Pollution and Self-Cleansing of an Urban River in a Developing Country: A Case Study in Dar es Salaam, Tanzania

Pollution and self-purification trends of an urban river namely, Msimbazi River, in Dar es Salaam City, Tanzania, were investigated. Site investigations and water quality analyses were done. The river is polluted in terms of high organic and nutrient concentrations, low dissolved oxygen, and high counts of indicator organisms. Biochemical oxygen demand (BOD₅) concentrations were 27– 340 mg/L. Dissolved oxygen was found to be as low as 0.9 mg O₂/L. Bacteriological pollution increased with distance downstream of the river, a trend attributable to an increase in the catchment of pollution sources, which are on-site sanitation systems. Although the river has an appreciable self-purification capacity, the capacity is strained by persistent pollution overloads. The pollution plight of the river is attributable to its being flanked by expanding human habitats and vibrant industrial, institutional, and socio-economic activities. Provision for pretreatment of discharges into the river is put forward as a remedial measure for the observed pollution. Matching nontechnical and techno-social remedial measures are also recommended. These include sensitization of polluters on merits of environmental protection practices such as cleaner production and strict enforcement of environmental protection laws.     

长江南通段江面风的观测分析

通过在长江南通段江面、江岸建立风观测站,并在江岸建设80m高的风梯度观测塔,与邻近气象站开展了较长时间的风同步观测,获得了实地观测数据.利用同步风观测数据进行对比分析,揭示出长江南通段江面风的观测事实,并利用风梯度观测资料,分析给出了风随高度的变化规律.在此基础上,结合邻近气象站长年的风观测资料,推算了该处的设计基本风速及其他工程设计风参数.分析表明,该处江面风况明显有别于邻近气象站,风参数计算结果也明显高于风工程理论推算值.     

塔里木河中下游的整治与基础设施建设

塔里木河中下游地区是南疆社会经济发展较快的地区，人类活动对塔河干流区生境干扰，在该区域表现得也较为突出，严重地影响了整个南疆地区的发展。在西部大开发中，塔河中下游的整治是基础建设的前提和保证，基础设施建设必须与塔河中下游整治结合起来。     

BRINGING DOWN OUR DAMS: TRENDS IN AMERICAN DAM REMOVAL RATIONALES1

ABSTRACT: Over 76,000 dams have been constructed on American rivers to provide services such as flood protection, water storage, hydroelectric power, and navigation. Although most dams continue to provide sufficient benefits to retain the structure, dam removal is becoming increasingly common. This study involved the construction of a dam removal database to analyze spatial and temporal trends in dam removal. The data included information on 417 cases of dismantled American dams, 153 with known rationales for removal. Database analysis indicated that the leading purposes for dismantling structures are safety concerns and interest in environmental restoration. There is substantial geographic variability in dam removal rationales, with California leading in razing dams for environmental purposes, and Wisconsin leading in economic and safety rationales. States with substantial removals tend to have programs that support and fund dam razing. Although removals for safety reasons have been increasing steadily in the past three decades, environmental removals made a rather dramatic and sudden entry into the dam removal arena in the 1990s. Analysis of spatial and temporal trends in dam razing are of particular significance given the likely increase in dam removals in the 21st Century.     

Securing water for people, crops, and ecosystems: New mindset and new priorities

A fundamentally new approach to water and human development will be needed during this new century if we are to secure sufficient freshwater to meet the needs of some 9 billion people while at the same time protecting the critical ecosystem services upon which the human economy depends. Signs of unsustainable water use — including falling water tables, shrinking lakes, and the drying up of rivers and streams — are widespread and spreading. In many regions, greater modification and appropriation of freshwater systems for human purposes will yield greater costs than benefits and create the risk of irreversible losses of species and ecosystem services. A new mindset is needed to guide water use and management in this new century, one that views the human water economy as a subset of nature's water economy. Living within nature's limits will require that societies satisfy the basic needs of people and ecosystems before non-essential water demands are met. It will require on the order of a doubling of water productivity. And it will require stronger institutions to encourage equitable sharing of water to alleviate tensions within and between countries.     

新疆河流水质调查及评价

采用2001年水质监测结果，用单项指标法对新疆河流水质进行评价，对新疆河流水质污染状况依据污染物标准做出分析判断。探讨污染途径及污染原因，寻找地下水水质恶化的根源，加强河流点源与非点源污染治理，为改善新疆河流水质提供依据。     

DEVELOPMENT OF LARGE SCALE GRIDDED RIVER NETWORKS FROM VECTOR STREAM DATA1

ABSTRACT: The Network Tracing Method (NTM) has been developed to determine gridded coarse river networks for modeling large hydrologic systems. For a coarse resolution grid, the NTM determines the downstream cell of each cell and the distance along the actual meandering flow paths between them. Unlike previously developed methods, the NTM uses fine resolution vector river networks as the source of information of the flow patterns rather than digital elevation models. The main advantage of using vector river networks as input is that they capture the hydrologic terrain features better than topographic data do, particularly in areas of low topographic relief. The NTM was applied to South America with a grid resolution of 1 degree by 1 degree and to the globe with a resolution of 2.815 degrees by 2.8125 degrees. Overall, the method captured the flow patterns well. Generated digital river networks and drainage divides showed minor disagreement with those obtained from existing maps, and most of them were consistent with the resolution of the coarse river network. The majority of estimated basin areas were also close to documented values. River lengths calculated with the NTM, however, were consistently underpredicted.     

河流及渔塘底质耗氧变化研究

底质耗氧是影响水体溶解氧含量的重要因素。通过对河流及渔塘的底质耗氧进行测定分析，相应得出了影响底质耗氧量变化的主要因素。     

景观格局对河流水质影响的尺度效应Meta分析

景观格局决定了陆域污染物的源汇过程,是影响河流水质状况的关键因素.由于尺度效应,不同尺度下景观格局与河流水质关系的研究结果不尽相同.然而,景观格局对河流水质影响的尺度效应问题尚缺乏系统研究.收集了国内外4 041条研究数据,采用Meta分析法定量分析了不同尺度下景观格局对河流水质的作用特征,识别了影响河流水质的关键时间和空间尺度以及景观指数.结果表明,相对于降水事件、平水期和年际尺度,丰水期下景观格局对河流水质的影响最大;相对于流域尺度,缓冲区尺度的景观格局对河流水质的影响更大;丰水期-缓冲区尺度是景观格局影响河流水质的关键时空耦合尺度.与耕地、水域、草地以及流域整体景观相比,林地和城镇用地的景观格局对河流水质的影响更大;破碎度是影响河流水质最重要的景观格局因子.在河流水质治理中,应重点考虑缓冲区的景观配置,增加缓冲区林地面积、减少林地和水域的斑块密度和减少城镇用地的面积占比和聚集度,以有效保护河流水质.     

磁种-磁滤技术处理污染河水的试验研究

采用磁种-磁滤技术处理广州市两条河涌的污染水,考察了磁种投加量、混凝剂用量、磁场强度和磁滤速度对出水浊度的影响,并确定了最佳试验条件。结果表明,该工艺对TP、SS和浊度的去除效果较好,去除率分别为96．2％、92．4％和93．9％,对CODCr有一定的去除效果,去除率为68．2％,但对NH4^ -N的去除效果较差,去除率仅为25％。