Wetland methane transport processes affect what portion of methane produced in wetlands reaches the atmosphere. We model what has been perceived to be the least important of these transport ...processes: hydrodynamic transport of methane through wetland surface water and show that its contribution to total methane emissions from a temperate freshwater marsh is surprisingly large. In our 1 year study, hydrodynamic transport comprised more than half of nighttime methane fluxes and was driven primarily by water column thermal convection occurring overnight as the water surface cooled. Overall, hydrodynamic transport was responsible for 32% of annual methane emissions. Many methane models have overlooked this process, but our results show that wetland methane fluxes cannot always be accurately described using only other transport processes (plant‐mediated transport and ebullition). Modifying models to include hydrodynamic transport and the mechanisms that drive it, particularly convection, could help improve predictions of future wetland methane emissions.
Key Points
We compare hydrodynamic methane transport and total methane flux at a temperate, freshwater marsh
Approximately one third of the total annual methane flux occurs via hydrodynamic transport
Hydrodynamic transport is largest at night because of thermal convection
Wetland biogeochemical transformations are affected by flow and mixing in wetland surface water. We investigate the influence of wind on wetland water flow by simultaneously measuring wind and ...surface water velocities in an enclosed freshwater wetland during 1 day of strong‐wind conditions. Water velocities are measured using a Volumetric Particle Imager while wind velocities are measured via sonic‐anemometer. Our measurements indicate that the wind interacting with the vegetation canopy generates coherent billows and that these billows are the dominant source of momentum into the wetland water column. Spectral analysis of velocity time series shows that the spectral peak in water velocity is aligned with the spectral peak of in‐canopy wind velocity, and that this peak corresponds with the Kelvin‐Helmholtz billow frequency predicted by mixing layer theory. We also observe a strong correlation in the temporal pattern of velocity variance in the air and water, with high variance events having similar timing and duration both above and below the air‐water interface. Water‐side variance appears coupled with air‐side variance at least down to 5 cm, while the theoretical Stokes' solution predicts momentum transfer down to only 2 mm assuming transfer via molecular viscosity alone. This suggests that the wind‐driven flow contributed to significant mixing in the wetland water column.
Key Points:
Direct observation of wind‐water coupling in wetland with emergent vegetation
Flow instability at canopy top causes periodic bursts of strong water stirring
Wind‐stirring impacts gas exchange, but mechanism is different from open water
Aerodynamic canopy height (ha) is the effective height of vegetation canopy for its influence on atmospheric fluxes and is a key parameter of surface‐atmosphere coupling. However, methods to estimate ...ha from data are limited. This synthesis evaluates the applicability and robustness of the calculation of ha from eddy covariance momentum‐flux data. At 69 forest sites, annual ha robustly predicted site‐to‐site and year‐to‐year differences in canopy heights (R2 = 0.88, 111 site‐years). At 23 cropland/grassland sites, weekly ha successfully captured the dynamics of vegetation canopies over growing seasons (R2 > 0.70 in 74 site‐years). Our results demonstrate the potential of flux‐derived ha determination for tracking the seasonal, interannual, and/or decadal dynamics of vegetation canopies including growth, harvest, land use change, and disturbance. The large‐scale and time‐varying ha derived from flux networks worldwide provides a new benchmark for regional and global Earth system models and satellite remote sensing of canopy structure.
Plain Language Summary
Vegetation canopy height is a key descriptor of the Earth surface and is in use by many modeling and conservation applications. However, large‐scale and time‐varying data of canopy heights are often unavailable. This synthesis evaluates the applicability and robustness of the calculation of canopy heights from the momentum flux data measured at eddy covariance flux tower sites (i.e., meteorological observation towers with high frequency measurements of wind speed and surface fluxes). We show that the aerodynamic estimation of annual canopy heights robustly predicts the site‐to‐site and year‐to‐year differences in canopy heights across a wide variety of forests. The weekly aerodynamic canopy heights successfully capture the dynamics of vegetation canopies over growing seasons at cropland and grassland sites. Our results demonstrate the potential of aerodynamic canopy heights for tracking the seasonal, interannual, and/or decadal dynamics of vegetation canopies including growth, harvest, land use change, and disturbance. Given the amount of data collected and the diversity of vegetation covered by the global networks of eddy covariance flux tower sites, the flux‐derived canopy height has great potential for providing a new benchmark for regional and global Earth system models and satellite remote sensing of canopy structure.
