Methane emissions from lakes in the Alpine region: insights from two years of mobile eddy covariance flux measurements

2020 ◽  
Author(s):  
Katharina Scholz ◽  
Federico Carotenuto ◽  
Beniamino Gioli ◽  
Franco Miglietta ◽  
Sylvie Pighini ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Trophic Status ◽  
Alpine Region ◽  
First Year ◽  
Lake Morphometry ◽  
Direct Measurements ◽  
Flux Measurements ◽  
The Alps ◽  
Abiotic And Biotic Factors ◽  
Dissolved Components

<p>Lakes are considered an important natural source of methane (CH<sub>4</sub>). However, direct measurements of lake-atmosphere gas exchange are still sparse especially in the Alpine region. To overcome this shortcoming, we designed a mobile eddy covariance (EC) station to measure CO<sub>2</sub>, CH<sub>4</sub>, and energy fluxes at various lakes in the Alps. EC measurements were compared to flux measurements using floating chambers and related to abiotic and biotic factors like temperature, lake morphometry, dissolved components and trophic status.</p><p>During the first year, measurements were conducted at 9 lakes at different elevations ranging from 200 to 1900 m.a.s.l. to capture the spatial variability. The following year, measurements were repeated more frequently at three contrasting lakes to capture the seasonal trends of the fluxes.</p><p>The results indicate that all lakes were supersaturated with CH<sub>4</sub>. However, there was a high variability in the magnitude of CH<sub>4</sub> emissions between lakes with generally higher emissions from warmer lakes at low elevation. In particular, the lake at the lowest elevation, Lake Caldaro, had highest dissolved CH<sub>4</sub> concentrations and emissions and showed a clear seasonal trend with emissions peaking during the hot summer months. In contrast, the lake at the highest elevation, Lake Zoccolo, showed low CH<sub>4</sub> concentrations and emissions with highest concentrations in fall when the water level was low.</p>

First eddy covariance flux measurements of gaseous elemental mercury over a grassland

2020 ◽  
Author(s):  
Stefan Osterwalder ◽  
Werner Eugster ◽  
Iris Feigenwinter ◽  
Martin Jiskra
Keyword(s):  
Detection Limit ◽  
Eddy Covariance ◽  
Net Ecosystem Exchange ◽  
Elemental Mercury ◽  
Terrestrial Ecosystems ◽  
Global Scale ◽  
Gaseous Elemental Mercury ◽  
Direct Measurements ◽  
The Us ◽  
Flux Measurements

<p>Direct measurements of the net ecosystem exchange (NEE) of gaseous elemental mercury (Hg<sup>0</sup>) are crucial to improve our understanding of global Hg cycling and ultimately Hg exposure in humans and wildlife. The lack of long-term, ecosystem-scale measurements causes large uncertainties in Hg<sup>0</sup> flux estimates. Today it remains unclear whether terrestrial ecosystems are net sinks or sources of atmospheric Hg<sup>0</sup>. Here, we present the first successful eddy covariance NEE measurements of Hg<sup>0</sup> over natural, low-Hg soils (41 - 75 ng Hg g<sup>-1</sup> topsoil [0-10 cm]) at a managed grassland site in Chamau, Switzerland. We present a detailed validation of the eddy covariance technique for Hg<sup>0</sup> based on a Lumex mercury monitor RA-915AM. The flux detection limit derived from a zero-flux experiment in the laboratory was 0.22 ng m<sup>-2</sup> h<sup>-1</sup> (maximum) with a 50 % cut-off at 0.074 ng m<sup>-2</sup> h<sup>-1</sup>. The statistical estimate of the Hg<sup>0</sup> flux detection limit under real-world outdoor conditions at the site was 5.9 ng m<sup>-2</sup> h<sup>-1</sup> (50 % cut-off). Based on our analysis we give suggestions to further improve the precision of the system and pinpoint challenges and interferences that occurred during the 34-day pilot campaign in summer 2018. The data were obtained during extremely hot and dry meteorological conditions. We estimated a net summertime grassland-atmosphere Hg<sup>0</sup> flux from -0.6 to 7.4 ng m<sup>-2</sup> h<sup>-1</sup> (range between 25<sup>th</sup> and 75<sup>th</sup> percentiles). The measurements revealed a distinct diel pattern with lower nighttime fluxes (1.0 ng m<sup>-2</sup> h<sup>-1</sup>) compared to daytime fluxes (8.4 ng m<sup>-2</sup> h<sup>-1</sup>). Drought stress during the campaign induced partial stomata closure of vegetation leading to a midday depression in CO<sub>2</sub> uptake, which did not recover during the afternoon. We suggest that partial stomata closure dampened Hg<sup>0</sup> uptake by vegetation as well, resulting in a NEE of Hg<sup>0</sup> dominated by soil emission. The new Eddy Mercury system seems suitable to complement existing research infrastructures such as ICOS RI in Europe or NOAA Observing Systems in the US built to calculate greenhouse gas balances with direct Hg<sup>0</sup> deposition and emission measurements. We anticipate our Eddy Mercury system to improve knowledge about Hg cycling between ecosystems and the atmosphere and to challenge model simulations on a regional and global scale.</p>

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;

scholarly journals Options to correct local turbulent flux measurements for large-scale fluxes using a LES-based approach

2021 ◽  
Author(s):  
Matthias Mauder ◽  
Andreas Ibrom ◽  
Luise Wanner ◽  
Frederik De Roo ◽  
Peter Brugger ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Large Scale ◽  
Heat Fluxes ◽  
Eddy Covariance Method ◽  
Boundary Layer Height ◽  
Secondary Circulations ◽  
Low Pass ◽  
Measurement Height ◽  
Flux Measurements ◽  
Dispersive Fluxes

