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791.
Primary production and rain use efficiency across a precipitation gradient on the Mongolia Plateau 总被引:25,自引:0,他引:25
Understanding how the aboveground net primary production (ANPP) of arid and semiarid ecosystems of the world responds to variations in precipitation is crucial for assessing the impacts of climate change on terrestrial ecosystems. Rain-use efficiency (RUE) is an important measure for acquiring this understanding. However, little is known about the response pattern of RUE for the largest contiguous natural grassland region of the world, the Eurasian Steppe. Here we investigated the spatial and temporal patterns of ANPP and RUE and their key driving factors based on a long-term data set from 21 natural arid and semiarid ecosystem sites across the Inner Mongolia steppe region in northern China. Our results showed that, with increasing mean annual precipitation (MAP), (1) ANPP increased while the interannual variability of ANPP declined, (2) plant species richness increased and the relative abundance of key functional groups shifted predictably, and (3) RUE increased in space across different ecosystems but decreased with increasing annual precipitation within a given ecosystem. These results clearly indicate that the patterns of both ANPP and RUE are scale dependent, and the seemingly conflicting patterns of RUE in space vs. time suggest distinctive underlying mechanisms, involving interactions among precipitation, soil N, and biotic factors. Also, while our results supported the existence of a common maximum RUE, they also indicated that its value could be substantially increased by altering resource availability, such as adding nitrogen. Our findings have important implications for understanding and predicting ecological impacts of global climate change and for management practices in arid and semiarid ecosystems in the Inner Mongolia steppe region and beyond. 相似文献
792.
Yu-San Han Yu-Liang Sun Yi-Fen Liao I-Chiu Liao Kang-Ning Shen Wann-Nian Tzeng 《Marine Biology》2008,155(6):613-621
The Japanese eel has dramatically declined in Asia since the 1970s. Over the past two decades, glass eel productivity in Taiwan has decreased, but is highly variable among each year catch, though the cause for this is unknown. The impact of both population decline and instability on genetic diversity, however, is unknown. In this study, we investigated changes in allele frequencies of Japanese eel recruitment events over the past 20 years using six polymorphic microsatellite DNA loci. Specimens of glass eels were collected yearly from a single location in northern Taiwan from 1986 to 2007. Overall genetic differentiation among all samples was very low but significant (FST = 0.002, P = 0.002), and only 2 out of 120 pairwise tests were significant. The relationship between genetic and temporal distance showed a slight but insignificant correlation (R2 = 0.03, P = 0.0504). There were no overall significant differences in allelic richness (P = 0.35) or genetic heterozygosity (P = 0.73) among annual recruitment events. No apparent loss of genetic diversity and occurrence of a genetic bottleneck for eel populations were observed. Estimates of the effective population size (Ne) generally exceeded 500, although confidence intervals were very wide. While El Niño /Southern Oscillation (ENSO) events had little impact on genetic diversity, they may account for the annual fluctuation in glass eel catch. These results indicate long-term stability of genetic diversity in the Japanese eel with little evidence for sweepstakes recruitment. 相似文献
793.
Human health risk assessment of explosives and heavy metals at a military gunnery range 总被引:1,自引:0,他引:1
In this research, a risk assessment was undertaken in order to develop the remediation and management strategy of a contaminated
gunnery site, where a nearby flood controlling reservoir is under construction. Six chemicals, including explosives and heavy
metals, posing potential risk to environmental and human health, were targeted in this study. A site-specific conceptual site
model was constructed, based on effective, reasonable exposure pathways, to avoid any overestimation of the risk. Also, conservative
default values were adapted to prevent underestimation of the risk when site-specific values were not available. The risks
posed by the six contaminants were calculated using the API’s Decision Support System for Exposure and Risk Assessment, with
several assumptions. In the crater-formed-area (Ac), the non-carcinogenic risks (i.e., HI values) of tri-nitro-toluene (TNT)
and Cd were slightly larger than 1, but for RDX (Royal Demolition Explosives) was over 50. The total non-carcinogenic risk
of the whole gunnery range was calculated to be 62.5, which was a significantly high value. The carcinogenicity of Cd was
estimated to be about 10−3, while that for Pb was about 5 × 10−4, which greatly exceeded the generally acceptable carcinogenic risk level of 10−4–10−6. It was concluded from the risk assessment that there is an immediate need for remediation of both carcinogens and non-carcinogens
before construction of the reservoir. However, for a more accurate risk assessment, further specific estimations of the changes
in environmental conditions due to the construction of the reservoir will be required; and more over, the effects of the pollutants
to the ecosystem will also need to be evaluated. 相似文献
794.
795.
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797.
交联阳离子淀粉的合成及其对重金属离子的吸附 总被引:9,自引:4,他引:5
通过正交实验合成了取代度为0.568的交联阳离子淀粉。考察了溶液pH、螯合剂用量、重金属离子初始浓度对交联阳离子淀粉去除重金属离子效果的影响。当重金属离子初始质量浓度为50mg/L、螯合剂投加量为0.5g/U时,Pb^2 ,Cu^2 ,Cr^3 在溶液pH为6时的去除率达到最高,分别为97.94%,99.46%,84.30%,而Cd^ 在溶液pH为7时的去除率达到最高,为99.36%。实验结果表明,交联阳离子淀粉是一种有效去除废水中重金属的处理剂。 相似文献
798.
2,3,7,8,-四氯苯噁英对NIH小鼠早期妊娠和生殖激素的影响 总被引:1,自引:0,他引:1
用不同剂量的2,3,7,8 四氯苯二英(2,3,7,8 tetrachlorodibenzopdioxin,TCDD)对小鼠胚胎附植数量和生长发育情况进行剂量反应评估,分析TCDD对假孕小鼠子宫蜕膜生长状况的影响以及比较胚胎种植前后染毒效果.所有样本采集血液,测定母体血清雌二醇和孕酮的浓度变化.结果表明,50和100ng·(kg·d)-1TCDD处理的孕鼠,胚胎附植数量明显减少(P<0 05),着床后胚胎出现发育迟缓,质量减轻(P<0 05);同等剂量TCDD处理的假孕小鼠,子宫蜕膜生长受到了极显著的抑制(P<0 01);种植前后染毒效果比较发现种植前期染毒的小鼠胚胎对TCDD更为敏感.母体血清雌二醇浓度随剂量和染毒时段有不同程度的升高,而孕酮浓度则极显著下降(P<0 01).由此表明低剂量TCDD可能通过对生殖激素的干扰,强烈影响NIH小鼠妊娠早期生殖生理状态和着床后胚胎的发育.实验同时证明小鼠也可作为早期妊娠毒物研究的供试动物,用以筛选动物和人类早期妊娠的有害化合物. 相似文献
799.
阻抑动力学光度法测定痕量邻二硝基苯 总被引:2,自引:0,他引:2
研究发现,在盐酸介质中,痕量邻二硝基苯能灵敏地阻抑溴酸钾氧化甲基红褪色的反应。研究了该阻抑褪色反应的最佳条件,建立了一种测定痕量邻二硝基苯的新方法。该方法线性范围为0.0~0.16μg,检测限为1.15×10-10gmL。用于环境水样中邻二硝基苯的测定,结果满意。 相似文献
800.