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

Abstract

We report, in 15 Ecuadorian mountainous lakes, dissolved concentrations of CO 2 , CH 4 , and N 2 O 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 2213 to 4361 m above sea level, as well as a gradient of lake surface area (0.003-6.1 km 2 ) and depth (1-74 m). Most lakes were characterized by lower values of the partial pressure of CO 2 (pCO 2 ) (644-2152 ppm) than usually attributed to tropical lakes (~ 1900 ppm). Three lakes influenced by volcanic inputs were characterized by the highest pCO 2 values (3269-10,069 ppm), while two lakes bordered by large cities were characterized by the lowest pCO 2 values (208-254 ppm). Dissolved CH 4 concentrations ranged between 170 and 24,908 nmol/L and were negatively correlated to lake area and depth. N 2 O saturation levels ranged between 64% and 101%. The surface waters were undersaturated in N 2 O with respect to atmospheric equilibrium, probably due to inputs of soil-water with low N 2 O 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 CO 2 and n = 16 for CH 4 ) to derive relations between CO 2 and CH 4 and lake surface area, allowing to compute CO 2 and CH 4 lacustrine emissions at the scale of the Amazon basin using the HydroLAKES spatial data set. The CO 2 and CH 4 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 CO 2 and CH 4 emissions from lakes represented a small fraction (8.6%) of total lentic and lotic CO 2 and CH 4 emissions at the scale of the Amazon basin. The lake and river emissions of CH 4 represented ~ 3% of total CH 4 emissions from all compartments of the Amazon basin, mainly attributable to wetlands. KeywordsAmazon River • Ecuador • Mountainous lakes • CO 2 • CH 4 • N 2 O * Alberto V. Borges

Seasonal and spatial variations of greenhouse gas (CO2, CH4 and N2O) emissions from urban ponds in Brussels

“…6E). Several studies reported a negative correlation between CH4 concentration and lake size (surface and/or depth) across spatial scales (local to global) (Borges et al, 2011;Kankaala et al, 2013;Holgerson and Raymond, 2016;Borges et al, 2022;Chiriboga et al 2024), yet one study reported no relationship (Peacock et al, 2019) and another a positive correlation (Rabaey et al, 2022). The positive relationship between CH4 concentration and pond size in the ponds of the city of Brussels was probably indirect and reflected another driver.…”

“…The levels of CO2 and CH4 in lakes vary as a function of lake size (Lapierre and del Giorgio, 2012;Kankaala et al, 2013;Raymond et al, 2013;Holgerson and Raymond, 2016;Casas-Ruiz et al, 2021;Borges et al, 2022;Chiriboga et al 2024) as well as land cover (Maberly et al, 2013). Combined lake size and land cover determine relative levels of allochthonous organic matter inputs to aquatic systems and the general balance of autotrophy and heterotrophy largely determining CO2 levels (del Giorgio and Peters, 1994), as well as benthic methanogenesis.…”