用灰色理论予测我区粮食产需平衡问题

本文是根据我区几年来,粮食生产和社会消费量的历史资料,用灰色系统理论建立了数学模型,经验证,模型符合要求,用此模型预测了我区近中期粮食生产和消费的变动趋势。根据预测结果的分析,到1995年实现我区粮食自给是可能的,但必须在提高单产和增加细粮生产的问题上,采取相应的对策。     

Hydropower and instream flow requirements for fish in Sweden

SwedPower AB, Stockholm, Sweden Standardized methods for determining instream flow needs in connection with hydropower development have still not been established in Sweden. However, claims related to conflicting uses of running waters have long engaged the Water Right Courts. Historically, the floating of timber has constituted a strong reason for regulating rivers. Later, the creation of large reservoirs and the subsequent alteration of the natural river flow have mainly been related to the generation of hydroelectricity. In recent decades, the expectations of stakeholders have also been directed at recreational fisheries and the maintenance of biodiversity. Dry channels below diversion points are no longer considered acceptable. Swedish legislation allows for a regular review and reissue of permits to regulate rivers and operate hydroelectric power plants. However, it is only possible to enforce changes which are economically reasonable. The maximum loss of electricity which must be endured by a producer without reciprocal demands of compensation amounts to 5%. Presently, fishing may be regarded as the second most important interest in terms of the use of river resources. Accumulated knowledge of fish ecology makes it possible to use models for the management of fish populations. However, decisions regarding minimum releases of water are usually still based on the natural hydrograph rather than on documented relationships between fish yield and the characteristics of the watercourse. Over the past 7 years, Vattenfall, the largest producer of hydroelectricity in Sweden, has carried out research and development to test, improve and introduce instream flow methods for the management of regulated rivers. Experiences regarding biotope adjustments as an alternative to increased releases of water are presented, and the economic and biodiversity aspects are discussed.     

Defining competition vectors in a temperate alley cropping system in the midwestern USA: 4. The economic return of ecological knowledge

We tested the economic value of ecological knowledge in a midwestern USA alley-cropping system where row crops are planted in alleys between fine hardwood trees grown for veneer. Economic models were constructed to compare among agroforestry designs as well as to compare agroforestry with traditional forest plantation culture and row crop monoculture and rotational management. The general modeling approach was to quantify production inputs and outputs, estimate costs and revenues, simulate tree growth and crop productivity in agroforestry configurations, and estimate discounted cash flows. We incorporated scenarios that controlled both above- and below-ground competition through appropriate management as found in our previous research. This research showed the importance of below-ground competition in determining crop yields and the period of time that crop income could be expected from the agroforestry interplanting. Net present values and internal rates of return showed that agroforestry systems were generally more favorable investments than traditional agriculture and forestry. More importantly, the use of simple management techniques targeted at reducing below-ground competition allowed longer cultivation of row crops, greatly increasing returns to the landowner. Thus, the economic benefit of understanding the ecological interactions within agroforestry plantings dictates that accurate assessment of agroforestry alternatives will require the modeling of agroforestry as an integrated, interactive system.This revised version was published online in November 2005 with corrections to the Cover Date.     

Irrigation with saline water: benefits and environmental impact

The shortage of water resources of good quality is becoming an important issue in the arid and semi-arid zones. For this reason the availability of water resources of marginal quality such as drainage water, saline groundwater and treated wastewater has become an important consideration. Nevertheless, the use of these waters in irrigated lands requires the control of soil salinity by means of leaching and drainage of excess water and salt. However, the leaching of salts, soil microelements and agro-chemicals can lower the quality of the drainage water in the irrigation scheme. The irrigation return flows with water or poor quality are a source of pollution of the surface water bodies situated downstream of the drainage outlet. Deep percolation could also contaminate the groundwater. Therefore, irrigation with saline water requires a comprehensive analysis even beyond the area where water is applied. The problem should be treated beyond the scope of the irrigation scheme, taking into consideration the groundwater and downstream surface water resources of the river basin. Consequently, the sustainable use of saline water in irrigated agriculture requires the control of soil salinity at the field level, a decrease in the amount of drainage water, and the disposal of the irrigation return flows in such a way that minimizes the side effects on the quality of downstream water resources. This paper describes the guidelines for a preliminary evaluation of the suitability of water for irrigation and the key factors for salinity control in lands irrigated with saline water. Options to improve the quality of the drainage water, strategies for the reuse of this water and alternatives for disposal of the outflow are also analysed. The final goal is to obtain sustainable agriculture and maintain the quality of the water resources in the river basin.     

