Algunos aspectos limnologicos de un lago altoandino: el lago San Pablo, Ecuador

Resumen

The limnology of Lake San Pablo (Ecuador) was followedfrom January 1998 to December 1999. The monomictic character ofthe lake was established. A period offull mixing occurred during summer (i.e. between June and August). During the rest of the year the water column was thermally stratified, albeit stratijication was of low stability because of small temperature differences down the water column (i.e. max. 4.5 "C). Furthermore, at night convective heat loss takes place, lowering water temperature. Intensive agricultural activities, land erosion at the catchment area and the inflow of untreated wastewater into the lake have contributed to its actual eutrophic state. However; the lake is relatively unproductive, apparently because nitrogen is a limiting nutrient. Few species of both phytoplankton andzooplankton were found, and densities were low. Thephytoplankton was represented primarily by the filamentous diatom Aulacoseira granula, the green algae Scenedesmus linearis and the Euglenophyceae Trachelomonas volvocina. The zooplankton was poor and is represented by Daphnia pulicaria, Metacyclops mendocinus and the rotatoria Keratella tropica, Trichocerca similis, Anuraeopsis fissa and Asplanchna sp.