The number, size, and shape of lakes are key determinants of the ecological functionality of a lake district. The lake area scaling relationships with lake number and volume enable upscaling biogeochemical processes and spatially considering organisms' metapopulation dynamics. These relationships vary regionally depending on the geomorphological context, particularly in the range of lake area 10⁴ m² and 50% of the water resources are held in a few ones (∼10) deeper than 18 m. Therefore, midlakes and large lakes are by far more biogeochemically relevant than ponds and shallow lakes in this tropical mountain lake district.

Water chemistry and its ecological implications have been extensively investigated in temperate high‐mountain lakes because of their role as sentinels of global change. However, few studies have considered the drivers of water chemistry in tropical mountain lakes underlain by volcanic bedrock. A survey of 165 páramo lakes in the Cajas Massif of the Southern Ecuador Andes identified 4 independent chemical variation gradients, primarily characterized by divalent cations (hardness), organic carbon, silica, and iron levels. Hardness and silica factors showed contrasting relationships with parent rock type and age, vegetation, aquatic ecosystems in the watershed, and lake and watershed size. Geochemical considerations suggest that divalent cations (and related alkalinity, conductivity, and pH) mainly respond to the cumulative partial dissolution of primary aluminosilicates distributed throughout the subsurface of watersheds, and silica and monovalent cations are associated with the congruent dissolution of large amounts of secondary aluminosilicates localized in former hydrothermal or tectonic spots. Dissolved organic carbon was much higher than in temperate high‐mountain lakes, causing extra acidity in water. The smaller the lakes and their watersheds, the higher the likelihood of elevated organic carbon and metals and low hardness. The watershed wetland cover favored metal levels in the lakes but not organic carbon. Phosphorus, positively, and nitrate, negatively, weakly correlated with the metal gradient, indicating common influence by in‐lake processes. Overall, the study revealed that relatively small tropical lake districts on volcanic basins can show chemical variation equivalent to that in large mountain ranges with a combination of plutonic, metamorphic, and carbonate rock areas.

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.