53 Search Results

The water vapor transport associated with latent heat flux (LE) in the planetary boundary layer (PBL) is critical for the atmospheric hydrological cycle, radiation balance, and cloud formation. The spatiotemporal variability of LE and water vapor mixing ratio (r_v) are poorly understood due to the scale-dependent and nonlinear atmospheric transport responses to land surface heterogeneity. Here, airborne in situ measurements with the wavelet technique are utilized to investigate scale-dependent relationships among LE, vertical velocity (w) variance (σ$${^2_w}$$), and r_v variance (σ$$^{2}_{H20}$$) over a heterogeneous surface during the Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectorsmore » 2019 (CHEESEHEAD19) field campaign. Our findings reveal distinct scale distributions of LE, σ$${^2_w}$$, and σ$$^{2}_{H20}$$ at 100 m height, with a majority scale range of 120 m–4 km in LE, 32 m–2 km in σ$${^2_w}$$, and 200 m–8 km in σ$$^{2}_{H20}$$. The scales are classified into three scale ranges, the turbulent scale (8–200 m), large-eddy scale (200 m–2 km), and mesoscale (2–8 km) to evaluate scale-resolved LE contributed by σ$${^2_w}$$ and σ$$^{2}_{H20}$$. The large-eddy scale in PBL contributes over 70% of the monthly mean total LE with equal parts (50%) of contributions from σ$${^2_w}$$ and σ$$^{2}_{H20}$$. The monthly temporal variations mainly come from the first two major contributing classified scales in LE, σ$${^2_w}$$, and σ$$^{2}_{H20}$$. These results confirm the dominant role of the large-eddy scale in the PBL in the vertical moisture transport from the surface to the PBL, while the mesoscale is shown to contribute an additional ~20%. This analysis complements published scale-dependent LE variations, which lack detailed scale-dependent vertical velocity and moisture information.« less

Abstract How convective boundary‐layer (CBL) processes modify fluxes of sensible ( SH ) and latent ( LH ) heat and CO ₂ ( F _c ) in the atmospheric surface layer (ASL) remains a recalcitrant problem. Here, large eddy simulations for the CBL show that while SH in the ASL decreases linearly with height regardless of soil moisture conditions, LH and F _c decrease linearly with height over wet soils but increase with height over dry soils. This varying flux divergence/convergence is regulated by changes in asymmetric flux transport between top‐down and bottom‐up processes. Such flux divergencemore » and convergence indicate that turbulent fluxes measured in the ASL underestimate and overestimate the “true” surface interfacial fluxes, respectively. While the non‐closure of the surface energy balance persists across all soil moisture states, it improves over drier soils due to overestimated LH . The non‐closure does not imply that F _c is always underestimated; F _c can be overestimated over dry soils despite the non‐closure issue.« less

Abstract Wetlands cover a small portion of the world, but have disproportionate influence on global carbon (C) sequestration, carbon dioxide and methane emissions, and aquatic C fluxes. However, the underlying biogeochemical processes that affect wetland C pools and fluxes are complex and dynamic, making measurements of wetland C challenging. Over decades of research, many observational, experimental, and analytical approaches have been developed to understand and quantify pools and fluxes of wetland C. Sampling approaches range in their representation of wetland C from short to long timeframes and local to landscape spatial scales. This review summarizes common and cutting-edge methodological approachesmore » for quantifying wetland C pools and fluxes. We first define each of the major C pools and fluxes and provide rationale for their importance to wetland C dynamics. For each approach, we clarify what component of wetland C is measured and its spatial and temporal representativeness and constraints. We describe practical considerations for each approach, such as where and when an approach is typically used, who can conduct the measurements (expertise, training requirements), and how approaches are conducted, including considerations on equipment complexity and costs. Finally, we review key covariates and ancillary measurements that enhance the interpretation of findings and facilitate model development. The protocols that we describe to measure soil, water, vegetation, and gases are also relevant for related disciplines such as ecology. Improved quality and consistency of data collection and reporting across studies will help reduce global uncertainties and develop management strategies to use wetlands as nature-based climate solutions.« less

Abstract Both carbon dioxide uptake and albedo of the land surface affect global climate. However, climate change mitigation by increasing carbon uptake can cause a warming trade-off by decreasing albedo, with most research focusing on afforestation and its interaction with snow. Here, we present carbon uptake and albedo observations from 176 globally distributed flux stations. We demonstrate a gradual decline in maximum achievable annual albedo as carbon uptake increases, even within subgroups of non-forest and snow-free ecosystems. Based on a paired-site permutation approach, we quantify the likely impact of land use on carbon uptake and albedo. Shifting to the maximummore » attainable carbon uptake at each site would likely cause moderate net global warming for the first approximately 20 years, followed by a strong cooling effect. A balanced policy co-optimizing carbon uptake and albedo is possible that avoids warming on any timescale, but results in a weaker long-term cooling effect.« less

We made a commitment to better include underrepresented members of our community in the publication pipeline of JGR: Biogeosciences. This commitment consists of regular updates on our policies and practices, and concrete actions we intend to implement over the next year. So far, our progress to tackle biases and ensure equitable research in the biogeosciences has focused on improving diversity of our associate editor and reviewer pools, increasing awareness of unconscious bias in peer-review, and promoting inclusion in global collaborations. In this update, we explore manuscript submissions and manuscript decisions by gender, and we present a pilot that aims tomore » promote ethical and equitable global collaborations in resource-poor settings. Here, we end our editorial by presenting our next set of actions that we plan on completing over the next year, which include a more thorough analysis of reviewer demographics.« less

