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841.
China's policy on structural adjustment of its agriculture is an effective instrument for increasing agricultural production and developing the rural economy. The policy interventions used included converting cultivated land from growing grain crops to cash crops and increasing the production of meat, eggs and milk. The impacts of these changes on grain supply between 1998 and 2004 are identified and quantified at national and regional levels. The data on cultivated land diverted to other purposes are presented for the benefit of the decision maker. The paper concludes that the policy had significant impacts on China's grain supply, which declined by 14.4% of the total grain output in 1998. However, nearly 40% of the cultivated land at national level could potentially be converted by 2010. Regional disparities in the extent of the reduction in grain supply and in land conversion are highlighted with reference to different economic conditions and policy directions. 相似文献
842.
Population genetics of Crassostrea ariakensis in Asia inferred from microsatellite markers 总被引:1,自引:0,他引:1
Jie Xiao Jan F. Cordes Haiyan Wang Ximing Guo Kimberly S. Reece 《Marine Biology》2010,157(8):1767-1781
Crassostrea ariakensis is an important aquacultured oyster species in Asia, its native region. During the past decade, consideration was given to
introducing C. ariakensis into Chesapeake Bay, in the United States, to help revive the declining native oyster industry and bolster the local ecosystem.
Little is known about the ecology and biology of this species in Asia due to confusion with nomenclature and difficulty in
accurately identifying the species of wild populations in their natural environment. Even less research has been done on the
population genetics of native populations of C. ariakensis in Asia. We examined the magnitude and pattern of genetic differentiation among 10 wild populations of C. ariakensis from its confirmed distribution range using eight polymorphic microsatellite markers. Results showed a small but significant
global θ
ST (0.018), indicating genetic heterogeneity among populations. Eight genetically distinct populations were further distinguished
based on population pairwise θ
ST comparisons, including one in Japan, four in China, and three populations along the coast of South Korea. A significant positive
association was detected between genetic and geographic distances among populations, suggesting a genetic pattern of isolation
by distance. This research represents a novel observation on wild genetic population structuring in a coastal bivalve species
along the coast of the northwest Pacific. 相似文献
843.
Journal of Material Cycles and Waste Management - The reclamation of waste rigid polyurethane foam (WRPUF) is capable of realizing both circulations of waste and protection of the environment. In... 相似文献
844.
Cong Li Jian Zhang Shuang Liang Huu Hao Ngo Wenshan Guo Yingying Zhang Yina Zou 《Environmental science and pollution research international》2013,20(8):5353-5360
Despite the many benefits of denitrifying phosphorus removal process, the significant generation of nitrous oxide (N2O), a potent greenhouse gas, remains a problem for this innovative and promising process. To better understand and more effectively control N2O generation in denitrifying phosphorus removal process, batch experiments were carried out to investigate the main causes of N2O generation, based on which the control measures were subsequently proposed. The results showed that N2O generation accounted for 0.41 % of the total nitrogen removal in denitrifying phosphorus removal process, whereas, in contrast, almost no N2O was generated in conventional denitrification process. It was further demonstrated that the weak competition of N2O reductase for electrons and the high nitrite accumulation were the two main causes for N2O generation, evidenced by N2O production and reduction rates under different conditions. Accordingly, the reduction of N2O generation was successfully achieved via two control measures: (1) the use of continuous nitrate addition reducing N2O generation by around 91.4 % and (2) the use of propionate as the carbon source reducing N2O generation by around 69.8 %. 相似文献
845.
Carrousel氧化沟的三维流场模拟与分析 总被引:1,自引:0,他引:1
利用CFD的Fluent软件,采用标准的三维K—ε紊流模型,对桂林市七里店污水处理厂1#氧化沟的流场进行了数值模拟,对导流墙和推进器附近的流速进行了计算分析。结果表明,氧化沟下层流速较低,局部区域流速低于0.2m/s。为了防止污泥沉降,应进一步降低推进器位置。能量损失分析表明,卡罗塞氧化沟能量损失主要来源于沿程摩擦损失和局部损失。可通过增加墙体光滑度、降低入口高度以及增加导流墙的曲率半径等措施减少能量损失,改善现有氧化沟的水力特征。 相似文献
846.
