In Louisiana’s
eroding coastal marshes, it’s common to see water lapping
hungrily at the front steps of camps once surrounded by solid
ground. “Most camps were originally built on banks and
levees,” says Michael Materne, plant specialist with
the USDA Natural Resources Conservation Service (NRCS) at
Louisiana State University. “But in an eroding environment,
where marsh plants are no longer there to buffer wave action,
tidal surges and wakes from boat traffic constantly hit the
bank and undermine the land so it just sloughs off.”
Though
individual camp owners have little opportunity to do anything
about subsidence and erosion in the interior marshes, they
can help to prevent erosion, and actually rebuild land in
the areas immediately around their camps. They can replace
the lost shoreline plants needed to absorb the force of the
wave energy before it can attack the banks near a camp.
“The
kinds of plants that work best are stiff-stemmed species,
called ‘edge’ plants, that grow in water. They
should be planted at the shoreline,” says Materne, whose
work with the NRCS has involved replanting many types of coastal
areas from marshes to island dunes. “Putting plants
on top of a bank has little protective effect if the bank
beneath them washes away. Even an enormous oak tree with its
huge root system just tumbles into the water if the land around
it is undermined.”
As waves
come against them, the stems of the edge plants break the
water’s force, reducing land-gobbling surges to gentle
eddies. “There are only a few species of plants that
can do that,” says Materne, “and the selection
depends on water salinity and depth.”
In a
salt or brackish marsh, the NRCS recommends planting smooth
cordgrass (Spartina alterniflora), which Materne
calls the ideal plant for erosion control. “This plant
grows from the water’s edge out to a depth of about
18 inches. It will spread upward toward the bank somewhat,
but it grows best in standing water.
For freshwater
habitats, giant cutgrass (Zizaniopsis miliacea) is
recommended. It also grows in standing water, forming dense
circular clumps that make an effective barrier to wave action.
“The real advantage of both these plants,” observes
Materne, “is that they grow well in standing water,
which is unusual for most plant species. They have stiff stems
and extensive root systems so they don’t fall over when
a wave hits them but just bend a bit.” Both smooth cordgrass
and giant cutgrass are perennials, native to Louisiana, and
common to the habitats where they can be replanted.
Bullwhip
(Scirpus californicus), also called giant bulrush,
is another edge-zone plant that grows in standing water and
can be used by landowners to replant shallow, interior lakes
where wind-whipped waves eat away shorelines. As their banks
erode, many small interior lakes and ponds gradually get wider,
opening up into several hundred acres of shallow water. In
these lakes, the NRCS has planted bullwhip either in hedge-like
rows radiating out from a bank or in parallel lines away from
the shore. As winds circulate the water, muddy bottom sediments
and organic matter are churned up and suspended in the water.
When the winds are broken by the rows of bullwhip, the suspended
sediments drop out and start building up behind the plant
barriers. Once the sediment accumulates to an elevation high
enough to support plants, new vegetation grows. Over time,
plant communities develop and a new marsh is formed.
“Smooth
cordgrass and cutgrass act in the same way but in different
habitats,” says Materne. “Once wave or wind energy
is broken, land can start building behind the plants. In time,
eroded banks can be reclaimed. You achieve protection with
these plants and also help to build land.”
Materne
emphasizes the advantage of living vegetation over rock or
riprap bulkheads. “Rocks are static barriers. When the
land starts to scour out behind them or from around their
edges, rocks lose their effectiveness and you still have the
erosion problem.” Smooth cordgrass, on the other hand,
is a perpetual living organism that maintains itself, spreading
into new areas as sediments are deposited.
“Using
plants allows you to continually reclaim more and more bank
area. The more land that builds around smooth cordgrass, the
more the plant grows out, so reclaiming is continual. It’s
a dynamic system as opposed to a static structure.”
Materne
says that wetland plants such as smooth cordgrass and giant
cutgrass are available in containers from most commercial
wetland nurseries. Nursery plants are usually healthy with
well-established root systems, which is important for plant
survival in a hostile environment. They are also commonly
found in the wild, but Materne cautions against digging up
and transplanting wild stock. “No matter how careful
you are, its not a good idea to rob Peter to pay Paul. In
trying to solve one problem, you may create another.”
Plants
for shoreline protection should be planted in rows parallel
to the shoreline, as close to each other as possible so that
they will grow together quickly. “Spacing depends on
how much material you have. With one-gallon containers, the
most common size available, put them about three feet apart.”
Staggering the plants in either one or two rows works also.
“The point is to get them to grow together as quickly
as possible because otherwise their effectiveness is limited,
“ says Materne.
Grasses should be planted at average or mean tideline. The
upper and lower intertidal zone is their primary habitat.
Using a shovel, plant each container of grass at the depth
of the soil ball of the plant, or slightly deeper, so that
a little soil is on the stems but the stems aren’t buried.
The plant should be deep enough so that the soil ball is well
anchored but high enough so that the stems can bend with the
wind. Single-stemmed plants can be placed in low-energy areas,
but they have little root mass and take longer to establish
dense stands.
Additional
fertilization is optional because the natural fertility of
Louisiana’s coastal soils is usually adequate. “We
sometimes add fertilizer in the form of an orchard tablet,
which comes in boxes of 500 and are about ten cents each,”
says Materne. “These are slow-release tablets that we
put in the soil next to the root ball at the time of planting.”
Download:
fighterosion.pdf
(145KB)
