摘要:

AbstractThe regulation of the Ebro River in the 1960s has changed the discharge pattern: spring floods have been reduced and, as the reservoirs are used for hydroelectrical purposes, discharge varies daily.The last 50 km of the river have been studied for two years (1986 and 1987). Our main purpose was to establish the particulate organic and inorganic transport of the river and its seasonal changes. Particulate material was sampled in surface and deep waters. Water conductivity ranges between 0.9 and 53 mS, and anoxia is common in summer situations. ParticulateCranges between 1 and 3 mg l−1with higher values in summer; particulateNis very similar along the year with values between 0.1 and 0.5 mg l−1.Effects of regulation seem to be important in supplying very high nutrient content to algae and producing a high biomass and production in the lower part of the river, especially in summer. Diatoms and Chlorophyta are the most abundant groups. Phosphorus is higher than 5 μmol l−1, with lower values in summer. Most of particulate material is very fine (between 0.45 and 50 μm). The high biomass also explains the presence of abundant filter‐feeders, such asHydropsycheandEphoron virgo.In some parts, where light reaches the bottom, stones and boulders are covered byCladophora.In this case, grazers such as the gastropodsMelanopsisandTheodoxusare

ISSN:0886-9375    

DOI:10.1002/rrr.3450030132

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper describes a process for cooperation in international river basin projects. The significance of multilateral projects is stressed and the most important tasks of common preparation are considered. The potential role of the United Nations and other international organizations are demonstrated. The example is given of the natural and economic background of the Danube River and some precedents are cited in connection with the problems of planning the Bős (Gabcikovo)‐Nagymaros Barrage Project. This project provides a good example of the way in which a general method can be adapted to international projects by the use of a suggested 33‐step sc

ISSN:0886-9375    

DOI:10.1002/rrr.3450030133

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper deals with the management of the Yellow River, and particularly the main problems of flood and sedimentation control in the river's lower reaches. The available and adoptable measures for managing the river are itemized. These various measures can be coordinated to obtain an integrated effect on flood prevention.

ISSN:0886-9375    

DOI:10.1002/rrr.3450030134

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractUntil today, the majority of the Zambian rivers have been able to keep their natural character. Impoundment has been the principal measure carried out so far. The Kafue River is the most important waterway for the national economy. Its middle and lower sections are regulated by the Itezhi‐tezhi and Kafue Gorge Reservoirs. The changes in the natural flow pattern have threatened the ecological equilibrium of the Kafue Flats. Conductivity, concentration of sulphates and chlorides are reduced in the regulated sectio

ISSN:0886-9375    

DOI:10.1002/rrr.3450030135

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe Orinoco River is one of the world's longest rivers (2060 km) and in terms of average water discharge (36000 m3s−1) it ranks third. Seventy per cent of its basin (1.1 × 106km2) is found in Venezuela and the rest in Colombia. Due to the uneven distribution of the population toward the northern coastal areas (97 per cent of the population inhabits 55 per cent of the country with only 16 per cent of the surface waters) plans have been carried out to develop resources in the Orinoco Basin. So far these programs include mining (mainly iron and bauxite), oil exploration and extraction from the Orinoco Oil Belt, industry, river transport, and hydroelectric exploitation. Development of the latter has involved the construction of two dams on the Caroní River (the most important blackwater tributary of the Orinoco) and two more are planned on this same river. Hydroelectric projects are also being considered for the Orinoco River. Physicochemical and biological characterization has been regarded as of major importance to establish base‐line information to detect and quantify possible alterations in this river which is considered to be in a pristine state. Systematic hydrobiological research has recently been carried out in the river, some of its major tributaries, and floodplain lakes, and a fair amount of knowledge has emerged mainly from its lower section.Phytoplankton studies have revealed the presence of over 400 species of algae. Zooplankton research has identified 116 taxa of rotifers and 58 taxa of cladocerans. In general plankton densities negatively correlate with water level. Diatoms were observed to predominate in the Orinoco River while Cyanophyta predominate in the studied floodplain lakes. Seventeen aquatic macrophyte species have been recorded in the lakes of the Orinoco with high densities ofEichhornia crassipes, Oxycarium cubense, andPaspalum repens. Rooted emergent and floating‐plant cover tends to increase rapidly during high water.Some 318 species and subspecies of fish have been reported for the Orinoco Basin, even though this number is far from complete. Preliminary data have revealed different species associations among relatively close lakes with biomasses ranging between 30 to 900kg ha−1displaying considerable variations in diversity and species richness. Fisheries along the Orinoco are mainly of a multispecific nature and their overall potential has been estimated as being in the order of 45 000t yr−1.In general, management plans have taken into consideration the multispecific potential of the Orinoco Basin but indicate a lack of sufficient knowledge of the physical, biological, and social aspects involved. Furthermore development plans tend to precede the generation of this basic knowledge, thereby increasing the risks of conflict among the various users of the resourc

ISSN:0886-9375    

DOI:10.1002/rrr.3450030136

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450030101

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY