植物对水中CH4的产生和释放有一定的促进作用,而藻类对于CH4没有显著的影响,随着生态系统中草-藻主导的转变,湖泊释放到大气的CH4可能会受到一定程度的抑制;而CO2的释放会随着藻类的主导而显著增加。总体来说,湖泊中正在进行的逆向演替可能会使湖泊在未来成为更大的大气碳源。 3. 要想估算区域尺度上生态系统的碳通量和收支,就需要构建适于该生态系统的数学模型。本研究以湿地和稻田等半水体生态系统中已有的CH4释放模型作参考,结合对湖泊水体CH4通量的研究经验,建立了湖泊水体生态系统水-气界面CH4的通量模型。通过该模型对藻型湖泊东湖和藻-草混合型湖泊扁担塘CH4通量模拟显示,尽管模型的模拟值与实测值之间存在一定的差异,但差异仍低于箱法自身的观测误差,且两组结果的相关系数较高,证明该模型适于长江中下游地区湖泊CH4通量的估算。同样对已有的水-气界面CO2通量模型进行对照分析,选取适合长江中下游淡水水体的模型,应用选定的CO2通量模型进行模拟,模拟值与实测值之间结果的对比显示:选定的模型适于长江中下游水体CO2通量的估算。 4. 运用本研究所建的CH4释放模型和选定的水-气界面CO2通量模型,结合正在开展的长江中下游地区湖群比较湖沼学的研究,对长江中下游地区30多个湖泊以及三峡水库水-气界面CH4和CO2释放进行估算。结果显示:长江中下游30多个湖泊和水库均是大气CH4的源,调查中水面总面积10 045.8 km2的水体释放的CH4形态碳为4.71±2.07×1010 g C y-1。长江中下游地区大约85%的湖泊水体是大气CO2的源,有少量的湖泊从大气中吸收CO2,综合所有水体CO2交换结果显示,每年从所调查水面释放的CO2形态碳为9.88±3.73×1011 g C y-1。对所调查结果外推得得到长江中下游地区淡水水体向大气释放总碳量达2.18±0.85 ×1012 C y-1。尽管与全球湖泊和水库释放的总碳量相比,我国长江中下游地区淡水水体的碳释放只占0.11%左右,但是在区域碳收支上由水面释放的碳却是相当重要的组分,由长江水面和长江中下游淡水湖泊等水体生态系统年释放的气态碳可能抵消全国农田土壤或造林年固定碳的16-20%。
英文摘要: Increasing atmospheric concentrations of the radiatively active gases CH4 and CO2 have stimulated extensive studies on carbon budget and greenhouse gas cycling from both terrestrial and aquatic environments. The carbon budget of freshwater ecosystems along the middle and lower reaches of the Yangtze River is an important part of carbon budget in the whole terrestrial ecosystems of China. Freshwater lakes in this region are characteristic of shallow water depth, high water temperature and high eutrophic level, and knowledge about carbon cycling in such systems is therefore an indispensable important part for understanding the mechanisms of carbon cycling in global aquatic ecosystems. A comprehensive study was conducted in freshwater lakes in the middle and lower reaches of the Yangte River and the main purposes were 1) to study the exchange and fluxes of CH4 and CO2 across air-water interface and the diel, seasonal and interannual variations of CH4 and CO2 fluxes with underlying mechanism controlling the variations, 2) to study the change of gaseous carbon budget during retrogressive succession of lakes, 3) to develop semi-empirical model of CH4 fluxes and 4) to estimate carbon release across air-water interface in these lakes by the developed models. The main contents and conclusions are as follows. 1. The static chamber and gas chromatography technique were used to study the fluxes of CH4 and CO2 across air-water interface in Lake Donghu. The diel studies of gas fluxes showed that there were great diel variations of CH4 and CO2 fluxes in all seasons, and the gas fluxes changed with two orders of magnitude in a diel cycle, and there were no significant relationships between gas fluxes and parameters in most studies. Only in summer, significant relationships between gas fluxes and biomass of phytoplankton could be observed, indicating that phytoplankton mainly regulated diel variation of carbon exchange across air-water interface in summer. In a year cycle, Lake Donghu was sources of CH4 and CO2 with respect to the atmosphere and the average fluxes of CH4 and CO2 were 23.37±18.6 and 332.37±160.1 mg m-2 d-1, respectively. The fluxes of CH4 and CO2 showed strong seasonal dynamics: CH4 emission rate was highest in summer, remaining low in other seasons, whereas CO2 was adsorbed from the atmosphere in spring and summer, exhibiting a large emission in winter. CH4 emission were correlated positively with net primary production (NPP) and temperature, while CO2 flux were correlated negatively with NPP and temperature; however, there were no significant relationships between the fluxes of CH4 and CO2 and dissolved organic carbon (DOC), which is significantly different from boreal lakes. This indicates that phytoplankton rather than allochthonous organic matter regulated C dynamics across air- water interface in subtropical autotrophic lakes enriched with nutrients. The amplitudes of interannual variations in fluxes of CH4 and CO2 were significant lower than those of seasonal and diel variations. During the period of three years, the carbon losses from surface water of Lake Donghu were 802.5 ± 416.5、875.1 ± 435.6、696.9 ± 356.9 tons, respectively, suggesting that Lake Donghu is a relative stable and consistent carbon source with respect to the atmosphere. 