Metal leaching and toxicity of denitrifying woodchip bioreactor outflow—Potential reuse application

The denitrifying woodchip bioreactor is designed to remediate nitrate-rich water, including those produced from aquaculture effluents. Reuse of treated bioreactor outflows in recirculating aquaculture would offer considerable water savings and valuable alkalinity recuperation. However, such bioreactors may leach detrimental wood-bound contaminants, preventing outflow reuse. To determine water reuse potential, woodchip media from two hardwood species (white ash, Fraxinus americana; Norway maple, Acer platanoides) were evaluated for 206 d under a range of operating conditions (start-up, steady-state, reducing conditions, and drying-rewetting cycles) for a spectrum of potentially harmful dissolved contaminants. Aerated outflows also were evaluated for acute and chronic toxicity to the biologically sensitive invertebrate Ceriodaphnia dubia. Dissolved metal leaching subsided within the first few weeks of operation, though initial concentrations of copper and zinc were detected at concentrations of concern. Elevated concentrations of tannins-lignin and total ammonia nitrogen were detected throughout the study and were influenced by operational phase. Acute toxicity was not generally detected, though chronic toxicity was observed during drying-rewetting cycles in the maple outflows. The measured toxicity was not correlated with water chemistry, indicating an additive effect of several toxicants. Overall, significant differences in outflow water quality between ash and maple wood species were negligible. Results indicated that bioreactor outflows may be applicable for aquacultural reuse, though reusing outflows immediately following start-up or restarting after a dry period would not be recommended.     

一类耗散非线性波动方程初边值问题整体解的存在与非存在性

本文考虑一类耗散非线性波动方程的初边值问题。用半(?)方法和先验估计论证了该问题小初值下在时间大范围的可解性、唯一性;并用凸性方法证明了(?)当条件下该问题的解在有限时间内发生爆破现象。     

河北山地森林的特点、地位和发展对策

河北的山地在植被上属于落叶阔叶林地带。河北山地的森林具有立地生产力较低，人工林和天然林年龄小，多与农田、果园和牧地等交叉分布的特点。河北的山地森林在改善山区的生态环境、维持生物多样性、供应城乡居民所需的用材和烧柴及果品、为人民提供游乐活动场所等方面起着重要的作用。河北山地森林应该遵循的发展方针是：要把山区的水土保持和生态环境建设列在首位；要以林为主，协调发展农、果、林、牧的关系；在培养森林上，要采取封山育林和人工造林并重的政策；要把经济林的发展和其他林种结合起来，重视自然保护区森林公园的建设。     

不同的施肥方式对剑麻施肥区域土壤微生物类群的影响

研究不同的施肥方式对剑麻施肥区域土壤微生物类群产生的影响。结果表明，不同施肥方式下土壤微生物总量各有差异，在总体数量上以细菌为主，真菌次之，再其次是放线茵，特殊生理类群是解磷茵居多，纤维素分解茵次之，固氮茵最少；但从土壤微生物多样性指数来看，则表现为土壤中主要微生物类群多样性指数是施肥点的土壤高于附近的土壤，而土壤中特殊生理微生物多样性指数则无此变化趋势，即微生物总数高的土壤，其多样性指数不一定高。因此评价土壤生物多样性应将二者结合起来。     

Spatial distribution of Aspergillus flavus and its toxigenic strains on commercial cottonseed from south Texas and its relationship to aflatoxin contamination

The structure of Aspergillus flavus communities associated with south Texas cottonseed was determined by analysing samples from 178 truckloads of commercial cottonseed from 35 gins, extending from Fort Bend County in the north to the Rio Grande Valley in the south, from September 1999 to October 2001. The number of colony-forming units (CFU) of A. flavus on the cottonseed, and the percentage of S strain (%S) were both correlated with aflatoxin contamination of cottonseed. The number of CFU differed between both regions and seasons, while %S differed only between regions. Comparison of maps of CFU and %S revealed that CFU shows a higher variation across years, while %S shows higher spatial variation. The Rio Grande Valley had significantly lower CFU and %S strain than the Coastal Bend and Upper Coast regions. Cottonseed produced in 1999 had significantly more A. flavus than that produced in either 2000 or 2001. Identification of factors dictating geographical variation in S-strain incidence may provide insights that will lead to improved aflatoxin management.     

休闲阅览室的建设

面对大量读者迫切的休闲需求，本文结合图书馆的实际，在一定实践经验的基础上，就为何要专设休闲阅览室和如何建设、管理好休闲阅览室等进行大胆深入的探讨。     

Seed survival and predation of Anoda cristata in soyabean crops

Anoda cristata is a troublesome annual broad-leaved weed in summer crops in the rolling Pampa in Argentina; seeds are the only source of regeneration of this species. Seed persistence or depletion is the result of survival and loss processes, including predation. The objective of this study was to determine survival at two burial depths in undisturbed soil and predation rates of A. cristata seeds in soyabean crops in different rotations and tillage systems. Survival was discontinuous and decreased to 25% after 35 months, after which no further reduction in survival was observed to the end of the experiment at 96 months. No differences in seed survival between seeds placed on the soil surface and buried 5 cm below the soil surface were found at 80 months, but at later times survival was lower for seeds placed on the soil surface. Predation rates ranged between 0.3% day⁻¹ and 6.7% day⁻¹. Of the models tested, a polynomial regression of the rate of predation with time gave the best representation of seed predation. From January to July, predation was higher in non-tillage plots in the wheat/soyabean rotation. There was no significant difference in predation rates between tillage systems in the soyabean monoculture and no difference between planting densities. Higher crop residue levels in non-tillage plots in the wheat/soyabean rotation was the dominant factor influencing seed predation, probably because such habitat favours the presence of seed predators.     

小麦条锈病流行程度趋势预测专家系统雏型

本文运用知识工程语言 M·1构造了一个用于小麦条锈病流行程度趋势预测的专家系统雏型。专家的知识用产生式规则来表示。知识库中的知识规则可相对独立,便于知识库的扩充和完善。