Seasonal drought effects on carbon sequestration of a mid-subtropical planted forest of southeastern China     

Sun Xiaomin  Wen Xuefa  Yu Guirui  Liu Yunfen  Liu Qijing 《中国科学D辑(英文版)》2006,49(2):110-118

Continuous measurement of carbon dioxide exchange using the eddy covariance (EC) technique is made at the Qianyanzhou mid-subtropical planted forest as part of the ChinaFLUX net-work. Qianyanzhou planted forest is affected by typical subtropical continental monsoon climate. It has plentiful water and heat resource but is in inconsistency of its seasonal distribution in the mid-subtropical region, thus seasonal drought frequently occurs in this planted forest. In this study, seasonal drought effect on ecosystem carbon sequestration was analyzed based on net ecosystem productivity (NEP), ecosystem respiration (RE) and gross ecosystem productivity (GEP) at the month scale in 2003 and 2004. In this drought-stressed planted forest, ecosystem carbon sequestration showed a clear seasonality, with low rates during seasonal drought and in winter. The declining degree of ecosystem carbon sequestration under the seasonal drought condition was determined by the accumulation of soil moisture deficits and a co-occurrence of high temperatures. Different drought effects are expected for RE and GEP. The net effect of ecosystem carbon balance depends on how these two quantities are affected relatively to each other. Summer drought and heat wave are two aspects of weather that likely play an important part in the annual NEP of forest in this region.  相似文献   

北冰洋西部表层沉积物矿物学特征及其物质来源          下载免费PDF全文

董林森  石学法  刘焱光  方习生  陈志华  王春娟  邹建军  黄元辉 《极地研究》2014,26(1):58-70

对北冰洋西部79个表层沉积物样品进行了全岩X射线衍射矿物组成分析,结合洋流和地质背景,探讨各矿物分区的物质来源。矿物组合分区表明研究区物质来源变化较为复杂:(1)在楚科奇海的中部靠近白令海峡处长石含量很高,主要是阿纳德尔流携带的来自阿纳德尔河的沉积物;在楚科奇海的西侧的长石含量也较高,且与其他矿物组合分区相比,角闪石含量较高,这是因为受阿纳德尔流和东西伯利亚沿岸流的双重影响,沉积物来自西伯利亚陆地的一些高含长石的火山岩及沉积岩等。在楚科奇海的东侧,石英含量很高,来源为阿拉斯加沿岸流携带的育空河及卡斯奎姆河的沉积物。在阿拉斯加北部,碳酸盐岩和石英含量高,这与马更些河搬运的沉积物有关;(2)北冰洋西部深水区中加拿大海盆的南端和中部方解石和白云石的含量较低,说明受波弗特环流携带的加拿大北极群岛的碳酸盐影响相对较小,且与其他矿物组合分区相比,云母含量最高,说明沉积物主要来源为来自拉普捷夫海的海冰沉积物;此外,一些黏土级细粒物质可能由大西洋中层水携带而来。深水区的其他海域以方解石和白云石含量高为特点,主要受波弗特环流的影响,来源主要为加拿大北极群岛的班克斯岛和维多利亚岛;此外,还受来自西伯利亚陆架,主要是拉普捷夫海沉积物的影响。  相似文献   