2. Due to serious eutrophication, overstocking of grass carp and many other human disturbances, large-scale declines of aquatic macrophytes and retrogressive succession were observed in many shallow lakes of China. A case study in Lake Biandantang was undertaken to investigate the change of carbon fluxes during such a regime shift. Dissolved carbon and gaseous carbon across air–water interface were compared in three sites with different vegetation covers. Dissolved carbon had no significant change with the progress of retrogressive succession in short time, but the gaseous carbon release showed great changes. Correlation analysis showed that macrophytes stimulated CH4 emission but suppressed CO2 release. On the whole, a larger carbon loss from surface water was observed in phytoplankton-dominated zone, indicating that with the decline of macrophytes and overgrowth of phytoplankton, the lakes will be larger carbon sources to the atmosphere. 3. To estimate carbon fluxes and budget in a regional scale,predictive models for regional ecosystems need to de developed. Based on the mechanisms of CH4 emission in lakes and a developed model for semi-freshwater ecosystem, a model of CH4 flux was developed for freshwater ecosystems along the middle and lower reaches of the Yangtze River. Comparison between simulated CH4 flux and measured values showed that the model can provide reliable prediction of CH4 emission from freshwater ecosystem. Similarly, the comparison between simulated CO2 flux and measured values showed that the selected CO2 flux model can effectively simulate CO2 exchange of freshwater ecosystems. 4. Based on limnological parameters of lakes along the middle and lower reaches of Yangtze River, the exchanges of CH4 and CO2 across the air-water interface of freshwater ecosystems were estimated using the flux models. The results showed that all the surveyed lakes and reservoir in this region were CH4 source with respect to the atmosphere, and the total CH4-C emission from the surveyed waters (10 045.8 km2) was estimated to be 4.71±2.07×1010 g C y-1. Except for a few lakes incorporating atmospheric CO2 into water, approximately 85% waters were supersaturated with respect to atmospheric pressures of CO2. The annual total CO2-C from the surveyed lakes and reservoir reached 9.88 ± 3.73×1011 g C y-1. If extrapolating the estimated results to the whole lake area (21 171.6 km2) along the middle and lower reaches of the Yangtze River, a total carbon release was estimated to be 2.18±0.85 ×1012 C y-1. Compared to the reported total carbon release from global lakes (0.14×1015 g y-1), the carbon release from freshwater ecosystems along the middle and lower reaches of Yangtze River only accounted for 0.11%. On the other hand, compared to other terrestrial ecosystems, carbon release from freshwater ecosystems in the region can offset about 16-20%of the annual carbon fixation by agriculture soil and forestation in China. Hence, carbon emission from surface waters is an important loss factor in both regional and global carbon budgets. For a better understanding of the global carbon cycling and budget, it is necessary to integrate carbon cycling and budget of aquatic ecosystems into the whole carbon budget study.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.ihb.ac.cn/handle/342005/12118
Appears in Collections:中科院水生所知识产出(2009年前)_学位论文

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长江中下游地区淡水湖泊水-气界面碳交换及机制研究.邢阳平[d].中国科学院水生生物研究所,2007.20-25
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