scholarly journals Technical Note: Novel triple O<sub>2</sub>-sensor aquatic eddy covariance instrument with improved time-shift correction reveals central role of microphytobenthos for carbon cycling in coral reef sands

2021 ◽  
Author(s):  
Alireza Merikhi ◽  
Peter Berg ◽  
Markus Huettel
Keyword(s):  
Coral Reef ◽  
Eddy Covariance ◽  
Organic Content ◽  
Utilization Efficiency ◽  
Time Shift ◽  
Overlying Water ◽  
Coral Sand ◽  
New Instrument ◽  
Flux Measurements

Abstract. The aquatic eddy covariance technique stands out as a method for benthic O2-flux measurements because it measures non-invasively, but in the conventional instruments, the spatial separation of the measuring locations of the velocity and O2 sensors causes a time-shift that can be substantial and difficult to correct. Here we introduce a triple O2-sensor-eddy covariance instrument (3OEC) that by positioning of the O2-sensors around the flow measuring volume allows eliminating these time-shifts through signal averaging. The new instrument was used to determine O2-production and consumption in an energetic coastal environment with highly permeable coral reef sands colonized by microphytobenthos. The measurement at ~10 m water depth revealed O2-fluxes that range among the highest reported for marine sediments despite relatively low organic content of the water and coarse sediment, indicating a central role of microphytobenthos for the carbon and nutrient cycling in the coral sand. High light utilization efficiency of the microphytobenthos and bottom currents increasing pore water exchange facilitated the high benthic production and respiration. The measurements documented a gradual transfer of the flux signal from the small turbulence generated at the sediment water interface to the larger wave-dominated eddies of the overlying water column with a delay influenced by the memory effect of eddies. These results demonstrate that the 3OEC can improve the precision of the flux measurements, including measurements in environments considered challenging for this technique, and thereby produce novel insights into the mechanisms that control flux. We consider the fluxes produced by this instrument for the permeable reef sands the most realistic achievable with present day technology.

scholarly journals Technical note: Novel triple O<sub>2</sub> sensor aquatic eddy covariance instrument with improved time shift correction reveals central role of microphytobenthos for carbon cycling in coral reef sands

2021 ◽  
Vol 18 (19) ◽  
pp. 5381-5395
Author(s):  
Alireza Merikhi ◽  
Peter Berg ◽  
Markus Huettel
Keyword(s):  
Coral Reef ◽  
Eddy Covariance ◽  
Current Flow ◽  
Time Shift ◽  
Overlying Water ◽  
Flow Measurements ◽  
Eddy Covariance Technique ◽  
New Instrument ◽  
O2 Concentration ◽  
Flux Measurements

Abstract. The aquatic eddy covariance technique stands out as a powerful method for benthic O2 flux measurements in shelf environments because it integrates effects of naturally varying drivers of the flux such as current flow and light. In conventional eddy covariance instruments, the time shift caused by spatial separation of the measuring locations of flow and O2 concentration can produce substantial flux errors that are difficult to correct. We here introduce a triple O2 sensor eddy covariance instrument (3OEC) that by instrument design eliminates these errors. This is achieved by positioning three O2 sensors around the flow measuring volume, which allows the O2 concentration to be calculated at the point of the current flow measurements. The new instrument was tested in an energetic coastal environment with highly permeable coral reef sands colonised by microphytobenthos. Parallel deployments of the 3OEC and a conventional eddy covariance system (2OEC) demonstrate that the new instrument produces more consistent fluxes with lower error margin. 3OEC fluxes in general were lower than 2OEC fluxes, and the nighttime fluxes recorded by the two instruments were statistically different. We attribute this to the elimination of uncertainties associated with the time shift correction. The deployments at ∼ 10 m water depth revealed high day- and nighttime O2 fluxes despite the relatively low organic content of the coarse sediment and overlying water. High light utilisation efficiency of the microphytobenthos and bottom currents increasing pore water exchange facilitated the high benthic production and coupled respiration. 3OEC measurements after sunset documented a gradual transfer of negative flux signals from the small turbulence generated at the sediment–water interface to the larger wave-dominated eddies of the overlying water column that still carried a positive flux signal, suggesting concurrent fluxes in opposite directions depending on eddy size and a memory effect of large eddies. The results demonstrate that the 3OEC can improve the precision of benthic flux measurements, including measurements in environments considered challenging for the eddy covariance technique, and thereby produce novel insights into the mechanisms that control flux. We consider the fluxes produced by this instrument for the permeable reef sands the most realistic achievable with present-day technology.

