Drivers of Decadal Carbon Fluxes Across Temperate Ecosystems

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.

Airborne Measurements of Scale‐Dependent Latent Heat Flux Impacted by Water Vapor and Vertical Velocity Over Heterogeneous Land Surfaces During the CHEESEHEAD19 Campaign

“…The CHEESEHEAD field campaign deployed a suite of observing platforms over a core 10 × 10 km 2 domain (the red dashed domain in Figure 1a) and a 30 × 30 km extended domain for airborne measurements. The study domain was partly chosen due to the history of atmospheric science research in the region (Davis et al., 2003; Desai, Murphy, et al., 2022). The EC tower network consisted of 17 flux towers from the National Center for Atmospheric Research (NCAR)—Integrated Surface Flux Station (ISFS) network (colored circles in Figure 1), two additional contributed towers in grassland and a lake, and the Department of Energy Ameriflux regional tall tower (US Pfa/WLEF; the star in Figure 1) (Desai, 2023).…”

Airborne Measurements of Scale-Dependent Latent Heat Flux Impacted by Water Vapor and Vertical Velocity over Heterogeneous Land Surfaces During the CHEESEHEAD19 Campaign

“…Measurements of CHEESEHEAD used a suite of observing platforms over a core 10 x 10 km 2 domain (the red dashed domain in Figure 1a) and a 30 km x 30 km extended domain for airborne measurements. The study domain was partly chosen due to the history of atmospheric science research in the region (Davis et al, 2003;Desai et al, 2022a). The EC tower network consisted of 17 flux towers from the National Center for Atmospheric Research (NCAR) -Integrated Surface Flux Station (ISFS) network (colored circles in Figure 1), two additional contributed towers in grassland and a lake, and the tall Department of Energy Ameriflux regional tower (US Pfa/WLEF; the star in Figure 1) (Desai, 2023).…”

Twenty Years of Progress, Challenges, and Opportunities in Measuring and Understanding Soil Respiration

“…At ecosystem scales, Rs dominates ecosystem respiration (Law et al, 2002). Rs variability can drive the carbon balance of ecosystems (Desai et al, 2022) to entire continents (Ballantyne et al, 2017;Metz et al, 2023). Rs is the second largest carbon flux in the earth system after photosynthesis (Friedlingstein et al, 2022), and almost an order of magnitude larger than anthropogenic carbon emissions (Bond-Lamberty and Thomson, 2010b), and can thus affect the terrestrial carbon cycle (Ballantyne et al, 2017).…”