Natural Habitat of the Coastal Wetlands of Louisiana

Grade Levels K-6
Subject(s)
· Science
· Geography

Overview: The coastal wetlands of Louisiana are a unique environment which is endangered.

Grade Levels 6-8
Subject(s)
· Science/Biology
· Geography/Mapping

Overview: The coastal wetlands of Louisiana are a unique environment which is very productive and at risk.

Grade Levels 9-12
Subject(s):
· Biology/Biodiversity
· Ecology
· Geography/Mapping

Overview: The coastal wetlands of Louisiana are a very important environment to the entire world. The environment is very diverse and consequently complex. Manmade canals, global warming, hurricanes, and pollution have all had a negative effect on the wetlands.

Curriculum Objectives:
The student will be exposed to the importance of the Louisiana Coastal Wetlands before taking the field trip into the swamp and wetlands environment enriching the highly practical experience of the field trip and reinforcing the value of classroom preparation.

How are Wetlands Defined:
Wetlands are areas that are covered by standing water for at least part of the year. The water may not be visible most of the time although the soil may be saturated just below the surface most of the time. What is used to determine an area is a wetland are "indicator species." These are plants which are characteristic of the wetlands ecosystem. In the Louisiana coastal wetlands, both swamps and marshes (marshes don't have trees) are wetlands. The most common swamp trees are the Bald Cypress, the Water Tupelo, Red Maple and Black Willow. The most common grass in the Louisiana coastal marshes is Oyster Grass.

The Story:
Over the past 200 years, half of the Nation's original wetland habitats have been lost. This is in part the result of a natural evolutionary process, but humans draining the wetlands and filling them and dredging canals as well as the levying of the Mississippi River have also caused the destruction. Louisiana's wetlands represent 40% of the wetlands of the continental US and 80% of the wetlands loss on the continent. Wetlands are important to purify water for the aquifers. They are the home for fish and other wildlife. In fact, when wetlands become dry, it changes the soil chemistry and the plant and animal community. When the habitats are dramatically reduced, some wide-ranging species are lost, replaced by a number of competitor, predator and parasite species tolerant of disturbed environments wrecking the rich diversity of the wetlands.

What causes coastal erosion is under investigation by state and federal authorities, but here is a brief summary.
The land in the Mississippi delta area is compacting over time. The 500 mile wide delta plain with its wetlands and barrier shorelines are the product of the continuous placement of sediments. Over the centuries, the river has shifted courses and stacked sands and mud in the river bed. Abandoned river channels formed sandy headlands and barrier beaches which were separated by shallow bays and lagoons from the mainlands, forming barrier islands. These barrier islands are important to the delta plain because they reduce the effects of ocean waves and currents on the estuaries and wetlands.

The loose sediments of the Mississippi delta region are redeposited in other areas when sea levels rise and during catastrophic storms. The barrier islands are eroding fast and are exposing the wetlands area to wave action, salt water intrusion, storm surge, tidal currents and sediment transport.

The extensive levee system built to contain the Mississippi River during high water, has meant that the river deposits silts farther out from the coast and into the Gulf of Mexico. This deprives the wetlands of vital sediments needed to build up the area (which is constantly sinking) and to provide needed nutrients to the habitat.

The wetlands have also been damaged by canals dredged for navigation and energy exploration. These canals were built as straight, wide paths for easy navigation, which allowed the salt water to easily intrude on fresh water environments and allow storm surges to move inland much faster, with much more water and force. In building the canals, the dredged sediment (spoil) was piled on the banks, smothering plant life. The canal edges then did not support the plant life which protects young species of aquatic life (small creatures like to hide and feed among the edge plants), and the edges were more vulnerable to erosion by wave action in the larger channels.

The intrusion of salt water into the wetlands changes the character of the environment. The process moves the salt water from the Gulf of Mexico into the brackish (somewhat salty) and freshwater wetlands. The diversity and range of the environments is what makes the Louisiana Coastal Wetlands so important as an area which supports extensive plant and animal life. In an estuary (where the river meets the sea) there is a gradient between fresh water and salt water. This gradient varies seasonally, but the mixing creates a high biological productivity and a diversity of species. The larvae of many fish species spend part of their life cycle in estuaries. Estuaries also have high concentrations of organisms that are used by fish for food. In fact, estuaries rival tropical rainforests and coral reefs in their diversity and productivity. 75% of the species caught by commercial fishermen are estuarine during all or part of their lives.

Hurricane effects are considerable. Hurricanes have accelerated the loss of land on the barrier islands, already under attack by a rising sea level and problems that the islands are not being naturally replenished by the Mississippi River. Habitat is lost in these storms. Hurricane Andrew stripped sand from 70 percent of the barrier islands. 80 percent of the oyster reefs behind the barrier islands were smothered by sediment. One quarter of the Seagrass beds, the basis for the Chandeleur Islands complex food chain, were lost. These islands were a major wintering habitat for endangered species like the piping plover and brown pelican.