scholarly journals Uncertainty analysis of eddy covariance CO<sub>2</sub> flux measurements for different EC tower distances using an extended two-tower approach

2015 ◽  
Vol 12 (4) ◽  
pp. 1205-1221 ◽  
Author(s):  
H. Post ◽  
H. J. Hendricks Franssen ◽  
A. Graf ◽  
M. Schmidt ◽  
H. Vereecken
Keyword(s):  
Eddy Covariance ◽  
Reference Method ◽  
Co2 Flux ◽  
Weather Conditions ◽  
Data Set ◽  
Random Uncertainty ◽  
Extended Approach ◽  
Uncertainty Estimates ◽  
Flux Measurements

Abstract. The use of eddy covariance (EC) CO2 flux measurements in data assimilation and other applications requires an estimate of the random uncertainty. In previous studies, the (classical) two-tower approach has yielded robust uncertainty estimates, but care must be taken to meet the often competing requirements of statistical independence (non-overlapping footprints) and ecosystem homogeneity when choosing an appropriate tower distance. The role of the tower distance was investigated with help of a roving station separated between 8 m and 34 km from a permanent EC grassland station. Random uncertainty was estimated for five separation distances with the classical two-tower approach and an extended approach which removed systematic differences of CO2 fluxes measured at two EC towers. This analysis was made for a data set where (i) only similar weather conditions at the two sites were included, and (ii) an unfiltered one. The extended approach, applied to weather-filtered data for separation distances of 95 and 173 m gave uncertainty estimates in best correspondence with an independent reference method. The introduced correction for systematic flux differences considerably reduced the overestimation of the two-tower based uncertainty of net CO2 flux measurements and decreased the sensitivity of results to tower distance. We therefore conclude that corrections for systematic flux differences (e.g., caused by different environmental conditions at both EC towers) can help to apply the two-tower approach to more site pairs with less ideal conditions.

scholarly journals Uncertainty analysis of eddy covariance CO<sub>2</sub> flux measurements for different EC tower distances using an extended two-tower approach

2014 ◽  
Vol 11 (8) ◽  
pp. 11943-11983
Author(s):  
H. Post ◽  
H. J. Hendricks Franssen ◽  
A. Graf ◽  
M. Schmidt ◽  
H. Vereecken
Keyword(s):  
Eddy Covariance ◽  
Reference Method ◽  
Co2 Flux ◽  
Weather Conditions ◽  
Co2 Fluxes ◽  
Random Uncertainty ◽  
Extended Approach ◽  
Uncertainty Estimates ◽  
Flux Measurements

Abstract. The use of eddy covariance CO2 flux measurements in data assimilation and other applications requires an estimate of the random uncertainty. In previous studies, the two-tower approach has yielded robust uncertainty estimates, but care must be taken to meet the often competing requirements of statistical independence (non-overlapping footprints) and ecosystem homogeneity when choosing an appropriate tower distance. The role of the tower distance was investigated with help of a roving station separated between 8 m and 34 km from a permanent EC grassland station. Random uncertainty was estimated for five separation distances with an extended two-tower approach which removed systematic differences of CO2 fluxes measured at two EC towers. This analysis was made for a dataset where (i) only similar weather conditions at the two sites were included and (ii) an unfiltered one. The extended approach, applied to weather-filtered data for separation distances of 95 m and 173 m gave uncertainty estimates in best correspondence with the independent reference method The introduced correction for systematic flux differences considerably reduced the overestimation of the two-tower based uncertainty of net CO2 flux measurements, e.g. caused by different environmental conditions at both EC towers. It is concluded that the extension of the two-tower approach can help to receive more reliable uncertainty estimates because systematic differences of measured CO2 fluxes which are not part of random error are filtered out.

