Organic carbon and total nitrogen variability in permafrost-affected soils in a forest tundra ecotone

Soils of the high latitudes are expected to respond sensitively to climate change, but still little is known about carbon and nitrogen variability in them. We investigated the 0.44-km(2) Little Grawijka Creek catchment of the forest tundra ecotone (northern Krasnoyarsk Krai, Russian Federation) in order (i) to relate the active-layer thickness to controlling environmental factors, (ii) to quantify soil organic carbon (SOC) and total nitrogen (NT) stocks, and (iii) to assess their variability with respect to different landscape units. The catchment was mapped on a 50 x 50 m grid for topography, dominant tree and ground vegetation, organic-layer and moss-layer thickness, and active-layer thickness. At each grid point, bulk density, and SOC and NT concentrations were determined for depth increments. At three selected plots, 2-m deep soil cores were taken and analysed for SOC, NT and C-14. A shallow active layer was found in intact raised bogs at plateaux situations and in mineral soils of north-northeast (NNE) aspect. Good drainage and greater solar insolation on the south-southwest (SSW) slopes are reflected in deeper active layers or lack of permafrost. Organic carbon stocks to a soil depth of 90 cm varied between 5 and 95 kg m(-2). The greatest stocks were found in the intact raised bogs and on the NNE slopes. Canonical correspondence analysis indicates the dominant role of active-layer thickness for SOC and NT storage. The 2-m soil cores suggest that permafrost soils store about the same amount of SOC from 90 to 200 cm as in the upper 90 cm. Most of this deep SOC pool was formed in the mid-Holocene (organic soils) and the late Pleistocene (mineral soils). Our results showed that even within a small catchment of the forest tundra, active-layer thickness and, hence, SOC and NT storage vary greatly within the landscape mosaic. This has to be taken into account when using upscaling methods such as remote sensing for assessing SOC and NT storage and cycling at a regional to continental level. [References: 44