Wetlands exist along the borders of water courses and water bodies, in topographically low lying areas. Wetlands are the interfaces between land and water. This module explains the importance of wetlands as promising ecosystems.

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ECOLOGY OF WETLANDS
by
Prof. A. Balasubramanian
Centre for Advanced Studies in Earth Science
University of Mysore, India

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Introduction:
Earth’s surface has uneven topography. The
elevations and depressions form a wide
variety of landscapes and ecosystems.
Topography, water availability and climatic
conditions control almost all the ecosystems
in the world. Among all terrestrial
ecosystems, like Mountains, Deserts, and
forests, we have yet another ecosystem to be
studied that is the wetland ecosystem.

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As the names implies, these are wet lands.
Such lands exist along the borders of water
courses and water bodies, in topographically
low lying areas. Wetlands are the interfaces
between land and water. Some good
watersheds may have large undeveloped
wetlands that store the flood waters and
help a lot of fauna and flora to survive.
Once upon a time, these lands were
considered as wastelands.

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Gradually, due to urbanization, most of them
are getting converted into urban, agricultural
or industrial lands.
Recenlty, their importance as a highly
productive ecosystem has been recognized
by the people in several countries.
Degrading wetlands are to be restored.
Hence, it is necessary to understand the
environmental conditions of wetlands.

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In this episode. the following aspects are
discussed::
1. An overview of Wetlands
2. Types of wetlands
3. Hydrological conditions
4. Biological functions
5. Site-specific conditions

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1. AN OVERVIEW OF WETLANDS
Wetlands are defined as "lands in low-lying
plains, Dominated by hydric soils;
inundated or saturated by surface water or
ground water and promoting only
hydrophytic vegetation”.
These zones are found between dry land and
waterlogged zones along the edges of
streams, rivers, lakes, and coastlines.

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Wetlands are integral parts of a watershed.
Their position in the landscape is influenced
by and influences the characteristics of a
watershed. Wetlands are characterized by
the following factors:
a. Topographically low land
b. Permanent inundation
c. Hydric soils
d. Reducing environment (absence of free
oxygen within the soil profile)

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e. Hydrophytic vegetation at shallow and
deep waters
Wetlands can function as
nutrient sinks, temporary water storage
areas, groundwater recharge areas, and
critical wildlife habitat.
Natural and anthropogenic (human-induced)
activities within a watershed influence the
functions of natural wetlands.

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For example, by changing the hydrology of
a wetland, the water retention and sediment
attenuation functions can be lost, resulting in
downstream hydrological and water quality
impacts; or vegetative species and
composition within and surrounding a
wetland might change, resulting in habitat
quality changes.
Topographically, they are saucer or bowl
shaped depressions.

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The surface area will change as water is
added through rainfall and runoff or lost due
to evaporation, plant transpiration and deep
seepage.
Saucer-shaped features tend to be temporary
and seasonal with large areas exposed as
water is lost (wading bird habitat).

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Bowl shaped features tend to be semi-
permanent to permanent with smaller
exposed areas as water is lost, but providing
long-term water to support bird species and
amphibians.
Wetlands are inundated or saturated within
major portions of the root zone (usually
within 12 inches of the surface) during the
growing season.

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The prolonged presence of water creates
conditions that favor the growth of specially
adapted plants called hydrophytes and
promote the development of characteristic
wetland soils called hydric soils.
Wetlands can be found in nearly every
county and climatic zone.
Some are wet all of the time and some may
appear to be dry most of the time.

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2. TYPES OF WETLANDS
All Wetlands are not alike. They vary
depending upon the location in a watershed
and also with reference to their abiotic
factors.
Differences in the characteristics like
hydrology, water chemistry,biological
functions, vegetation,site-specific factors,
the climate and geology of the region,
landscape position, and soils.

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create more type of wetlands.
These factors are not independent, but form
a complex interrelationship to make each
wetland type a unique one.
Based on their physical, i.e.
geomorphological conditions, chemical, and
biological characteristics wetlands are
classified into various types.

