海底管道泄漏风险演化复杂网络分析

为了控制海底管道泄漏连锁风险,基于复杂网络,提出针对管道系统泄漏演化的半定量风险演化评价方法,将复杂的事故风险发展过程转化为简洁的网络分析计算。首先,构建包含30个风险节点与54条连接边的海底管道泄漏演化复杂网络模型;其次,采用无权有向网络中的节点出入度和聚类系数进行风险分析,确定影响管道泄漏的关键节点,提出断链控制方案;最后,将演化模型转化为带权的有向网络,采用Dijkstra算法计算各初始事件导致泄漏事故的最短路径。结果表明:海底管道系统泄漏网络的聚类系数为0.13,网络聚集程度偏低而演化性较强;各初始事件的最短路径均不超过10,表现出明显的小世界网络特征,初始事件的风险经少数几步传递即可导致泄漏事故的发生。海底管道泄漏风险演化规律的研究可为抑制初始事件、控制传递事件和减轻后果事件提供理论依据,对预防海底管道泄漏事故发生、保障管道持续安全运行具有现实意义。     

Responses of decomposition rate and nutrient release of floating-leaved and submerged aquatic macrophytes to vertical locations in an urban lake (Nanhu Lake,China)

A leaf-bag field experiment was conducted to investigate the decomposition and release of nutrients from leaves of two aquatic macrophytes (floating-leaved Trapa bispinosa and submerged Vallisneria natans) deposited in the four vertical locations (i.e. air-water interface, AW; sediment-water interface, SW; buried at a depth of 10?cm, B10; buried at a depth of 20?cm, B20) of littoral zone in Nanhu Lake, China, for 60 days from July to August 2015. Leaf initial quality significantly influenced mass loss and nutrient release except TN (total nitrogen) remaining. Compared to V. natans, T. bispinosa leaves decomposed faster under the same treatments. The decomposition was greatly affected by both leaf chemical quality and the location of deposition. With the increasing depth of vertical locations, leaf biomass loss and nutrient release of both T. bispinosa and V. natans decreased. In addition, initial N:P ratio and cellulose were the major determinants for decomposition in AW and SW treatments while total phenol in B10 and B20. Our results suggest that the combined effect of leaf chemical quality and burial could mediate macrophyte mass loss and release of nutrients and carbon, which in turn can influence organic matter accumulation and nutrient cycling in shallow freshwater lakes.     

NUTRIENT CONTENT OF CROP CANOPY THROUGHFALL PRECIPITATION IN EASTERN SOUTH DAKOTA1

ABSTRACT: Nutrient contents of canopy throughfall precipitation (TFP) from fertilized and unfertilized crops were analyzed and compared to determine the importance of fertilization on this source of nutrients in runoff. Continuous barley, corn, oats, rye, and wheat plots, that had been unfertilized since 1941 and divided and half fertilized since 1959, were studied. TFP soluble PO₄, total PO₄, and soluble K amounts were usually larger from fertilized plots in comparison to unfertilized ones but the differences usually were not significant. NH₄-N and NO₃-N may have been adsorbed from precipitation by corn canopies.     

华东地区中强震孕育过程中的中小地震动态演化特征

引用有关地震活动的频度面积S值方法,对华东地区1970年以来中强震前后的中小地震活动进行了研究,发现地震的S值在震前和震后的异常变化特征主要表现为:在震前S值异常为高值或低值异常,震后下降或上升;对特定区域研究发现,华东地区陆地区域的中强震的孕震区,中小地震活动的S值震前异常主要为高值,震后下降;而海域的中强震孕震区中小地震活动的S值震前主要表现为低值异常。因此,通过对华东地区中强震孕震区中小地震活动的频度面积S值方法的动态追踪,利用其变化规律可以为中强震的预测预报提供一种判定指标。     

COST MINIMIZATION OF NUTRIENT REDUCTION IN WATERSHED MANAGEMENT USING LINEAR PROGRAMMING1

ABSTRACT: Linear programming is applied to identify the least cost strategy for reaching politically specified phosphorus and total suspended solids reduction targets for the Fox-Wolf river basin in Northeast Wisconsin. The programming model uses data collected on annualized unit reduction costs associated with five categories of sources of phosphorus and total suspended solids discharge in each of the 41 sub-watersheds in the basin to determine the least cost management strategy. Results indicate that: (1) cost-effective nutrient reduction requires careful selection of geographic areas and source categories to address throughout the watershed; (2) agricultural sources are the most cost-effective to address in the basin; and (3) care should be exercised in setting nutrient reduction targets, given that there are likely to be significantly increasing marginal costs of nutrient reduction; the model predicts that lowering the most restrictive target by 33 percent would cut reduction expenditures by about 75 percent. Policy implications of the model include support for the investigation and potential development of institutional arrangements that enable cost-effective nutrient reduction activities to occur, such as the creation of an agency with authority over a given watershed, coordinated watershed management activities, or nutrient trading programs.     

