Influence from Surrounding Land on the Turbulence Measurements Above a Lake

Rutgersson, Anna; Podgrajsek, Eva; Bergström, Hans

doi:10.1007/s10546-013-9868-0

Cited by 31 publications

(36 citation statements)

References 49 publications

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“…These dynamics are more pronounced during warm days, explaining the seasonal shift, and concealed during periods with a high wind velocity. The obtained diurnal trend is in accordance with findings of Sahlée et al (2014) and Lai et al (2012), who reported higher nighttime and lower daytime CH 4 emissions for a lake site in Sweden and an ombrotrophic bog in Canada, respectively. However, an opposing tendency was found by Deshmukh et al (2014), who reported higher daytime and lower nighttime CH 4 emissions from a newly flooded subtropical freshwater hydroelectric reservoir within the Nam Theun river valley, Laos.…”

Section: Application To An Exemplary Field Studysupporting

confidence: 91%

A simple calculation algorithm to separate high-resolution CH4 flux measurements into ebullition- and diffusion-derived components

et al. 2017

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Abstract. Processes driving the production, transformation and transport of methane (CH 4 ) in wetland ecosystems are highly complex. We present a simple calculation algorithm to separate open-water CH 4 fluxes measured with automatic chambers into diffusion-and ebullition-derived components. This helps to reveal underlying dynamics, to identify potential environmental drivers and, thus, to calculate reliable CH 4 emission estimates. The flux separation is based on identification of ebullition-related sudden concentration changes during single measurements. Therefore, a variable ebullition filter is applied, using the lower and upper quartile and the interquartile range (IQR). Automation of data processing is achieved by using an established R script, adjusted for the purpose of CH 4 flux calculation. The algorithm was validated by performing a laboratory experiment and tested using flux measurement data (July to September 2013) from a former fen grassland site, which converted into a shallow lake as a result of rewetting. Ebullition and diffusion contributed equally (46 and 55 %) to total CH 4 emissions, which is comparable to ratios given in the literature. Moreover, the separation algorithm revealed a concealed shift in the diurnal trend of diffusive fluxes throughout the measurement period. The water temperature gradient was identified as one of the major drivers of diffusive CH 4 emissions, whereas no significant driver was found in the case of erratic CH 4 ebullition events.

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Section: Application To An Exemplary Field Studysupporting

confidence: 91%

A simple calculation algorithm to separate high-resolution CH4 flux measurements into ebullition- and diffusion-derived components

et al. 2017

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“…We assume the process of convective mixing of the water column (e.g. Godwin et al, 2013;Poindexter and Variano, 2013;Podgrajsek et al, 2014;Sahlée et al, 2014;Koebsch et al, 2015) to be crucial for the diurnal pattern of CH 4 emissions at our study site. This is indicated by the concurrent timing of convective mixing and daily peak CH 4 emissions and a generally high fractional source area coverage of the open water, which shows higher rates of CH 4 release than emergent vegetation.…”

Section: Diurnal Variability Of Ch 4 Emissionsmentioning

confidence: 99%

High net CO2 and CH4 release at a eutrophic shallow lake on a formerly drained fen

et al. 2016

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Abstract. Drained peatlands often act as carbon dioxide (CO 2 ) hotspots. Raising the groundwater table is expected to reduce their CO 2 contribution to the atmosphere and revitalise their function as carbon (C) sink in the long term. Without strict water management rewetting often results in partial flooding and the formation of spatially heterogeneous, nutrient-rich shallow lakes. Uncertainties remain as to when the intended effect of rewetting is achieved, as this specific ecosystem type has hardly been investigated in terms of greenhouse gas (GHG) exchange. In most cases of rewetting, methane (CH 4 ) emissions increase under anoxic conditions due to a higher water table and in terms of global warming potential (GWP) outperform the shift towards CO 2 uptake, at least in the short term.Based on eddy covariance measurements we studied the ecosystem-atmosphere exchange of CH 4 and CO 2 at a shallow lake situated on a former fen grassland in northeastern Germany. The lake evolved shortly after flooding, 9 years previous to our investigation period. The ecosystem consists of two main surface types: open water (inhabited by submerged and floating vegetation) and emergent vegetation (particularly including the eulittoral zone of the lake, dominated by Typha latifolia). To determine the individual contribution of the two main surface types to the net CO 2 and CH 4 exchange of the whole lake ecosystem, we combined footprint analysis with CH 4 modelling and net ecosystem exchange partitioning.The CH 4 and CO 2 dynamics were strikingly different between open water and emergent vegetation. Net CH 4 emissions from the open water area were around 4-fold higher than from emergent vegetation stands, accounting for 53 and 13 g CH 4 m −2 a −1 respectively. In addition, both surface types were net CO 2 sources with 158 and 750 g CO 2 m −2 a −1 respectively. Unusual meteorological conditions in terms of a warm and dry summer and a mild winter might have facilitated high respiration rates. In sum, even after 9 years of rewetting the lake ecosystem exhibited a considerable C loss and global warming impact, the latter mainly driven by high CH 4 emissions. We assume the eutrophic conditions in combination with permanent high inundation as major reasons for the unfavourable GHG balance.

