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Abstract The heterogeneity of carbon dioxide (CO2) and methane (CH4) sources within and across watersheds presents a challenge to understanding the contributions of different ecosystem patch types to stream corridor and watershed carbon cycling. Changing hydrologic connections between corridor patches (e.g., streams, vernal pools, hillslopes) can influence stream corridor greenhouse gas emissions, but the spatiotemporal dynamics of emissions within and among corridor patches are not well‐quantified. To identify patterns and sources of carbon emissions across stream corridors, we measured gas concentrations and fluxes over two summers at Coweeta Hydrologic Laboratory, NC. We sampled CO2and CH4along four stream channels (including flowing and dry reaches), adjacent vernal pools, and riparian hillslopes. Stream CO2and CH4emissions were spatially heterogeneous. All streams were sources of CO2to the atmosphere (median = 97.2 mmol m−2d−1) but were sources or sinks of CH4depending on location (−0.19 to 4.57 mmol m−2d−1). CO2emissions were lower during the drier of two sampling years but were stable from month to month in the drier summer. CO2and CH4emissions also varied by both corridor and patch type; the presence of a vernal pool in the corridor had the strongest impact on emissions. Vernal pool patches emitted more CO2and CH4(246 and 1.95 mmol m−2d−1, respectively) than their adjacent streams. High resolution sampling of carbon fluxes from patches within and among stream corridors improves our understanding of the connections between terrestrial, riparian, and aquatic zones in a watershed and their contributions to overall catchment carbon emissions.
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This content will become publicly available on November 15, 2025
Nitrate Loads From Land to Stream Are Balanced by In‐Stream Nitrate Uptake Across Seasons in a Dryland Stream Network
Abstract Exploring nitrogen dynamics in stream networks is critical for understanding how these systems attenuate nutrient pollution while maintaining ecological productivity. We investigated Oak Creek, a dryland watershed in central Arizona, USA, to elucidate the relationship between terrestrial nitrate (NO3−) loading and stream NO3−uptake, highlighting the influence of land cover and hydrologic connectivity. We conducted four seasonal synoptic sampling campaigns along the 167‐km network combined with stream NO3−uptake experiments (in 370–710‐m reaches) and integrated the data in a mass‐balance model to scale in‐stream uptake and estimate NO3−loading from landscape to the stream network. Stream NO3−concentrations were low throughout the watershed (<5–236 μg N/L) and stream NO3−vertical uptake velocity was high (5.5–18.0 mm/min). During the summer dry (June), summer wet (September), and winter dry (November) seasons, the lower mainstem exhibited higher lateral NO3−loading (10–51 kg N km−2 d−1) than the headwaters and tributaries (<0.001–0.086 kg N km−2 d−1), likely owing to differences in irrigation infrastructure and near‐stream land cover. In contrast, during the winter wet season (February) lateral NO3−loads were higher in the intermittent headwaters and tributaries (0.008–0.479 kg N km−2 d−1), which had flowing surface water only in this season. Despite high lateral NO3−loading in some locations, in‐stream uptake removed >81% of NO3−before reaching the watershed outlet. Our findings highlight that high rates of in‐stream uptake maintain low nitrogen export at the network scale, even with high fluxes from the landscape and seasonal variation in hydrologic connectivity.
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- Award ID(s):
- 2224662
- PAR ID:
- 10555380
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 129
- Issue:
- 11
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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