Geoscience Reference
In-Depth Information
salt Marsh: nowhere to Move
many square miles of salt marsh have been
eradicated to make way for urban develop-
ment, recreation (e.g., marinas), farming,
aquaculture, salt making, and industry
(especially in Taiwan). Boston, San Fran-
cisco, Tokyo, and Rotterdam have all ex-
panded over salt marshes. And of course
storm water runoff and sewage create local
but widespread problems for the health of
salt marshes.
Adding to the woes of the world's salt
marshes is the sea level rise. Marshes can
handle the rise with ease: they simply move
back. Unfortunately the land next to salt
marshes is highly treasured by humans,
and inevitably such land is “protected”
from erosion, which means that the shore-
line is not allowed to retreat. Thus as the
water level rises, the marsh narrows and
will eventually disappear. The impact of
the rising sea level is manifested along
many of the world's estuarine shorelines
by the line of dead trees whose roots have
been flooded by either fresh or saltwater
as the water table moves up apace with the
sea.
Salt marshes, sometimes known as tidal
marshes, live on flat areas, covered with a
continuous carpet of salt-tolerant vegeta-
tion, next to shorelines between the high
and low tide lines. Salt marshes range in
width from a meter or two to several miles.
The size of the marsh may depend on the
tidal amplitude: the higher the amplitude,
the wider the marsh. In river deltas the
areal extent of the marsh depends on the
size of the deltaic platform built by the river.
Salt marshes are characterized by ex-
traordinarily low plant diversity, because
few plants can tolerate saltwater. They are
highly productive environments, creating
through decomposition nutrients that feed
a long chain of organisms. “Low marshes,”
which are inundated by almost every tidal
cycle, generally have a single plant spe-
cies, which on the shorelines of the east-
ern United States is the smooth cordgrass
Spartina alterniflora
. Plant diversity in-
creases slightly in “high marshes” that are
inundated only occasionally by saltwater.
Beyond the high marsh in long estuaries
or on very low-lying land are freshwater
marshes, some of them huge, like the Flor-
ida Everglades.
Humans have created many problems for
salt marshes. U.S. East Coast salt marsh
grass has become an invasive species in
Washington State and is taking over the
mudflat environment, edging out local
plants and animals. Ditto for the European
salt marsh grass in New Zealand. Globally
land plants and animals
Anecdotes of changes in the life cycles of
plants and animals, apparently related to
global change, are legion. Perhaps the most
famous of these changes is the displace-
ment of the polar bear (chapter 4), which
in some areas of the Arctic is losing the
sea ice essential for its seal hunting. Polar