Spatial observations of large eddies and cross-canopy coupling with joint fiber-optic distributed sensing and eddy covariance flux measurements

2020 ◽  
Author(s):  
Olli Peltola ◽  
Karl Lapo ◽  
Christoph Thomas ◽  
Timo Vesala
Keyword(s):  
Eddy Covariance ◽  
Wind Shear ◽  
Fiber Optic ◽  
Distributed Sensing ◽  
Carbon Dioxide Transport ◽  
Stable Conditions ◽  
Sonic Anemometers ◽  
Flux Measurements ◽  
Large Eddies

&lt;p&gt;Air flows above forest canopies are typically governed by large coherent eddies generated mechanically by inflected mean wind velocity profile or thermally by buoyancy in the convective regime. A significant body of research have been devoted to the role of these eddies on ecosystem scalar (gases and heat) exchange since they are likely related to the energy balance closure problem observed at the eddy covariance (EC) stations and turbulent flux divergence under stable stratification. Here we utilize fiber-optic distributed sensing on a tall mast to observe the turbulent fluctuations of air temperature with high spatial (25 cm) and temporal resolution (1 Hz) from the forest floor up to 120 m above the ground. These unique measurements resolved the continuous vertical profile of scalar turbulence and hence enabled us to study the topology (height &amp;#8211; time space) of the turbulent eddies in different stability regimes. For example, the inclination angle of the eddies changed with stability and the scalar ramps often observed in canopy flows were evident only close to the canopy top, whereas higher up thermal eddies dominated the flow. Furthermore, the measurements permitted the identification of coupled air layers and hence analysis on the dynamics of below-canopy decoupling. During stable conditions with wind shear large eddies and the related inverted ramps in the temperature time series were observed at the top of the decoupling layer, however when the wind shear decreased the flow switched to submeso regime with canopy waves. These analyses were then combined with concurrent turbulence measurements with 3D sonic anemometers at several heights and EC gas flux measurements at one height to gain new insights on the role of these eddies on gas (e.g. carbon dioxide) transport. The measurements were conducted during summer 2019 at the Hyyti&amp;#228;l&amp;#228; SMEAR II station located in central Finland and the permanent ICOS measurements at the site were utilized to the fullest.&lt;/p&gt;

scholarly journals Physiological and interactomic analysis reveals versatile functions of Arabidopsis 14-3-3 quadruple mutants in response to Fe deficiency

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jing Gao ◽  
Paula J. M. van Kleeff ◽  
Ka Wan Li ◽  
Albertus H. de Boer
Keyword(s):  
Iron Acquisition ◽  
Tca Cycle ◽  
Utilization Efficiency ◽  
Fe Deficiency ◽  
Transcriptional Level ◽  
Functional Aspects ◽  
Clear Explanation ◽  
Physiological Analysis ◽  
Proper Operation

AbstractTo date, few phenotypes have been described for Arabidopsis 14-3-3 mutants or the phenotypes showing the role of 14-3-3 in plant responding to abiotic stress. Although one member of the 14-3-3 protein family (14-3-3 omicron) was shown to be involved in the proper operation of Fe acquisition mechanisms at physiological and gene expression levels in Arabidopsis thaliana, it remains to be explored whether other members play a role in regulating iron acquisition. To more directly and effectively observe whether members of 14-3-3 non-epsilon group have a function in Fe-deficiency adaptation, three higher order quadruple KOs, kappa/lambda/phi/chi (klpc), kappa/lambda/upsilon/nu(klun), and upsilon/nu/phi/chi (unpc) were generated and studied for physiological analysis in this study. The analysis of iron-utilization efficiency, root phenotyping, and transcriptional level of Fe-responsive genes suggested that the mutant with kl background showed different phenotypes from Wt when plants suffered Fe starved, while these phenotypes were absent in the unpc mutant. Moreover, the absence of the four 14-3-3 isoforms in the klun mutant has a clear impact on the 14-3-3 interactome upon Fe deficiency. Dynamics of 14-3-3-client interactions analysis showed that 27 and 17 proteins differentially interacted with 14-3-3 in Wt and klun roots caused by Fe deficiency, respectively. Many of these Fe responsive proteins have a role in glycolysis, oxidative phosphorylation and TCA cycle, the FoF1-synthase and in the cysteine/methionine synthesis. A clear explanation for the observed phenotypes awaits a more detailed analysis of the functional aspects of 14-3-3 binding to the target proteins identified in this study.

