Boreal soil carbon vulnerability under a changing climate
Boreal and arctic ecosystems contain vast stocks of soil carbon, much of it frozen or waterlogged. There has been considerable research and concern about the fate of this carbon as these regions warm, particularly since high latitudes are projected to warm more than most lower latitudes in the coming century. Our research has focused on understanding the factors that control carbon stabilization in these settings, how these factors are influenced by disturbance, and what will happen to these carbon stocks in the future.
Research Results
Most of the lab's research has taken place in Interior Alaska and Siberia. Our work has been supported by the National Science Foundation, the USGS and the US Department of Energy. A annotated bibliography of our work in this area is provided below. More information about our ongoing DOE-Supported modeling project and links to modeling publications can be found here. One major control on future boreal C release is forest fire and links to our publications (boreal and elsewhere) on fire impacts on soils and carbon storage can be found here.
K.P. Wickland and J.C. Neff (2008). Decomposition of black spruce forest soils: environmental and chemical controls. Biogeochemistry. 10.1007/s10533-007-9166-3. This manuscript presents data from a series of laboratory incubation studies from three different black spruce drainage classes (ranging from well- to poorly-drained). The study shows a strong temperature response function for decomposition (similar to many other studies) but is also unusual in having a moisture response function for decomposition as well. Both response functions are presented in a manner that is suitable for modeling. The study also includes a pyroylsis-GC/MS analysis of soil organic matter structure that suggests that SOM structures do vary acrosss these drainage conditions and play a role in the control of decomposition. PDF
Neff, J.C., J. Finlay, S.A. Zimov, S. Davydov, J.J. Carrasco, E.A.G. Schuur, A. Davydova. (2006) Seasonal changes in the age and structure of dissolved organic carbon in Siberian Rivers and streams. Geophysical Research Letters. 33(23), L23401, 10.1029/2006GL028222. This study illustrates a strong seasonal change in the chemical composition (determined with py-GCMS) and age (determined with 14C) of DOC in the Kolyma river and several smaller tributaries. The study illustrates that the primary source of lignin-derivatives in this large river is the leaching of surface soils early in the growing season with later season DOC showing contributions from older and likely-more decomposed sources of carbon. The 14C record here, combined with other recent studies will provide an important baseline for detection of changes in soil carbon dynamics as the active layer thickens in coming years. PDF
Randerson, J.T., H. Liu, M.G. Flanner, S.D. Chambers, Y. Jin, P.G. Hess, G. Pfister, M.C. Mack, K.K. Treseder, L.R. Welp, F.S. Chapin, J.W. Harden, M.L. Goulden, E. Lyons, J.C. Neff, E.A.G. Schuur, C.S. Zender. (2006). The Impact of Boreal Forest Fire on Climate Warming. Science V314 (5802). This manuscript presents a comprehensive analysis of the full radiative impact of boreal forest fire on atmospheric radiative balance. The study includes both the direct effects of fire and regrowth on atmospheric CO2 but also the impacts of changes in land surface energy exchange (at the site of fire and elsewhere due ot aerosol deposiion). PDF available on request
Dutta, K., E.A.G. Schuur, J.C. Neff, and S.A. Zimov. (2006) Potential carbon release from permafrost soils of Northeastern Siberia, Global Change Biology.Published article online: 25-Oct-2006. doi: 10.1111/j.1365-2486.2006.01259.x This study is a laboratory based analysis of the potential decomposibility of Yedoma soils from Siberia. These soils, similar to loess deposits in Alaska and elsewhere, contain very high concentrations of terrestrial carbon with origins in the Pleistocene. Once thawed, this study shows this material to be highly decomposible and therefore a potential source of carbon to the atmosphere. PDF
Harden J. W. , K. L. Manies, M.R. Turetsky, and J. C. Neff. (2006) Effects of wildfire and permafrost on soil organic matter and soil climate in interior Alaska. Global Change Biology. Published article online: 18-Oct-2006. doi: 10.1111/j.1365-2486.2006.01255.x This manuscript describes a study of soil carbon losses due to fire in interior Alaska. The study identifies drainage condition and permafrost presence as two fo the important controls on ground fuel C storage and loss. The presence of the deep soils layers, in partictular, is shown here to have a large influence on both carbon storage between burns, carbon loss with burning and is suggested to play an important role in regional regrowth patterns. PDF
Wickland, K. P., R. G. Striegl, J. C. Neff, and T. Sachs (2006), Effects of permafrost melting on CO2 and CH4 exchange of a poorly drained black spruce lowland, J. Geophys Res., 111, G02011, doi:10.1029/2005JG000099. This paper presents the results of a field study near Fairbanks, AK. The study examined the fluxes of trace gases from an area that had recently lost permafrost and an adjacent control site. Thermokarst formation led to large increases in methane emission from this site while CO2 emissions were largely similar to adjacent areas. PDF
Finlay J. , J.C. Neff, S. Zimov, A. Davydova, and S. Davydov. (2006) Snowmelt dominance of dissolved organic carbon in high-latitude watersheds: implications for characterization and flux of river DOC. Geophysical Research Letters. Vol. 33, No. 10, L10401. This manuscript describes a field study of DOC fluxes in a range of rivers in Siberia. This work was one of the first to show the overwhelming dominance of the snowmelt period on annual DOC fluxes in arctic rivers. The field study, combined with a literature revew illustrates that nearly all the annual DOC export from these ecosystems happens during the spring/early summer period of flooding; a time period that is difficult to sample. PDF
Neff J.C., J.W. Harden, and G. Gleixner. Fire effects on soil organic matter content and composition in boreal interior Alaska. 2005. Canadian Journal of Forest Research. 35(9): 2178-2187 We present the results of a study of a burned area (from 1999) near Delta Junction, AK. We use several techniques to estimate pre and post fire soil carbon stocks and highlight the uncertainty in these different approaches to soil carbon estimation across heterogeneous boreal landscapes. We also use a combination of py GCMS and thermogravimetry to examine the structural changes that occur in soils with burning and suggest that these changes are dominated by the loss of thermally labile compounds rather than the creation of new char products. PDF
Harden, J. W.; Neff, J. C.; Sandberg, D. V.; Turetsky, M. R.; Ottmar, R.; Gleixner, G.; Fries, T. L.; Manies, K. L. Chemistry of burning the forest floor during the FROSTFIRE experimental burn, interior Alaska, 1999 Global Biogeochem. Cycles, Vol. 18, No. 3, GB3014 10.1029/2003GB002194 28 August 2004 This study focused on an experimental burn in the Poker/Caribou Creek experimental watershed near Fairbanks, AK. The study presents a technique for estimating soil organic matter consumption based on the concentrations of immobile elements in the soil profile (similar to weathering estimates). One additional interesting component of this study are the high concentrations of rock-derived minerals in the organic layers of this forest. These elements, which must largely be derived from dust, may play an important role in forest regeneration following fire. PDF
Neff J.C. and D.U. Hooper (2002) Vegetation and climate controls on the potential production of CO2, DOC and DON production in northern latitude soils. Global Change Biology. 8: 872-884.This study was one of the first to illustrate the relativley extreme lability of boreal and arctic soils. The study is based on a laboratory incubation of soils collected from the arctic to boreal regions of alaska and shows that for most vegetation types and most latitudes, the soils are very decomposible with adequate moisture and temperature. PDF