基于“多宜性—稀缺性—多样性”的粤港澳大湾区土地利用冲突识别

精准识别土地利用冲突是国土空间治理的重要前提。该研究引入一个基于土地利用多宜性、土地资源稀缺性和需求多样性的土地利用冲突识别新框架，系统评估粤港澳大湾区土地利用冲突。结果表明：1）粤港澳大湾区土地利用冲突以中等为主，占比高达43.67%；其次为高冲突（29.80%），低冲突区域所占比例最小（26.53%）。2）粤港澳大湾区土地利用冲突呈现显著的城乡差异特征。高冲突区集中在城镇和城乡过渡地带，尤其是城镇化快速发展的惠州市、江门市以及肇庆市；中冲突地区广泛分布在乡镇生产生活区域；低冲突区分布在土地利用适宜性低的山地丘陵地区。3）土地利用高冲突区域耕地和生态用地适宜性高，并且土地资源稀缺性普遍较高；中冲突区主要由于土地资源稀缺性、人类需求多样性高导致。在国土空间利用及相关规划中，应充分考虑潜在的土地利用冲突，建立土地利用冲突预警机制，并纳入相关规划监督实施体系，为优化国土空间格局提供科学依据。     

基于需求层级理论的城市绿地系统规划内容研究

随着社会经济的发展和生活质量的不断提高，人们的休闲行为模式更加多元化，对城市绿地系统提出更高、更深层次的需求。文章依据马斯洛的心理需求层次理论，分析城市绿地系统在满足不同层次需求时所发挥的作用，探讨城市绿地系统规划设计时发挥这些作用应遵循的规划设计思路；运用其他研究中对绿地发挥生态作用的数据成果，提出规划设计应加强和重视城市边缘地区绿地类型的建议。     

乡村振兴背景下贫困地区农村面向青少年的数字文化环境建设——基于留守儿童网络使用和图书馆服务需求的调查分析

[目的 /意义]数字乡村背景下图书馆等公共文化机构如何为贫困地区农村儿童创建更好的数字文化环境值得重视。[方法 /过程]研究通过问卷调查、个案访谈和焦点小组访谈等混合研究方法,调查了湖南省湘西土家族苗族自治州龙山县两个乡镇中学学生及其教师和家长,分析了留守儿童网络使用行为以及他们对图书馆服务的需求和期待。[结果 /结论]研究发现,农村青少年网络使用存在严重的娱乐偏好,其网络使用行为与留守经历关系不大,但与性别、监护人、周边环境显著相关。贫困农村地区缺乏面向青少年的良好数字文化环境和社会支持体系。学校和公共图书馆等需要针对青少年需求和行为特征完善功能和服务,特别是数字文化服务。     

Using rainfall simulation to guide planning and management of rehabilitated areas: Part II. Computer simulations using parameters from rainfall simulation

This paper reports computer simulations carried out using data from a rainfall simulator study on a steeply sloping revegetated area (a soundbund) at the NorthParkes Mine, near Parkes in New South Wales, Australia. Simulations of slope stability used a combination of daily time‐step models to consider soil water balances and runoff, growth of grass/legume pasture and soil erosion. Simulations indicated that long‐term erosion rates on the soundbund would be low (1·01–1·27 t ha⁻¹ yr⁻¹) due to low runoff rates and good vegetative cover. The simulations highlighted that peak vegetative growth occurred prior to the period of peak erosion hazard, with carry‐over dry matter being crucial for erosion control during the period of peak rainfall erosivity. This, in turn, indicated that grazing during the periods of peak growth and peak erosion hazard should be avoided (to avoid loss of dry matter). It also indicated that there was value in establishing grass species that would give greater growth during summer months, and that may produce dry matter that is more persistent through time. Simulations of stormwater flows in channels draining various lifts on the soundbund compared a range of alternatives with respect to channel length, gradient and roughness. The simulations indicated little effect of channel length on peak flow rates or depths once channel lengths exceeded 250 m and also showed little effect of vegetative roughness on peak flow rates or depths once Manning's n values exceeded 0·05. Implications of these results for design of drainage channels and drop structures on the soundbund are discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

畜禽粪污治理政策演化研究

畜禽养殖规模不断扩大,畜禽养殖产生的粪污逐渐成为畜禽养殖产业不可忽视的部分,其带来的生态环境压力日益显现。基于制度变迁理论、外部性理论和可持续发展理论,系统分析中国畜禽粪污治理相关政策的演化过程,对中国畜禽粪污治理相关政策进行阶段划分,结合中国现行畜禽粪污治理政策,分析畜禽粪污治理政策演变的动因,探讨畜禽粪污治理政策实施中存在的问题。研究表明,改革开放40年以来的畜禽粪污治理政策可分为粪污治理空白阶段、分散型自发综合利用阶段、强制治理与意识形成阶段、技术规范与理念普及阶段、综合治污与资源化利用5个阶段。推动政策演化的主体逐渐从政府向社会公众转变,政策演化方式逐渐从强制性制度变迁向诱致性制度变迁转变,政策逐渐从笼统性、原则性向针对性、可操作性转变的特征。但是,政策系统性有待完善、治理主体间制衡关系较为复杂、政策执行与落实不到位、畜禽粪污治理市场体系尚未形成等问题依然存在。因此,从制度供给和制度需求两个角度提出完善政策系统性、明确利益制衡关系、加强政策落实和促进畜禽粪污治理市场体系形成等政策建议。