Seminar: Hella van Asperen

We present the first continuous measurements of dissolved CO₂ , CH₄, N₂ O and CO in the Rio Negro, between the cities of Manaus and São Gabriel de Cachoeira (~1000 km). From a moving research vessel, water was sampled continuously from a depth of 50 cm and passed through a bubble-type-equilibrator. A closed air stream was circulated through the equilibrator, and continuously measured by an in-situ FTIR analyzer. In addition, variables such as pH, air and water temperature, DOC and coliform bacteria were determined.

All measured gases were supersaturated in the water with respect to the atmosphere, indicating an outgoing flux toward the atmosphere. CH₄ concentrations showed elevated concentrations in the middle Rio Negro, contrasting with CO₂ , which peaked in the upper and lower Rio Negro. Both CH₄ and CO₂ displayed distinct hotspot regions, many of which were centered around human settlements and are therefore likely of anthropogenic origin, as also confirmed by the observed bacterial communities. A few hotspots appeared to be linked to surrounding wetlands, which may release large amounts of CH₄ during the rising water phase when reconnected to the main river. N₂ O showed elevated concentrations in the upper Rio Negro, possibly linked to the extensive white sand forest areas in this part of the catchment. CO concentrations showed a clear diurnal pattern, with highest concentrations coinciding with highest incoming solar radiation.