Abstract. The eddy-covariance method provides the most direct estimates for fluxes between ecosystems and the atmosphere. However, dispersive fluxes can occur in the presence of secondary circulations, which can inherently not be captured by such single-tower measurements. In this study, we present options to correct local flux measurements for such large-scale transport based on a non-local parametric model that has been developed from a set of idealized LES runs for three real-world sites. The test sites DK-Sor, DE-Fen, and DE-Gwg, represent typical conditions in the mid-latitudes with different measurement height, different terrain complexity and different landscape-scale heterogeneity. Different ways to determine the boundary-layer height, which is a necessary input variable for modelling the dispersive fluxes, are applied, either from operational radio-soundings and local in-situ measurements for the flat site or from backscatter-intensity profile obtained from collocated ceilometers for the two sites in complex terrain. The adjusted total fluxes are evaluated by assessing the improvement in energy balance closure and by comparing the resulting latent heat fluxes with evapotranspiration rates from nearby lysimeters. The results show that not only the accuracy of the flux estimates is improved but also the precision, which is indicated by RMSE values that are reduced by approximately 50 %. Nevertheless, it needs to be clear that this method is intended to correct for a bias in eddy-covariance measurements due to the presence of large-scale dispersive fluxes. Other reasons potentially causing a systematic under- or overestimation, such as low-pass filtering effects and missing storage terms, still need to be considered and minimized as much as possible. Moreover, additional transport induced by surface heterogeneities is not considered.

Field Scale N2O Flux Measurements from Grassland Using Eddy Covariance

2004 ◽  
Vol 4 (6) ◽  
pp. 143-149 ◽  
Author(s):  
C. Di Marco ◽  
U. Skiba ◽  
K. Weston ◽  
K. Hargreaves ◽  
D. Fowler
Keyword(s):  
Eddy Covariance ◽  
Field Scale ◽  
N2o Flux ◽  
Flux Measurements

scholarly journals Eddy-covariance flux measurements with a weight-shift microlight aircraft

2012 ◽  
Vol 5 (7) ◽  
pp. 1699-1717 ◽  
Author(s):  
S. Metzger ◽  
W. Junkermann ◽  
M. Mauder ◽  
F. Beyrich ◽  
K. Butterbach-Bahl ◽  
...  
Keyword(s):  
Heat Flux ◽  
Eddy Covariance ◽  
Low Cost ◽  
Sensible Heat Flux ◽  
Flux Measurement ◽  
Wind Measurement ◽  
Airborne Measurements ◽  
Weight Shift ◽  
Flux Measurements

Abstract. The objective of this study is to assess the feasibility and quality of eddy-covariance flux measurements from a weight-shift microlight aircraft (WSMA). Firstly, we investigate the precision of the wind measurement (σu,v ≤ 0.09 m s−1, σw = 0.04 m s−1), the lynchpin of flux calculations from aircraft. From here, the smallest resolvable changes in friction velocity (0.02 m s−1), and sensible- (5 W m−2) and latent (3 W m−2) heat flux are estimated. Secondly, a seven-day flight campaign was performed near Lindenberg (Germany). Here we compare measurements of wind, temperature, humidity and respective fluxes between a tall tower and the WSMA. The maximum likelihood functional relationship (MLFR) between tower and WSMA measurements considers the random error in the data, and shows very good agreement of the scalar averages. The MLFRs for standard deviations (SDs, 2–34%) and fluxes (17–21%) indicate higher estimates of the airborne measurements compared to the tower. Considering the 99.5% confidence intervals, the observed differences are not significant, with exception of the temperature SD. The comparison with a large-aperture scintillometer reveals lower sensible heat flux estimates at both tower (−40 to −25%) and WSMA (−25–0%). We relate the observed differences to (i) inconsistencies in the temperature and wind measurement at the tower and (ii) the measurement platforms' differing abilities to capture contributions from non-propagating eddies. These findings encourage the use of WSMA as a low cost and highly versatile flux measurement platform.

Biology and Management of Inland Striped Bass and Hybrid Striped Bass

2013 ◽  
Keyword(s):  
Striped Bass ◽  
Prey Availability ◽  
Biotic Interactions ◽  
Early Life History ◽  
Mountain Lake ◽  
First Year ◽  
Fish Prey ◽  
Abiotic And Biotic Factors

<em>Abstract</em>.—The stocking of fingerling striped bass <em>Morone saxatilis</em> in freshwater impoundments has led to the development of successful put-grow-take fisheries throughout the southern United States. However, first-year survival of stocked fingerlings is often low. To enhance stocking success of striped bass, a better understanding is needed on the impacts of different stocking strategies on early life-history dynamics. In this review paper, we first examined the existing literature on the role of abiotic and biotic factors on recruitment dynamics of stocked piscivores in inland freshwater systems. Second, we compiled the results of a progressive series of studies that were completed over a 25-year period in Smith Mountain Lake, Virginia, that focused on understanding the relationship between striped bass stocking success and biotic interactions, forage-fish prey availability and dynamics, and first-year recruitment. This case study demonstrated that differential intra-cohort growth and poor first-year winter survival are the primary factors limiting stocking success and that stocking fingerlings at a greater number of sites throughout the lake at lower densities improved recruitment to age 1. With this information, we provide stocking size, time, density, and location strategy recommendations that should yield increased survival and stocking success of striped bass in freshwater impoundments.

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