CO2 and CH4 dynamics in a eutrophic tropical Andean reservoir.

We studied the dynamics of methane (CH₄) and carbon dioxide (CO₂) in a eutrophic tropical reservoir located in the Colombian Andes. Temporal and spatial dynamics were addressed through sampling during six field campaigns conducted throughout a two-year period. We monitored fluxes at the air-water interface, dissolved gas concentrations, physical and chemical properties of the water column, microstructure profiles of turbulence, and meteorological conditions. Throughout the study period, the reservoir was a persistent source of CH₄ to the atmosphere with higher emissions occurring in the near inflow region. During periods of low water levels, both the emissions and surface concentrations of CH₄ were higher and more spatially heterogeneous. The measured CO₂ fluxes at the air-water interface changed direction depending on the time and location, showing alternating uptake and emissions by the water surface. Mass balances of dissolved CH₄ in the surface mixed layer revealed that biochemical reactions and gas evasion were the most significant processes influencing the dynamics of dissolved CH₄, and provided new evidence of possible oxic methane production. Our results also suggest that surface CH₄ concentrations are higher under more eutrophic conditions, which varied both spatially and temporally. [ABSTRACT FROM AUTHOR]