Hydrologic transport of dissolved organic carbon (DOC) from peat soils
may differ to organo-mineral soils in how they responded to changes in
flow, because of differences in soil profile and hydrology. In
well-drained organo-mineral soils, low flow is through the lower
mineral layer where DOC is absorbed and high flow is through the upper
organic layer where DOC is produced. DOC concentrations in streams
draining organo-mineral soils typically increase with flow. in
saturated peat soils, both high and low flows are through an organic
layer where DOC is produced. Therefore, DOC in stream water draining
peat may not increase in response to changes in flow as there is no
switch in flow path between a mineral and organic layer. To verify
this, we conducted a high-resolution monitoring study of soil and
stream water at an upland peat catchment in northern England. Our data
showed a strong positive correlation between DOC concentrations at -1
and -5 cm depth and stream water, and weaker correlations between
concentrations at -20 to -50 cm depth and stream water. Although near
surface organic material appears to be the key source of stream water
DOC in both peat and organo-mineral soils, we observed a negative
correlation between stream flow and DOC concentrations instead of a
positive correlation as DOC released from organic layers during low and
high flow was diluted by rainfall. The differences in DOC transport
processes between peat and organo-mineral soils have different
implications for our understanding of long-term changes in DOC exports.
While increased rainfall may cause an increase in DOC flux from peat
due to an increase in water volume, it may cause a decrease in
concentrations. This response is contrary to expected changes in DOC
exports from organo-mineral soils, where increase rainfall is likely to
result in an increase in flux and concentration. (C) 2007 Elsevier B.V.
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