Reply on RC2

Abstract

Permafrost-affected soils contain large quantities of soil organic carbon (SOC). Changes in the SOC pool of a particular ecosystem can be related to its net ecosystem carbon balance (NECB) in which the balance of carbon (C) influxes and effluxes is expressed. For polygonal tundra landscapes, accounts of ecosystem carbon balances in the literature are often solely based on estimates of vertical carbon fluxes. To fill this gap, we present data regarding the lateral export rates of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) from a polygonal tundra site in the North-Siberian Lena River Delta, Russia. We use water discharge observations in combination with concentration measurements of water-borne carbon to derive the lateral carbon fluxes from one season (2 June–8 September 2014 for DOC, 8 June–8 September 2014 for DIC). To put the lateral C fluxes into context, we furthermore present the surface–atmosphere eddy covariance fluxes of carbon dioxide (CO2) and methane (CH4) from this study site. The results show cumulative annual lateral DIC and DOC fluxes of 0.31–0.38 g m-2 and 0.06–0.08 g m-2, respectively. Vertical turbulent fluxes of CO2-C and CH4-C accumulated to -19.0 ± 1.2 g m-2 and 1.0 ± 0.02 g m-2 during the 93-day observation period (8 June–8 September 2014). Thus, the lateral C export represented about 2 % of the net ecosystem exchange of CO2 (NEE). However, the relationship between lateral and surface–atmosphere fluxes changed over the observation period. At the beginning of the growing season (early June), the lateral C flux outpaced the surface-directed net vertical turbulent CO2 flux, causing the polygonal tundra landscape to be a net carbon source during this time of the year. Later in the growing season, the vertical turbulent CO2 flux dominated the NECB. Notably, the surface–atmosphere C flux served as a good approximation for the NECB at our study site during the growing season.