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Lower-cost eddy covariance for CO 2 and H 2 O fluxes over grassland and agroforestry

2024; Copernicus Publications; Volume: 17; Issue: 20 Linguagem: Inglês

10.5194/amt-17-6047-2024

1867-8548

Justus van Ramshorst, Alexander Knohl, José Ángel Callejas Rodelas, Robert Clement, Timothy C. Hill, Lukas Siebicke, Christian Markwitz,

Plant responses to elevated CO2

Abstract. Eddy covariance (EC) measurements can provide direct and non-invasive ecosystem measurements of the exchange of energy, water (H2O) and carbon dioxide (CO2). However, conventional eddy covariance (CON-EC) setups (ultrasonic anemometer and infrared gas analyser) can be expensive, which recently led to the development of lower-cost eddy covariance (LC-EC) setups (University of Exeter). In the current study, we tested the performance of an LC-EC setup for CO2 and H2O flux measurements at an agroforestry and adjacent grassland site in a temperate ecosystem in northern Germany. The closed-path LC-EC setup was compared with a CON-EC setup using an enclosed-path gas analyser (LI-7200, LI-COR Inc., Lincoln, NE, USA). The LC-EC CO2 fluxes were lower compared to CON-EC by 4 %–7 % (R2=0.91–0.95), and the latent heat (LE) fluxes were higher by 1 %–5 % in 2020 and 23 % in 2021 (R2=0.84–0.91). The large difference between latent heat fluxes in 2021 seemed to be a consequence of the lower LE fluxes measured by the CON-EC. Due to the slower response sensors of the LC-EC setup, the (co)spectra of the LC-EC were more attenuated in the high-frequency range compared to the CON-EC. The stronger attenuation of the LC-EC led to larger cumulative differences between spectral methods of 0.15 %–38.8 % compared to 0.02 %–11.36 % of the CON-EC. At the agroforestry site where the flux tower was taller compared to the grassland, the attenuation was lower because the cospectrum peak and energy-containing eddies shift to lower frequencies which the LC-EC can measure. It was shown with the LC-EC and CON-EC systems that the agroforestry site had a 105.6 g C m−2 higher carbon uptake compared to the grassland site and 3.1–14.4 mm higher evapotranspiration when simultaneously measured for 1 month. Our results show that LC-EC has the potential to measure EC fluxes at a grassland and agroforestry system at approximately 25 % of the cost of a CON-EC system.