Impact of using the friction velocity filter on annual carbon estimates on natural pasture ecosystems
DOI:
https://doi.org/10.5902/2179460X45315Keywords:
CO2 flux, Eddy covariance, Pampa biome, Friction velocity filterAbstract
Annual carbon estimation of the most diverse ecosystems is a recurring theme in meetings that address climate change mitigation, as it is essential to have a realistic inventory of carbon stock in the biosphere and the ability to assimilate atmospheric carbon. Measurements of CO2 flux over ecosystems after being taken undergo rigorous post-processing to remove spurious and unrealistic data. In addition, a correction for low turbulence situations, where the eddy-covariance technique may be underestimated, is to take the friction velocity (u*) as a threshold to establish valid measurements, especially at night. This method, although widely used by the scientific community, is not unanimous. Especially since u* is itself a flow and consequently its value correlates with the time scale used for the analysis. This paper presents the annual carbon estimate of a natural pasture ecosystem, Pampa biome, in an experimental site established in Santa Maria - RS. We evaluated three distinct situations in the annual carbon estimate (NEP): i) without a u* filter; ii) with a fixed filter u* for all evaluated years and; iii) with the filter u* varying seasonally. The methodology used to estimate u* is the same as that used by Papale et al. (2006). The results show a total annual carbon sequestration variability of up to 10% depending on the methodology employed. The ecosystem in question, regardless of the method used, proved to be a carbon sink. However, the use of one methodology or another in ecosystem situations that are close to carbon assimaltion neutral should be closely scrutinized for an accurate annual balance.
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ACEVEDO, O.; MORAES, O.; DEGRAZIA, G.; FITZJARRALD, D.; MANZI, A.; CAMPOS, J. Is friction velocity the most appropriate scale for correcting nocturnal carbon dioxide fluxes. Agricultural and Forest Meteorology, Elsevier, 149, 1-10, 2009.
ACOSTA, R. Estimativas das interações biosfera-atmosfera em ecossistema de pastagem natural do bioma Pampa. 84 f. Tese (Doutorado em Meteorologia) — Universidade Federal de Santa Maria, Santa Maria, 2019
BARR, A.; RICHARDSON, A.; HOLLINGER, D.; PAPALE, D. ARAIN, M.; BLACK, T.; BOHRER, G.; DRAGONI, D.; FISCHER, M. GU, L. Use of change-point detection for friction--velocity threshold evaluation in eddy-covariance studies. Agricultural and forest meteorology, Elsevier, 171, 31-45, 2013.
PAPALE,D.; REICHSTEIN, M.; AUBINET, M.; CANFORA, E.; BERNHOFER, C.; KUTSCH, W. LONGDOZ, B.; RAMBAL, S.; VALENTINI, R.; VESALA, T. Towards a standardized processing of Net Ecosystem Exchange measured with eddy covariance technique: algorithms and uncertainty estimation. Biogeosciences, Copernicus GmbH, 3, 571 – 583, 2006.
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