A carbon balance of Norway: terrestrial and aquatic carbon fluxes

Abstract

Northern landscapes accumulate carbon in vegetation and soils while rivers transport significant amounts of land-derived carbon to coastal areas. Here, we quantify carbon sources and sinks in main ecosystems (forests, peatlands, mountains, agricultural areas, lakes) in Norway for 1990-2008, and compare riverine carbon transport with terrestrial carbon accumulation in Norway's four major discharge areas. Mean annual carbon accumulation (6.0 ± 0.9 Tg C; 19 g C m-2) in terrestrial ecosystems balanced 40% of national greenhouse gas emissions. The area-normalized terrestrial sink strength declined in the following order (in g C m-2 yr-1): tree biomass (40±3) >peatlands (19±15) >forest soils (9±1) >>lakes (2±1) >mountains (0.5±0.3), while agricultural soils were sources of carbon (-36±74). The most precise estimate in the carbon balance was for tree biomass, because of the underlying forest inventory data. Poor data on land management and soil type in agricultural soils, and on (former) drainage and peatland type resulted in high uncertainty in carbon loss and uptake estimates in agricultural soils and peatlands, which impacted the uncertainty in total terrestrial carbon accumulation. Also, carbon losses from disturbance in organic soil types were poorly constrained. Riverine coastal inputs of land-derived organic carbon (OC) were 1.0 ± 0.1 Tg C yr-1 (3.0 g C m-2 yr-1), with highest area-specific riverine export in western (4.5 g C m-2 yr-1) and lowest (1.7 g C m-2 yr-1) in subarctic Norway. In west and middle Norway, river OC export was approximately equal to carbon accumulation in soils and wetlands, while it was 50% of soil and wetland carbon accumulation in southeast and subarctic Norway. Lateral aquatic transport of carbon is not explicitly accounted for in forest soil carbon accumulation estimates, although aquatic fluxes represent a climate-dependent carbon loss from soil carbon pools. The lack of methods that adequately account for lateral fluxes in carbon balances adds considerable uncertainty to soil carbon sink estimates. Climate warming and associated changes in precipitation may result in substantial alterations of terrestrial and aquatic carbon fluxes, with uncertain implications for the terrestrial carbon sink of northern landscapes.

From greening to browning: Catchment vegetation development and reduced S-deposition promote organic carbon load on decadal time scales in Nordic lakes

“…For example, in Norway, tree-lines have moved upwards by more than 40 meters or advanced northwards by 15 km, likely as a combined response of climate change, reduced grazing by domestic animals and elevated nitrogen deposition272829. Also, forest biomass has increased with 27% since 1990 15, comparable with biomass changes in Sweden3031 and Finland30. The increase in biomass has in part been attributed to reduced harvesting intensity in managed European forest but climate warming and N deposition32 are also promoting forest growth.…”

Aquatic DOC export from subarctic Atlantic blanket bog in Norway is controlled by seasalt deposition, temperature and precipitation

“…In northern landscapes, peatland cover is a good predictor of catchment DOC export (Dillon and Molot 1997), and a key driver of riverine DOC fluxes at larger spatial scales (Raike et al 2012). The role of lateral aquatic carbon fluxes in global (Cole et al 2007) and regional (Buffam et al 2011;de Wit et al 2015) carbon budgets is large and conceptually easy to grasp (i.e., Chapin et al 2006). However, terrestrial carbon fluxes have different sensitivities to environmental drivers than aquatic carbon fluxes.…”

Large Carbon Dioxide Fluxes from Headwater Boreal and Sub-Boreal Streams

“…In the past, this flux has been ignored in the construction of carbon budgets for forested watersheds and is now predicted to be higher than expected [7]. In Sweden, annual estimates of carbon sequestration in forests are 10% lower if aquatic carbon losses are included [8]; similar amounts are expected for Norway [9]. In the USA, stream and river CO 2 loss may be five times greater than previously thought [10].…”