Tropical high mountain lakes in the Andean area of Ecuador are a
special type of lake, that had not been studied. They are cold water
lakes situated 3,000 to 4,000 m above sea level, directly on the equa-
tor. Limnological investigations were undertaken to determine the
succession of phyto- und zooplankton and to elucidate basic limno-
logical processes, such as thermal stratification and mixing process-
es.
Today Lake San Pablo, the largest lake in Ecuador, is a eutrophic
lake due to the input of sewage and other nutrients from the catch-
ment area, which originate from intensive agriculture and land ero-
sion. Some data on water chemistry of the lake are presented. Lake
San Pablo is a monomictic lake with a short mixing period during
July to September. Stratification of the lake and mixing processes
caused by nocturnal cooling are of great significance for the eu-
trophication, which occurred mainly during the last decade.
Initial data on the phytoplankton, zooplankton and macrophytes
are provided, which show that the biocoenosis has low diversity.
Considering the high nutrient level, phytoplankton biomass is low.