Abstract ID: 3.10810 | Accepted as Talk | Talk/Oral | TBA | TBA

Eddy covariance measurements are the backbone of in-situ ecosystem CO2 budget estimations, serving as the primary means to understand and quantify the terrestrial CO2 sink’s role in the global carbon cycle. Conventionally, this technique relies on an above-canopy eddy covariance setup to quantify vertical turbulent flux divergence, often supplemented by a profile system for estimating changes in CO2 storage. However, the complete CO2 mass balance for an ecosystem includes several additional exchange terms, including advection, horizontal flux divergence, and dispersive fluxes. The common practice is to assume these terms are negligible. However, it has been recognized that this assumption is flawed, particularly during stable, nighttime conditions. This assumption may be even less valid for complex terrain, where persistent thermally induced flows in combination with surface heterogeneities can lead to significant contributions from advection or dispersive fluxes. In the absence of a suitable and practical measurement technique for the unmeasured terms, engineering-type filtering methods are applied to measurements, without knowing the true biosphere-atmosphere exchange or the contributions of single components. High-resolution numerical modeling of the atmospheric flow can be a promising method to investigate the exchange processes at the ecosystem scale.
Here these problems in the context of complex situations of mountainous terrain and forests are summarized, and limitations and implications of current approaches to derive in-situ ecosystem CO2 estimations are highlighted. Furthermore, I am giving an outlook to my upcoming work, where Large Eddy Simulations will be used to gain insights into the CO2 exchange on an ecosystem scale.