Seasonal dynamics of vegetation effect on peatland surface energy balance

Abstract. Peatland ecosystems play a major role in regulating the climate by storing carbon and modulating surface energy fluxes. While energy fluxes in these ecosystems are strongly influenced by climate conditions, separating the influence of climate and vegetation remains challenging. Here, we analyse eddy covariance measurements collected in 2023 at a degraded raised bog in northwest Germany. Using high-frequency gas flux and meteorological observation data we (1) characterize the annual and seasonal dynamics of radiative and turbulent energy fluxes, (2) quantify the climatic and biotic (i.e., stomatal regulation) controls on latent heat flux (LE), and (3) identify the periods d when vegetation becomes a weaker driver of LE due to stomatal regulation.

To assess the biotic controls on latent heat flux (LE), we examined the role of canopy stomatal conductance and vegetation gross primary productivity (GPP). Canopy conductance (gc) was estimated using the inverted Penman–Monteith equation, which allowed us to model a continuous time series of gc. Abiotic drivers of energy fluxes were evaluated by analysing daily and seasonal patterns of radiation, air temperature, vapor pressure deficit (VPD), and water table depth (WTD). The relative effect sizes of biotic and abiotic drivers were quantified using generalized least squares with autoregressive errors (GLSAR). Our results show that mean daily LE peaks ranged from 8.5 to 215 W m⁻² in 2023, with seasonal variations in vegetation productivity exerting a strong influence. GPP, VPD, and net radiation emerged as the dominant drivers of LE dynamics, while no relationship with WTD was observed. These findings highlight that both GPP and VPD must be jointly considered in analyses of turbulent energy fluxes, as their interactions exert nonlinear effects on ecosystem–atmosphere exchange of energy.