Floodplain forest carbon exchange – a micrometeorological point of view

Since the eddy covariance (EC) method became a key method for measurements of the energy and greenhouse gas exchange between ecosystems and the atmosphere, a large number of studies was conducted to understand the mechanisms driving the carbon exchange in forest ecosystems. In recent years, case studies further focused on testing and validating the applicability of the EC technique above forest ecosystems, also assessing the spatial and temporal variability of sub canopy fluxes. These studies led to the conclusion that there is a high probability of overestimating the forest carbon sink strength with EC measurements above the forest canopy only, as these measurements may miss respiration components from within and below the canopy due to insufficient mixing across the canopy. Additional below canopy EC measurements were suggested to tackle this problem and to get information about potential decoupling between below and above forest canopy air masses as well as potentially missing respiration components in the above canopy derived signal.

The overall goal of the study here is to derive an as detailed as possible understanding of the carbon exchange in Lanžhot floodplain forest with the help of concurrent EC measurements below and above the forest canopy. Lanžhot floodplain forest is situated 6.5 km north of the confluence of the Morava and Thaya rivers in Czech Republic (48.6815483 N, 16.9463317 E). The long-term average annual precipitation at this site is around 517 mm and the mean annual temperature is 9.5 °C. The average groundwater level is -2.7 m. Since a long time flooding occurs here very rarely, the last flooding event was in 2013. In addition, the site is hydrologically managed. Consequently, the water regime of the site changed over the years and represents nowadays relatively dry conditions for such type of ecosystem.

To reach our research goal we evaluate different single- and two-level filtering strategies of the above canopy derived carbon exchange values and the impact of these filterings on the annual ecosystem carbon exchange rates. Our hypothesis is that conventional single-level EC flux filtering strategies like the u_*-filtering might not be sufficient to fully capture the carbon exchange of the studied floodplain forest ecosystem. We further hypothesize that additional below canopy EC measurements are mandatory to achieve unbiased forest carbon exchange values with the EC technique.