NUTRIENT FLUXES IN PRECIPITATION,THROUGHFALL, AND STEMFLOW IN AN OAK-HICKORY FOREST1

ABSTRACT: Nutrient fluxes in precipitation, throughfall, and stemflow were studied in an oak-hickory forest in southern Illinois for a three-year period beginning in 1973. Nutrient inputs in these water related pathways were approximately one-half those of litterfall; a major nutrient return mechanism. Considering these water carried nutrients (116 kg/ha/yr), 38% was contributed by precipitation, 35% by throughfall and approximately 27% by stemflow. Although the total nutrient input is only one-half that of litterfall, the net impact on short-term nutrient requirements is considerable because of their immediate availability. Nutrient inputs in litter represent a delayed return mechanism because of the relatively slow decomposition process.     

PHOSPHORUS LOADING TO A MOUNTAIN RESERVOIR IN SOUTHERN CALIFORNIA1

Phosphorus loading from precipitation and more than a dozen tributaries of Big Beat Lake, Woman, was determined for the period from January to December 1978. Direct precipitation contributed 1120 kg·P·yr^-1 (0.096 g P·m^-2·yr^-1) while tributary runoff contributed 21,560 kg for a total P loading of 1.84 g P·m^-2 Rathbone creek, although accounting for only 4 percent of the hydro-logic input to Big Bear Lake, contributed >27 percent of the annual phosphorus load. Phosphorus loading increased with increased impervious geology and increased development. Nitrogen loading exhibited similar loading patterns. Big Beat Lake is currently eutrophic and is likely to remain eutrophic. Calculations based on Vollenweider's critical phosphorus loading concept indicated that tributary P-loading would have to be reduced by >95 percent to achieve mesotrophic conditions. The completion of Big Bear Dam created a “naturally” eutrophic re mix which dl require proper management to enhance its resource potential.     

PHYSICOCHEMICAL FACTORS AND THEIR EFFECTS ON ALGAL GROWTH IN A NEW SOUTHERN CALIFORNIA RESERVOIR1

ABSTRACT: Some physical and chemical characteristics of Lake Perris, a new southern California reservoir, were investigated with regard to their influence on phytoplankton biomass and community structure. The concentration of three major nutrients – nitrogen, phosphorus, and iron – was approximately equivalent to the demand ratio of fresh water plants. Large increases in iron and phosphorus concentrations in late summer due to releases from sediments, however, tended to shift the balance toward a nitrogen-limited situation. Nitrogen limitation favored nitrogen-fixing blue-green algae, and after a decline of competing algae during the summer, the blue-green population bloomed in September. Series of measurements taken over one-day periods during summer stratification showed that some iron, phosphorus, and manganese from the hypolimnion could move upward, corresponding to diel shifts in the thermocline depth. Vertical transport of nutrients could thus occur long before complete lake mixing and could support summer/fall algal blooms.     

A Comparative Analysis of the Vegetation and Topsoil Cover Nutrient Status between Two Similarly Rehabilitated Ash Disposal Sites

The aim of this paper is to compare the rehabilitation result between two ash disposal sites with regard to its vegetation establishment and soil nutrient status. The study areas were situated in close proximity, in the Mpumalanga coalfield, South Africa. Although both areas received a similar amelioration treatment and were seeded with similar seed mixture the vegetation composition were significantly different. Both areas were poor in essential nutrients, this probably being one of the most limiting factors for vegetation establishment. No serious phytotoxic conditions, as is frequently experience with coal ash, could be identified. A regular monitoring and low level maintenance program is therefore proposed to improve the sustainability of the vegetation. The study proposed that results form such evaluations be used to identify performance standards for rehabilitated derelict land.     

COST‐EFFECTIVE POINT‐NONPOINT TRADING: AN APPLICATION TO THE SUSQUEHANNA RIVER BASIN1

ABSTRACT: Point‐nonpoint trading has been suggested as a relatively efficient approach for reducing nutrient pollution in the Chesapeake Bay and elsewhere. However, relatively little economic research has examined the design of trading programs involving nonpoint sources. The purpose of this paper is to investigate the economics of several fundamental design choices for point‐nonpoint trading programs. The Susquehanna River Basin (SRB) in Pennsylvania as an example, although many of the insights should generally apply to other regions as well.