RIPARIAN CARBON STORAGE IN HEADWATER STREAMS OF THE COLORADO ROCKY MOUNTAIN

Recent work suggests that rivers are a dynamic component of the global carbon cycle, but only refers to storage of carbon in fluvial networks without considering how specifics of process and form in rivers influence carbon partitioning among the atmosphere, geosphere, and oceans. Global estimates of forest carbon budgets also do not currently distinguish carbon in riparian areas from those used to estimate reservoirs of adjacent uplands. With respect to the geosphere component of river networks, only a few studies quantify carbon storage in floodplains, and these studies focus on large rivers or low gradient streams along which deposition is typically substantial. Additionally, these studies do not examine processes that influence the volume and turnover time of floodplain sediment and associated carbon storage. The influence of valley geometry has been long recognized as a major influence on channel planform, and we now extend this relationship to consider potential for carbon to be incorporated into floodplains and riparian areas. Recent work in mountainous streams of Wild Basin, Rocky Mountain National Park, Colorado suggests that multithread channels, which occur only in unconfined valleys where beaver or old-growth forests (>200 y) are present, store a disproportionately large amount of carbon (~80% carbon in ~20% of total river km) compared to single-thread channels in at least partly confined valleys with younger forests. Riparian areas in Wild Basin account for only 1% of the entire catchment surface area and store ~25% of the total estimated carbon in adjacent uplands. Using systematic soil sampling and radiocarbon dating along 12 study reaches with drainage areas that vary from 10 to 200 km², we examine the potential role of drainage area and the influence of local disturbance gradients on long-term (10² – 10³ y) riparian carbon storage and floodplain sediment turnover time associated with old-growth and young forests in confined, partly confined, and unconfined valley segments. Preliminary results reflect the importance of multithread channels for carbon storage and potential importance of climate change, ecosystem structure and land-use management on the formation of multithread channels.