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In general,
Two major categories of wetlands are
recognized as:
a) Inland wetlands.
b) Coastal wetlands.
Inland wetlands are non-tidal environments
and coastal wetlands may have a tidal
influence.

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The Inland wetlands include:
a. Inland freshwater marshes
b. Peatlands
c. Deepwater swamps
d. Riparian wetlands

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The Coastal wetlands include:
e. Tidal salt marshes
f. Tidal freshwater marshes
g. Mangrove wetlands
Inland wetlands are most common
on floodplains along rivers and streams, and
also in isolated depressions surrounded by
dry land.

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They are found along the margins of lakes
and ponds, and in other low-lying areas
where the groundwater intercepts the soil
surface or where the precipitation is more to
saturate the soil always.
Inland wetlands include marshes and wet
meadows dominated by herbaceous plants,
swamps dominated by shrubs, and wooded
swamps dominated by trees.

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These areas are characterized by sluggish or
standing water that can create an open-water
habitat for some wildlife.
Coastal wetlands are areas bordering
coastlines.
They are closely linked to some estuaries,
where the sea water mixes with the fresh
water bodies to form an environment of
varying salinities.

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The salt water and the fluctuating water
levels (due to tidal action) combine to create
a rather difficult environment for most
plants.
Many shallow coastal areas are unvegetated
mud flats or sand flats.
The Cowardin classification system uses a
salinity criterion of 0.5 ppt ocean-derived
salinity to differentiate between estuarine
and freshwater wetlands.

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The differences in salinity will be reflected
in the species composition of plants and
animals.
Wetlands are further divided into different
types based on the soil type and plant life.
They are:
bogs, Fens
swamps, and marshes.

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A bog is an acidic peat land (peat bog).
Bogs are freshwater wetlands, often formed
in old glacial lakes, characterized by spongy
peat deposits, evergreen trees and shrubs,
and a floor covered by a thick carpet of
sphagnum moss.
A fen is a freshwater peat land with
chemically basic (which roughly means
alkaline) ground water. This means that it
contains a moderate or high proportion of
hydroxyl ions (pH value greater than 7).

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Fens are covered mostly by grasses, sedges,
reeds, and wildflowers.
A fresh-water marsh's main feature is its
openness, with only low-growing or
"emergent" plants.
It may include grasses, rushes, reeds, typhas,
sedges, and other herbaceous plants
(possibly with low-growing woody plants)
in a context of shallow water.

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A coastal salt marsh may be associated with
estuaries and along waterways between
coastal barrier islands and the inner coast.
The plants may extend from reed in mildly
brackish water to salicornia on otherwise
bare marine mud.
It may be converted to human use as pasture
(salting) or for salt production (saltern).
A swamp is wetland with more open water
surface and deeper water than a marsh.

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In some countries like, it is dominated by
trees and woody bushes rather than grasses
and low herbs.
In Africa, swamps may be dominated by
papyrus.
A mangrove swamp or mangal is a salt or
brackish water environment dominated by
the mangrove species of tree, such as
Sonneratia.

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The Intertidal wetlands provide an excellent
example of invasion, modification and
succession. The invasion and succession
process is establishment of seagrasses.
These help stabilize sediment and increase
sediment capture rates. The trapped
sediment gradually develops into mud flats.
Mud flat organisms become established
encouraging other life forms changing the
organic composition of the soils.

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Tidal wetlands are further classified into:
1. Sub-tidal - The substrate is
permanently flooded with tidal water.
2. Irregularly Exposed- The land surface
is exposed by tides less often than sub-tidal.
3. Regularly Flooded- Tidal water
alternately floods and exposes the land
surface at least once a day.

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4. Irregularly Flooded- Tidal water
floods the land surface less often than the
previous type.
Non-tidal Wetlands
1. Permanently Flooded- Water covers
the land surface throughout the year in all
years. Vegetation is composed of obligate
hydrophytes.

