The use of water chemistry and benthic diatom communities for qualification of a polluted tropical river in Costa Rica

The water quality of several sections of a tropical river subjected to severe pollution was studied through physico-cbemical water analysis and benthic diatom assemblages. The methodology follows the concept of differential species groups and that of its modification for the groups of nutrient- differentiating species for rivers rich in both oxygen and inorganic nutrients. The trophic indication of the latter authors corresponded clearly with the results of chemical observations made in this study. The most abundant species found in this river were Navicula goeppertiana, Gomphonema parvulum, Gomphonema sp. aff. pumilum, Nitzschia palea, Nitzschia amphibia, Nitzschia clausii Nitzschia inconspicua, Navicula seminulum, Navicula sp. aff. cryptocephala, Navicula schroeterii var. escambia, Cymbella sinuata and Surirella sp. aff. roba. These species are known to be tolerant to organic pollution and eutrophication. Therefore we may conclude that diatoms are useful for biological monitoring of disturbed tropical riversLa calidad del agua de varias secciones de un rio tropical contaminado se estudi6 considerando factores qufmicos y biol6gicos. Los resultados confirman el alto grado de d e terioro de la cuenca del Rfo Grande de Tarcoles , situaci6n reflejada en el alto porcentaje de especies de diatomeas tolerantes a fuerte descarga de nutrientes y materia organica. Especies resistentes a fuertes condiciones de contaminaci6n, especies moderadamente resistentes y especies sensitivas a un sistema acuiitico deteriorado han servido de base para cJasificar diferentes niveles sapr6bicos en los sitios estudiados. Para ello se utiliz6 el concepto de grupos de diatomeas desarollado por Lange-Bertalot (1978, 1979, 1986) Y Steinberg and Schiefele (1988). Las especies mas abundantes fueron las siguientes: Navicula goeppertiana, Gomphonema parvulum. Gomphonema s p . aff. pumilum. Nitzschia palea. Nitzschia amphibia. N. clausii. N. inconspicua, Navicula seminulum, Navicula sp. aff. c ryptocephala . Navic ula schroeterii var. esca mbia . CymbeUa sinuata y Surirella sp. aff . roba