Quantification of storage change at two contrasting eddy covariance sites

Abstract

Eddy covariance (EC) flux measurements are relevant for the study of global change biology when integrated over long-term periods (Baldocchi, 2019). This could lead to researchers being reluctant to adopt state-of-the-art correction methods, especially for sites that have collected continuous data and trends for the last 20 years. The storage change (SC) correction has often been overlooked and simplified and is generally under-investigated in the literature. The present study highlights the dynamics of the storage change term in two different landscapes and proposes a simple correction factor that can be applied backwards to historical data in a forested ecosystem. The first studied site is a mixed deciduous forest in Denmark (DK-Sor), where a sequential vertical profile system (12 heights) has been installed in 2021 to characterize the vertical component of the storage change more accurately. We compare the often-used 1 point method with the results from the profile system for CO2 and H2O. We study the SC component in terms of its diurnal course, its impact on the annual carbon budget, and its relation to atmospheric stability parameters. The second site is a Danish rural area (DK-Hove), where four different greenhouse gas fluxes are measured with EC sensors installed at 3 heights on a 200 m tall telecommunication tower. The SC profile system here consists of 5 levels and needs to adapt to the dynamic eddy covariance measurement height of the landscape-scale GHG monitoring system. We present 6 months of SC data from the tall tower for CO2, CH4, N2O and CO, their diurnal courses and relation to meteorological variables. Overall, this work aims at bringing an additional contribution to shed light on the often-neglected SC term.   Reference: Baldocchi, Dennis D. How eddy covariance flux measurements have contributed to our understanding of Global Change Biology. United Kingdom: N. p., 2019. Web. doi:10.1111/gcb.14807.