Key Points
Aerodynamic canopy height can be calculated robustly and routinely from the eddy covariance momentum flux data
Our estimates match well with in situ measurements of canopy heights across a wide variety of vegetation and ecosystem types
Aerodynamic canopy height can be used to track the dynamics of vegetation canopies, including plant growth, harvest, and disturbance
Methane, carbon dioxide, and oxygen are exchanged between wetlands and the atmosphere through multiple pathways. One of these pathways, the hydrodynamic transport of dissolved gas through the surface ...water, is often underestimated in importance. We constructed a model wetland in the laboratory with artificial emergent plants to investigate the mechanisms and magnitude of this transport. We measured gas transfer velocities, which characterize the near‐surface stirring driving air‐water gas transfer, while varying two stirring processes important to gas exchange in other aquatic environments: wind and thermal convection. To isolate the effects of thermal convection, we identified a semiempirical model for the gas transfer velocity as a function of surface heat loss. The laboratory results indicate that thermal convection will be the dominant mechanism of air‐water gas exchange in marshes with emergent vegetation. Thermal convection yielded peak gas transfer velocities of 1 cm h−1. Because of the sheltering of the water surface by emergent vegetation, gas transfer velocities for wind‐driven stirring alone are likely to exceed this value only in extreme cases.
Key Points
Gas transfer velocities are measured in a model wetland in the laboratoryGas transfer varied non‐linearly with wind speed and surface heat lossThermal convection likely drives most hydrodynamic gas transport in wetlands
Extreme precipitation from climate change may strain many existing stormwater systems. While studies have evaluated such effects on stormwater infrastructure, other sources of uncertainty not yet ...explored should also be considered. This paper presents an analysis of adaptation costs for new stormwater infrastructure to mitigate increases in design storm precipitation depth with climate change, including how economic and managerial uncertainty related to life cycle unit costs and knowledge of existing infrastructure affect costs. For case study areas in California, we quantify adaptation costs for new green infrastructure capacity by evaluating future design storms. Results indicate that design storm depths increase by an average of 28%, but lack of knowledge of the condition of existing infrastructure and life cycle unit costs result in wide cost ranges. The findings illustrate how climate change planning for stormwater should also consider economic and managerial uncertainty when estimating long-term adaptation costs.
Aerodynamic canopy height (ha) is the effective height of vegetation canopy for its influence on atmospheric fluxes and is a key parameter of surface-atmosphere coupling. However, methods to estimate ...ha from data are limited. This synthesis evaluates the applicability and robustness of the calculation of ha from eddy covariance momentum-flux data. At 69 forest sites, annual ha robustly predicted site-to-site and year-to-year differences in canopy heights (R2 = 0.88, 111 site-years). At 23 cropland/grassland sites, weekly ha successfully captured the dynamics of vegetation canopies over growing seasons (R2 > 0.70 in 74 site-years). Our results demonstrate the potential of flux-derived ha determination for tracking the seasonal, interannual, and/or decadal dynamics of vegetation canopies including growth, harvest, land use change, and disturbance. The large-scale and time-varying ha derived from flux networks worldwide provides a new benchmark for regional and global Earth system models and satellite remote sensing of canopy structure.
