Carbon fluxes and In-Stream Metabolism in a High-Altitude Tropical Peatland Ecosystem of The Andes Mountains

The importance of rivers and streams to the global carbon cycle is well established, and increasingly. research has emphasized the role of in-stream metabolism on carbon transformation within aquatic environments. However, while stream metabolism studies are abundant in northern latitudes, research on tropical streams remains notably scarce. In this study, we characterized carbon fluxes into and out of a small stream in a tropical, peatland-rich ecosystem of the Andes mountains. We measured dissolved oxygen, carbon dioxide, and discharge every 15 minutes at 4 locations downstream of a large peatland. Measurements were collected semi-continuously for a period of 12 months. CO₂evasion was both measured directly and estimated indirectly for comparison. We used continuous dissolved oxygen to estimate daily ecosystem respiration (ER) and gross primary production (GPP) throughout the study period using a Bayesian-based metabolism model. Our results unveiled both seasonal and event-driven patterns in carbon dynamics throughout the year. At the peatland outlet, the stream channel was strongly heterotrophic throughout the study period (GPP << ER), GPP averaged 0.1896 g O₂ m^-2 d^-1, and ER averaged -1.862 g O₂ m^-2 d^-1. ER and GPP were suppressed directly following high flow events, but ER rates rebounded to higher than pre-storm levels in the following days. Seasonally, rates of ER were highest during dry months of the year, but rates of GPP were lowest during the dry season. Aquatic CO₂ concentrations were also elevated during the dry season, but discharge was much lower. As a result, we found the majority of CO₂ was exported from the peatland during the wet season when hydrologic connectivity was highest. Taking together, our results provide much needed process understanding of carbon dynamics in understudied, high-elevation tropical catchments.