Comparison between lower-cost and conventional eddy covariance setups for CO2 and evapotranspiration measurements above monocropping and agroforestry systems

Novel, lower-cost setups of eddy covariance systems may offer a potential solution to the spatial replication problem of single flux towers. Prior to their widespread application, it is essential to conduct comprehensive testing against conventional eddy covariance setups to ensure the accuracy and precision of the measurements. In this study, we performed a comparison between three lower-cost eddy covariance setups based on lower-cost (approximately 33 % of the cost of a conventional infrared gas analyzer) slow-response carbon dioxide (CO2) and relative humidity (RH) sensors and a conventional eddy covariance setup for measuring carbon dioxide and evapotranspiration (ET) fluxes above a monocropping agricultural site in Northern Germany. The fluxes measured by these setups were further compared with a fourth lower-cost eddy covariance setup in an adjacent agroforestry field. The three lower-cost setups demonstrated satisfactory agreement with the conventional eddy covariance setup, with the slopes of the linear regression models for the 30-min flux time series ranging from 0.95 to 1.05 (R2 from 0.88 to 0.92) for CO2 fluxes and from 0.78 to 0.99 (R2 from 0.7 to 0.85) for latent heat (LE) fluxes. All lower-cost setups reproduced well diel and seasonal CO2 flux and ET dynamics. Furthermore, the lower-cost eddy covariance setups were able to measure ecosystem differences between agroforestry and monocropping, with differences in fluxes between both land uses being higher than differences between different setups. Despite the necessity for enhanced spectral corrections and the higher uncertainty associated with the lower-cost setups, the findings of this study illustrate the potential of these lower-cost setups to validate and replicate conventional eddy covariance setups, thereby enhancing the spatial representativity of measurements of energy, trace gases and momentum exchanges between terrestrial ecosystems and the atmosphere.