Greenhouse Gas (Co2, Ch4, N2o) Emissions from Ecuadorian Mountainous Streams and High Elevation Lakes

• Main Author: G, Gonzalo Chiriboga
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2023
• Subjects: Carbon dioxide; Climate Change; Emissions; Greenhouse gases; Latin American Studies; Rivers; Venus
• ISBN: 9798384140788

Rivers and streams contribute substantially to global emissions of carbon dioxide (CO2) and methane (CH4). Most riverine GHG emissions are from the tropics, ~60-80% for CO2, ~70% for CH4, and ~79% for nitrous oxide (N2O). Nevertheless, the total stream surface area (SSA) in the tropics (24°N-24°S) corresponds to ~44% of the total SSA globally, implying that riverine areal emissions of GHGs (per m2) are higher than in other climatic zones. Ecuador localizes on the tropics, and it is the smallest of the 17 megadiverse countries in the world harboring an astounding number of ecosystems, which offers the conditions to study in a relatively short space the GHG evasions of both, an important river tributary to the Amazon, as well as a diverse lacustrine system. The present thesis is divided into two sections. Firstly, we report for the first time the dissolved concentrations CO2, CH4, and N2O in Andean headwater and piedmont streams in the Napo River basin in Ecuador, part of the Amazon River catchment. We found that concentrations increased exponentially with elevation decrease, i.e., between 3,990 and 175 m above sea level. Conversely, Andean mountainous headwater and piedmont streams are hotspots of CO2 and CH4emissions; the respective areal fluxes are 1.7 and 4.5 higher in headwater streams and 1.2 and 6.6 higher in piedmont streams than in lowland streams.Secondly, report the dissolved GHGs of 15 lakes along an elevational gradient ranging from 2,213 to 4,361 m. Lakes were grouped into three clusters as a function of their characteristics and obtained outcomes. Most lakes showed 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, denoted higher pCO2 values (3,269-10,069 ppm), while two lakes bordered by large cities showed the lowest pCO2 values (208-254 ppm), the remaining ten lakes had moderated pCO2 and the highest dissolved organic carbon concentrations (8.3 to 12.8 mg L-1) that is characteristic of páramo lakes (644-2,152 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 regarding atmospheric equilibrium, probably due to soil-water inputs with low N2O levels due to soil denitrification. By upscaling to lakes in the whole Amazon basin, we found that the average areal FCH4 (per m2) was 1.3 times higher in highland lakes (0.75 gC m-2 yr-1) than in lowland lakes (0.58 gC m-2 yr-1) owing to the combination of higher dissolved CH4 concentration (265 nmol L-1 versus 179 nmol L-1) and higher gas transport velocity (k) values (3.5 cm h-1 versus 2.5 cm h-1). Meanwhile, the average areal FCO2 was 11 times lower in the highlands (23 gC m-2 yr-1) than in the lowlands (255 gC m-2 yr-1) owing to the lower pCO2values (530 ppm versus 2,909 ppm)