The production and release of dissolved organic carbon (DOC) from peat
soils is thought to be sensitive to changes in climate, specifically
changes in temperature and rainfall. However, little is known about the
actual rates of net DOC production in response to temperature and water
table draw-down, particularly in comparison to carbon dioxide (CO2)
fluxes. To explore these relationships, we carried out a laboratory
experiment on intact peat soil cores under controlled temperature and
water table conditions to determine the impact and interaction of each
of these climatic factors on net DOC production. We found a significant
interaction (P < 0.001) between temperature, water table draw-down and
net DOC production across the whole soil core (0 to -55 cm depth). This
corresponded to an increase in the Q(10) (i.e. rise in the rate of net
DOC production over a 10 degrees C range) from 1.84 under high water
tables and anaerobic conditions to 3.53 under water table draw-down and
aerobic conditions between -10 and - 40 cm depth. However, increases in
net DOC production were only seen after water tables recovered to the
surface as secondary changes in soil water chemistry driven by sulphur
redox reactions decreased DOC solubility, and therefore DOC
concentrations, during periods of water table draw-down. Furthermore,
net microbial consumption of DOC was also apparent at - 1 cm depth and
was an additional cause of declining DOC concentrations during dry
periods. Therefore, although increased temperature and decreased
rainfall could have a significant effect on net DOC release from
peatlands, these climatic effects could be masked by other factors
controlling the biological consumption of DOC in addition to soil water
chemistry and DOC solubility. These findings highlight both the
sensitivity of DOC release from ombrotrophic peat to episodic changes
in water table draw-down, and the need to disentangle complex and
interacting controls on DOC dynamics to fully understand the impact of
environmental change on this system.