Aquatic Sciences Meeting, Albuquerque 2001

SS40 Long-Term Research Programs in the Twenty-first Century (Spatial and Temporal Connections)

Date: Thursday, February 15, 2001, Time: 9:45:00 AM

Location: Ruidoso/Pecos

Blanco, J, F, Departamento de Biologia, Facultad de Ciencias, Universidad de Valle, A.A. 25360, Cali, Colombia, jfblanco@teachers.org

ECOLOGICAL COMPARISON OF THE 1997-1998 EL NIÑO AND THE 1998-1999 LA NIÑA IN A NEOTROPICAL STREAM IN SOUTHWESTERN COLOMBIA

This work was aimed to comparatively determine the changes in a neotropical stream (Río Pescador, Colombia) during El Niño and La Niña events. The stream-flow and some water chemistry parameters were measured and macroinvertebrates collected at two sites (upper and lower reach) twice a month during 1998 (El Niño) and 1999 (La Niña). Floods were common in the stream during the El Niño year but increased in both magnitude and frequency during the La Niña year. These peak discharges caused macroinvertebrate wash-out specially in 1999. The community composition exhibited low persistence between years. It also was consistently in an early succession state due to the high frequency of disturbances within and between years. Both number of taxa and individuals were lower during the La Niña year. The composition of trophic guilds remained stable between years but taxa and individuals of the dominant groups declined during the La Niña year. Dominance by scrappers and omnivores reflected the limitations of food. During the La Niña , dissolved oxygen was reduced, nitrogen flux increased , and temperature was lower, which seemed to favor the colonization of the lower site by organisms washed-out from the upstream.

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Aquatic Sciences Meeting, Albuquerque 2001

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