Long-term erosion on granitic roadcuts based on exposed tree roots

Exposed roots were used to estimate soil and bedrock erosion on the cut slopes of a 45-year-old road constructed in granitic soils of the Idaho Batholith. The original roadcut surface was defined by projecting a straight line from the toe of the cut past the end of the exposed root to the intersection of a straight line projected along the surface of the hillslope. A cross-sectioning technique was then used to determine erosion to the present roadcut surface. A total of 41 exposed root sites were used to estimate erosion on a 1350 m-long section of road. Average erosion was 1·0 and 1·1 cm/year for soil and bedrock respectively. Buttressing by tree roots caused lower erosion rates for soil as compared to bedrock. Both soil and bedrock erosion rates showed statistically significant correlations with the gradients of the original cut slope. The bedrock erosion data provide a reasonable estimate of the disintegration rate of exposed granitic bedrock exhibiting the weathering and fracturing properties common to this area. The road is located in a study watershed where long-term sediment yield data are available. Sediment data from adjacent study watersheds with no roads were compared to sediment data from the roaded watershed to estimate the long-term increase in sediment yield caused by the road. The increase amounts to about 2·4 m³/year. This figure, compared to the average annual on-site road erosion, provides an erosion to sediment delivery ratio of less than 10 per cent. Based on study results, road construction and maintenance practices are suggested for helping reduce roadcut erosion.     

陕南河流泥沙输移比问题

通过分析陕南河流泥沙的输移比现状、输移比的时空变化及发展趋势,指出在特定的自然地理条件下,泥沙中推移质比例较大,致使该区泥沙输移比远小于１,这是陕南河流泥沙运移的重要特征;输移比在空间上有明显差异并且沿程逐渐增大。从时间上看,自５０年代以来,输移比有不断减小的趋势,今后一段时间,随着区内河流径流量的减少和人为侵蚀作用的加剧,泥沙输移比仍会减小。     

Challenging spatial and seasonal distribution of fish landings—Experiences from vertically integrated trawlers and delivery obligations in Norway

The highly seasonal Norwegian cod fisheries give rise to problems downstream in the value chain and the authorities have introduced several schemes to counter the strong incentives for seasonal harvesting. This paper studies how the trawler delivery obligation (TDO) regime influences aspects of the harvesting pattern, focusing on the temporal and geographic distribution of landings. The analysis shows that the trawlers as a group have far less seasonal variations in their cod landings compared to the coastal fleet. While the Norwegian fleet lands about 75% during the first half-year, the corresponding share for trawlers is about 50%. Contrary to the initial hypothesis, the independent trawlers fished the most off-season; about 57% of their total landings. Trawlers controlled by vertically integrated firms landed considerably less (about 45%) and independently owned trawlers with landing obligations fell between these two strategic groups (about 50%). Vertically integrated vessels have a higher fulfilment of their landing obligations than the independently owned. The differences between the strategic groups are relatively high, at 68% vs. 38%. These results indicate that delivery obligations alone are not sufficient to provide control over the geographic distribution.     

基于GIS的物流分区配送方法研究

采用分区配送的方法，对车辆路径选择(VRP)问题的数学模型进行了探讨，并采用GIS技术进行了相关实验工作，证明该方法得出的近似解可以较好地解决上述问题。     

基于WEBGIS的农业气象信息共享与发布技术应用研究

气象部门观测台站通信网络,开展了基于WebGIS技术的农业气象信息共享与发布技术研究。根据气象行业标准和网络数据标准,对农业气象信息进行标准化处理,选用SQ L Server 2000建立了WebGIS应用系统所需的网络共享数据库,利用IIS、ArcIMS (Internet Map Server) 构建农业气象信息服务WebGIS平台。采用JavaScript、ArcXML和ActiveX编程方式,结合ArcGIS和ArcIMS Manager地理信息软件和管理工具,开发服务端的相关应用软件。在客户端实现了从属性到空间和空间到属性的农业气象信息双向查询以及农业气象信息专题地图分析功能,为用户提供详细、丰富、高质量的农业气象信息服务。     

A field methodology for quantifying phosphorus transfer and delivery to streams in first order agricultural catchments

An understanding of the relative importance of different hydrological pathways in phosphorus delivery from land to water is currently constrained by a lack of appropriate methods available to quantify the delivery process. New monitoring tools are needed which will provide a framework for understanding phosphorus (P) transfer and delivery at a range of scales in agricultural catchments. A field methodology incorporating the techniques of event-based, on-site observation and sampling within a flexible, non-plot based structure is described and applied to a first order stream catchment in Southern England, UK. The results show that P transfers to the stream reach monitored were dominated by inputs from one field drain, and that overland flow inputs, despite being directly connected to the stream and containing higher P concentrations (maximum 3708 μg l⁻¹), contributed less to the stream P flux. The processes of P transfer and delivery to the stream were complex, changing both within flow pathways and temporally over an event.