Geoscience Reference
In-Depth Information
A
B
Figure 2-2.
Water is the primary ingredient for wetlands. A. Nigula Bog, southwestern Estonia (see Color Plate
2-2A). Water i lls numerous shallow pools of irregular size and shape.
Sphagnum
moss (reddish brown) surrounds
each pool, and in between the pools, low hummocks are covered with heather and dwarf pines. A wooden
walkway about half a meter wide is laid directly on the bog surface and runs across the bottom and right sides of
the scene. Kite aerial photo (Aber et al. 2002). B. Salt marsh and tidal-channel complex of the Rowley River in
northeastern Massachusetts, United States. Note linear drainage ditches in lower portion of scene. View eastward;
Atlantic Ocean on the horizon. Blimp aerial photo by J.S. Aber, S.W. Aber and V. Valentine.
l ooded daily, and many wetlands experience
deeper l oods from time to time. Standing water
in pools and hollows is usually too deep to walk
through but too shallow to swim in, although
coral reefs are a popular exception to the swim-
ming limitation. For quiet, shallow water, hip
waders, canoes, pirogues, or kayaks are the best
way to get around (Fig. 2-3).
Notice that water quality is not specii ed
-
salinity varies from fresh, to brackish, to marine,
to hypersaline. Acidity and oxygen content
may span the entire scales of natural pH and
Eh values, and temperature may range from
permafrost to hot springs (Fig. 2-4). Turbidity
varies from crystal-clear tropical seas to glacier
outwash rich with rock l our (Fig. 2-5). Quantity
and quality of surface and ground water may
be quite stable for some wetlands. In contrast,
the water conditions often change dramatically
in other wetlands as a consequence of tides,
storms, seasons, long-term drought-and-l ood
cycles, and human activities.
From Siberian tundra to Saharan oasis,
wetlands are present in all climatic and topo-
graphic settings around the world. Wetlands are
relatively common in tropical and temperate