无震脊或海山链俯冲对超俯冲带处的地质效应   总被引：3，自引：1，他引：2  

鄢全树  石学法 《海洋学报》2014,36(5):107-123

全球海底分布着众多的无震脊或海山链,且在太平洋、印度洋及大西洋均存在靠近俯冲带的海岭。除小安德列斯弧外的巴拉克达脊和蒂勃朗脊起源自转换断层外,一般认为它们由与板块构造动力学迥异的地幔柱动力学所形成的。在板块汇聚边缘处,与扩张脊处所形成的正常洋壳一起,无震脊或海山链俯冲于陆缘弧或洋内弧之下,其对弧及弧后地区的地质效应(构造、地貌、地震以及岩浆作用等)有别于正常洋壳俯冲。无震脊或海山链的俯冲通常造成俯冲带地区的上驮板块的局部异常抬升、俯冲剥蚀作用效应的加强、海沟的向陆迁移以及地震强度的增加。同时,无震脊或海山链俯冲时,其携带的具富集地球化学特征的物质不仅影响着地幔地球化学,也对弧及弧后火山熔岩化学产生明显影响,并对超俯冲地区的热液矿床的形成产生重要影响。最后,本文指出了我国有关无震脊或海山链俯冲的可能的研究方向包括黄岩海山链俯冲对吕宋岛弧的可能影响、印度洋无震脊俯冲对青藏高原局部地区的影响,有我国学者参与的IODP344航次的研究对象——科科斯脊俯冲对哥斯达黎加地震成因的效应以及位于西太平洋地区靠近俯冲带的一些无震脊等。  相似文献   

Geochemistry of mafic rocks and melt inclusions and their implications for the heat source of the 14.0°S hydrothermal field,South Mid-Atlantic Ridge     

Bing Li  Xuefa Shi  Yaomin Yang  Jun Ye  Jingjing Gao  Wenqin Zheng 《中国地球化学学报》2014,33(4):325-335

Fresh rocks sampled from the 14.0°S hydrothermal field of the South Atlantic Ridge can be divided into two categories： olivine-gabbro and basalt. The olivine-gabbro is composed mainly of three types of minerals： olivine, clinopyroxene and plagioclase, while a multitude of melt inclusions occur in the plagioclase phenocrysts of the basalts. We analyzed the whole-rock, major and trace elements contents of the basaks, the mineral chemistry of phenocrysts and melt inclusions in the basalts, and the mineral chemistry of olivine-clinopyroxene-plagioclase in the olivine-gabbro, then simulated magma evolution within the crust using the COMAGMAT program. The whole-rock geochemistry shows that all the basalts exhibit typical N-MORB characteristics. In addition, the mineral chemistry characteristics of the olivine-gabbro （low-Fo olivine, low-Mg# clinopyroxene, high-TiO2 clinopyroxene, low-An plagioclase）, show that strong magma differentiation occurred within the crust. Nevertheless, significant discrepancies between those minerals and phenocrysts in the basalts （high-Fo olivine, high-An plagioclase） reflect the heterogeneity of magma differentiation. High Mg# （-~0.72） melt inclusions isobaric partial crystallization simulations suggest that the magma differentiation occurred at the depth shallower than 13.03 km below the seafloor, and both the vertical differentiation column shows distinct discrepancies from that of a steady-state magma chamber. Instead, a series of independent magma intrusions probably occurred within the crust, and their corresponding crystallized bodies, as the primary high-temperature thermal anomalies within the off-axis crust, probably act as the heat source for the development of the 14.0°S hydrothermal system.  相似文献   

Grain-size related nitrogen distribution in southern Yellow Sea surface sediments   总被引：1，自引：0，他引：1  

吕晓霞宋金明  袁华茂李学刚  詹天荣李宁高学鲁  石学法 《中国海洋湖沼学报》2005,23(3):306-316

Forty-eight surface sediments of the southern Yellow Sea are separated into three grain-size fractions. Four forms of extractable nitrogen (nitrogen in ion-exchangeable form (Nie), nitrogen in weak-acid extractable form (Nwa), nitrogen in strong-alkali extractable form (Nsa) and nitrogen in strong-oxidant form (N50))are obtained by the sequential extraction. The results show that the contents and the distributions of the extractable nitrogen in the southern Yellow Sea surface sediments are closely related to sediment grain size. The distributions ofNie, Nso and total nitrogen (TN) present positive correlations with fine particles content, while Nwa and Nsa does not have such correlation. The net contents of all the forms of nitrogen increase with sediment grain size finer.  相似文献   

Seasonal variation of carbon exchange of typical forest ecosystems along the eastern forest transect in China     