The flow of water in wetlands may exert significant influence on wetland biogeochemistry, and specifically interfacial gas exchange. Measuring currents in wetlands requires caution. The acoustic ...Doppler velocimeter (ADV) is widely used for the characterization of water flow and turbulence. However, deployment of ADVs in low-flow environments is hampered by a unique source of bias related to the ADV's mode of operation. The extent of this bias is revealed by Particle image velocimetry (PIV) measurements of an ADV operating in quiescent fluid. Image-based flow measurement techniques such as PIV may provide improved accuracy in low-flow environments like wetlands. Such techniques were applied to observe wind-driven flows in a wetland with emergent vegetation and investigate the effects of the wind shear on gas transfer across the air-water interface. Wind speed is the parameter most often used to model interfacial gas exchange in other aquatic environments. In wetlands with emergent vegetation, the emergent vegetation will attenuate wind speed above the water surface, modify fluid shear at the water surface, and influence stirring beneath the water surface. Direct measurements of gas transfer in a model wetland in the laboratory indicated that unless wind speeds are extreme, interfacial gas transfer in wetlands is typically dominated by another physical force: surface cooling-induced thermal convection. In an application of these lab results, gas transfer across the air-water interface due to thermal convection in the water column is shown to account for a sizable portion of total methane fluxes from a restored marsh in California's Sacramento-San Joaquin Delta.
Observational data are fundamental for scientific research in almost any domain. Recent advances in sensor and data management technologies are enabling unprecedented amounts of observational data to ...be collected and analyzed. However, an essential part of using observational data is not currently as scalable as data collection and analysis methods: data quality assurance and control. While specialized tools for very narrow domains do exist, general methods are harder to create. This paper explores the identification of data issues that lead to the creation of data tests and tools to perform data quality control activities. Developing this identification step in a systematic manner allows for better and more general quality control tools. As our case study, we use carbon, water, and energy fluxes as well as micro-meteorological data collected at field sites that are part of FLUXNET, a network of over 400 ecosystem-level monitoring stations. In an effort toward the release of a new global data set of fluxes, we are doing data quality control for these data. The experience from this work led to the creation of a catalog of issues identified in the data. This paper presents this catalog and its generalization into a set of patterns of data quality issues that can be detected in observational data.
Wetland biogeochemical transformations are affected by flow and mixing in wetland surface water. We investigate the influence of wind on wetland water flow by simultaneously measuring wind and ...surface water velocities in an enclosed freshwater wetland during one day of strong-wind conditions. Water velocities are measured using a Volumetric Particle Imager while wind velocities are measured via sonic-anemometer. Our measurements indicate that the wind interacting with the vegetation canopy generates coherent billows and that these billows are the dominant source of momentum into the wetland water column. Spectral analysis of velocity timeseries shows that the spectral peak in water velocity is aligned with the spectral peak of in-canopy wind velocity, and that this peak corresponds with the Kelvin-Helmholtz billow frequency predicted by mixing layer theory. We also observe a strong correlation in the temporal pattern of velocity variance in the air and water, with high variance events having similar timing and duration both above and below the air-water interface. Water-side variance appears coupled with air-side variance at least down to 5 cm, while the theoretical Stokes' solution predicts momentum transfer down to only 2 mm assuming transfer via molecular viscosity alone. This suggests that the wind-driven flow contributed to significant mixing in the wetland water column.
Data quality control is one of the most time consuming activities within Research Infrastructures (RIs), especially when involving observational data and multiple data providers. In this work we ...report on our ongoing development of data rogues, a scalable approach to manage data quality issues for observational data within RIs. The motivation for this work started with the creation of the FLUXNET2015 dataset, which includes carbon, water, and energy fluxes plus micrometeorological and ancillary data measured in over 200 sites around the world. To create an uniform dataset, including derived data products, extensive work on data quality control was needed. The unpredictable nature of observational data quality issues makes the automation of data quality control inherently difficult. Developed based on this experience, the data rogues methodology allows for increased automation of quality control activities by systematically identifying, cataloging, and documenting implementations of solutions to data issues. We believe this methodology can be extended and applied to others domains and types of data, making the automation of data quality control a more tractable problem.
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