Resolving heterogeneous fluxes from tundra halves the growing season carbon budget
<p>Landscapes are often assumed to be homogeneous when interpreting eddy covariance fluxes, which can lead to biases when gap-filling and scaling up observations to determine regional carbon budgets. Tundra ecosystems are heterogeneous at multiple scales. Plant functional types, soil moisture,...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2024-03-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/21/1301/2024/bg-21-1301-2024.pdf |
| _version_ | 1797258270358896640 |
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| author | S. M. Ludwig S. M. Ludwig L. Schiferl L. Schiferl J. Hung S. M. Natali R. Commane R. Commane |
| author_facet | S. M. Ludwig S. M. Ludwig L. Schiferl L. Schiferl J. Hung S. M. Natali R. Commane R. Commane |
| author_sort | S. M. Ludwig |
| collection | DOAJ |
| description | <p>Landscapes are often assumed to be homogeneous when interpreting eddy covariance fluxes, which can lead to biases when gap-filling and scaling up observations to determine regional carbon budgets. Tundra ecosystems are heterogeneous at multiple scales. Plant functional types, soil moisture, thaw depth, and microtopography, for example, vary across the landscape and influence net ecosystem exchange (NEE) of carbon dioxide (<span class="inline-formula">CO<sub>2</sub></span>) and methane (<span class="inline-formula">CH<sub>4</sub></span>) fluxes. With warming temperatures, Arctic ecosystems are changing from a net sink to a net source of carbon to the atmosphere in some locations, but the Arctic's carbon balance remains highly uncertain. In this study we report results from growing season NEE and <span class="inline-formula">CH<sub>4</sub></span> fluxes from an eddy covariance tower in the Yukon–Kuskokwim Delta in Alaska. We used footprint models and Bayesian Markov chain Monte Carlo (MCMC) methods to unmix eddy covariance observations into constituent land-cover fluxes based on high-resolution land-cover maps of the region. We compared three types of footprint models and used two land-cover maps with varying complexity to determine the effects of these choices on derived ecosystem fluxes. We used artificially created gaps of withheld observations to compare gap-filling performance using our derived land-cover-specific fluxes and traditional gap-filling methods that assume homogeneous landscapes. We also compared resulting regional carbon budgets when scaling up observations using heterogeneous and homogeneous approaches. Traditional gap-filling methods performed worse at predicting artificially withheld gaps in NEE than those that accounted for heterogeneous landscapes, while there were only slight differences between footprint models and land-cover maps. We identified and quantified hot spots of carbon fluxes in the landscape (e.g., late growing season emissions from wetlands and small ponds). We resolved distinct seasonality in tundra growing season NEE fluxes. Scaling while assuming a homogeneous landscape overestimated the growing season <span class="inline-formula">CO<sub>2</sub></span> sink by a factor of 2 and underestimated <span class="inline-formula">CH<sub>4</sub></span> emissions by a factor of 2 when compared to scaling with any method that accounts for landscape heterogeneity. We show how Bayesian MCMC, analytical footprint models, and high-resolution land-cover maps can be leveraged to derive detailed land-cover carbon fluxes from eddy covariance time series. These results demonstrate the importance of landscape heterogeneity when scaling carbon emissions across the Arctic.</p> |
| first_indexed | 2024-04-24T22:50:52Z |
| format | Article |
| id | doaj.art-0ce60ddb9ae34e2aa545484be651dfb3 |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-04-24T22:50:52Z |
