Abstract
Long-running eddy covariance flux towers provide insights into how the terrestrial carbon cycle operates over multiple timescales. Here, we evaluated variation in net ecosystem exchange (NEE) of carbon dioxide (CO2) across the Chequamegon Ecosystem-Atmosphere Study AmeriFlux core site cluster in the upper Great Lakes region of the USA from 1997 to 2020. The tower network included two mature hardwood forests with differing management regimes (US-WCr and US-Syv), two fen wetlands with varying levels of canopy sheltering and vegetation (US-Los and US-ALQ), and a very tall (400 m) landscape-level tower (US-PFa). Together, they provided over 70 site-years of observations. The 19-tower Chequamegon Heterogenous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors 2019 campaign centered around US-PFa provided additional information on the spatial variation of NEE. Decadal variability was present in all long-term sites, but cross-site coherence in interannual NEE in the earlier part of the record became weaker with time as non-climatic factors such as local disturbances likely dominated flux time series. Average decadal NEE at the tall tower transitioned from carbon source to sink to near neutral over 24 years. Respiration had a greater effect than photosynthesis on driving variations in NEE at all sites. Declining snowfall offset potential increases in assimilation from warmer springs, as less-insulated soils delayed start of spring green-up. Higher CO2 increased maximum net assimilation parameters but not total gross primary productivity. Stand-scale sites were larger net sinks than the landscape tower. Clustered, long-term carbon flux observations provide value for understanding the diverse links between carbon and climate and the challenges of upscaling these responses across space.
| Original language | English |
|---|---|
| Article number | e2022JG007014 |
| Journal | Journal of Geophysical Research: Biogeosciences |
| Volume | 127 |
| Issue number | 12 |
| DOIs | |
| State | Published - Dec 2022 |
| Externally published | Yes |
Funding
The authors acknowledge the work of many dedicated technicians, students, and researchers who worked in constructing, operating, and analyzing instruments and observations from the ChEAS core site cluster, the CHEESEHEAD19 sites, and related sites for the past quarter century. The authors are in extraordinary debt to the pioneering vision from the original “ChEAS”‐head Professor Ken Davis of The Pennsylvania State University, and key early contributions and labor by Peter Bakwin (NOAA), Bruce Cook (NASA), Brad Berger, Paul Bolstad (U Minnesota), and Arlyn Andrews (NOAA) on whose design, instrumentation, and methodology we still rely. The authors also acknowledge the support of our land holders, the US Forest Service Chequamegon‐Nicolet National Forest and Ottawa National Forest, the State of Wisconsin Department of Natural Resources, and State of Wisconsin Educational Communications Board. The authors would like to thank Christina Staudhammer for statistical advice. The authors also recognize that our field research occurs on the traditional territories of the Ojibwe people, which have been unjustly ceded and whose ancestors were the original scientists and naturalists who stewarded the land, air, and waters we are fortunate to observe, reflect, and hopefully help continue to flourish. Funding agencies that supports the towers include Department of Energy (DOE) AmeriFlux Network Management Project contract to the ChEAS core site cluster, NSF Grants 0845166 and 1822420, Wisconsin Focus on Energy, EERD 10‐06, USDA North Central Research Station, Department of Energy, NICCR Midwest, 050516Z19, DOE Terrestrial Carbon Processes, and NASA Carbon Cycle. This manuscript was a joint project of the UW Ecometeorology lab members and collaborators conducted over the pandemic in weekly lab meetings. The authors acknowledge the work of many dedicated technicians, students, and researchers who worked in constructing, operating, and analyzing instruments and observations from the ChEAS core site cluster, the CHEESEHEAD19 sites, and related sites for the past quarter century. The authors are in extraordinary debt to the pioneering vision from the original “ChEAS”-head Professor Ken Davis of The Pennsylvania State University, and key early contributions and labor by Peter Bakwin (NOAA), Bruce Cook (NASA), Brad Berger, Paul Bolstad (U Minnesota), and Arlyn Andrews (NOAA) on whose design, instrumentation, and methodology we still rely. The authors also acknowledge the support of our land holders, the US Forest Service Chequamegon-Nicolet National Forest and Ottawa National Forest, the State of Wisconsin Department of Natural Resources, and State of Wisconsin Educational Communications Board. The authors would like to thank Christina Staudhammer for statistical advice. The authors also recognize that our field research occurs on the traditional territories of the Ojibwe people, which have been unjustly ceded and whose ancestors were the original scientists and naturalists who stewarded the land, air, and waters we are fortunate to observe, reflect, and hopefully help continue to flourish. Funding agencies that supports the towers include Department of Energy (DOE) AmeriFlux Network Management Project contract to the ChEAS core site cluster, NSF Grants 0845166 and 1822420, Wisconsin Focus on Energy, EERD 10-06, USDA North Central Research Station, Department of Energy, NICCR Midwest, 050516Z19, DOE Terrestrial Carbon Processes, and NASA Carbon Cycle. This manuscript was a joint project of the UW Ecometeorology lab members and collaborators conducted over the pandemic in weekly lab meetings.
| Funders | Funder number |
|---|---|
| ChEAS core site cluster | |
| State of Wisconsin Educational Communications Board | |
| Wisconsin Focus on Energy | EERD 10‐06 |
| National Science Foundation | 1822420, 0845166 |
| U.S. Department of Energy | |
| National Aeronautics and Space Administration | |
| National Oceanic and Atmospheric Administration | |
| U.S. Department of Agriculture | 050516Z19 |
| U.S. Forest Service | |
| Pennsylvania State University | |
| Wisconsin Department of Natural Resources |
Keywords
- AmeriFlux
- CHEESEHEAD19
- carbon fluxes
- eddy covariance
- forests
- wetlands