旅行成本法在我国应用中存在的几个问题

我国旅行成本法案例研究多数未分清旅行成本与旅游目的地本身价格的关系,推导的游憩需求曲线是旅行成本-旅游人次模型,而不是旅游目的地本身的价格-旅游人次需求曲线。文章具体说明了区域旅行成本法的基本原理及操作方法,并用乔光华文章数据重新对达里诺尔国家级自然保护区游憩价值进行计算,对旅行成本的构成等问题进行了讨论,得出其消费者剩余为0.9221×108元a/,比原研究中的0.0937×108元a/高出近10倍。认为乔光华等的研究在推断游憩需求曲线时存在方法上的问题,直接将旅行成本和时间价值作为游憩价值不符合旅行成本法的基本原理和公共物品无(或低)市场价格的经济理论。还对调整后的旅行成本数据进行了计算,得到保护区游憩价值为1.3581×108元a/。     

Long-term winter observation of nitrous acid in the urban area of Beijing

The particulate matter (PM) pollution has been significantly improved by carrying out various valid emission control strategies since 2013 in China. Meanwhile the variation trend of nitrous acid (HONO) is worthy to investigate due to its vital role in the atmospheric oxidation process. In this study, field observation in the winter is conducted to investigate the concentration of HONO in an urban area of Beijing. In the winter of 2019, the mean HONO concentration is 1.38 ppbV during the whole winter. Photo-enhanced NO₂ heterogeneous reactions on the ground and aerosol surfaces were found as the possible daytime sources of HONO. Compared to O₃, photolysis of HONO dominates the primary OH sources during the winter time. To understand the HONO pollution patterns by years variation, multi-year data is summarized and finds that primary pollutants including CO and NO decreased, but secondary pollutants i.e., HONO (mostly generated via secondary process) increased. Our study highlights the requirement to mitigate secondary pollution by control HONO concentration.     

我国大型游乐设施风险分析研究

通过对我国大型游乐设施的发展概况、风险管理现状、危险因素辨识、风险评价和风险控制等五个方面进行了分析总结.研究发现,目前已初步建立游乐设施法规体系,逐渐形成了法律、法规、规章、安全技术规范和技术标准的五层次体系,大型游乐设施运营单位安全管理正在向标准化、体系化管理方向发展.我国还没有对各类大型游乐设施进行危险性分析,有关标准和规范中并没有提到明确的风险分析和评估方法,在游乐设施的设计、制造、安装、使用、改造、修理和检测过程中也没有形成一套系统、科学的风险分析和评估方法.     

Persistence of the sulfonylurea herbicide iodosulfuron-methyl in the soil of winter wheat crops

On four winter wheat fields grown on soils of different textures in Belgium, 10?g a.i.?ha^?1 of the sulfonylurea herbicide iodosulfuron-methyl-sodium was applied post-emergence in the spring. A procedure was developed for the analysis in field soils of iodosulfuron-methyl 1 and of its metabolites iodosulfonamide 2 and iodosaccharin 3 with a sensitivity limit of 0.3?µg of equivalents of iodosulfuron-methyl 1 kg^?1 dry soil. GC and GC-MS was used after purification of the soil extracts by repeated TLC, and methylation. The results of the chemical analyses were confirmed by means of bioassays using sugar beet as test plants. On a winter wheat crop grown on sandy loam soil of pH 6.2 at Melle, iodosulfuron-methyl-sodium 1 was applied at the beginning of April. The iodosulfuron-methyl 1 soil half-life in the 0–10?cm surface soil layer was 60 days. At the end of June, the sum of the concentrations of the metabolites 2 and 3 in the 0–10?cm surface soil layer attained a maximum corresponding to 27% of the applied dose. Green manures were sown after the harvest of the wheat at the end of August. No phytotoxicity at all was observed during the growth of the green manures, in spite of the very low residues of iodosulfuron-methyl 1 remaining in soil in September and October. At the mid of November, iodosulfuron-methyl 1 and its metabolites 2 and 3 were no more detected in soil. On three other winter wheat crops grown on clay soils of pH of about 8 at Leke, Gistel and Zevekote, iodosulfuron-methyl-sodium 1 was applied at the beginning of May. The soil half-life of iodosulfuron-methyl 1 in the 0–10?cm surface soil layer was between 30 and 44 days. Since the application and until the mid of November, in all the trials made on sandy loam or clay soils, iodosulfuron-methyl 1 (and its metabolites 2 and 3 in the trial made on sandy loam soil) were never detected in the 10–15 and 15–20?cm surface soil layers, indicating their low mobilities in the field soils.     