Zhang Leiming  Yu Guirui  Sun Xiaomin  Wen Xuefa  Ren Chuanyou  Song Xia  Liu Yunfen  Guan Dexin  Yan Junhua  Zhang Yiping 《中国科学D辑(英文版)》2006,49(2):47-62

The long-term and continuous carbon fluxes of Changbaishan temperate mixed forest (CBS), Qianyanzhou subtropical evergreen coniferous forest (QYZ), Dinghushan subtropical evergreen mixed forest (DHS) and Xishuangbana tropical rainforest (XSBN) have been measured with eddy covariance techniques. In 2003, different responses of carbon exchange to the environment appeared across the four ecosystems. At CBS, the carbon exchange was mainly determined by radiation and temperature. 0°C and 10°C were two important temperature thresholds; the former determined the length of the growing season and the latter affected the magnitude of carbon exchange. The maximum net ecosystem exchange (N _EE) of CBS occurred in early summer because maximum ecosystem photosynthesis (G _PP) occurred earlier than maximum ecosystem respiration (R _e). During summer, QYZ experienced severe drought and N _EE decreased significantly mainly as a result of the depression of G _PP. At DHS and XSBN, N _EE was higher in the drought season than the wet season, especially the conversion between carbon sink and source occurring during the transition season at XSBN. During the wet season, increased fog and humid weather resulted from the plentiful rainfall, the ecosystem G _PP was dispressed. The Q ₁₀ and annual respiration of XSBN were the highest among the four ecosystems, while the average daily respiration of CBS during the growing season was the highest. Annual N _EE of CBS, QYZ, DHS and XSBN were 181.5, 360.9, 536.2 and ?320.0 g·C·m^?2·a^?1, respectively. From CBS to DHS, the temperature and precipitation increased with the decrease in latitude. The ratio of N _EE/R _e increased with latitude, while R _e/G _PP, ecosystem light use efficiency (L _UE), precipitation use efficiency and average daily G _PP decreased gradually. However, XSBN usually escaped such latitude trend probably because of the influence of the south-west monsoon climate which does not affect the other ecosystems. Long-term measurement and more research were necessary to understand the adaptation of forest ecosystems to climate change and to evaluate the ecosystem carbon balance due to the complexity of structure and function of forest ecosystems.  相似文献   

Hydrologic implications of the isotopic kinetic fractionation of open-water evaporation     

Wei Xiao  Yufei Qian  Xuhui Lee  Wei Wang  Mi Zhang  Xuefa Wen  Shoudong Liu  Yongbo Hu  Chengyu Xie  Zhen Zhang  Xuesong Zhang  Xiaoyan Zhao  Fucun Zhang 《中国科学:地球科学(英文版)》2018,61(10):1523-1532

The kinetic fractionation of open-water evaporation against the stable water isotope H_2 ~(18)O is an important mechanism underlying many hydrologic studies that use ~(18)O as an isotopic tracer. A recent in-situ measurement of the isotopic water vapor flux over a lake indicates that the kinetic effect is much weaker(kinetic factor 6.2‰) than assumed previously(kinetic factor14.2‰) by lake isotopic budget studies. This study investigates the implications of the weak kinetic effect for studies of deuterium excess-humidity relationships, regional moisture recycling, and global evapotranspiration partitioning. The results indicate that the low kinetic factor is consistent with the deuterium excess-humidity relationships observed over open oceans.The moisture recycling rate in the Great Lakes region derived from the isotopic tracer method with the low kinetic factor is a much better agreement with those from atmospheric modeling studies than if the default kinetic factor of 14.2‰ is used. The ratio of transpiration to evapotranspiration at global scale decreases from 84±9%(with the default kinetic factor) to 76±19%(with the low kinetic factor), the latter of which is in slightly better agreement with other non-isotopic partitioning results.  相似文献   

