July 2008

 
KINDS OF WETLANDS


Swamps have mostly trees and marshes have mainly grasses, sedges, and rushes. The swamps at The Refuge have cypress trees. Cypress swamps make up only about 1% the area. The remainder of The Refuge is overwhelmingly marsh. Within the marsh about 5% of the area are tree islands that are neither marsh nor swamp because they are never under water.


The depth of water and the timing of the rise and fall of water level determines whether a wetland is a swamp or a marsh. In The Refuge during the dry season water covers saw-grass sloughs and water lily prairies. Water is gone from cypress swamps for 2-3 months of the year. Water never covers tree islands which have species such as bay, gumbo limbo, and dahoon holly. Amazingly the difference in elevation from deepest marsh to highest tree island is only 2-3 feet.


Wetland animals must deal with the rate at which the water level falls in the dry season and rises in the wet season. During the dry season as the water level falls, fish and shrimp become concentrated in shallower and smaller areas. So, wading birds can more easily find and catch the numbers of fish and shrimp needed to feed their fast-growing young. During the wet season in July as water levels rise rapidly, birds find it harder to find and catch and fish and shrimp. Birds that have not raised their young are in trouble. On the other hand in July fish and shrimp start to do well. As the water spreads over large areas plants have a growth spurt and all the fish, shrimp, crayfish and aquatic insects show a burst of reproduction.


An added benefit to high water is that the large areas of wetland and their plants evaporate water that will become rain. Remember from my May column that wetlands are part of the rain machine! This is one example of "wetland services".


WETLAND SERVICES


Wetlands provide invaluable services both to nature and humans. Think of how a wetland is like a sponge, a cradle and a house, and a combination of a dam, chemical factory, composter, and purifying filter.


A wetland is like a sponge because it quickly soaks up water during floods and slowly releases it during droughts. Unfortunately the wetlands of river flood plains are often drained for farming and then rimmed by levees to protect the farmlands from flooding.


When we drain river wetlands and also straighten and deepen rivers by dredging, called channelization, flooding increases. Removing the man-made channels in the Kissimmee River is one of the great successes in Everglades restoration. Within 1-3 years after the channel was plugged the SS in KiSSimmee returned and the meanders, floodplains and associated plants and animals re-appeared. The speed of restoration amazed managers and even some ecologists. Art Marshall would not have been amazed because he predicted recovery if flow were restored. In the 1970s he wrote the following. "No one really knew if Einstein was correct in his theory -- not even he was absolutely certain of its validity -- until that bomb went off at Alamogordo. My (experimental) bomb will be the Kissimmee Ditch restored".


Wetlands, including river floodplains, are like a cradle and a house because they provide habitat for young and adult plants and animals. Wetlands are habitat for plants such as willows, sawgrass (a sedge), spike rush, beaked rush, maiden cane (a grass), pickerel weed and duck potato, white and yellow water lily, and bladderworts. Wetlands are also habitat for animals such as snails and snail kites, many fish, crayfish and shrimp, alligators and turtles, ibis and wood storks, herons and egrets, plus marsh rabbits and otters.


Wetlands build soil, remove nutrients, and purify water because they act like dams, chemical factories, decomposers, and purifying filters. The plants in wetlands are responsible for all these functions:

 
Dense plants are like a series of dams. They slow the flow of water and cause large particles to settle to the bottom and accumulate. Plants thus trap these particles of dead plants and silt that contain chemically attached plant nutrients like potassium, phosphate, and nitrate.


Growing plants are like a chemical processing factory. They take up soil water and nutrients and air carbon dioxide during growth. The roots take up water and nutrients needed for photosynthesis. The leaves take up carbon dioxide (CO2) and use the energy from sunlight to photosynthetically produce sugars to grow. Tissues of living plants in effect store CO2 for the life of the plant and so slow global warming. Dead plant parts, shed leaves and branches, also keep CO2 out of circulation.


The combination of plant growth and decomposition of dead parts acts to purify water. Plants take up nutrients and contaminants. And, the organic matter and clays in the soil bind both nutrient and contaminant molecules. So the water is purified as it seeps through the soil zone and into the underlying limestone aquifers which provide our drinking water.

PEAT, MUCK, AND OOZE


Peat, muck, and ooze vary in size of organic matter particles and completeness of decomposition. Each has advantages (+) and disadvantages (-). Peat is mostly non-decomposed plant matter with the pieces so big that they are recognizable as plant material. It feels rough. It is an especially effective sponge (+) and allows good air circulation (+) but has too little available nutrient to be good soil (-). Peat moss, from northern sphagnum moss bogs, is one kind of peat.

 

Ooze is very fine organic matter that is recognizable with a microscope as dead one-celled algae. It feels slimy. It is not even a poor sponge (-) and is too easily compacted to allow good air circulation (-) but it has a lot of chemically bound plant nutrients (+). Muck soils are intermediate between ooze and peat. Muck combines the advantages of ooze and peat with none of the disadvantages. Farmers south of Lake Okeechobee call it "black gold".


Art Marshall intuitively understood the difference between ooze and muck when he wrote, "Water flowing through The Everglades, no matter how slowly, produces muck. Standing water produces ooze. The difference, muck or ooze, is akin to the dramatic difference between being old and being dead."


Peat, muck, and ooze form under different conditions. Ooze forms in lakes and reservoirs with no flow whereas peat and muck form in wetlands with flow. In the marsh interior of The Refuge the muck and peat is 10 - 30 feet thick. Peat tends to form on the bottom of saw-grass sloughs and muck on the bottom of wet prairies.

POP-UP ISLANDS IN A SEA OF MARSH


In The Refuge most tree islands start when gasses from decomposition loosen a mat of partially decomposed muck on the bottom of a wet prairie and cause it to float. Once floating, the mini island can grow bigger by the process of plant succession. Different plants colonize over time. First rushes and saw-grass grow, then wax myrtle shrubs, and then willow and buttonbush shrubs. Finally, as the island becomes taller and drier in the middle, trees such as dahoon holly, bay, and gumbo limbo colonize. Thus we have distinct zones of plants from the driest at the center to the wettest at the edges of the island.


REVIEW QUESTIONS  

a. Wetlands remove nutrients and contaminants from water.
b. Wetlands are like a cradle and a house.
c.  A river changed to a straight ditch with levees floods less.
d. Ooze is better than muck as a soil for plant growth.
e. Tree islands are zoned from grasses to shrubs to trees.