Diversidad acuática en la zona de influencia de un campo de gas y petróleo en la provincia Carrasco (Cochabamba, Bolivia)

Abstract

AQUATIC DIVERSITY IN A RIVER ADJACENT TO A GAS AND PETROLEUM EXPLOITATION SITE IN THE PROVINCE CARRASCO (COCHABAMBA, BOLIVIA) El rio Izozog (Carrasco, departamento de Cochabamba) recibe desechos liquidos difusos de la actividad petrolera desarrollada en la zona. La diversidad acuatica en este rio fue estudiada, y los impactos posibles de contaminacion por los derrames sobre la diversidad acuatica fueron investigados. El efecto sobre la calidad del agua es poco apreciable tanto en epoca de estiaje como en periodo de lluvias: unicamente en la zona de muestreo rio abajo de las descargas, se detecto un incremento en conductividad, D00 (Demanda Quimica de Oxigeno) e Hidrocarburos Totales. Macroinvertebrados bentonicos fueron muestreados con un surber sampler en rapidos y con una draga Van Veen en pozas. La comunidad de peces fue muestreada con un equipo portatil de pesca electrica (Smith-Rooth) en rapidos. Los macroinvertebrados bentonicos del rio Izozog pertenecen a 19 familias. Los 497 peces que fueron capturados pertenecen a 17 taxas. Characidae y Loricariidae fueron las familias mejor representadas tanto en terminos de numero de especies como en numero de individuos. B imii>8cto de la contaminacion se evidencio sobre las comunidades de bentos rio abajo del area de contaminacion difusa durante la epoca seca; sin embargo, en epoca de lluvias el efecto sobre el bentos no fue significativo. No hubo un impacto detectable de la contaminacion sobre los peces. Empero, fue dificil discriminar entre variaciones naturales y cambios inducidos por contaminacion. Una discusion sobre estrategias de muestreo para detectar impactos ambientales esta incluida. Palabras clave: Contaminacion, petroleo, bentos, peces, rio Izozog, Cochabamba, Bolivia. ABSTRACT The Izozog River receives contaminated water from a number of non-point sources, generated by oil exploration activities in the Carrasco Province of the State of Cochabamba. The aquatic diversity in this river was studied and possible impacts of oil contamination on aquatic diversity were assessed. In general, the effect on water quality was minor in both the rainy and dry season. Only in samples collected downriver from the pollution source, was an increase in conductivity, 00D (Chemical Oxygen Oemand), and Total Hydrocarbon Concentration observed. In rapids, the benthic macroinvertebrates were sampled with a surber sampler while in pools, a Van Veen sampler was used. In rapids, the fish community was sampled with a portable electrical fishing apparatus (Smith-Root). The benthic macroinvertebrates recorded in the Izozog River belonged to 19 different families. A total of 497 fish, belonging to 17 different taxa, were collected. In terms of species number and number of individuals, Characidae and Loricariidae were most numerous. The impact of the contamination on the benthic community in the sample point immediately downstream from the non-point contamination sources was observed during the dry season, whereas the impact on the fish community was never detectable. The overall impact during the rainy season was small. However; it was difficult to distinguish between natural variation and contamination-induced changes in community structure. A discussion on sample strategies to detect environmental impacts of petroleum contamination is also presented. Key words: Contamination, petroleum, benthos, bio-indication, river Izozog, Cochabamba, Bolivia.