Dissolved greenhouse gas (CO2, CH4, and N2O) emissions from highland lakes of the Andes cordillera in Northern Ecuador

We report, in 15 Ecuadorian mountainous lakes, dissolved concentrations of CO2, CH4, and N2O and a suite of ancillary biogeochemical variables (dissolved inorganic nutrients, oxygen, major cations, dissolved and particulate organic carbon, and the stable isotope composition of dissolved inorganic carbon and water). The sampled lakes were located in the páramos of Salve Facha and Antisana y Mojanda (northern region of Ecuadorian Andes), along an elevational gradient from 2,213 to 4,361 m above sea level, as well as a gradient of lake surface area (0.003 to 6.1 km2) and depth (1 to 74 m). Most lakes were characterized by lower values of the partial pressure of CO2 (pCO2) (644-2,152 ppm) than usually attributed to tropical lakes (~1,900 ppm). Three lakes influenced by volcanic inputs were characterized by the highest pCO2 values (3,269-10,069 ppm), while two lakes bordered by large cities were characterized by the lowest pCO2 values (208-254 ppm). Dissolved CH4 concentrations ranged between 170 and 24,908 nmol L-1 and were negatively correlated to lake area and depth. N2O saturation levels ranged between 64% and 101%. The surface waters were under-saturated in N2O with respect to atmospheric equilibrium, probably due to inputs of soil-water with low N2O levels owing to denitrification in soils. The data obtained in the sampled highland lakes was combined with published data from lowland lakes (elevation <500 m, n=17 for CO2 and n=16 for CH4) to derive relations between CO2 and CH4 and lake surface area, allowing to compute CO2 and CH4 lacustrine emissions at the scale of the Amazon basin using the HydroLAKES spatial data-set. The CO2 and CH4 emissions from highland lakes (elevation > 500 m) only represented 0.4% and 2% of the total lacustrine emissions at the scale of the Amazon basin, respectively. Total CO2 and CH4 emissions from lakes represented a small fraction (8.6%) of total lentic and lotic CO2 and CH4 emissions at the scale of the Amazon basin. The lake and river emissions of CH4 represented ~3% of total CH4 emissions from all compartments of the Amazon basin, mainly attributable to wetlands.