Non-native plants, fish and animals have also led to the destruction of the wetlands. Nutria feed on important grasses. This kills the grasses, and the wetlands lose their ability to clean the water and hold the soils against erosion. Carp increase the turbidity of the water, limiting the species which can live in the water. Water Hyacinth fills the wetlands and threaten water quality. All of these species were introduced to the environment by human action.

Pollution has also caused plant, fish and animal loss in the productive wetlands environment. The wetlands are a natural cleaning system for water. However, excessive nitrogen and phosphorus in the water, usually fertilizer runoff from agricultural lands, or sewage and pollutants in storm water runoff, can contribute to algae blooms which decrease the oxygen in the water and contribute to fish disease and kill important grasses. Shellfish also suffer from contaminants.

Three Environments:

There are three important wetlands environments which students will see in the Honey Island Swamp: Cypress-Tupelo Swamp, Bottomland Hardwoods, and both fresh and saltwater marshes. All have been effected by the damage to Louisiana Coastal Wetlands.

The Cypress-Tupelo Swamps of Coastal Louisiana were forever changed by the timber industry of the 1800s and early 1900s. The deep water swamps were home to very large trees over 700 years old. They were trees with great commercial value because they were impervious to rot. The trees were timbered for construction and what remains are new growth forest.

Mammals such as beaver, otter, muskrat and nutria live in the swamp. Fish that are permanent swamp residents are those which can tolerate low oxygen levels in the water like gar and bowfin, or those that can gulp oxygen by sticking their heads out of the water like mosquito fish (Gambusia). However, many fish use the swamp for a nursery, so the swamp environment is important in maintaining high fish populations. Reptiles and amphibians like alligators, lizards and lots of frogs are well adapted to swamps. Birds are also important to the swamp. You can find predators like the Barred Owl, Marsh Hawk or Redtailed Hawk; perching birds like warblers, woodpeckers and wrens and waterbirds like ducks or wading birds also make the swamp their home.

Within the swamp on high ridges and alongside rivers is a special environment of bottomland hardwoods. These hardwoods usually grow on an area that is seasonally flooded. In Louisiana, these ecosystems take advantage of even a small rise in elevation. Hardwoods are often Gum and Oak. The French called the small hills or ridges of bottomland hardwoods a Chenier which means Oak in French. Sometimes built of soil with a high concentration of shells, the ground is porous and capable of reducing the risk and severity of flooding in nearby developed areas by holding floodwater. These wetlands also improve water quality by filtering the water, removing nutrients and pollutants and reducing the sediment content of water. Early explorers reported an abundance of species in this environment that are now extinct (or nearly so) such as the panther, the red wolf, the passenger pigeon, and the ivory billed woodpecker.

Between the swamps and the coast are the marsh environments. The Gulf Coast contains about 60% of the coastal marshland of the entire United States. These coastal marshes are formed from a constant struggle between two opposing forces: subsidence or lowering of the sea floor in the Gulf of Mexico, and the raising of the marsh above sea level by the accumulation of organic peat and the deposition of new sediment.

These marsh areas are without trees but covered with grasses. The grasses are so thick that the ground is spongy as if you are not really walking on the ground but on a carpet of grass above the water. In the winter, the marshes provide habitat to more than two thirds of the waterfowl population of the Misssissippi Flyway. They provide a home to several federally listed threatened and endangered species including bald eagle, brown pelican, Arctic peregrine falcon and piping plover.

The marshes of coastal Louisiana actually move through four different ecosystems from freshwater marsh to intermediate marsh to brackish marsh to salt marsh. What distinguishes each environment is the amount of salt in the water.

In the fresh water marshes you find maidencane, bulltongue, alligatorweed, cattails and spikerush. You find turtles, ducks, alligators, muskrats, mink otters, egrets, herons and hawks.

In the intermediate marsh you find more salinity and a slight change of grasses with an addition of three-corner grass, arrowhead, cordgrass, Roseau cane, deer pea and water hyssop. Intermediate marsh is a nursery habitat for brown shrimp, blue crab and other fish. You will also find fur bearers and waterfowl.

The brackish marsh is again saltier and is affected by tidal action as well as water movement from the fresh water marsh. It is dominated by cordgrass or wiregrass. The plant diversity is lower than in fresh water or intermediate marshes but higher than in a salt marsh. Louisiana fisheries rely on the productive vitality of brackish marshes. Blue crab, shrimp, speckled trout, and redfish flourish in brackish marshes as do muskrats, raccoons, mink, otters and other mammals.

