The Orinoco river: A review of hydrobiological research

Abstract

The Orinoco River is one of the world's longest rivers (2060 km) and in terms of average water discharge (36000 m3 s-') it ranks third. Seventy per cent of its basin (1.1 X 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 Caroni 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 of Eichhornia crassipes, Oxycarium cubense, and Puspalurn repens. Rooted emergent and floating-piant 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 biornasses ranging between 30 to 900 kg ha-' displaying 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 45000 t yr-I.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 resources involved.

Zooplankton Associations in the Middle Niger‐Sokoto Basin (Nigeria: West Africa)

“…the Paran5 (PAGGI 1978), the Volga (DZYUBAN 1979), the Murray-Darling (SHIEL 1981;SHIEL et af. 1982), the Amazon (SIOLI 1984;ROBERTSON & HARDY 19ff4) and the Orinoco (PAOLINI et al 1983;LEWIS 1988;VASQUEZ 1989), current knowledge of the hydrochemistry, hydrobiology and sediment trvsport of the Middle Niger-Sokoto Basin is more limited.…”