Stream greenhouse gas dynamics in a tropical landscape

Streams and rivers contribute significant emissions of carbon dioxide, methane, and nitrous oxide to the atmosphere, and have the potential to offset the terrestrial carbon sink. However, global and regional estimates of greenhouse gas (GHG) fluxes from fluvial ecosystems remain uncertain. The majority of studies that investigate GHG dynamics and fluxes come from temperate streams and rivers, with less research being done in tropical ecosystems. Using a nested watershed approach, we sampled six streams weekly in the Luquillo Mountains in Puerto Rico for a period of five years. This allowed us to examine spatial and temporal greenhouse gas dynamics using watersheds of contrasting lithology, vegetation, and precipitation patterns. Streams and rivers in the Luquillo Mountains were consistently supersaturated with respect to the atmosphere for all three GHGs. Spatial variability in methane concentrations appears to be related to differences in lithology and sediment characteristics, but controls on carbon dioxide and nitrous oxide variability are more cryptic in this landscape. Elucidating controlling factors and determining fluxes of GHGs from tropical ecosystems is imperative to understanding the variability in fluxes across biomes and will help improve global GHG estimates from streams and rivers.