Environmental variation in the Grande de Térraba river and some of its tributaries, south Pacific coast of Costa Rica. Río Grande de Térraba drains one of the largest basins in Costa Rica, with a growing human population. It has been deforested in its lower region for the development of agriculture, but has attracted little attention on its environmental challenges. The river was studied once in the dry and wet season for a period of four years (1999-2003). A total of 13 sites were studied along its course, from the upper middle reach to near a mangrove forest. We measured temperature, dissolved oxygen, conductivity, total hardness, turbidity, suspended solids, nitrate and phosphate, macrobenthic taxa richness and a water quality index (BMWP) in order to assess river deterioration. The level of oxygenation was high, with the exception of the lowest point (Palmar Norte), which means that organic pollution is restricted to localized areas near pollution sources. However, erosion in the agricultural lands and the loss of forest cover in the basin, produced high levels of turbidity and suspended solids at the lower reaches of the river, mainly during the rainy season. This was also reflected by a decrease in the species richness and the BMWP index value at the most affected sites. Rev. Biol. Trop. 54 (Suppl. 1): 265-272. Epub 2006 Sept. 30.
Keywords: Tropical rivers, seasonality, environmental parameters, macroinvertebrates, species richness, water quality, Costa Rica