Contribution of advection to the carbon budget measured by eddy covariance at a steep mountain slope forest in Switzerland

Abstract

Abstract.We calculated the contribution of advection to the C budget measured by the eddy covariance (EC) technique for a steep and forested mountain site (CarboEurope site CHLae, Lägeren, Switzerland) during the growing season 2007 (May to August). Thereby we followed two approaches: (1) the physical correction of the EC data for directly measured advection terms and (2) the u * filter approach that replaces periods with u * below a site-specific threshold with empirically modelled fluxes. We found good agreement between the two approaches in terms of daily (linear regression slope: 0.78 ± 0.04, intercept: 0.68 ± 0.29 µmol m −2 s −1 , adj. R 2 = 0.78) and seasonal sums of gross fluxes (difference ≤12%), when using a u * threshold of 0.3 m s −1 and correcting EC for horizontal advection only. Incorporating also vertical advection into the mass balance equation resulted in unrealistic and highly erratic fluxes. However, on a daily basis vertical advection cancelled out to nearly zero. The u * filter seems to account primarily for respiration fluxes, which are mainly affected by horizontal advection. We could confirm our corrections by a cross-validation with independent approaches, such as soil respiration chamber measurements, light curves and energy budget closure. Our results show that flux measurements on steep sites with complex topography are possible. Actually, sloping sites seem to have the advantage over flat sites that advection measurements can be reduced to a simplified two-dimensional measurement approach due to the two-dimensional characteristics of the wind field at those sites.

Mineralisation, leaching and stabilisation of <sup>13</sup>C-labelled leaf and twig litter in a beech forest soil

“…This hill range is situated about 20 km NW of Zurich (47 • 28 40.8 N, 8 • 21 55.2 E) and belongs to the easternmost part of the Jura mountain range. As a contribution to the CarboEurope IP, netecosystem CO 2 exchange and soil respiration have been measured routinely there for several years (Etzold et al, 2010;Ruehr et al, 2010). The mean annual temperature is 8.4 • C and mean annual precipitation is 930 mm.…”

“…The temperature dependency of the soil CO 2 effluxes was fitted with the following equation (see Fang and Moncrieff, 2001):…”

Pooling of CO2within a small valley in a tropical seasonal rain forest

“…Etzold et al (2010) presented a physical correction for EC data comprising directly measured advection terms at a steeply sloping alpine forest in Switzerland; however, direct measurements of advection do not help to solve the night-time CO 2 closure problem or the problem of incompatibility with biologically driven fluxes (Aubinet et al 2010); further research is required in this regard.…”

Measured and Estimated Water Vapor Advection in the Atmospheric Surface Layer

“…Advection also plays an important role in the net ecosystem exchange of CO 2 (Etzold et al 2010;Feigenwinter et al 2004Feigenwinter et al , 2008Staebler and Fitzjarrald 2004). The effect of advection on scalar transport efficiency and turbulence spectra was investigated by Kroon and Debruin (1995).…”