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2. Intermittently Exposed-. Surface
water is present throughout the year, except,
in years of extreme drought.
3. Semi-permanently Flooded- Surface
water persists throughout the growing
season in most years.
When surface water is absent, the water
table is usually at or very near the land
surface.

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4. Seasonally Flooded- Surface water is
present for extended periods, especially
early in the growing season, but is absent by
the end of the season in most years.
When surface water is absent, the water
table is often near the land surface.
5. Saturated- The substrate is fully
saturated upto the surface during the
growing season, but no surface water is
seen.

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6. Temporarily Flooded- Surface water
is present for brief periods during the
growing season, but the water table usually
lies well below the soil surface for most of
the season.
7. Intermittently Flooded- The substrate
is usually exposed, but surface water is
present for variable periods without
detectable seasonal periodicity. Weeks,
months, or even years may intervene
between periods of inundation.

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The dominant plant communities under this
regime may change with reference to the
change in soil moisture.
8. Artificially Flooded- The amount and
duration of flooding are controlled by means
of pumps or siphons in combination with
dikes or dams. Vegetation present cannot be
considered a reliable indicator of the water
regime.

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Wetlands are permanent in some places or
seasonal in some places.
They may be wet only periodically.
The quantity of water present and the timing
of its presence in part determine the
functions of a wetland and its role in the
environment.

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5. HYDROLOGICAL CONDITIONS
The hydrologic conditions in a wetland
affect the abiotic factors such as
salinity, soil oxygen availability, and
nutrient availability.
These factors in turn greatly influence the
flora and fauna present in a wetland.

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Water depth and the natural hydroperiod in
a wetland also directly influence
vegetative composition and density,
primary productivity, organic accumulation,
nutrient cycling and availability, and
the types and density of aquatic and
terrestrial fauna in a wetland.
Stormwater inflows into wetlands can
directly affect the natural hydrology of
wetlands by changing water depths and
altering the hydroperiod of the ecosystems.

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The impacts of stormwater runoff on the
water quality in a wetland are dependent on
the volume and composition of the
stormwater.
Pollutants found in runoff from urban areas
tend to include sediments,
oxygen-demanding substances, nutrients,
heavy metals, pesticides,hydrocarbons,
trash and debris.

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Changes in turbidity,oxygen levels, and
water temperature in a wetland can have
direct impacts on the flora and fauna in the
wetland.
In addition, the assimilation of heavy metals,
pesticides, and hydrocarbons associated with
stormwater runoff by the flora and fauna in a
wetland can result in negative impacts to the
ecological characteristics of the wetland.

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The periods of saturation or dryout in
wetlands have strong implications for the
characteristic structures that develop in
wetlands. This is known as hydroperiod.
Each wetland type exhibits a unique
hydroperiod.
A Hydroperiod is defined as the periodic or
regular occurrence of flooding and/or
saturated soil conditions.

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A hydroperiod is calculated as the ratio of
flood duration divided by flood frequency
over a given period of time.
The hydroperiod for a particular wetland is a
function of the water budget (i.e., inflow and
outflow water balance) and storage capacity.
It is affected by the surface contours of the
landscape and subsurface soil, geology, and
groundwater conditions.

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Since wetlands typically represent a
transition between terrestrial and open-water
ecosystems, the effects of changed
hydrology are extremely variable.
Hydrology of wetlands lead to unique
vegetation composition, but can limit or
enhance the species richness also.

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Hydrology is the most important factor in
the establishment and maintenance of
wetlands and their processes.
Precipitation, surface water inflow and
outflow, groundwater exchange, and
evapotranspiration are the major factors
influencing the hydrology of most wetlands.

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6. BIOLOGICAL FUNCTIONS
Wetlands are often called as “nurseries of
life.”
They provide the habitat for thousands of
species of aquatic and terrestrial plants and
animals.

