Wetlands are complex ecosystems where land and water environments meet and where changing water levels are a feature. The transition zone between these environments provides diverse habitats and a rich food source, making them ideal breeding and feeding grounds for birds, fish, bugs and other animals. The interaction between the land, water, plants and animals at a wetland demonstrates their interdependence. Just as a healthy wetland provides the conditions needed to sustain a diverse range of plants and animals, the wildlife present at a wetland will influence the ability of a wetland to improve water quality. Therefore, the success of a wetland system can be determined by the diversity and population of animals and insects present in and around the wetland.

Adapting to Life in a Wetland
The plants and animals found at a wetland are adapted to live in these unique environments, and are able to survive changing water levels and conditions, for example:

• Frogs, fish, birds and bugs only breed when conditions are suitable and there is a good food source.
• Some fish and birds travel great distances to breed and feed in wetlands.
• Many aquatic plants can survive periods of drought, regenerating when water levels increase.
• The duration of life cycle stages of frogs and aquatic macroinvertebrates (eg. tadpole and larvae stage) vary according to environmental conditions.
• The eggs of some macroinvertebrates lay dormant during dry periods, hatching when the water returns.
• Nymphs can burrow into the mud, or even crawl under damp leaf litter on the edge of a wetland pond, when water levels are low.
• Mosquitoes have very short life cycles, needing very little time and water to reproduce.
• Yabbies burrow and hibernate when water levels drop.

FOOD CHAINS

Food Chain: a ‘chain’ of organisms, through which energy is transferred. Each organism in the chain feeds on and obtains energy from the one preceding it, and in turn is eaten by and provides energy for the one following it. (e.g. plant to herbivore to carnivore)

Almost all food chains begin with plants, which transform and store the sun’s energy. Plants are called producers because they produce their own food. Many wetland inhabitants, including some insects and fish, eat plants. They are called primary consumers. These plant eaters are eaten by other animals at a wetland, such as larger fish and birds, which are called secondary consumers.

The ability to adapt to changing environmental conditions and the availability of good quality water, habitat, nutrients and sunlight are the main factors which affect wetland food chains. In turn, the ability of an animal to change its diet is reliant on the wetland ecosystem to provide an alternative food source. Human impacts, such as stormwater pollution, irrigation, land clearing and introduced species can have a major influence on wetland food chains. As in all ecosystems, if one component of a food chain is altered in some way (i.e. introduced species deplete the food supply or pollution kills the plants), this will impact on all aspects of the ecosystem.

Wetland Food Chain Example 1

Wetland Food Chain Example 2

We will discuss basic wetland food chains but, in reality, no ecosystem has simple independent food chains like the examples above. Food chains are more complex because of seasonal diet changes and multiple links. For example, not all bugs eat plants, many eat other insects. Fish eat a variety of bugs, depending on the season, and some fish species feed on plant matter. The pelican, like many wetland birds, eats a variety of fish and bugs. This complex interdependence of species is called a food web.

Links in a Food Chain 

SUN
The sun is the driving force of a food chain.

PRODUCERS

Producers are green plants that use the sun, water, nutrients and carbon dioxide to produce energy which they store as glucose in their cells. This process is called photosynthesis, and also produces oxygen. Producers are the largest group in a food chain. Basic producers such as phytoplankton and algae are found in all wetlands, along with many different species of aquatic and terrestrial plants.

CONSUMERS

Swamp Hens - Omnivores

All organisms which eat other organisms are called consumers. They include:

• HERBIVORES – animals that eat plants
• CARNIVORES – animals that eat other animals
• OMNIVORES – animals that eat plants and animals
• PARASITES – animals that live off other organisms
• SCAVENGERS – animals that eat dead animal carcasses

Congolli - Carnivores

Primary Consumers
Animals that feed on plants (herbivores) are the primary consumers.

Secondary Consumers
Animals that eat primary consumers are called secondary consumers.

