Variability in above- and belowground Carbon Stocks in a Siberian Larch Watershed

• Main Authors: Webb, Elizabeth E., Heard, Kathryn, Natali, Susan M., Bunn, Andrew Godard, Alexander, Heather D., Berner, Logan T., Kholodov, Alexander, Loranty, Michael M., Schade, John D., Spektor, Valentin, Zimov, Nikita
• Format: Text
• Language: English
• Published: Western CEDAR 2017
• Subjects: Permafrost soils; Carbon in global vegetation; Larch watershed; Siberian forests; Environmental Studies; Forest Sciences; Kolyma; Sakha; Snag; Ice; kolyma river; permafrost; Sakha Republic; wedge*
• Online Access: https://cedar.wwu.edu/esci_facpubs/58; https://cedar.wwu.edu/cgi/viewcontent.cgi?article=1057&context=esci_facpubs

Permafrost soils store between 1330 and 1580Pg carbon (C), which is 3 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 undersampling 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 undersampled, 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 20 sites representing a gradient of stand age and structure in a larch watershed of the Kolyma River, near Chersky, Sakha Republic, Russia. We found that the majority of C stored in the top 1m of the watershed was stored belowground (92%), with 19% in the top 10cm of soil and 40% in the top 30cm. Carbon was more variable in surface soils (10cm; coefficient of variation (CV) = 0.35 between stands) than in the top 30cm (CV = 0.14) or soil profile to 1m (CV = 0.20). Combined active-layer and deep frozen deposits (surface – 15m) contained 205kgCm−2 (yedoma, non-ice wedge) and 331kgCm−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 2 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 (8%) of the C stocks in the watershed, aboveground processes were linked to thaw depth and belowground C storage. Thaw depth was negatively related to stand age, and soil C density (top 10cm) was positively related to soil moisture and negatively ...