Modelling carbon balances of coastal arctic tundra under changing climate

Abstract

Rising air temperatures are believed to be hastening heterotrophic respiration (Rh) in arctic tundra ecosystems, which could lead to substantial losses of soil carbon (C). In order to improve confidence in predicting the likelihood of such loss, the comprehensive ecosystem model ecosys was first tested with carbon dioxide (CO2) fluxes measured over a tundra soil in a growth chamber under various temperatures and soil‐water contents (θ). The model was then tested with CO2 and energy fluxes measured over a coastal arctic tundra near Barrow, Alaska, under a range of weather conditions during 1998–1999. A rise in growth chamber temperature from 7 to 15 °C caused large, but commensurate, rises in respiration and CO2 fixation, and so no significant effect on net CO2 exchange was modelled or measured. An increase in growth chamber θ from field capacity to saturation caused substantial reductions in respiration but not in CO2 fixation, and so an increase in net CO2 exchange was modelled and measured. Long daylengths over the coastal tundra at Barrow caused an almost continuous C sink to be modelled and measured during most of July (2–4 g C m−2 d−1), but shortening daylengths and declining air temperatures caused a C source to be modelled and measured by early September (∼1 g C m−2 d−1). At an annual time scale, the coastal tundra was modelled to be a small C sink (4 g C m−2 y−1) during 1998 when average air temperatures were 4 °C above normal, and a larger C sink (16 g C m−2 y−1) during 1999 when air temperatures were close to long‐term normals. During 100 years under rising atmospheric CO2 concentration (Ca), air temperature and precipitation driven by the IS92a emissions scenario, modelled Rh rose commensurately with net primary productivity (NPP) under both current and elevated rates of atmospheric nitrogen (N) deposition, so that changes in soil C remained small. However, methane (CH4) emissions were predicted to rise substantially in coastal tundra with IS92a‐driven climate change (from ∼20 to ∼40 g C m−2 y−1), causing a substantial increase in the emission of CO2 equivalents. If the rate of temperature increase hypothesized in the IS92a emissions scenario had been raised by 50%, substantial losses of soil C (∼1 kg C m−2) would have been modelled after 100 years, including additional emissions of CH4.

Subpixel heterogeneity of ice-wedge polygonal tundra: a multi-scale analysis of land cover and evapotranspiration in the Lena River Delta, Siberia

“…The differences in summer ET rates seem to be primarily controlled by the combination of high net radiation and low precipitation, which has also been pointed out by other studies on Samoylov Island (Boike et al, 2008;Langer et al, 2011a) and at other locations on the Arctic coastal plain (Liljedahl et al, 2011). The tundra at the study site is dominated by mosses, which can strongly control the water vapour flux at the surface (Rouse, 2000;Grant et al, 2003;McFadden et al, 2003). Mosses lack stomatal control of water loss (Oechel and Sveinbjo¨rnsson, 1978).…”

Global climate change and its impacts on the terrestrial Arctic carbon cycle with special regards to ecosystem components and the greenhouse‐gas balance

“…According to Loya et al (2002), vegetation productivity and microbial activity both benefit from a growing pool of available nutrients, although in different ways (Mack et al, 2004). At the moment, nutrients are generally rare in many northern ecosystems owing to the unfavorable soil environment (Hobbie et al, 2002;Grant et al, 2003;Callaghan et al, 2004b;ACIA, 2005).…”

“…) estimate the amount of potential C release from permafrost and global wetlands by 2100 to 100 Pg C in each case. According to Grant et al (2003) and Zhuang et al (2004), climate warming is likely to increase present CH 4 emissions from Arctic ecosystems (17-70 Tg CH 4 y -1 ) in the future. As most CH 4 originates from northern wetlands (peatlands), this prognosis is largely consistent with the global trend for wetland emissions: On the global scale, present wetland CH 4 efflux (60-237 Tg CH 4 y -1 ) is predicted to rise to 500-600 Tg CH 4 y -1 by the end of this century using a simple CH 4 emission scheme (Gedney et al, 2004).…”

Predicting wood production and net ecosystem carbon exchange of Pinus radiata plantations in south-western Australia: Application of a process-based model

“…In recent years, such models have been applied on various ecosystems around the world (e.g. grasslands, Coughenour and Chen, 1997; alpine forests, Hasenauer et al, 1999;Mediterranean forests, Sabate et al, 2002; coastal arctic tundra, Grant et al, 2003; pine and fir plantations in Italy, Magnani et al, 2004).…”