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在天然气水合物发育区海底沉积物中甲烷厌氧氧化作用(AOM)是碳循环的重要组成部分。通过定量计算表层沉积物中甲烷迁移转化通量,可以更准确评估甲烷来源碳对沉积物碳库和海洋深部碳库影响。本文利用反应―运移模型对采集于南海神狐水合物发育区两个站位(SH-W19-PC、SH-W23-PC)采集的孔隙水SO42-、溶解无机碳(DIC)、Ca2+剖面进行拟合,同时对DIC碳同位素进行分析,确定近海底沉积物中的碳循环。研究显示两个站位孔隙水中SO42-和Ca2+浓度在剖面上随深度呈线性减少,DIC浓度随深度逐渐增加,其δ13CDIC值随深度逐渐降低至约-25‰,表明两个站位存在一定程度的AOM。模拟计算两个站位沉积物孔隙水溶解甲烷向上的通量分别为25.9和18.4 mmol·m-2 a-1,AOM作用产生的DIC分别占其总DIC量的70.7%和60%。由沉积物向海水中释放的DIC通量占DIC汇的约60%。因此,在天然气水合物发育区向海底渗漏甲烷大部分以DIC的形式进入上覆海水,这些具有极负碳同位素值的甲烷来源的DIC可能对局部深海碳库产生一定的影响。 相似文献
3.
ABSTRACT Understanding temporal patterns in restored environments is important for identifying potential barriers to recovery and improved management of degraded habitats. In this paper, we use temporal beta diversity analyses to compare invertebrate community recovery trajectories in three restored agricultural stream sites under different integrated catchment plans, a native forest reference site, and two unmodified pasture control stream sites over 24 years. The restored sites diverged from their initial community composition over time and became more similar to the reference site community, which was relatively stable over time. Variation partitioning showed that prior to restoration beta diversity was primarily associated with environmental and spatial drivers, whereas post-restoration beta diversity was more influenced by temporal and environmental drivers, including changes in substrate size, fine sediments, water clarity, and nutrients, as well as temperature and flow regime. Species’ contributions to beta diversity varied between sites and years, with sensitive EPT taxa contributing more in reference and control sites. However, contributions of some EPT species, particularly mayflies, increased in restored sites post-ICM. In summary, after nearly two decades of ICM, restored stream sites show recovery towards reference conditions, yet differences persist, indicating that rehabilitation may take longer, depending on the restoration goals. 相似文献
4.
Abstract. The production of the hymenosomatid crab Elamenopsis kempi was calculated for a period of 18 months from a subtidal area of the Garmat-Ali river, southern Iraq. The highest average individual somatic energy was attained in spring. Maximum population biomass and production were attained by the summer cohort and the minimum values were exhibited by the overwintering cohort. The fluctuations of the average population biomass were followed throughout the sampling period. Average total annual population production was 13.2 g DW · m-2 · a-1 and the P/B ratio was 5.9. These values were compared with those of the most common crustaceans in the region. 相似文献
5.
《Limnologica》2020
Partitioning beta diversity into its two components of spatial turnover and nestedness is a more robust method for checking spatial variability in biological communities than calculating the total beta diversity alone. The relative contribution of spatial turnover and nestedness has been used to test the effects of climatic, environmental, spatial and temporal variables on community composition. In this study, we tested the effects of environmental factors and microhabitat features on total beta diversity and its spatial turnover and nestedness components using a comprehensive dataset of aquatic Heteroptera collected from four types of permanent freshwater habitats (i.e. streams, ponds, rock tanks and reservoirs) in the Western Ghats of India. We observed that communities in all four types of habitats were predominantly shaped by dissimilarity caused due to spatial turnover (>85 %). Each type of habitat showed the presence of one or more species uniquely associated with it, which might contribute to the turnover between communities. The abiotic environment (climatic factors, topological factors, soil characteristics and microhabitat features) as well as assemblage structure differed significantly between habitat types. Communities in each type of habitat were affected by different environmental factors, such as precipitation and temperature patterns for streams, altitude and rocky substrate for rock tanks, and soil characteristics and the presence of aquatic macrophytes for ponds and reservoirs. Assemblages observed in the four types of permanent habitats are thus compositionally distinct due to species replacements between local communities, which in turn are strongly influenced by environmental variables. Similar to previous studies, our results show that spatial turnover largely measures the same phenomenon as total beta diversity on a regional scale. 相似文献
6.
