Link between cattle and the trophic status of tropical high mountain lakes in páramo grasslands in Ecuador

The high-altitude páramo grasslands of the Andes Mountains are rich in lakes that represent a source of high-quality water for the region. Páramo grasslands are mainly used for cattle grazing. The aim of this study was to investigate the influence of cattle on the trophic status of páramo lakes. In a survey of 30 lakes in Cajas National Park (NP), a semi-quantitative estimate for cattle abundance in the vicinity of the lakes was the best predictor of the chlorophyll-a concentrations in the lakes. Cattle abundance was also significantly related to phytoplankton community composition, being associated with a shift from chlorophytes to diatoms and dinoflagellates. Lake Culibrillas, a lake situated in the Sangay National Park (Sangay NP), a region with much more intensive cattle farming than Cajas NP exhibited a chlorophyll-a concentration greater than twice as much as the largest concentration measured in the Cajas NP lakes, being characterized by a dinoflagellate bloom. Although chlorophyll-a concentrations increased with cattle abundance, the concentrations in all the study lakes remained low (0.02–1.8 μg/L), indicating that extensive cattle farming does not cause severe eutrophication. The results of this study nevertheless indicate that intensification of livestock farming in páramo grasslands might result in a deterioration of water quality in the páramo lakes.