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The Aquatic plants of wetlands are called
as hydrophytic plants or hydrophytes.
Living on or under the water surface
requires numerous special adaptations and
these plants posses those features.
These hydrophytes have several survival
characteristics:
1. A thin (or no) cuticle. The primary
function of cuticles is to prevent water loss,
thus most hydrophytes have no need for
cuticles.

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2. Stomata that are open most of the time: so
water is (abundant). This means that guard
cells on the stomata are generally inactive.
3. An increased number of stomata, that can
be on either side of leaves.
4. A less rigid structure: water pressure
supports them.
5. Large flat leaves on surface plants for
flotation.
6. Air sacs for flotation.

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7. Smaller roots: water can diffuse directly
into leaves.
8. Feathery roots: no need to support the
plant.
9. Specialized roots designed to take in
oxygen
The notable aquatic vascular plants can be
ferns or angiosperms (from both monocot
and dicot families).

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Good amount of nutrients, and primary
productivity are ideal for the development of
organisms that form the base of the food
web and feed many species of animals.
Wetlands provide unique and critical habitat
for thousands of species of animals ranging
from fish, birds, mollusks, mammals,
amphibians, reptiles and insects.

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There are many types of vegetation in
wetlands.
There are plants such as
Cattails, bulrushes, Sedges, Arrowhead,
Water Lilies, Blue Flag, and Floaters like
common duckweed.
Pondweed is also another type of plant that
grows in wetlands.
Peatland can be dominated by red maple,
silver maple, and Elm trees.

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Swamps can also have white Cedar,
Tamarack, and White Pine.
Coastal wetlands are characterized by the
following types of plant species :
1. Spartina alterniflora: Salt Marsh
Cordgrass (Smooth Cordgrass)
Salt marsh cordgrass is the most common
plant and prime indicator of a coastal
wetland. It forms 1-foot- to 8-feet-tall
meadows that grow just up to the open
water's edge.

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Lush and green in the warmer months, salt
marsh cordgrass becomes golden-brown in
the fall and dies back in the winter. Salt
marsh cordgrass is frequently flooded.
2. Juncus roemerianus:
Black Needlerush
Black needlerush has tall (3 to 5 feet)
needle-like blades in shades of dark green or
gray with sharp blackish tips.

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It grows in the higher areas of the marsh, or
where salt water completely covers the land
only during unusually high tides. In higher
elevations of the marsh, needlerush replaces
cordgrass.
3. Salicornia spp.: Glasswort
Glasswort is found throughout the marsh,
mixed in with cordgrass or on the mud flats.
Glasswort grows low to the ground (rarely
over 2 feet tall) and has short fleshy green
stubby spikes extending from a main stem.

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Glasswort looks like long green pipe
cleaners attached to a long stem. Three
species are found in coastal marshes, and
turns pink colored in the fall.
4. Distichlis spicata: Salt (or Spike) Grass.
Salt grass is a short, green, wiry grass that
lives among the salt meadow grass above
the high tide line.
5. Limonium spp.: Sea Lavender
Sea Lavender grows at the fringe of the
upper intertidal marsh.

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The plant looks delicate, with long, skinny
leaves that sprout small stems as they grow
upward. These stems are covered with tiny
purplish-white flowers in the summer and
fall.
6. Scirpus spp.: Bulrush
With its roots immersed in the mud or water,
the bulrush grows into large, thick colonies.
The plants can reach up to 10 feet tall, and
the tops are crowned with spikelets.

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7.Cladium jamaicense: Saw Grass
Saw grass grows to about 6 or 7 feet tall,
with long, slender, narrow leaves that look
like tall blades of grass. These leaves are
stiff and tough, with tiny saw teeth around
the edges. The top of saw grass has many
branches and branchlets
8. Typha spp.: Cattail
Cattails are easily recognizable by their
flower spikes, or cat tails.