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“…The tower (EC1) was equipped with the following EC instrumentation 4.7 m above the lake surface: sonic anemometer (WindMonitor, Gill Instruments, Lymington, UK) for measurements of the 3-D wind components and virtual (sonic) temperature, LI-7700 open gas analyser for CH 4 measurements (LI-COR Inc., Lincoln, NE, USA) and LI-7500A open path gas analyser for CO 2 and water vapour measurements (LI-COR Inc., Lincoln, NE, USA). Additional instrumentation in the tower is described in and Sahlée et al (2014). Between 7 June 2011 and 9 June 2011 a first intensive flux measuring field campaign was conducted.…”

Section: Instrumentation and Data Collectionmentioning

confidence: 99%

“…During recent years EC measurements have been made also over lakes, mainly for CO 2 flux (e.g. Eugster et al, 2003;Huotari et al, 2011;Jonsson et al, 2008;Vesala et al, 2006) but in a few cases also for CH 4 flux (Eugster et al, 2011;Sahlée et al, 2014;Schubert et al, 2012). The EC method yields continuous measurements with limited labour, but requires expensive instrumentations and extensive data post-processing.…”

Section: Introductionmentioning

confidence: 99%

Comparison of floating chamber and eddy covariance measurements of lake greenhouse gas fluxes

et al. 2014

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Abstract. Fluxes of carbon dioxide (CO 2 ) and methane (CH 4 ) from lakes may have a large impact on the magnitude of the terrestrial carbon sink. Traditionally lake fluxes have been measured using the floating chamber (FC) technique; however, several recent studies use the eddy covariance (EC) method. We present simultaneous flux measurements using both methods at lake Tämnaren in Sweden during field campaigns in 2011 and 2012. Only very few similar studies exist. For CO 2 flux, the two methods agree relatively well during some periods, but deviate substantially at other times. The large discrepancies might be caused by heterogeneity of partial pressure of CO 2 (pCO 2w ) in the EC flux footprint. The methods agree better for CH 4 fluxes. It is, however, clear that short-term discontinuous FC measurements are likely to miss important high flux events.

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Influence from Surrounding Land on the Turbulence Measurements Above a Lake

Cited by 31 publications

References 49 publications

A simple calculation algorithm to separate high-resolution CH<sub>4</sub> flux measurements into ebullition- and diffusion-derived components

A simple calculation algorithm to separate high-resolution CH<sub>4</sub> flux measurements into ebullition- and diffusion-derived components

High net CO<sub>2</sub> and CH<sub>4</sub> release at a eutrophic shallow lake on a formerly drained fen

Comparison of floating chamber and eddy covariance measurements of lake greenhouse gas fluxes

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Influence from Surrounding Land on the Turbulence Measurements Above a Lake

Cited by 31 publications

References 49 publications

A simple calculation algorithm to separate high-resolution CH&lt;sub&gt;4&lt;/sub&gt; flux measurements into ebullition- and diffusion-derived components

A simple calculation algorithm to separate high-resolution CH&lt;sub&gt;4&lt;/sub&gt; flux measurements into ebullition- and diffusion-derived components

High net CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; release at a eutrophic shallow lake on a formerly drained fen

Comparison of floating chamber and eddy covariance measurements of lake greenhouse gas fluxes

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A simple calculation algorithm to separate high-resolution CH<sub>4</sub> flux measurements into ebullition- and diffusion-derived components

A simple calculation algorithm to separate high-resolution CH<sub>4</sub> flux measurements into ebullition- and diffusion-derived components

High net CO<sub>2</sub> and CH<sub>4</sub> release at a eutrophic shallow lake on a formerly drained fen