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- Title
Aquatic Carbon Export and Dynamics in Mountain Headwater Streams of the Western U.S.
- Authors
Clow, D. W.; Akie, G. A.; Striegl, R. G.; Penn, C. A.; Sexstone, G. A.; Keith, G. L.
- Abstract
Mountain headwater streams actively cycle carbon, receiving it from terrestrial landscapes and exporting it through downstream transport and gas exchange with the atmosphere. Although their importance is now widely recognized, aquatic carbon fluxes in headwater streams remain poorly characterized. In this study, aquatic carbon fluxes were measured in 15 mountain headwater streams and were used in a geostatistical analysis to determine how landscape characteristics influence aquatic carbon fluxes. In‐stream sensors were used to measure fluorescent dissolved organic matter (fDOM) (a surrogate for dissolved organic carbon (DOC)) at a subset of sites to characterize dynamic responses to hydroclimatic events. Wetlands have a positive influence on aquatic carbon fluxes, whereas perennial snow/ice has the opposite effect, reflecting differences in soil organic matter content in these landscapes. Mean annual temperature (MAT) has a complex influence on DOC, with peak DOC exports in basins with MAT of 0–2°C. Precipitation has a strong positive influence on aquatic carbon fluxes, and declining snowpacks in the western United States may reduce future aquatic carbon exports. fDOM (and by implication DOC) and HCO3‐ ${{\text{HCO}}_{3}}^{\mbox{-}}$ showed strong dynamic responses to snowmelt and rain events, with fDOM increasing and HCO3‐ ${{\text{HCO}}_{3}}^{\mbox{-}}$ decreasing during events. Combining results from this study with those from a companion study on CO2 exchange yielded total aquatic carbon fluxes of 7.2–15.7 g C m−2 yr−1 (median = 12.22), similar to those from forests and peatlands. Given net ecosystem production (NEP) of similar magnitude, NEP calculations that do not account for losses via the aquatic pathway can substantially overestimate terrestrial carbon sequestration. Plain Language Summary: Small mountain streams play an important role in the global carbon cycle, receiving carbon from the surrounding landscape and exporting it via streamflow and gas exchange with the atmosphere. In this study, we quantified downstream transport of aquatic carbon in 15 headwater streams in the western United States and characterized temporal dynamics at a subset of sites in Rocky Mountain National Park. Snowmelt was the main driver of aquatic carbon fluxes in the study basins, and future changes in snowpacks could have a substantial effect on carbon cycling in them. Rainstorms caused sharp changes in aquatic carbon concentrations, reflecting dynamic responses to major hydroclimatic events. The amount of carbon exported from mountain streams by streamflow and gas exchange is large and can have an important influence on net ecosystem carbon budget estimates. Key Points: Aquatic carbon fluxes in seasonally snow‐covered catchments are driven by hydrologic flushing of organic‐rich soils during snowmeltClimate and hydrology are primary influences on aquatic carbon fluxes at a wide range of time scales (annual, seasonal, diel, and event)Mountain headwater streams release substantial carbon received from terrestrial landscapes, similar in amount to net ecosystem production
- Subjects
ROCKY Mountain National Park (Colo.); UNITED States; DISSOLVED organic matter; CARBON cycle; WETLANDS; CARBON sequestration; CARBON; RAINFALL
- Publication
Journal of Geophysical Research. Biogeosciences, 2023, Vol 128, Issue 11, p1
- ISSN
2169-8953
- Publication type
Article
- DOI
10.1029/2023JG007538