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Cattail spikes can grow up to a foot long and
are densely packed with tiny brown flowers.
The cattail plant can grow to 10 feet tall.
Cattails also commonly grow outside coastal
wetlands along freshwater ponds, lakes,
rivers and ditches.

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9. Spartina patens:
Salt Meadow Grass (or Hay)
Salt meadow hay is a low- to medium-height
perennial wire-like grass, 1-foot- to 3-feet-
tall. It forms dense mats of plants just above
the high tide line.

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10. Spartina cynosuroides: Salt Reed or
Giant Cordgrass
Salt reed is a member of the same family as
salt marsh cordgrass, and they have similar
features. As its name might suggest, this
grass grows taller (up to 10 feet) and thicker
than Spartina alterniflora.

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7. SITE-SPECIFIC CONDITIONS
Changes in the volume or quality of
stormwater runoff resulting from changing
activities in a watershed can affect the
functions and values of a natural wetland by
altering the hydrologic, water quality,
and sediment or soil characteristics of a
wetland.

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Alteration of the physical and chemical
characteristics of a wetland.
This can adversely affect the biological
community and result in negative impacts to
the ecological functions of a wetland.
Wetlands and people:
Only recently have we begun to understand
the importance of the functions that
wetlands perform.

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Far from being useless, disease-ridden
places, wetlands provide values that no other
ecosystem can, including natural water
quality improvement, flood protection,
shoreline erosion control, opportunities for
recreation and aesthetic appreciation, and
natural products for our use at no cost.
Wetlands can provide one or more of these
functions.

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Protecting wetlands in turn can protect our
safety and welfare.
Major Causes of Wetland Loss and Degradation are:
Human Actions
Drainage
Dredging and stream channelization
Deposition of fill material
Diking and damming
Tilling for crop production
Levees
Logging

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Mining
Construction
Runoff
Air and water pollutants
Changing nutrient levels
Releasing toxic chemicals
Introducing nonnative species
Grazing by domestic animals

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Natural Threats are:
Erosion
Land Subsidence
Sea level rise
Droughts
Hurricanes and other storms

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Education
In the past, wetlands were regarded as
wastelands.
Education campaigns have helped to change
public perceptions and foster public support
for the wetlands.
Due to their location in the catchment area,
education programs need to teach about total
catchment management programs.

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Educational /awareness programs include
guided tours for the general public, school
visits, media liaison, and information
centers.
Regardless of their name, wetlands are
valuable because they often support diverse
species of plants, wildlife, insects and fish.
Many endangered species inhabit wetlands
during part of their life cycles.

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They are often referred to as “nature’s
kidneys” because they retain and cycle
nutrients from the soil and water.
Amphibians like frogs and salamanders
often rely on wetland areas for mating,
laying eggs and early development of
young.
Wetlands are important for flood reduction
and control.

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Wetlands also help reduce erosion by
trapping soil that is washed off of farm
fields and other open areas.
Many local economies rely on wetland areas
used for wildlife and waterfowl
preservation, and hunting. In addition,
some wetlands help replenish water supplies
for local drinking water sources.

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The common threats to wetlands are:
Area development. Because of their fertile
soil and location, many wetland areas are
desirable for farming, business and housing
developments.
Other threats come from fertilizers,
herbicides and pesticides that are applied to
surrounding areas and washed into wetlands
with storm water.

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Use GIS:
Geographic Information Systems (GIS) is
used to locate potential wetland restoration
and enhancement sites. It also identifies the
type of wetland that could be restored or
enhanced as well as the type of disturbance
that has occurred at each site.

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The Wetlands Conservation Plan has several
components:
 a wetlands inventory;
 functional assessment;
 wetland restoration;
 agency coordination;
 coastal area wetland policies;
 local land-use planning.

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Wetlands are an important part of our
national heritage.
The economic well-being and quality of life
largely depend on a nation's wealth of
natural resources.
Wetlands are the vital link between our land
and water resources.