Abstract
The expansion of the agricultural frontier in Colombia has exerted significant pressure on its aquatic ecosystems during the last few decades. In order to determine the impacts of different agricultural land uses on the biotic and abiotic characteristics of first and second order streams of La Vieja river watershed, we evaluated 21 streams located between 1,060 and 1,534 m asl in the municipalities of Alcalá, Ulloa, and Cartago (Valle del Cauca, Colombia). Seven streams were protected by native vegetation buffers, eight had influence of coffee and plantain crops, and six were influenced by cattle ranching. Habitat conditions, channel dimensions, water quality, and aquatic macroinvertebrates were studied in each stream. Streams draining cattle ranching areas had significantly higher dissolved solids, higher phosphorus, higher alkalinity, higher conductivity, and lower dissolved oxygen than those covered by cropland and forests. Coarse substrates and diversity of flow regimes were significantly higher in cropland and protected streams when compared to streams affected by cattle ranching, whereas the percent of silt and slow currents was significantly higher in the latter. A total of 26,777 macroinvertebrates belonging to 17 orders, 72 families and 95 genera were collected. The most abundant groups were Diptera 62.8%, (Chironomidae 49.6%, Ceratopogonidae 6.7%), Mollusca 18.8% (Hydrobiidae 7.2%, Sphaeriidae 9.6%) and Trichoptera 5.7% (Hydropsychidae 3.7%). The Ephemeroptera, Trichoptera, and Plecoptera orders, known for their low tolerance to habitat perturbation, had high abundance in cropland and forested streams, whereas Diptera and Mollusca were more abundant in those impacted by cattle ranching. Results indicate that streams draining forests and croplands have better physical and biological conditions than those draining pastures, and highlight the need to implement protective measures to restore the latter.
Highlights
En las regiones tropicales se ha presentado una extensiva transformación del paisaje en las cuencas hidrográficas con consecuencias adversas para los ecosistemas acuáticos que se originan en ellas (Murgueitio & Ibrahim, 2009)
Los tres órdenes de insectos (Diptera, Trichoptera, Coleoptera) mejor representados en el conjunto de quebradas evaluadas se han reportado como los grupos más abundantes en quebradas de bajo orden en otros estudios (Posada, Roldán & Ramírez, 2000; Quinn, Boothroyd & Smith, 2004; Winckler-Sosinski, Silveira, Schulz & Schwarzbold, 2008)
Aunque no se encontraron diferencias significativas para la familia Chironomidae entre los usos de suelo evaluados, hubo mayor abundancia de estos organismos en las quebradas de zonas ganaderas y agrícolas
Summary
Área de estudio: La cuenca del río La Vieja se encuentra en el centro-occidente de Colombia en jurisdicción de los departamentos del Quindío, Risaralda y Valle del Cauca. El presente estudio se llevó a cabo en quebradas de primer y segundo orden ubicadas en la cuenca media del río La Vieja, en los municipios Alcalá, Ulloa y Cartago, en el norte departamento del Valle del Cauca. Para la selección de las quebradas se tuvo en cuenta que fueran influenciadas solo por uno de los usos de suelo de interés en este estudio y que no estuvieran afectadas por descargas de aguas residuales de origen doméstico o agroindustrial. En cada una de las quebradas se escogió un tramo representativo de 100m de longitud, evitando que recibiera tributarios importantes y que estuviera influenciado por carreteras, puentes o cualquier obra que pudiera afectar las características del agua o el hábitat. Se realizó una caracterización general de cada microcuenca que incluyó información sobre tipo de vegetación, presencia de erosión, fuentes de contaminación, carreteras, cobertura de dosel y ancho del corredor ribereño. CUADRO 1 Caracterización general de quebradas evaluadas con distintos usos de suelo en la cuenca del río La Vieja, Colombia
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