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Geochemistry of the "Morichales" rivers from the Venezuelan eastern plains

Abstract:

Monthly (Sept 2002-Sept 2003) water samples were collected in eight stations at the Areo, Morichal Largo, Uracoa and Yabo rivers, to determine the seasonal behavior of some physicochemical variables in these "Morichales" rivers. Parameters such as pH, dissolved O2 and conductivity were measured in situ, whereas concentrations of nutrients (NO3, NH4+, total N and total P), dissolved major ions (Cl, Na, K, Ca, Mg) and dissolved trace elements (Fe and Al) were measured in the laboratory. All the evaluated species showed higher concentrations in the wet season, indicating that, in these aquatic ecosystems, the contribution by rains and the washing of soils prevails over the dilution by river flow increase. Elements such as Na, Mg, and chlorides are principally provided by rainfall, whereas Fe, Al, total P and most of the dissolved Ca are leached from the substratum. The pH values correlated positively with dissolved Ca provided from the substratum. The relationships found between Fe, Al and total N indicate that their solubilities increase due to the presence of soluble N-rich organic matter. The results show that the water chemistry of these rivers is controlled by the sandy nature of the soils, the distance from the sea and the kind of vegetation found in these aquatic ecosystems.