Ecosystem scale methane fluxes in a natural temperate bog-pine forest in southern Germany

Methane (CH₄) and carbon dioxide (CO₂) exchange were investigated over 15 months above a natural bog-pine site in the pre-alpine region of southern Germany. The measurements indicate annual methane emissions of +5.3±0.34gCm^-2a^-1 and an annual CO₂ uptake of -62±20gCm^-2a^-1, resulting in a global warming potential balance of -50±74g [CO₂ eq.]m^-2a^-1. Air temperature was identified as the environmental parameter showing the highest correlation with methane production, except for periods with low water table (<-0.12m). Furthermore, we compared three different methane flux gap-filling methods: the mean daily variation approach (MDV), a look up table (LUT) with various control parameters and an exponential regression function between methane flux and air temperature (NLR). It turns out that the LUT provides the best result for the gap-filling of half-hourly CH₄ fluxes for the present data. By increasing the number of parameters in the LUT, the CH₄ flux prediction could be considerably improved. Except for dry periods, day to day variations could be reproduced very well by the NLR method, but results for sub-daily fluctuations were poor. The choice of gap-filling method affects the annual methane budget estimate by at most ±0.5gCm^-2a^-1, or about 10% of the annual flux.This study presents one of the first eddy covariance based annual methane- and CO₂-exchange estimates over a natural bog-pine ecosystem outside the boreal zone.