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Dr. Swarzenski: We are only about 15 miles away
from New Orleans and the Mississippi River in a
beautiful example of a floating marsh that has been
pretty much unmanaged for many, many years---decades.
There’s fire that comes through here, and that may be
about the only disturbance. It’s a continuous, almost prairie-like
expanse of a marsh, a freshwater marsh, without any
interruptions by little waterways or ponds or lakes.
This is just a solid, solid meadow of a freshwater marsh.
Narrator: Extensive floating marshes occur in a few
locations around the world. Papyrus swamps of tropical
Africa occur along the White Nile, the Okavango and Niger
deltas, and along the shoreline of Lake Victoria. There
are extensive Phragmites swamps in the Danube Delta in Romania.
Seasonal and permanent floating meadows are found in the middle
Amazon flood plain. And in the Mississippi River
Delta Plain, there are large expanses of floating
marsh, which are the focus of this video. This
unique ecosystem is dominated by a variety of
grasses and forbs, which can create a buoyant
mat that floats on a layer of water. Different
terms are used to describe floating marshes
and reflect the country of origin. In Louisiana,
they are often referred to as flotant or prairie tremblant.
The best way to get around floating marshes is by airboat.
Dr. Swarzenski: If you stay in one place for any
length of time, eventually the water...your ankles
will start being inundated with water, but this kind
of marsh pretty much never on its own, never gets
flooded. It’s always dry, and there’s always one or
two inches of unsaturated zone near the, near the top,
and then it’s almost always saturated below that.
Narrator: Floating marsh, or flotant, forms a
buoyant mat of air-filled roots and rhizomes, which
allows the marsh to float up and down as water levels change.
Over time, the marsh mat may thicken, becoming
strong enough to support woody plants such as
wax myrtle. Periodic fires, however, keep the woody
growth in check, allowing the herbaceous plants
to continue to dominate the marsh.
Dr. Swarzenski: There’s some buoyancy to this marsh.
This is what we would call about a five on a scale
of one to five in terms of buoyancy. You can see the
water’s going around my ankles because I’ve been
standing here for a while. And I’m going to walk
away from here, and then everything will rebound.
Narrator: Peat buoyancy varies among marsh types.
From most to least buoyant, are maidencane, bulltongue, and wiregrass.
Dr. Swarzenski: This area gets burned regularly..uhm.. so
there’s nothing crowds out other species.
Nobody really takes over….no one species takes over,
and there’s a huge diversity of plants and grasses
and forbs and orchids. There’s four to five species of
orchid that we’ve seen out here. This is
Calopogon tuberosus right here. There’s two
different kinds of ferns….Thelypteris palustris
and Osmunda regalis. This is Thelypteris. Wax myrtle
would start invading this area, if it was not burned
every year and eventually there would be 10, 15 feet
tall wax myrtle thickets out here.
In Nova Scotia, there’s these areas of wet meadows,
wet bogs, called red orchid bogs. And they have
the Calopogon; they have the Pogonia that we see
out here, The, the Junonia, the buckeye… common
buckeye. Here’s an example of an orchid. And then just a lot of ferns.
Ah..it’s also common in Nova Scotia. So this is all
northern temperate environment with very harsh
winters. And yet here we are in Louisiana a few miles
away from New Orleans and we see a very similar kind
of a peat system. The soils here are highly organic;
there’s almost no clay or silt. Even though the
Mississippi River is close; it of course is kept from
coming in here by the flood control levees.
Narrator: Floating marshes form when an attached
marsh forms an organic mat that later detaches
from the underlying mineral soil. They may also
form through infilling as floating fragments expand
and as vegetation extends from an adjacent marsh
forming a floating mat over a body of water.
Dr. Urbatsch: They’re usually pretty early bloomers…
Dr. Swarzenski: OK so you already have.. what you..
I mean, it’s worth.. going and looking for.
Dr. Urbatsch: Well, yeah, I’d like to find one in flower.
Dr. Swarzenski: A few weeks ago in that same area
there were a lot of them, and now I just saw one.
Right here is Habenaria nivea, which is a very good name for it.
Dr. Urbatsch: It’s a winner, It’s been reported for
Louisiana, we actually don’t have a specimen of it.
Dr. McKee: OK.
Dr. Urbatsch: So it’s that rare.
Dr. Swarzenski: Right. We’re in the subtropics at 29
degrees and there’s these half a foot to 12 inch tall
peat mounds that may be as much as 10, 15 yards in
diameter and they just cover this whole area where
we’re at. They grow..Panicum grows through it uhm..
it survives burning. It seems to have come in recently…
since about 2000. Before that I didn’t notice…
any of these…I saw some small mounds, but
nothing of the scale that we see now.
Somebody from Quebec ended up with two samples
of Sphagnum from the national park, which is about
five miles to the east here. And he identified two separate
species of Sphagnum moss down here. And he,
working up in Canada, was kind of surprised to
see these two species in the sub-tropics.
Title: The Floating Marshes of Louisiana: A Unique Ecosystem
Extensive floating marshes occur in a few locations around the world. Papyrus swamps of tropical Africa occur along the White Nile, the Okavango and Niger deltas, and along the shoreline of Lake Victoria. There are extensive Phragmites swamps in the Danube Delta in Romania. Seasonal and permanent floating meadows are found in the middle Amazon flood plain. In the Mississippi River Delta Plain, there are large expanses of floating marsh, which are the focus of this video. This unique ecosystem is dominated by a variety of grasses and forbs, which can create a buoyant mat that floats on a layer of water. How these marshes form and some of their unique features are described.
Location: LA, USA
Date Taken: 5/1/2011
Video Producer: Karen L. McKee , U.S. Geological Survey
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