The salt marsh occurs closest to and along the shoreline and has the greatest salt concentrations. These marshes are affected by wind and tide and are regularly flooded by the Gulf of Mexico. Numerous fish like Redfish, speckled trout, blue crabs, and shrimp move in and out of the salt marsh at different stages of their life cycles

Solutions:
There are several processes which have been undertaken to restore the coastal wetlands. The first is a restoration of barrier islands through renourishment. This involves adding materials to the gulf side of the islands which can in turn attract sediments and build up the island.

The second restoration process is to distribute dredged materials into the wetlands, building up the levels of the land and adding vegetation to the new soils.

The third restoration process is to build navigation channels allowing the river to overflow into the surrounding delta and proceed through normal cycles of flooding and depositing sediment.

Resources substantially used to prepare this essay:
http://www.pulitzer.org/year/1997/public-service/works/
There is an 8 day series entitled "Oceans of Trouble" published by the Times
Picayune which won a Pulitzer Prize for journalism and covers the scientific as well
as the human costs of coastal erosion.

http://www.marine.usgs.gov/fact-sheets/LAwetlands/lawetlands.html
There are several USGS.gov fact sheets about the issues related to coastal wetlands.

http://www.challenge.state.la.us/wetlands/communities/cm.html
There are good descriptions of the environments here.

Glossary:
AQUIFER - an underground layer of rock and sand that contains water
BARRIER ISLAND - long, narrow strips of sand forming islands that protect inland areas from ocean waves and storms
BOTTOMLAND HARDWOOD FORESTS - forested, periodically flooded wetlands found along rivers
BRACKISH MARSH - marshes occurring where salinity ranges from 3-15 parts per thousand (ppt); dominated by Spartina patens (wiregrass)
CHENIER - a ridge formed by the lateral transport and reworking of deltaic sediments, usually containing large amounts of shell deposits; named for the oak trees (chene -French for oak) found growing on the ridges
DELTA - an area formed from the deposition of sediments near the mouth of a river
DETRITUS - dead, decaying plant material
DREDGING - the removal of sediment from a channel to produce sufficient depths for navigation
DUNE - a low hill of drifted sand in coastal areas that can be bare or covered with vegetation
ESTUARY - an environment where terrestrial, freshwater, and seawater (saline) habitats overlap, often where a river or freshwater lake merges into the sea
FOOD CHAIN - transfer of food energy from plants to one or more animals; a series of plants and animals linked by their food relationships
FOOD WEB - a series of linked food chains
FRESHWATER MARSH - grassy wetlands that occur along rivers and lakes; dominated by grasses, reeds, rushes, and sedges
GLOBAL WARMING - an increase of the earth's temperature by a few degrees resulting in an increase in the volume of ocean water which contributes to sea-level rise
INTERMEDIATE MARSH - a marsh occurring where the salinity is about 3 parts per thousand (ppt) - a transitional area between fresh and brackish marshes; common plants are bull tongue, roseau cane, and wiregrass
MARSH - an environment where terrestrial and aquatic habitats overlap; a wetland dominated by grasses
MUDFLAT - a muddy, low-lying strip of ground usually submerged, more or less completely, by the rise of the tide; found in association with barrier islands and cheniers along the gulf coast
NONPOINT SOURCE POLLUTION - indirect or scattered sources of pollution that enter a water system such as drainage or runoff from agricultural fields, airborne pollution from cropdusting, runoff from urban areas (construction sites, etc.)
POINT SOURCE POLLUTION - pollution originating from a single point such as pipes, ditches, wells, vessels, and containers
ppt - parts per thousand - a unit used to indicate salinity
SALTWATER INTRUSION - the invasion of freshwater bodies by denser salt water
SALTWATER MARSH - saltwater (15-18 parts per thousand or greater) wetlands occurring along the coast; dominated by saltwater grasses such as Spartina alterniflora (oyster grass)
SEA-LEVEL RISE - a rise in the surface of the sea due to increased water volume of the ocean and/or sinking of the land
SPOIL - the material removed from channels and canals by dredging
SUBSIDENCE - a gradual sinking of land with respect to its previous level
SWAMP - forested low, spongy land generally saturated with water and covered with trees and aquatic vegetation; may be a deepwater swamp, such as the cypress tupelo, which has standing water all or part of the growing season or bottomland hardwood forests which are only flooded periodically
TOPOGRAPHIC MAP - a line and symbol representation of natural and artificially created features in an area
WATERSHED - an area drained by a river
WETLANDS - land areas that are wet due to a close relationship to a body of water or groundwater, or land areas that are flooded regularly; they support vegetation adapted for life in saturated soil conditions