| publishDate | 2024-03-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-0ce60ddb9ae34e2aa545484be651dfb32024-03-18T10:51:11ZengCopernicus PublicationsBiogeosciences1726-41701726-41892024-03-01211301132110.5194/bg-21-1301-2024Resolving heterogeneous fluxes from tundra halves the growing season carbon budgetS. M. Ludwig0S. M. Ludwig1L. Schiferl2L. Schiferl3J. Hung4S. M. Natali5R. Commane6R. Commane7Department of Earth and Environmental Science, Columbia University, New York, NY, United States of AmericaLamont-Doherty Earth Observatory, Palisades, NY, United States of AmericaLamont-Doherty Earth Observatory, Palisades, NY, United States of AmericaHarvard John A. Paulson School of Engineering and Applied Sciences, Cambridge, MA, United States of AmericaWoodwell Climate Research Center, Woods Hole, MA, United States of AmericaWoodwell Climate Research Center, Woods Hole, MA, United States of AmericaDepartment of Earth and Environmental Science, Columbia University, New York, NY, United States of AmericaLamont-Doherty Earth Observatory, Palisades, NY, United States of America<p>Landscapes are often assumed to be homogeneous when interpreting eddy covariance fluxes, which can lead to biases when gap-filling and scaling up observations to determine regional carbon budgets. Tundra ecosystems are heterogeneous at multiple scales. Plant functional types, soil moisture, thaw depth, and microtopography, for example, vary across the landscape and influence net ecosystem exchange (NEE) of carbon dioxide (<span class="inline-formula">CO<sub>2</sub></span>) and methane (<span class="inline-formula">CH<sub>4</sub></span>) fluxes. With warming temperatures, Arctic ecosystems are changing from a net sink to a net source of carbon to the atmosphere in some locations, but the Arctic's carbon balance remains highly uncertain. In this study we report results from growing season NEE and <span class="inline-formula">CH<sub>4</sub></span> fluxes from an eddy covariance tower in the Yukon–Kuskokwim Delta in Alaska. We used footprint models and Bayesian Markov chain Monte Carlo (MCMC) methods to unmix eddy covariance observations into constituent land-cover fluxes based on high-resolution land-cover maps of the region. We compared three types of footprint models and used two land-cover maps with varying complexity to determine the effects of these choices on derived ecosystem fluxes. We used artificially created gaps of withheld observations to compare gap-filling performance using our derived land-cover-specific fluxes and traditional gap-filling methods that assume homogeneous landscapes. We also compared resulting regional carbon budgets when scaling up observations using heterogeneous and homogeneous approaches. Traditional gap-filling methods performed worse at predicting artificially withheld gaps in NEE than those that accounted for heterogeneous landscapes, while there were only slight differences between footprint models and land-cover maps. We identified and quantified hot spots of carbon fluxes in the landscape (e.g., late growing season emissions from wetlands and small ponds). We resolved distinct seasonality in tundra growing season NEE fluxes. Scaling while assuming a homogeneous landscape overestimated the growing season <span class="inline-formula">CO<sub>2</sub></span> sink by a factor of 2 and underestimated <span class="inline-formula">CH<sub>4</sub></span> emissions by a factor of 2 when compared to scaling with any method that accounts for landscape heterogeneity. We show how Bayesian MCMC, analytical footprint models, and high-resolution land-cover maps can be leveraged to derive detailed land-cover carbon fluxes from eddy covariance time series. These results demonstrate the importance of landscape heterogeneity when scaling carbon emissions across the Arctic.</p>https://bg.copernicus.org/articles/21/1301/2024/bg-21-1301-2024.pdf |
| spellingShingle | S. M. Ludwig S. M. Ludwig L. Schiferl L. Schiferl J. Hung S. M. Natali R. Commane R. Commane Resolving heterogeneous fluxes from tundra halves the growing season carbon budget Biogeosciences |
| title | Resolving heterogeneous fluxes from tundra halves the growing season carbon budget |
| title_full | Resolving heterogeneous fluxes from tundra halves the growing season carbon budget |
| title_fullStr | Resolving heterogeneous fluxes from tundra halves the growing season carbon budget |
| title_full_unstemmed | Resolving heterogeneous fluxes from tundra halves the growing season carbon budget |
| title_short | Resolving heterogeneous fluxes from tundra halves the growing season carbon budget |
| title_sort | resolving heterogeneous fluxes from tundra halves the growing season carbon budget |
| url | https://bg.copernicus.org/articles/21/1301/2024/bg-21-1301-2024.pdf |
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