A limnological assessment of the diverse waterscape in the Cordillera Vilcanota, Peruvian Andes

A pre-Inca pot from underwater ruins discovered in an Andean lake provides a sedimentary record of marked hydrological change

“…The Fragilaria sensu lato complex that dominate the diatom profile (Fig. 4) are consistent with their high abundances in cold, circumneutral-to-alkaline lakes in Arctic and alpine regions 1,17–20 . Cocconeis neuquina , the only non-fragilarioid taxon to exceed 5% relative abundance prior to ~1970 CE, has been documented as a periphytic taxon in shallow Patagonian lakes characterized by circumneutral to alkaline pH, with generally cool temperatures (1.7 to 16.4 °C) and varying conductivity (37–1390 µS/cm) 21 .…”

“…The Pomacanchi meteorological station (3,200 m asl), ~60 km west-southwest of Laguna Sibinacocha, records mean minimum and maximum daily temperatures of 2.8 and 17.2 °C, respectively, and mean annual precipitation of 851 mm (1985–2014). The Ccatcca and Pomacanchi climate stations record significant (P < 0.01) warming trends for both maximum and minimum daily temperatures over their period of measurement 1 .…”

“…Laguna Sibinacocha is circumneutral (pH = 7.9), ultra-oligotrophic (total phosphorus = 3.3 µg/L) and relatively dilute (conductivity = 380 µS/cm). It is a cold-water lake (temperatures < 12 °C) that is well-mixed with only brief periods of weak thermal stratification 1 . An actively melting glacier 33 drains into the northern basin of the lake but this does not result in any temperature gradient along its ~15 km length 1 .…”

“…Laguna Sibinacocha is an important tributary to the Amazon River and a critical water supply to downstream communities and cities. Despite its cultural, ecological and societal significance, only recently has basic limnological data been provided on its water chemistry, maximum depth, and thermal regime 1 . Adding to the mystery of the lake is the recent discovery of pre-Hispanic artifacts and architecture submerged in its nearshore waters.

Figure 1Location of Laguna Sibinacocha in the Peruvian Andes showing the region of the lake where the study pot was recovered (red rectangle).

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Mountain lakes: Eyes on global environmental change

“…Warming temperatures are also resulting in a loss of glaciers and rock glaciers, which reduces water resources, but also can degrade water quality with potential toxic effects to aquatic organisms (Bain, 2017). A limnological survey in the Cordillera Vilcanota of Peru showed that much of the variability in nutrient and metal concentrations among sites could be linked to whether or not the lake was connected to a glacial watershed, with lakes in glacial catchments having elevated metals and nutrients due to glacial runoff over freshly comminuted bedrock (Michelutti et al, 2019). In some mountain regions changes in ice coverage has exposed sulfidebearing bedrock, leading to oxidation of sulfide minerals and acid rock drainage (Fortner et al, 2011;Ilyashuk et al, 2017).…”