古海洋生产力与氧化还原指标——元素地球化学综述

海洋表层初级生产力大小以及水体氧化还原条件是古海洋和古气候研究的重要内容,而元素地球化学是研究初级生产力以及氧化还原条件最常用的手段。主量元素Fe和Si是限制生物的营养元素,痕量金属元素Cu、Ni和Zn是微营养元素,而营养条件是沉积生产力的限制因素,因此这些元素的含量能反映初级生产力大小。Ba和Mo是随有机质一起沉淀下来的,与水体的有机碳通量有关,也是古生产力大小的指标。对氧化还原敏感的痕量金属元素含量（如Cr、V和U）以及元素比值（如V/（V＋Ni）、V/Cr、Ni/Co、U/Th和V/Sc）常用来重构水体的氧化还原条件。     

1959-2008长江源被净初级生产力对气候变化的响应

基于长江源区1959-2008年月平均气温、最高气温、最低气温、相对湿度、降水量、风速和日照时数等气候要素资料,应用修订的Thornthwaite Memorial模型计算了50a被净初级生产力,分析其年际和年代际变化特征及其对气候变化的响应.结果表明：1959-2008年间,研究区年NPP变化呈显著上升趋势,NPP变...     

2008年夏季西北冰洋观测区叶绿素a和初级生产力粒级结构

对2008年夏季在西北冰洋172°～143.6°W的楚科奇海及其北部海区对粒度分级叶绿素a和初级生产力现场观测资料,对观测区的空间分布特征进行了研究.结果表明,观测海区表层叶绿素a浓度为0.013～19.367 μg/dm3,平均值为0.677士2.2661 μg/dm3,次表层水叶绿素a浓度高于其它水层.水柱叶绿素a...     

Nitrogen uptake and primary productivity rates in the Mid-Atlantic Bight (MAB)

Nutrient concentrations, primary productivity, and nitrogen uptake rates were measured in coastal waters of the Mid-Atlantic Bight over a two-year period that included measurements from all four seasons. In order to assess carbon productivity and nitrogen demand within the context of the physical environment, the region was divided into three distinct hydrographic regimes: the Chesapeake and Delaware Bay outflow plumes (PL), the southern Mid-Atlantic shelf influenced by the Gulf Stream (SS), and the mid-shelf area to the north of the Chesapeake Bay mouth (MS). Annual areal rates of total nitrogen (N) uptake were similar across all regions (10.9 ± 2.1 mol N m⁻² y⁻¹). However, annual areal rates of net primary productivity were higher in the outflow plume region (43 mol C m⁻² y⁻¹), than along the Mid-Atlantic shelf and in areas influenced by the Gulf Stream (41 and 34 mol C m⁻² y⁻¹, respectively). Rates of net primary productivity were not well correlated with Chl a concentrations and were uncoupled with net N uptake rates. Seasonally averaged annual areal rates of net primary productivity for the Mid-Atlantic Bight measured in this study were higher than those calculated in previous decades and provide important validation information for biogeochemical models and satellite remote sensing algorithms developed for the region.     

Response of the shortgrass steppe plant community to fire

Fire is an important driver of ecological pattern and process in grasslands worldwide, although its role in semi-arid systems is less well known. We used published studies and new experimental research to 1) provide a synthesis of existing knowledge of fire in the semi-arid grasslands of the North American Great Plains, and 2) assess the degree of similarity in semi-arid and mesic grassland responses to fire in this region. Based on published studies, burning has neutral to negative effects on aboveground productivity in semi-arid grasslands and variable effects on plant communities. To more rigorously assess fire effects, replicated experimental plots were established in ungrazed shortgrass steppe in northern Colorado and prescribed spring fire was applied in 2006 and 2007, 2006 only, or not at all. Aboveground net primary productivity decreased or remained unchanged with burning. Plant community changes included increases in perennial forbs, decreases in annual grasses and a positive response in annual forbs to the combination of fire and a wet spring in 2007. Combined, these results indicate that post-fire changes in productivity in semi-arid grasslands are neutral to negative, in contrast to positive responses in mesic grasslands, and not strongly negative as previously assumed.     

土层厚度对紫色土坡地生产力的影响

通过紫色土坡地土层厚度的调查与不同土层厚度的小区对比试验,研究紫色土薄层坡地的生产力特性. 结果表明,约73%的紫色土坡耕地土层厚度为20-60 cm.土层厚度是紫色土生产力的基本限制条件.土层越薄, 作物株高、生物量和产量愈低,生产力愈低;土层越厚,生物量、产量愈高,生产力愈高,土层厚度的影响在玉米季尤 为突出,20 cm、40 cm小区夏玉米产量仅为60 cm小区的50%、74%,为80 cm小区的28%、40%,100 cm小区的23%、34%.当土壤厚度超过60 cm,小麦、玉米的株高、生物量及根重差异不显著,而土壤蓄水可抵御紫色丘陵区连续20 d的夏旱,因此,可初步判定60 cm土层为紫色土生产力临界土层.60cm以上厚度的紫色土可维持基本稳定的生产力水平.     

