Impacto do uso do filtro “velocidade de fricção” em estimativas anuais de carbono sobre ecossistemas de pastagem natural

Abstract

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.

Sazonalidade e Correlação entre Emissões de Gases Estufa e Variáveis Ambientais em Áreas Florestais Distintas na Amazônia

“…Dados espúrios foram detectados conforme método de Papale et al (2006), e o preenchimento de falhas de dados diurnos de CO 2 foi feito usando curvas de luz com a radiação PAR, enquanto os preenchimentos de fluxos fracos devido baixa turbulência foram preenchidos com médias de dados válidos, conforme as metodologias descritas por Hutyra et al (2007) e Costa (2015). A técnica de Eddy covariance na estimativa de fluxos de energia e CO 2 é amplamente empregadas na literatura, tanto para estudos em área de floresta (Araújo et al, 2002;Rocha et al, 2009;Rocha et al, 2002;Hutyra et al, 2007;Campos et al, 2019), agroecossistemas (Veeck et al, 2018), assim como para estimativas em área de pastagem (Acosta et al, 2020;Alves, 2015) ou outras superfícies peculiares, como reservatórios (Vale et al, 2016), sendo no caso deste artigo, o fluxo líquido do ecossistema é considerado como proxy do fluxo turbulento medido pelo Eddy Covariance (sem dados de armazenamento), e a respiração trata dos dados noturnos do mesmo dado.…”