Geoscience Reference
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Figure 5-14. Blanket bog covers much of Dartmoor in southwestern England. Traces of former peat cutting are
evident on the hillside and three tors (bedrock outcrops) are visible in the background. Modii ed from original
photograph by Nilfanion; obtained from Wikimedia Commons < http://commons.wikimedia.org/ > .
water and remove potentially harmful sub-
stances. This ability is exploited in artii cial wet-
lands designed to treat contaminated water (see
chapter 13).
It should be stressed at this point that pro-
longed saturation by water and the resulting lack
of oxygen are key factors for the development of
hydric soils in which organic carbon may accu-
mulate. Hydric soils are, thus, sources and sinks
for greenhouse gases, namely carbon dioxide
and methane. Although the summer growing
season determines the annual carbon gas
exchanges for boreal mires, winter l uxes may
also be important as long as the soil is not frozen
(Leppälä, Laine and Tuittila 2011). Likewise,
hydric soils, especially peat, are major reservoirs
for carbon at the Earth's surface (see section
10.2). Raised and blanket bogs cover substantial
regions and represent organically constructed
deposits that build up through time and, thereby,
transform the landscape (Fig. 5-14).
According to the Ramsar wetland dei nition,
however, the continental shelf out to six meters
deep is included (see section 2.1). Thus, rocky
and sedimentary substrates must be considered
in fresh and marine environments (see Table
2-1). Types of substrate materials range from
soft mud to crystalline bedrock and fall into
several discrete categories:
• Well-consolidated bedrock, such as granite,
slate, sandstone, limestone, etc. Bedrock is
typically exposed where erosion takes place
in high-energy environments with rapid
water l ow, strong wave action, and high
turbulence. Mountain streams and coastal
headlands are typical situations (Figs. 5-15
and 5-16).
• Unconsolidated terrigenous (clastic) sedi-
ment consisting of gravel, sand, silt and clay
derived from erosion of land areas (Fig.
5-17). Rock fragments, quartz and feldspar
grains, and clay minerals are typical compo-
nents and are deposited according to sedi-
ment size, water l ow, turbulence, and
distance from sources.
• Unconsolidated bioclastic sediment com-
prised of whole or fragmented hard parts of
carbonate or siliceous invertebrate organ-
isms. Some are microscopic - radiolarians,
diatoms, foraminifera, and others are
macroscopic - echinoderm spines, gastropod
5.5 Submerged wetland substrates
The substrates of many wetlands are submerged
more or less continuously under a few to several
meters of water. In customary usage, the term
“soil” would not apply to the l oors or shores
of shallow lakes, streams or seas below the
limit of low tide or continuous submergence.
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