Current carbon cycle models focus on the effects of climate and land-use change on primary productivity and microbial-mineral dependent carbon turnover in the topsoil, while less attention has been paid to vertical soil processes and soil-dependent response to land-use change along the profile. In this study, a spatial-temporal analysis was used to estimate soil organic carbon (SOC) change in topsoil/A horizon and subsoil/B horizon at National Ecological Observatory Network (NEON) sites, USA over 30 years. To separate the effects of land-use, environmental, and edaphic factors on SOC change, space-for-time substitution was used in combination with the Continuous Change Detection andmore » Classification algorithm and Structural Equation Modeling. Results showed that (a) under natural vegetation, Spodosols and Inceptisols found in the eastern NEON sites had substantial topsoil SOC accumulation (+0.4 to +1.2 Mg C ha^–1 year^–1), while Inceptisols and Andisols in the west had a comparable magnitude of topsoil SOC loss (–0.5 to –1.8 Mg C ha^–1 year^–1); (b) Mollisols and Alfisols in the Central Plains sites were susceptible to significant SOC loss under farming and grazing; (c) Runoff/erosion and leaching potential, vertical translocation, and mineral sorption were the most important factors controlling SOC variation across the NEON sites. Our work could be used to parameterize ecosystem models simulating SOC change.« less

Wetlands are responsible for 20%–31% of global methane (CH₄) emissions and account for a large source of uncertainty in the global CH₄ budget. Data-driven upscaling of CH₄ fluxes from eddy covariance measurements can provide new and independent bottom-up estimates of wetland CH₄ emissions. Here, we develop a six-predictor random forest upscaling model (UpCH4), trained on 119 site-years of eddy covariance CH₄ flux data from 43 freshwater wetland sites in the FLUXNET-CH4 Community Product. Network patterns in site-level annual means and mean seasonal cycles of CH₄ fluxes were reproduced accurately in tundra, boreal, and temperate regions (Nash-Sutcliffe Efficiency ~0.52–0.63 and 0.53).more » UpCH4 estimated annual global wetland CH₄ emissions of 146 ± 43 TgCH₄ y^—1 for 2001–2018 which agrees closely with current bottom-up land surface models (102–181 TgCH₄ y^—1) and overlaps with top-down atmospheric inversion models (155–200 TgCH₄ y^—1). However, UpCH4 diverged from both types of models in the spatial pattern and seasonal dynamics of tropical wetland emissions. We conclude that upscaling of eddy covariance CH₄ fluxes has the potential to produce realistic extra-tropical wetland CH₄ emissions estimates which will improve with more flux data. To reduce uncertainty in upscaled estimates, researchers could prioritize new wetland flux sites along humid-to-arid tropical climate gradients, from major rainforest basins (Congo, Amazon, and SE Asia), into monsoon (Bangladesh and India) and savannah regions (African Sahel) and be paired with improved knowledge of wetland extent seasonal dynamics in these regions. The monthly wetland methane products gridded at 0.25° from UpCH4 are available via ORNL DAAC (https://doi.org/10.3334/ORNLDAAC/2253).« less

Abstract Wetlands are the largest natural source of methane (CH ₄ ) to the atmosphere. The eddy covariance method provides robust measurements of net ecosystem exchange of CH ₄ , but interpreting its spatiotemporal variations is challenging due to the co‐occurrence of CH ₄ production, oxidation, and transport dynamics. Here, we estimate these three processes using a data‐model fusion approach across 25 wetlands in temperate, boreal, and Arctic regions. Our data‐constrained model—iPEACE—reasonably reproduced CH ₄ emissions at 19 of the 25 sites with normalized root mean square error of 0.59, correlation coefficient of 0.82, and normalized standard deviation of 0.87.more » Among the three processes, CH ₄ production appeared to be the most important process, followed by oxidation in explaining inter‐site variations in CH ₄ emissions. Based on a sensitivity analysis, CH ₄ emissions were generally more sensitive to decreased water table than to increased gross primary productivity or soil temperature. For periods with leaf area index (LAI) of ≥20% of its annual peak, plant‐mediated transport appeared to be the major pathway for CH ₄ transport. Contributions from ebullition and diffusion were relatively high during low LAI (<20%) periods. The lag time between CH ₄ production and CH ₄ emissions tended to be short in fen sites (3 ± 2 days) and long in bog sites (13 ± 10 days). Based on a principal component analysis, we found that parameters for CH ₄ production, plant‐mediated transport, and diffusion through water explained 77% of the variance in the parameters across the 19 sites, highlighting the importance of these parameters for predicting wetland CH ₄ emissions across biomes. These processes and associated parameters for CH ₄ emissions among and within the wetlands provide useful insights for interpreting observed net CH ₄ fluxes, estimating sensitivities to biophysical variables, and modeling global CH ₄ fluxes.« less

This is the AmeriFlux version of the carbon flux data for the site US-PFf NW5 Grass-1 CHEESEHEAD 2019. Site Description - This tower (2m tripod) is located in the northwestern quadrant of the 10 x 10km study domain. It is located in a grassy field. It is ocassionally mowed. It was located near (~200m) several different types of sounding systems.

This is the AmeriFlux version of the carbon flux data for the site US-PFo SE1 Lake-2 CHEESEHEAD 2019. Site Description - This tower (1.17m buoy) is located in the southeastern quadrant of the 10 x 10km study domain. It is located on a buoy (1.17 m asl) in the center of a small bog lake (50-70 m across) surrounded by mixed hardwood forest (maple, oak) about 16 m high.