ABSTRACTIn the past, population growth in Australia's Northern Territory, as in other peripheral parts of high-income countries, has been driven by internal labour migration and migration from outside of Australia. These have been contributing to the high population turnover experienced in peripheral areas. Since 2010, the Northern Territory has experienced low (and even negative) population growth, and public policy is currently focused on migration as a lever to reverse this trend. However, the extent to which the characteristics of migrants influence the potential for longer-term population growth is poorly understood. This paper uses a new method to analyse the contributions of various types of migrants to both population turnover and retention. Two major sets of findings emerge: First, the significance of separating newer in-migrants from longer-term residents when analysing migration patterns; and secondly, the contribution of age, gender, Indigenous status, international origin, wages and industry of employment to the Northern Territory's population turnover. The research suggests that current forms of migration favour people who are likely to stay for only short periods, and have high wage demands. The main policy inference is that long-term population growth will likely not eventuate unless new forms of migration can be stimulated. 相似文献
7.
新型城镇化建设鼓励农村剩余劳动力向城市转移,同时农村劳动力转移的持续发展又进一步加大了对新型城镇化建设的支持力度.由于劳动者的整体素质较低以及务工领域低端化等因素的存在,农村劳动力转移具有一定的脆弱性.甘肃省城镇化水平滞后、城乡差距较大等问题依然突出,农户作为农村地区最主要的经济活动主体与最基本的决策单位,劳动力转移的状况直接影响到其生计水平和区域生态安全.以甘肃省14个地州市为研究区,通过对可持续生计框架的应用,揭示劳动力转移的关键性因素,定量评估劳动力转移对农户生计资本的影响程度,总结出有利于提高甘肃省农户发展能力、改善农户生计水平的政策建议,从而为促进西部地区可持续发展、缓解贫困、实现精准扶贫提供参考依据. 相似文献
8.
为了明确折扣方式下应税金额的确定方法,分别从计税销售额、营业额和所得额等方面进行分析,其结果将使纳税人的财务会计处理和具体纳税操作更为规范和准确。 相似文献
9.
This study investigated the distribution of Molgolaimus species (Nematoda) at different hierarchical spatial scales and observed the turnover of species along bathymetrical transects and among transects in two separate geographical regions. Samples from six transects (200–2000 m) from the Southern Oceans (SO) and four bathymetric transects (50–2000 m) from the Western Indian Ocean (WIO) were compared. Of the 30 species recorded, only one was common to both regions. WIO had higher local species richness than the SO. In both regions, the local scale was the greatest contributor to the total species richness. In the SO, there was no difference between species turnover at the different spatial scales, however, in the WIO, the turnover along bathymetrical transects was higher than among separated transects. For the particular genus studied, the evidence suggests that the study area in WIO has more widespread species and was better sampled, while the SO has many restricted species and it is most probably characterized by different biogeographical provinces. At the ocean scale (i.e. WIO versus SO), evolutionary histories may have strongly influenced nematodes species composition, while at local and regional scales, ecological processes are probably promoting species co‐existence and speciation. The high co‐existence of certain species at local scale is partially explained by species preference for different sediment layers. 相似文献
10.
Shizuo Tsunogai Kentaro Kawada Shuichi Watanabe Takafumi Aramaki 《Journal of Oceanography》2003,59(5):685-693
The distributions of CFC (chlorofluorocarbon) in the water column was determined twice in 2000 and 2001 in the northwestern
Japan Sea. In 2000 the CFC-11 concentration decreased almost exponentially with depth from 6 pmol/kg at a few hundred m deep
to 0.3 pmol/kg or less at the bottom of about 3400 m depth at three stations (40–41°N, 132–133°E) about 300 km off Vladivostok.
In 2001 the CFC-11 concentration increased sharply up to 2 pmol/kg in the bottom water, while it did not increase at a station
(42.0°N, 136.5°E) about 450 km away to the northeast. This is due to the renewal of the bottom water which is replaced by
the surface water flowing down along the continental slope, as suggested by Tsunogai et al. (1999), who proposed the continental shelf pump. Furthermore, an increase in the CFC-11 concentration was observed throughout
the entire water column above 3000 m depth, although the proportion of the increase was about 20%, which was one order of
magnitude smaller than that in the bottom water. The increase in inventory is almost four times larger than that in the bottom
water below 3000 m depth which is equivalent to about 1/6 of the total inventory found in 2000. The increase also means that
3% of the deep water was replaced by the recent surface water, or, if the turnover occurs every year, that the turnover time
of the deep water to be about 30 years.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献