Most of the dissolved organic carbon (DOC) exported from catchments is
transported during storm events. Accurate assessments of DOC fluxes are
essential to understand long-term trends in the transport of DOC from
terrestrial to aquatic systems, and also the toss of carbon from
peatlands to determine changes in the source/sink status of peatland
carbon stores. However, many long-term monitoring programmes collect
water samples at a frequency (e.g. weekly/monthly) less than the time
period of a typical storm event (typically < 1-2 days). As widespread
observations in catchments dominated by organo-mineral soils have shown
that both concentration and flux of DOC increases during storm events,
lower frequency monitoring could result in substantial underestimation
of DOC flux as the most dynamic periods of transport are missed.
However, our intensive monitoring study in a UK upland peatland
catchment showed a contrasting response to these previous studies. Our
results showed that (i) DOC concentrations decreased during autumn
storm events and showed a poor relationship with flow during other
seasons; and that (ii) this decrease in concentrations during autumn
storms caused DOC flux estimates based on weekly monitoring data to be
over-estimated, rather than under-estimated, because of over rather
than under estimation of the flow-weighted mean concentration used in
flux calculations. However, as DOC flux is ultimately controlled by
discharge volume, and therefore rainfall, and the magnitude of change
in discharge was greater than the magnitude of decline in
concentrations, DOC flux increased during individual storm events. The
implications for long-term DOC trends are therefore contradictory, as
increased rainfall could increase flux but cause an overall decrease in
DOC concentrations from peatland streams. Care needs to be taken when
interpreting tong-term trends in DOC flux rather than concentration; as
flux is calculated from discharge estimates, and discharge is
controlled by rainfall, DOC flux and rainfall/discharge will always be
well correlated. (c) 2007 Elsevier B.V. All rights reserved.