Discovering the importance of lateral CO2 transport from a temperate spruce forest

Our study investigated the concentration of dissolved carbon at the point when water leaves the pedosphere and whether this amount represents a significant proportion of terrestrial carbon cycling. The investigations were carried out in a temperate forest catchment (Black Forest, Germany) over a period of 1 year. The annual export of dissolved C compounds (14.4 g C m−2 year−1) was dominated by CO2 (9.7 vs. 4.7 g C m−2 year−1 DOC). Even though the direct CO2 degassing at the spring was inferior (0.4 kg C year−1), considerably lower CO2 concentrations were measured 17 m downstream of the spring. This shows that a large proportion of dissolved CO2 (93%) originating from the pedosphere is not captured anymore within a short distance from the spring. The measured lateral C-transport was in the same order of magnitude as reported for the net ecosystem exchange (NEE) observed for German spruce forests (−4 to −55 g C m−2 year−1). Therefore, the results clearly demonstrated that the lateral transport of dissolved carbon can be a significant part of terrestrial carbon budgets and for this study site CO2 was dominating this ‘indirect’ pathway. However, for generalisation, it is important to extend this investigation to other landscapes and climatic zones.