Limnologica 33, 29-43 (2003) © Urban& FischerVerlag http://www.urbanfischer.de/journals/limno LIMNOLOGICA Ecology of a high Andean stream, Rio Itambi, Otavalo, Ecuador Patricia Carrera Burneo 1,*, GiJnter GunkeP Pontificia Universidad Cat61ica del Ecuador (PUCE), Quito, Ecuador 2Technical University of Berlin, Department of Water Quality Control, Berlin, Germany Received October 30, 2002 • Accepted January 27, 2003 Abstract A high Andean stream in the equatorial zone of Ecuador, the Rio Itambi, located at 2,600 to 4,600 m a.s.l., was studied to describe its physical structure, geomorphology, water chem- istry and biodiversity. The Itambi catchment basin is characterized in its upper part by the volcanic sierra with > 70% slope, and in its lower part by lake deposits. The length of Rio Itambi is 17 km with a catchment basin of 11,271 ha; the annual flow amounts to 0.07-0.5 m3/s. Stream structure is evaluated using a modification of the German "Geomorphological Structure Classification Method" with six main parameters (development of stream bed, longitudinal profile, transversal profile, bed structure, stream bank structure, and surrounding environment). Nowadays an impact of Rio Itambi's stream structure occurs due to anthropogenic activities. The water quality of Rio Itambi is presented on the basis of a monthly monitoring, and a comparison of rainy and dry season is given. An impact on quality is caused by human activ- ities (sewage input, cattle raising), by landslides with a remodelling of the stream bed and by a low oxygen concentration due to altitude. Flora of stream banks as well as diatoms, macrophytes and fauna of stream bed were deter- mined, and within the stream, biodiversity is low. In the upper part of the stream, this seems to be an effect of low oxygen saturation values and of landslide that remodel the stream bed, and in the lower part of the stream it is due to anthropogenic damage by sewage input. Key words: Rio Itambi - Lago San Pablo -Andes - Ecuador - running water - stream - water quality - physical structure - geomorphology - biodiversity Introduction Few studies have been carried out on the ecology of high Andean streams in Ecuador. TURCOTTE ~; HARPER (1982) investigated the macroinvertebrate species of a small stream located in the Cajas mountains in southern Ecuador. Since 1995, the University of Copenhagen and the Pontificia Universidad Cat61ica del Ecuador have been conducting limnological studies of high mountain and subtropical streams, focused on anthropogenic in- fluences (JACOBSEN et al. 1997; JACOBSEN 1998; JACOB- SEN & ENCALADA 1998), but until now little is known about the limnic ecosystems, the ecological processes and the dynamic of running waters of high Andean streams. This research focuses on Rio Itambi, a high Andean stream and main affluent of Lago San Pablo (Lake San Pablo). The objectives of this work are: *Corresponding author: Dr. Patricia Carrera Burneo, Universidad Cat61icadel Ecuador (PUCE),Av. 12 de Octubre y Patria, RO.Box 17-01-2184, Quito, Ecuador; Phone/Fax:0059 32 2509571, e-mail: pcarrera@puceuio.puce.edu.ec 0075-9511/03/33/01-029 $15.00/0 Limnologica (2003) 33, 29--43