Distribution of phytoplankton community and its influence factors in an urban river network,East China

To reveal the distribution characteristics of phytoplankton and the main influence factors under different conditions in the urban rivers, the investigations were conducted during autumn and winter 2014 in Changzhou City, East China. 178 taxa of phytoplankton belonging to 28 functional assemblages were identified. In autumn, the phytoplankton community compositions have high similarity for enhanced hydrological connectivity. The chlorophytes and diatoms (prevailing functional groups C, F, J, P), together with euglenoids (W1), showed high proportions of biomass in the main rivers and connected rivers. It was related to the well mixed eutrophic conditions. The phytoplankton community exhibited spatiotemporal heterogeneity in winter. Affected by the low water level and temperature, the free-living phytoflagellates (X2) replaced groups F and J in the main rivers. Phytoplankton productivity was the highest in the Tongji River. Chlorophytes Dictyosphaerium ehrenbergianum and Chlamydobotrys stellata had an overwhelming superiority during the winter bloom. They were significantly correlated with ammonium, total phosphorus and biochemical oxygen demand. Affected by tail water supply, the diatoms (MP) and euglenoids (W1) dominated in a beheaded river. The multivariate analyses based on the phytoplankton functional groups helped to evaluate the relationships and variations between the urban rivers. The redundancy analysis (RDA) results showed that nitrate nitrogen, water temperature, total nitrogen and total suspended solids were the main influence factors on the phytoplankton community. Except MP, the prevailing groups all showed significant negative correlations with nitrate nitrogen. Availability and utilization of dissolved inorganic nitrogen and hydrodynamic conditions affected the phytoplankton distribution.

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Public parks as an element of urban planning: a missing piece in Accra's growth and development

Public parks are important to urban environments, residents, and visitors. Among other functions, they provide environmental services, such as air and water purification, and they increase both recreational opportunities and the attractiveness of the urban environment. Because of their importance, urban parks serve as public spaces that provide visitors and urban residents with rights to the city. This paper identifies the dearth of urban public parks in Accra-Tema city-region as worrying. The Accra Plan 1958 underscored the significance of green spaces and designated the coastal strip for parks development but the areas have been lost to various urban uses. We argue that the continual neglect of public parks within urban planning and community development schemes in the Accra-Tema city-region is a major concern because it is depriving the citizens a right to the city and its public spaces. A number of factors have worked adversely against the provision of public parks and green spaces in the city-region. These include development pressures, undue political interference, a complex land delivery system, and ad hoc planning. The paper concludes by offering policy suggestions as to how to resolve the dearth of parks and green spaces in the city-region.     

Monetary assessment of the recreational benefits of improved water quality – description of a new model and a case study

The European Union Water Framework Directive (WFD) has created a demand for comparing the benefits and costs of the remedial measures. A major part of the benefits from improved water quality relate to the increased recreational value. However, there is a lack of easily operative and widely applicable quantitative methods to assess the benefits of improved water quality for recreational use. We present a new model to link physical indicators of water quality, water feasibility indicators for different recreational uses, individuals’ perceptions concerning the current feasibility of water for recreational purposes and monetary measures of water-related recreation benefits. The model has been applied to nine lakes, three rivers and one large coastal area in Finland. In this paper, we present the principles of the method and the results from one case study. In Finland, the method has been applied for the economic analysis required in the WFD.     

Recreation benefits of natural area characteristics at the El Yunque National Forest

The paper applies the Contingent Valuation Method using a visitor survey to determine trip values to three rivers in northeastern Puerto Rico. Sample data were obtained from 984 interviews conducted in 13 sites during the summer months. The trip value is statistically decomposed into components representing natural features and recreation activities. The median net economic value of a river visit without waterfalls or foot trails is $96. Recreation at rivers with both waterfalls and foot trails has a median value of $138 per trip. The presence of waterfalls accounts for $23 and foot trails $19 per trip. This information can be pertinent for managers in selecting recreation site locations and protecting them from competing uses.     

冬季水网藻对源水水质的净化作用

为保护源水水质,控制水质富营养化,利用水网藻来以藻治藻。中试结果表明,水网藻在冬季仍能正常生长,但生长速度下降,这与气候有密切关系。与对照测点比较,网袋内氨氮、生化需氧量和总磷的浓度分别下降了15.6％、28.6％和7.5％,水网藻在冬季仍可作为净化水源水质的一项生态工程措施。藻类的演替,与光照、水温和氮磷比等环境因素有关,由于这些因素难以控制,只能因地制宜,利用现有的种类净化水质。