Deji Reservoir is situated in the middle of Taiwan on the upstream catchment of the Dajia stream with an area of over 60,160 ha. The embankment stands 180 m high and is the tallest concrete arch dam in Taiwan. This dam stores 1.7 billion cubic meters of valid volume water. It provides over 370 million kilowatt-hours of electricity annually. It is also an important facility for operating flood control, hydroelectricity, irrigation, public water supply, etc. Seventy-two percent of the terrain is at 2,000- to 3,000-m altitude, and 5.2% is above 3,200-m altitude. More than 59% of the area is covered with steep topography of 55% slope. Only 7.9% of the area is shown with gentle slopes of less than 30% slope, which are located among the two banks of main streams with the altitudes ranging from 1,500 to 2,500 m. Most of the gentle slopes are used for temperate zone fruit, vegetable, and tea plantations. This land-use immediately adjoins a reservoir catchment region, resulting in an enormous impact on the mountainous environment. This study reviewed human-developed land-use area to properly address and evaluate norms for mitigating the impacts on the reservoir. The initial investigation brought up the parameters of gradient, slope movement types and processes, distance to the reservoir, location of developed area and distance with the farm road, etc. Local investigation and global information system technology were conducted in this research. We focused on segregating the terrain types of indisposed land-use. A different land-use management strategy is also analyzed. 相似文献
847.
Permeable reactive barriers (PRBs) are an alternative technology to treat mine drainage containing sulfate and heavy metals. Two column experiments were conducted to assess the suitability of an organic carbon (OC) based reactive mixture and an Fe0-bearing organic carbon (FeOC) based reactive mixture, under controlled groundwater flow conditions. The organic carbon mixture contains about 30% (volume) organic carbon (composted leaf mulch) and 70% (volume) sand and gravel. The Fe0-bearing organic carbon mixture contains 10% (volume) zero-valent iron, 20% (volume) organic carbon, 10% (volume) limestone, and 60% (volume) sand and gravel. Simulated groundwater containing 380 ppm sulfate, 5 ppm As, and 0.5 ppm Sb was passed through the columns at flow rates of 64 (the OC column) and 62 (the FeOC column) ml d− 1, which are equivalent to 0.79 (the OC column) and 0.78 (the FeOC column) pore volumes (PVs) per week or 0.046 m d− 1 for both columns. The OC column showed an initial sulfate reduction rate of 0.4 µmol g (OC)− 1 d− 1 and exhausted its capacity to promote sulfate reduction after 30 PVs, or 9 months of flow. The FeOC column sustained a relatively constant sulfate reduction rate of 0.9 µmol g (OC)− 1 d− 1 for at least 65 PVs (17 months). In the FeOC column, the δ34S values increase with the decreasing sulfate concentration. The δ34S fractionation follows a Rayleigh fractionation model with an enrichment factor of 21.6‰. The performance decline of the OC column was caused by the depletion of substrate or electron donor. The cathodic production of H2 by anaerobic corrosion of Fe probably sustained a higher level of SRB activity in the FeOC column. These results suggest that zero-valent iron can be used to provide an electron donor in sulfate reducing PRBs. A sharp increase in the δ13C value of the dissolved inorganic carbon and a decrease in the concentration of HCO3− indicate that hydrogenotrophic methanogenesis is occurring in the first 15 cm of the FeOC column. 相似文献
848.
849.
850.
Cao Xinchun Wu Mengyang Zheng Yalian Guo Xiangping Chen Dan Wang Weiguang 《Regional Environmental Change》2018,18(2):465-475
Regional Environmental Change - China faces the dual challenge of water scarcity and food security with continued population growth. This paper explores methods to meet that demand without... 相似文献