冲绳海槽表层沉积物放射虫属种空间分布特征及其影响因素     

董智  石学法  邹欣庆  邹建军  杨宝菊  刘季花  程振波 《地学前缘》2020,27(6):300-312

为探究冲绳海槽放射虫属种的空间分布特征及其海洋学意义,对采自冲绳海槽北部、中部和南部3个海域的34个表层沉积物中的放射虫群落组成特征进行了系统研究。总体看来,冲绳海槽表层沉积物放射虫丰度较高,群落组成以热带-亚热带暖水放射虫属种为主,其中优势种为Tetrapyle octacantha group、Spongodiscus resurgens和Euchitonia furcata。结果表明冲绳海槽放射虫属种存在明显的区域差异性,除T.octacantha group以外,其余暖水指示种含量总体上均呈现南高北低的变化趋势。冲绳海槽北部陆架-陆坡区受长江冲淡水的影响,温度和盐度变化较为剧烈,因此可能不利于大多数放射虫暖水指示种的发育,但T.octacantha group却因自身适宜生存的温度范围较大,进而得以在冲绳海槽北部陆坡区呈现出高值。较高的中层水温度可能是抑制亚北极中层水指示种Cycladophora davisiana在冲绳海槽分布的主要因素,而冲绳海槽的高海槛则限制了太平洋深层水种Carpocanistrum papillosum和Cornutella profunda的入侵。冲绳海槽放射虫的空间分布对区域海洋环境特征有着很好的响应,因此可以为古环境重建研究提供重要依据。  相似文献   

渤海地区全新世孢粉序列及古环境演化   总被引：2，自引：0，他引：2  

陈金霞  石学法  乔淑卿 《海洋学报》2012,34(3):99-105

通过对取自黄河口外泥质区的BH-264孔的沉积孢粉进行分析,对渤海地区全新世古植被和古环境演化历史进行了恢复。在早全新世(距今9.5~7.6 ka)渤海地区气候温暖湿润,在陆缘海滨地带出现大量沼泽湿地,上面生长着莎草和香蒲等植被,在周围的山地、丘陵和平原地区植被以松属和落叶栎属为主,并伴生着桦木属、榆科、桑科等树种;在中全新世(距今7.6~5.8 ka)温度的升高和海平面上升,使BH-264孔沉积孢粉中松属占主导地位,不利于远距离传播的草本植物花粉含量降为全新世最低值;在距今5.8 ka以后东亚夏季风减弱和降雨量减少导致渤海西部陆源海滨地带植被以旱生草本藜科、蒿属和菊属为主,黄河三角洲的形成缩短了研究区的离岸距离,使这些草本植物花粉易于传播到BH-264孔中沉积。  相似文献   

Distribution of major and trace elements in surface sediments of Hangzhou Bay in China   总被引：2，自引：0，他引：2  

LIU Shengf  LIU Yanguang  YANG Gang  QIAO Shuqing  LI Chaoxin  ZHU Zhiwei  SHI Xuefa 《海洋学报(英文版)》2012,31(4):89-100

The Inductively Coupled Plasma Optical Emission Spectrometer was used to analyze sediment samples collected from the Hangzhou Bay to determine major and trace elemental concentrations. Based on these concentrations, the study area can be classified into three geochemical provinces. Province I covers the northern Hangzhou Bay area and contains high concentrations of Al₂ O₃ , Fe₂ O₃ , MgO, Na₂ O, K₂ O, MnO, Cr, Cu, Ni, Pb, V, Co and Zn. Province III is located in the western Hangzhou Bay, near the Qiantang River mouth, and contains high concentrations of SiO₂ , Na₂ O, P₂ O₅ , TiO₂ , Cr, Sr, Zr. Province II is located in the middle and eastern Hangzhou Bay, with the medium concentrations of major and trace elements. The results also demonstrate that the grain size is the dominating factor controlling the spatial variations of elemental concentrations, and the Changjiang River （Yangtze River） and Qiantang River sediments play an important role in the distribution of these elements. Anthropogenic impact on heavy metal concentrations （especially Cr, Sr and Zr） can be detected in the surface sediments near the Qiantang River mouth.  相似文献