Kristen Bretz

VT Biological Sciences;Virginia Tech

Subject Areas: Biogeochemistry, hydrology, Ecohydrology, ecology, watershed management

 Recent Activity

ABSTRACT:

Non-perennial headwaters experience extremes in flow conditions that likely influence carbon fate. As surface waters contract through dry periods, reconnect during storms, and re-expand or dry again, there is a great deal of variability in carbon emissions and export. We measured discharge, dissolved oxygen (DO), carbon dioxide (CO2), and dissolved organic carbon (DOC) continuously in a persistent pool at the base of a non-perennial, forested headwater stream in the southeastern United States to characterize how flow changes affect carbon emissions and export as the stream expands and shrinks. We also compared carbon concentrations and export during different stream flow categories before and after fall wet-up. CO2 concentrations were high when discharge was lowest (median = 10.2 mg L-1) and low during high flows (3.2 mg L-1) and storms (1.1 mg L-1). High CO2 concentrations led to high emissions on a per area basis during low flow times, but whole-channel stream CO2 emissions were limited by the small surface area of the stream during periods of surface water disconnection. DOC concentration varied by season (range = 0.1 - 16.2 mg L-1) with large pulses during smaller summer storms. We found that CO2 and DOC concentrations differed among binned stages of stream flow. As non-perennial streams become more prevalent across the southeastern United States due to shifts in climate, the relationships between flow and carbon movement into and out of stream networks will become increasingly critical to understanding stream carbon biogeochemistry.

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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., stream, riparian wetland, hillslope) 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 CO2 and CH4 along four stream channels (including flowing and dry reaches), adjacent wetlands, and riparian hillslopes. Stream CO2 and CH4 emissions were spatially heterogeneous. All streams were sources of CO2 to the atmosphere (median = 97.2 mmol m-2d-1) but were sources or sinks of CH4 depending on location (-0.19 to 4.57 mmol m-2d-1). CO2 emissions were lower during the drier of two sampling years but were stable from month to month in the drier summer. CO2 and CH4 emissions also varied by both corridor and patch type; the presence of a riparian wetland in the corridor had the strongest impact on emissions. Wetland patches emitted more CO2 and 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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IntegratingEcosystemPatchContributionsStreamCO2CH4_Data
Created: Feb. 25, 2021, 6:57 p.m.
Authors: Bretz, Kristen · Alexis Jackson · Sumaiya Rahman · Jonathon Monroe · Erin Hotchkiss

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., stream, riparian wetland, hillslope) 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 CO2 and CH4 along four stream channels (including flowing and dry reaches), adjacent wetlands, and riparian hillslopes. Stream CO2 and CH4 emissions were spatially heterogeneous. All streams were sources of CO2 to the atmosphere (median = 97.2 mmol m-2d-1) but were sources or sinks of CH4 depending on location (-0.19 to 4.57 mmol m-2d-1). CO2 emissions were lower during the drier of two sampling years but were stable from month to month in the drier summer. CO2 and CH4 emissions also varied by both corridor and patch type; the presence of a riparian wetland in the corridor had the strongest impact on emissions. Wetland patches emitted more CO2 and 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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C_Biogeo&Export_NonPStream_Data
Created: April 30, 2023, 3:37 p.m.
Authors: Bretz, Kristen · Hotchkiss, Erin R · Natalie Murphy

ABSTRACT:

Non-perennial headwaters experience extremes in flow conditions that likely influence carbon fate. As surface waters contract through dry periods, reconnect during storms, and re-expand or dry again, there is a great deal of variability in carbon emissions and export. We measured discharge, dissolved oxygen (DO), carbon dioxide (CO2), and dissolved organic carbon (DOC) continuously in a persistent pool at the base of a non-perennial, forested headwater stream in the southeastern United States to characterize how flow changes affect carbon emissions and export as the stream expands and shrinks. We also compared carbon concentrations and export during different stream flow categories before and after fall wet-up. CO2 concentrations were high when discharge was lowest (median = 10.2 mg L-1) and low during high flows (3.2 mg L-1) and storms (1.1 mg L-1). High CO2 concentrations led to high emissions on a per area basis during low flow times, but whole-channel stream CO2 emissions were limited by the small surface area of the stream during periods of surface water disconnection. DOC concentration varied by season (range = 0.1 - 16.2 mg L-1) with large pulses during smaller summer storms. We found that CO2 and DOC concentrations differed among binned stages of stream flow. As non-perennial streams become more prevalent across the southeastern United States due to shifts in climate, the relationships between flow and carbon movement into and out of stream networks will become increasingly critical to understanding stream carbon biogeochemistry.

Show More