Surface sediments were collected from 122 sites in the upstream of the Yellow River, China. The concentration of Fe, Mn, Cu, Ni, Zn, Cr, Pb, and Cd in sediments was investigated to explore the spatial distribution based on statistics and interpolation method. The results suggested that the concentrations of heavy metals were lower than potential effect levels (PEL). The samples above threshold effect level (TEL) for Pb and Zn were less than 10%, while almost 50% of samples for Ni exceeded PEL. Pb and Zn in sediments performed little or no adverse effects on the aquatic ecosystems. Higher concentrations of all heavy metals occurred in Qinghai and Gansu sections; the concentrations of Cu, Ni, and Zn were significantly higher than the Inner Mongolia section. Lower concentration of Fe, Mn, Cu, Ni, and Zn appeared in Qinghai section; the concentrations of Fe, Mn, Cr, and Pb manifested relatively steady and similar distributions and approximately decreasing tendency along the upstream of Yellow River.
河流生态系统的生物组成、结构和功能依赖于河流水流的天然动态变化特征,即河流水文情势。变异性范围法(Range of Variability Approach,RAV)被广泛应用于评估河流生态系统是否得到维护。将RVA法的思路扩展到生态流量的计算,提出了一种简便、立足整体河流水文情势的生态流量估算方法。该方法使用均值与RVA阈值差计算了生态流量值,为维持河流健康生态系统提供支持。将该方法应用于南水北调西线一期工程中泥曲河的生态流量估算,得到引水坝址仁达处年可调径流量为6.44亿m3,与其他生态需水估算方法的结论基本一致。另提出了可支配系数反映河流流量可调用状况。南水北调西线一期工程计划从泥曲调水8亿m3·a-1,从RVA法的理念来看,该方案对仁达至朱巴河段的生态系统将构成威胁,需谨慎实施。 相似文献
The base catalyst LZ-2, which was the mixture of CaO and Na–NaOH/Al2O3·3H2O, was chosen for the decomposition of phenol tar to generate valuable chemicals. The selectivity of LZ-2 for dimethyl phenyl carbinol, α-methyl styrene dimer and cumenyl phenol was 100%, 100% and 98%, respectively. Under the optimum operating conditions of catalyst 2.5 wt%, operating temperature 603.15 K and decomposition time 3.5 h, decomposition ratios of cumenyl phenol and dimethyl phenyl carbinol were 98.7% and 99.97%, respectively. In addition, the experimental repeatability demonstrated that the total yield of valuable chemicals still reached 90.1% after the catalyst being used five times. Mass and energy balance indicated that the catalytic decomposition was a high potential for the recycling of chemicals from phenol tar. 相似文献
Sustainable water use is seriously compromised in the North China Plain (NCP) due to the huge water requirements of agriculture,
the largest use of water resources. An integrated approach which combines the ecosystem model with emergy analysis is presented
to determine the optimum quantity of irrigation for sustainable development in irrigated cropping systems. Since the traditional
emergy method pays little attention to the dynamic interaction among components of the ecological system and dynamic emergy
accounting is in its infancy, it is hard to evaluate the cropping system in hypothetical situations or in response to specific
changes. In order to solve this problem, an ecosystem model (Vegetation Interface Processes (VIP) model) is introduced for
emergy analysis to describe the production processes. Some raw data, collected by investigating or observing in conventional
emergy analysis, may be calculated by the VIP model in the new approach. To demonstrate the advantage of this new approach,
we use it to assess the wheat-maize rotation cropping system at different irrigation levels and derive the optimum quantity
of irrigation according to the index of ecosystem sustainable development in NCP. The results show, the optimum quantity of
irrigation in this region should be 240–330 mm per year in the wheat system and no irrigation in the maize system, because
with this quantity of irrigation the rotation crop system reveals: best efficiency in energy transformation (transformity = 6.05E + 4 sej/J);
highest sustainability (renewability = 25%); lowest environmental impact (environmental loading ratio = 3.5) and the greatest
sustainability index (Emergy Sustainability Index = 0.47) compared with the system in other irrigation amounts. This study
demonstrates that application of the new approach is broader than the conventional emergy analysis and the new approach is
helpful in optimizing resources allocation, resource-savings and maintaining agricultural sustainability. 相似文献