scholarly journals Eddy covariance flux measurements confirm extreme CH<sub>4</sub> emissions from a Swiss hydropower reservoir and resolve their short-term variability

2011 ◽  
Vol 8 (9) ◽  
pp. 2815-2831 ◽  
Author(s):  
W. Eugster ◽  
T. DelSontro ◽  
S. Sobek
Keyword(s):  
Greenhouse Gas ◽  
Eddy Covariance ◽  
Land Surface ◽  
Lake Level ◽  
Driving Forces ◽  
Open Water ◽  
Short Term ◽  
Flux Measurements ◽  
Floating Chamber ◽  
Hydropower Reservoir

Abstract. Greenhouse gas budgets quantified via land-surface eddy covariance (EC) flux sites differ significantly from those obtained via inverse modeling. A possible reason for the discrepancy between methods may be our gap in quantitative knowledge of methane (CH4) fluxes. In this study we carried out EC flux measurements during two intensive campaigns in summer 2008 to quantify methane flux from a hydropower reservoir and link its temporal variability to environmental driving forces: water temperature and pressure changes (atmospheric and due to changes in lake level). Methane fluxes were extremely high and highly variable, but consistently showed gas efflux from the lake when the wind was approaching the EC sensors across the open water, as confirmed by floating chamber flux measurements. The average flux was 3.8 ± 0.4 μg C m−2 s−1 (mean ± SE) with a median of 1.4 μg C m−2 s−1, which is quite high even compared to tropical reservoirs. Floating chamber fluxes from four selected days confirmed such high fluxes with 7.4 ± 1.3 μg C m−2 s−1. Fluxes increased exponentially with increasing temperatures, but were decreasing exponentially with increasing atmospheric and/or lake level pressure. A multiple regression using lake surface temperatures (0.1 m depth), temperature at depth (10 m deep in front of the dam), atmospheric pressure, and lake level was able to explain 35.4% of the overall variance. This best fit included each variable averaged over a 9-h moving window, plus the respective short-term residuals thereof. We estimate that an annual average of 3% of the particulate organic matter (POM) input via the river is sufficient to sustain these large CH4 fluxes. To compensate the global warming potential associated with the CH4 effluxes from this hydropower reservoir a 1.3 to 3.7 times larger terrestrial area with net carbon dioxide uptake is needed if a European-scale compilation of grasslands, croplands and forests is taken as reference. This indicates the potential relevance of temperate reservoirs and lakes in local and regional greenhouse gas budgets.

Eddy covariance flux measurements of momentum, heat and carbon dioxide in Hudson Bay at the onset of sea ice melt 

2021 ◽  
Author(s):  
Richard Sims ◽  
Brian Butterworth ◽  
Tim Papakyriakou ◽  
Mohamed Ahmed ◽  
Brent Else
Keyword(s):  
Carbon Dioxide ◽  
Gas Exchange ◽  
Sea Ice ◽  
Eddy Covariance ◽  
Open Water ◽  
The Arctic ◽  
Gas Transfer ◽  
Hudson Bay ◽  
Flux Measurements ◽  
Ice Fraction

&lt;p&gt;Remoteness and tough conditions have made the Arctic Ocean historically difficult to access; until recently this has resulted in an undersampling of trace gas and gas exchange measurements. The seasonal cycle of sea ice completely transforms the air sea interface and the dynamics of gas exchange. To make estimates of gas exchange in the presence of sea ice, sea ice fraction is frequently used to scale open water gas transfer parametrisations. It remains unclear whether this scaling is appropriate for all sea ice regions. Ship based eddy covariance measurements were made in Hudson Bay during the summer of 2018 from the icebreaker CCGS Amundsen. We will present fluxes of carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;), heat and momentum and will show how they change around the Hudson Bay polynya under varying sea ice conditions. We will explore how these fluxes change with wind speed and sea ice fraction. As freshwater stratification was encountered during the cruise, we will compare our measurements with other recent eddy covariance flux measurements made from icebreakers and also will compare our turbulent CO&lt;sub&gt;2&amp;#160;&lt;/sub&gt;fluxes with bulk fluxes calculated using underway and surface bottle pCO&lt;sub&gt;2&lt;/sub&gt;&amp;#160;data.&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document