北冰洋西部楚科奇海盆晚第四纪生源沉积物及其古海洋学意义

通过北冰洋西部楚科奇海盆M03孔晚第四纪以来生源沉积物,有孔虫丰度和冰筏碎屑(Ice．Rafted Detritus,IRD)的综合研究表明,海洋氧同位素(Marine Isotope Stage,MIS)7期以来,碳酸钙(CaCO )含量和浮游有孔虫丰度在间冰期的增加和冰期的降低,分别指示大西洋水输入的加强和减弱。而有机碳(TOC)和生源蛋白石(Biogenic Opa1)含量的变化可能主要与输入到海底的TOC降解和Opal溶解作用与底层水中的溶解氧有关。间冰期低的TOC和Opal含量可能反映楚
科奇海盆海冰覆盖减少,营养盐供给多,表层生产力增加,通气作用好,底层水富氧,降解和溶解作用增强,保存在沉积物中的TOC和Opal减少;而冰期相对高的TOC和Opal含量可能反映楚科奇海盆海冰覆盖时间较长,营养盐供给少,表层生产力较低,通气作用差,底层水少氧,降解和溶解作用减弱,保存在沉积物中的TOC和Opal增多。     

1999/2000年夏季环南极表层海水叶绿素a和初级生产力

中国第 1 6次南极考察期间 ,作者随雪龙船于 1 999年 1 1月 2 2日至 2 0 0 0年 1月 1 8日从澳洲西南部到达东南极普里兹湾 ,后经南印度洋 -南大西洋 -德雷克海峡 -南大西洋 -南印度洋返回普里兹湾。航渡中定时采集表层海水 ,进行水温、盐度、营养盐、浮游生物现存量和光合作用速率的现场观测 ,研究环绕南极海域表层水叶绿素 a和初级生产力的分布特征。结果表明 ,南大洋表层水营养物质、浮游生物现存量和初级生产力分布具明显的区域性特征 ,南极辐合带以南的南极水营养盐浓度高于亚南极水和亚热带水。叶绿素 a浓度与营养物质的分布趋势一致 ,南极水、亚南极水和亚热带水的平均叶绿素 a浓度分别为 1 .77、1 .40和 0 .2 1 μg/dm3。在环绕南极的大洋中 ,南大西洋海域营养物质丰富 ,海水最为肥沃 ,叶绿素 a浓度和初级生产力高于南印度洋和德雷克海峡。在短期往返东南极 -西南极 -东南极的航渡观测中 ,由于南极夏季水温的升高 ,陆缘冰融化 ,冰藻释放 ,长城湾至普里兹湾的西 -东向航渡中观测的初级生产力、浮游植物细胞丰度、叶绿素 a浓度和光合作用同化数分别比普里兹湾至长城湾的东 -西向航渡中高 1 45%、1 1 3%、68%和 1 8%。与 1 0年前的观测结果比较 ,南大西洋仍为高生物量和高生产力海区 ;1 999/2 0 0 0     

森林经营措施对土壤的扰动和压实影响

根据森林经营措施对林地土壤的扰动和压实及其对树木生长和森林生产力的影响 ,指出森林经营措施对土壤造成的干扰是长期存在的 ,干扰强度越大 ,对林地生产力的影响越严重。从伐区作业、林地清理、整地、幼林抚育等方面提出减少土壤受扰动和压实的具体措施 ,为减少经营措施对林地生态系统的影响 ,从而改进传统的森林经营措施 ,实现森林可持续经营提供借鉴。     

Economic development in tropical Africa from a geographical perspective: a comparative study of African economies

Tropical Africa is often seen to have problem economies that are very much alike and suffer from the same development problems. This view is questioned in exploratory analyses of levels of wealth, spatial productivity, the structure of the economy and aspects of the openness of economies and the way they have changed between 1965 and 1995. The analyses reveal differences between economies in both degree and kind. Change to economies was not unidirectional so that they became more disparate and differentiated. The exploratory analyses were extended using factor analysis as a diagnostic tool on a 19-variable by 25 country data set for 1985, 1990 and 1995. This confirmed the findings of the exploratory analyses and revealed changes in the structure of the factors reflecting development in the period. The results are discussed in the context of the literature in a search for explanation and policy formulation.