Geoscience Reference
In-Depth Information
Figure 2-23.
Moss, lichens and small shrubs cover a
knob of basalt in south-central Iceland. These plants
contribute to the formation of peat in blanket bogs and
depend for nutrients entirely on rain, snow, and
atmospheric deposits. Knob is
∼
3 m across; photo
by J.S. Aber.
Figure 2-22.
Peat samples from the Danish Stone Age
(early Holocene) along the northwestern coast of
Denmark. Plant macrofossils are well preserved and
clearly evident. Photo by J.S. Aber.
• Peat characteristics - Botanical composition,
nutrient content and structure, or human
applications
-
fuel, horticulture, etc.
that consist of more than 65 percent organic
matter (dry weight). Moss, grass, herbs, shrubs
and trees may contribute to the buildup of
organic remains, including stems, leaves, l owers,
seeds, nuts, cones, roots, bark and wood.
Through time, the accumulation of peat creates
the substrate, inl uences ground-water condi-
tions, and shapes surface morphology of the
wetland. Several factors are considered impor-
tant for classii cation of peatland types (Charman
2002):
From these diverse criteria, water supply and
nutrient status are considered the most funda-
mental elements for classifying peatlands. A gra-
dient exists from nutrient-rich, alkaline water
(fens) to nutrient-poor, acidic water (bogs), and
so peatlands are generally divided in two broad
categories (Charman 2002):
• Ombrotrophic - Raised or blanket bogs that
receive all water and nutrients from direct
precipitation (Fig. 2-23). Neither ground
water nor runoff from surrounding land
reaches the surface of the bog. Rain and
snow provide the water source and nutrients.
The latter also are derived from whatever is
carried or blown in
-
dust and ash, leaves,
bird droppings and feathers, spider webs,
and animal fur (Fig. 2-24). Water chemistry
tends to be acidic, and nutrients for plant
growth are in extremely short supply. Only a
few plants can survive such harsh conditions;
namely
Sphagnum
(peat moss) and pine.
• Minerotrophic - Fens and swamps located
in depressions that receive surface runoff
and/or ground-water discharge from adja-
cent or underlying mineral-soil sources
(Fig. 2-25). Nutrients are more abundant and
• Floristic - Plant composition of vegetation
communities, which may be used as proxies
for environmental factors.
• Physiognomy - Structure of the dominant
plants, particularly used in Scandinavian and
Russian schemes.
• Morphology - Three-dimensional shape of
the peat deposit and geomorphology of the
wetland surface.
• Hydrology - Source of the supply and l ow
regime for surface and ground water.
• Stratigraphy - Vertical layering, composi-
tion, and nature of underlying peat deposits.
• Chemistry - Chemical characteristics of
surface water, particularly acidity and
content of nutrients.
