USGS Multimedia Gallery: (Video)--The Floating Marshes of Louisiana: A Unique Ecosystem

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.

[laughter]

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.

[laughter]

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.

[distant voices]