Carbon dioxide dynamics in an agricultural headwater stream driven by hydrology and primary production

[摘要] Headwater streams are known to be hotspots for carbon dioxide ( CO 2 ) emissions to the atmosphere and are hence important components in landscape carbon balances. However, surprisingly little is known about stream CO 2 dynamics and emissions in agricultural settings, a land use type that globally covers ca. 40 % of the continental area. Here we present hourly measured in situ stream CO 2 concentration data from a 11.3 km 2 temperate agricultural headwater catchment covering more than 1 year (in total 339 d excluding periods of ice and snow cover). The stream CO 2 concentrations during the entire study period were generally high (median 3.44 mg C L −1 , corresponding to partial pressures ( p CO 2 ) of 4778  µ atm) but were also highly variable (IQR  =  3.26 mg C L −1 ). The CO 2 concentration dynamics covered a variety of different timescales from seasonal to hourly, with an interplay of hydrological and biological controls. The hydrological control was strong (although with both positive and negative influences dependent on season), and CO 2 concentrations changed rapidly in response to rainfall and snowmelt events. However, during growing-season base flow and receding flow conditions, aquatic primary production seemed to control the stream CO 2 dynamics, resulting in elevated diel patterns. During the dry summer period, rapid rewetting following precipitation events generated high CO 2 pulses exceeding the overall median level of stream CO 2 (up to 3 times higher) observed during the whole study period. This finding highlights the importance of stream intermittency and its effect on stream CO 2 dynamics. Given the observed high levels of CO 2 and its temporally variable nature, agricultural streams clearly need more attention in order to understand and incorporate these considerable dynamics in large-scale extrapolations.

[学科分类] 大气科学