Organic carbon and total nitrogen stocks in soils of the Lena River Delta

Abstract

The Lena River Delta, which is the largest delta in the Arctic, extends over an area of 32 000 km(2) and likely holds more than half of the entire soil organic carbon (SOC) mass stored in the seven major deltas in the northern permafrost regions. The geomorphic units of the Lena River Delta which were formed by true deltaic sedimentation processes are a Holocene river terrace and the active floodplains. Their mean SOC stocks for the upper 1m of soils were estimated at 29 kgm(-2) +/- 10 kgm(-2) and at 14 kgm(-2) +/- 7 kgm(-2), respectively. For the depth of 1 m, the total SOC pool of the Holocene river terrace was estimated at 121 Tg +/- 43 Tg, and the SOC pool of the active floodplains was estimated at 120 Tg +/- 66 Tg. The mass of SOC stored within the observed seasonally thawed active layer was estimated at about 127 Tg assuming an average maximum active layer depth of 50 cm. The SOC mass which is stored in the perennially frozen ground at the increment 50-100 cm soil depth, which is currently excluded from intense biogeochemical exchange with the atmosphere, was estimated at 113 Tg. The mean nitrogen (N) stocks for the upper 1m of soils were estimated at 1.2 kgm(-2) +/- 0.4 kgm(-2) for the Holocene river terrace and at 0.9 kgm(-2) +/- 0.4 kgm(-2) for the active floodplain levels, respectively. For the depth of 1 m, the total N pool of the river terrace was estimated at 4.8 Tg +/- 1.5 Tg, and the total N pool of the floodplains was estimated at 7.7 Tg +/- 3.6 Tg. Considering the projections for deepening of the seasonally thawed active layer up to 120 cm in the Lena River Delta region within the 21st century, these large carbon and nitrogen stocks could become increasingly available for decomposition and mineralization processes

Permafrost soils and carbon cycling

“…Redistribution of organic matter within the soil profile due to cryoturbation is most common in the Arctic, where patterned ground processes are active -such as sorted and nonsorted circles and ice-wedge polygons (Washburn, 1973;Michaelson et al, 2008;Walker et al, 2008;Kanevisky et al, 2011;Zubrzycki et al, 2013;Ping et al, 2008bPing et al, , 2014. In early studies, SOC stocks were measured only at shallower depths -mostly limited to the rooting zones at depths less than 50 cm, due to logistics (Brown, 1969;Everett and Brown, 1982).…”

“…Ice-wedge polygons also dominate river floodplains, valleys, lowland areas and thermokarst depressions in Arctic foothills and the subArctic, e.g., interior Alaska, northern Canada, and central Yakutia, Russia (Péwé, 1975;French, 2007;Schirrmeister et al, 2011b;Strauss et al, 2012;Zubrzycki et al, 2013). During ice-wedge development, soils on both sides of the ice wedge are pushed apart and heaved to form rims on SOIL, 1, 147-171, 2015…”

“…However, with time, the ice wedges can degrade, forming deep troughs (Jorgenson et al, 2006). Relatively, polygon interiors then become high centered, surface cracking increases, and greater cryoturbation associated with the cracks leads to formation of soils (Histoturbels) with greater organic matter accumulations Zubrzycki et al, 2013).…”

“…Intermittent burial by eolian, alluvial, colluvial, and lacustrine sediments can lead to accumulation of significant SOC stocks in these depositional environments (Shur and Jorgenson, 1998;Schuur et al, 2008;Tarnocai et al, 2009;Grosse et al, 2011;Schirrmeister et al, 2008Schirrmeister et al, , 2011bZubrzycki et al, 2013). These processes are often accompanied by syngenetic permafrost growth, where the upward growth of the permafrost surface follows the accumulation of sediments and peat layers at the surface (Shur, 1988).…”

“…These processes are often accompanied by syngenetic permafrost growth, where the upward growth of the permafrost surface follows the accumulation of sediments and peat layers at the surface (Shur, 1988). Deltas and thaw lakes with ice-rich permafrost are abundant along the Arctic coastal plains, such as at Barrow in northwestern Alaska , the Colville Delta in northern Alaska (Shur and Jorgenson, 1998;Ping et al, 2011) and the Lena River Delta in northern Russia Zubrzycki et al, 2013). In the Colville Delta, buried organic soils are found as deep as 3 m (Shur and Jorgenson, 1998).…”