Carbon Dioxide (CO2) Fluxes from Terrestrial and Aquatic Environments in a High-Altitude Tropical Catchment

High-altitude tropical grasslands, known as “páramos", are characterized by their high solar radiation, high precipitation, and low temperature. They exhibit some of the highest rates of ecosystem carbon storage per unit area on Earth. Recent observations have shown that paramos may be a net source of CO2 to the atmosphere as a result of climate change; however, little is known about the source of this excess CO2 in these mountainous environments or whether specific landscape positions may be disproportionally contributing more CO2 than others. We evaluated the spatial and temporal variability of surface CO2 fluxes from adjacent terrestrial and aquatic environments based on a suite of field measurements performed over seven weeks. Our findings revealed the importance of hydrologic dynamics in regulating the magnitude and likely fate of dissolved carbon in the stream. While headwater catchments are known to contribute disproportionately larger amounts of carbon to the atmosphere than their downstream counterparts, our study highlights the spatial heterogeneity of CO2 fluxes within and between aquatic and terrestrial landscape elements in headwater catchments of complex topography. Stream carbon flux to the atmosphere appeared to be transport-limited (i.e., controlled by flow characteristics, turbulent flow, water velocity) in the upper reaches of the stream, and source limited (i.e., controlled by carbon availability) in the lower reaches of the stream. These findings represent first step in understanding ecosystem carbon cycling at the interface of terrestrial and aquatic ecosystems in high-altitude, tropical, headwater catchments.