A catchment-scale carbon and greenhouse gas budget of a subarctic landscape.

This is the first attempt to budget average current annual carbon (C) and associated greenhouse gas (GHG) exchanges and transfers in a subarctic landscape, the Lake Torneträsk catchment in northern Sweden. This is a heterogeneous area consisting of almost 4000 km2 of mixed heath, birch and pine forest, and mires, lakes and alpine ecosystems. The magnitudes of atmospheric exchange of carbon in the form of the GHGs, CO2 and CH4 in these various ecosystems differ significantly, ranging from little or no flux in barren ecosystems over a small CO2 sink function and low rates of CH4 exchange in the heaths to significant CO2 uptake in the forests and also large emissions of CH4 from the mires and small lakes. The overall catchment budget, given the size distribution of the individual ecosystem types and a first approximation of run-off as dissolved organic carbon, reveals a landscape currently with a significant sink capacity for atmospheric CO2. This sink capacity is, however, extremely sensitive to environmental changes, particularly those that affect the birch forest ecosystem. Climatic drying or wetting and episodic events such as insect outbreaks may cause significant changes in the sink function. Changes in the sources of CH4 through increased permafrost melting may also easily change the sign of the current radiative forcing, due to the stronger impact per gram of CH4 relative to CO2. Hence, to access impacts on climate, the atmospheric C balance alone has to be weighed in a radiative forcing perspective. When considering the emissions of CH4 from the mires and lakes as CO2 equivalents, the Torneträsk catchment is currently a smaller sink of radiative forcing, but it can still be estimated as representing the equivalent of approximately 14000 average Swedish inhabitants' emissions of CO2. This can be compared with the carbon emissions of less than 200 people who live permanently in the catchment, although this comparison disregards substantial emissions from the non-Swedish tourism and transportation activities.

Potential NH4 + and NO3 - uptake in seven Sphagnum species.

The rate of nitrogen uptake by seven Sphagnum species, which from a gradient from hummock to hollow and from ombrotrophic to minerotrophic conditions, was measured as the decrease in the concentrations of NH4 + and NO3 - from solutions in which capitula were grown under laboratory conditions. The highest uptake rate was by individuals of each species with large capitula and a high number of ion exchange sites, i.e. lawn species (S. pulchrum, S. fallax, S. papillosum and S. magellanicum). On a dry-mass basis, the most effective species were the hummock species (S. fuscum and S. rubellum), even though these species have a low dry mass. Hummock species, which occur in high densities and have high potential N-uptake rates on a dry-mass basis, were the most effective species in retaining available nitrogen.