Limnological dynamics of methane (CH4) and carbon dioxide (CO2) emissions from a tropical hypertrophic reservoir lake

Abstract

Methane (CH4) and carbon dioxide (CO2) emissions from tropical freshwater ecosystems have been understudied, particularly in terms of their interaction with limnological dynamics, their cycling, and the emission mechanisms of CH4. To help reduce that knowledge gap, this study addressed these processes in Valle de Bravo (VB), a tropical (19° 11. 65′ N) reservoir lake, that provides water supply to Mexico City metropolitan area. CH4 and CO2 concentrations and emissions from VB were measured during four field campaigns distributed along the annual limnological cycle of the reservoir. Dissolved CH4 concentration varied over four orders of magnitude (0.015–176.808 μmol L−1), and dissolved CO2 varied from below atmospheric saturation (15.062 μmol L−1) to 10 times that concentration (219.505 μmol L−1). CH4 fluxes ranged from 23.25 to 1220.80 μmol m−2 day−1, while CO2 fluxes ranged from −60.11 to 254.99 mmol m−2 day−1. Seasonal monitoring also allowed the assessment of the annual emissions as well as the greenhouse gas (GHG) storage during thermal stratification, which accounted for >58% of the total GHG annual emissions from VB. Overall, VB is a source of GHG, and its major contribution is the CH4 released during the autumn overturn. HIGHLIGHTS The limnological dynamics of freshwater bodies have important effects on their GHG emissions.; Because of this, CH4 emissions from VB varied seasonally by two orders of magnitude (23.25–1,220.80 μmol m−2 day−1).; Overall, VB was a net source of CH4 and CO2, but during stratification, it was a net sink of both GHGs.; Most of the emissions were associated with the storage during the stratification period.;

Keywords

• climate change
• emissions
• greenhouse gas
• limnological dynamics
• overturn
• storage