Fjölrit RALA - 15.06.2004, Blaðsíða 113

Soil carbon fluxes during leaching of a Histic Andosol, Iceland - evaluation
of scale and sampling techniques.
B. Sigfusson1, G.l. Paton2 and S.R. Gislason1
1) Science Institute, University of Iceland, Reykjavik, Iceland
2)University of Aberdeen, School of Biological Sciences, Cruickshank Building, AB243UU, Aberdeen UK
Soil pore water carbon from a Histic Andosol from Westem Iceland was studied at three
different scales; in the field, in undisturbed outdoor mesocosms and in laboratory repacked
microcosms. Pore water was extracted using suction cup lysimeters and hollow-fibre tube
sampler devices. There were significant differences in all measured variables, dissolved
inorganic carbon (DIC), dissolved organic carbon (DOC) and pH values between the scales of
the experiment. Concentrations of DIC and pH values varied between samphng devices used.
Gaseous constituents of soil solution and pH were more susceptible to changes in scale and
the type of sampling devices used. DOC concentrations were significantly different near the
surface but differences were diminished below 35 cm depth. Field studies considering long
anthropogenic changes in pedogenesis require considerable experimental duration though
more rapid experiments can be conducted with confidence in micro- and mesocosms as in this
research.
For the soils studied, nearly twenty percent of the organic carbon bound annually in the soil
surface horizon under field conditions was lost by leaching of DOC and through
decomposition forming DIC in disturbed non-vegetated microcosms. This percentage
increased to 38 % in undisturbed vegetated mesocosms highlighting the importance of surface
vegetation on the tumover of carbon in soils.
Soils in Iceland become more fertile as aeolian-andic deposition rates increase. The aeolian-
andic material partially dissolves at the soil’s surface therefore increasing soil pH values as
well as the nutrient status. This results in increased microbial activity and decompostion of
carbon. Furthermore allophane will form rather than metal humus complexes at pH above 5.
As a consequence carbon is increasingly leached from the soil rather than sequestered at high
pH values.
Vegetation cover plays an important role in the soils carbon cycle. Vegetation at the soil’s
surface binds carbon by photosynthesis. New unstable soil carbon is then leached to
groundwater. When the vegetation cover is absent the primary process conceming carbon will
be decomposition. Although leaching of carbon is much higher from soil with a vegetative
cover, carbon is sequestered due to photosynthesis at the soils surface.
90