Variability in Above and Belowground Carbon Stocks
in a Siberian Larch Watershed
Elizabeth E. Webb1, Kathryn Heard2, Susan M. Natali1, Andrew G. Bunn3, Heather D. Alexander4, Logan T. Berner5, Alexander Kholodov6, Michael M. Loranty7, John D. Schade1, Valentin Spektor8, and Nikita Zimov91Woods Hole Research Center, 149 Woods Hole Road, Falmouth, MA, 02540 2Western Washington University, 516 High Street, Bellingham, WA 98225 Bellingham, Washington 3Department of Environmental Science, Western Washington University, 516 High Street, Bellingham, WA 98225 4Department of Forestry, Forest and Wildlife Research Center, Mississippi State University, MS 39762 5Department of Forest Ecosystems and Society, Oregon State University, 321 Richardson Hall, Corvallis, Oregon, 97331 6University of Alaska, 903 Koyukuk Dr., Fairbanks, AK, 99775 Institute of Physical-Chemical and Biological Problems of Soil Science RAS, 2 Institutskaya str., Pushchino, Russia 7Department of Geography, Colgate University, 13 Oak Dr, Hamilton, New York 13346 8Melnikov Permafrost Institute, Siberian Branch of the Russian Academy of Sciences, Yakutsk, Siberia 9Northeast Science Station, Cherskiy, Russia
Received: 14 Mar 2017 – Accepted for review: 22 Mar 2017 – Discussion started: 03 Apr 2017
Abstract. Permafrost soils store between 1,330–1,580 Pg carbon (C), which is three times the amount of C in global vegetation, almost twice the amount of C in the atmosphere, and half of the global soil organic C pool. Despite the massive amount of C in permafrost, estimates of soil C storage in the high latitude permafrost region are highly uncertain, primarily due to under sampling at all spatial scales; circumpolar soil C estimates lack sufficient continental spatial diversity, regional intensity, and replication at the field-site level. Siberian forests are particularly under sampled, yet the larch forests that dominate this region may store more than twice as much soil C as all other boreal forest types in the continuous permafrost zone combined. Here we present above and belowground C stocks from twenty sites representing a gradient of stand age and structure in a larch watershed of the Kolyma River near Cherskiy, Sakha Republic, Russia. We found that the majority of C stored in the top 1 m of the watershed was stored belowground (91 %), with 20 % in the top 10 cm of soil and 42 % in the top 30 cm. Carbon was more variable in surface soils (10 cm; coefficient of variation (CV) = 0.35 between stands) than in the top 30 cm (CV = 0.14) or soil profile to 1 m (CV = 0.12). Combined active layer and deep frozen deposits (surface – 15 m) contained 205 kg C m-2 (yedoma, non-ice wedge) and 331 kg C m-2 (alas), which, even when accounting for landscape-level ice content, is an order of magnitude more C than that stored in the top meter of soil and two orders of magnitude more C than in aboveground biomass. Aboveground biomass was composed of primarily larch (53 %) but also included understory vegetation (30 %), woody debris (11 %) and snag (6 %) biomass. While aboveground biomass contained relatively little (9 %) of the C stocks in the watershed, aboveground processes were linked to thaw depth and belowground C storage. Thaw depth was significantly negatively related to stand age, and variability of soil C in the top 10 cm was related to soil moisture and moss and lichen cover. These results suggest that as the climate warms, changes in stand age and structure may be as important as direct climate effects on belowground environmental conditions and permafrost C vulnerability.
Webb, E. E., Heard, K., Natali, S. M., Bunn, A. G., Alexander, H. D., Berner, L. T., Kholodov, A., Loranty, M. M., Schade, J. D., Spektor, V., and Zimov, N.: Variability in Above and Belowground Carbon Stocks
in a Siberian Larch Watershed, Biogeosciences Discuss., doi:10.5194/bg-2017-88, in review, 2017.