DECOMPOSERS

Bacteria and very small organisms break down dead leaves and animals through a process called decomposition. Decomposers convert dead matter into small particles and gases which are released back into the water, air and soil. This recycling of nutrients is an important process in wetland ecosystems.

Blood Worm - Decomposer

THE IMPORTANCE OF PLANTS

There are many different types of plants living around, on and in wetlands. Some are only found in certain wetland areas, while others are common throughout South Australia . These plants are adapted to life in a wetland and are dependent on wetland flooding and drying cycles to provide nutrients, distribute seeds, break down leaf litter and control insect populations. Plants are extremely important to wetland ecosystems and help to maintain good water quality.

The function of plants at a wetland

Food Source
Plants are the first link in a food chain and many birds, fish, bugs and other animals depend on plant material such as seeds, root tubers and nectar to survive. Herbivores, which feed on plants, are a food source for wetland consumers. Algae, which often attaches itself to submerged water plants, rocks and sediment, is a rich food source for small creatures such as mayflies and water snails. Some invertebrates and bacteria feed on rotting plant matter (detritus) and microscopic particles of algae. These animals also help to improve water quality by removing dead plant material from the wetland.

Habitat
The trees and shrubs on the banks of a wetland and the emergent water plants (growing on the water’s edge) provide shelter and habitat for water birds, insects, yabbies and turtles. Submerged plants offer valuable habitat and safe areas for fish, frogs and aquatic invertebrates to feed, hide, breed and deposit their eggs.

Caddis Fly

Caddis fly larvae use dead leaves and reed stems to make their homes. They also feed on detritus.

The reed warbler makes its nest in large stands of the Common Reed, Phragmites australis. They feed on the feather-like seed heads of the reed, and take shelter in the long stems. A pair of nesting reed warblers requires at least 100m of thick Phragmites for nesting.

Common Reed

Oxygenating the water
Water plants produce oxygen during the photosynthesis process and release it into the water. This increases dissolved oxygen levels in the wetland, making the water suitable for aquatic life. Still wetlands and those which contain a lot of rotting organic matter often have low oxygen levels in the water and may become stagnant.

Bank stabilisation
Emergent plants such as bulrushes, common reeds and sedges help to stabilise the banks of wetlands and streams. Without these deep-rooted plants, much of the mud and soil would be eroded away during periods of high rainfall and rising water levels.

Slowing the water flow and reducing turbidity

As water passes through reeds and other water plants, it slows down. As a result, the particles of dirt and pollution are also slowed down and heavier particles settle to the bottom of the wetland (sedimentation) or are trapped at the base of the plants. Slowing the flow of incoming water also reduces bank erosion.

Removing excess nutrients
All plants need nutrients to grow. Wetland plants take up nutrients from the water and soil through their roots. Stormwater entering a wetland often contains high levels of nutrients, particularly phosphate and nitrate. These nutrients are present in fertilisers, detergents, animal waste and organic matter which gets washed into urban wetlands from gardens, parks, roads and footpaths . By removing these excess nutrients from the water, plants help to limit algal growth and thus reduce the chance of algal blooms.

Habitat Zones

Water plants associated with wetlands, rivers and creeks are often called macrophytes. There are many different types of macrophytes, which are most commonly grouped according to their habitat zones and growth form.

This diagram shows some of the different habitats where wetland plants are found.

Growth Forms

General categories used to group different species are: Trees, shrubs and grasses Submerged Emergent Floating attached Free floating

Trees and Shrubs
The trees and shrubs found at wetlands usually grow above the highest water level, in areas that are only wet for short periods of time. Species include: Eucalypts, Wattles, Sheoak, Grasses and Herbs.	Eucalypt Golden Wattle

Emergent Plants
These plants are usually rooted in mud or silt with their stems, leaves and flowers growing above the surface of the water. Some plant species can grow in water up to 2 metres deep. These plants adjust their growth cycles to suit changes in water levels. Common emergent plants are Reeds, Sedges (e.g. Cyperus sp.), Rushes (e.g. Juncus sp.) and Knotweed.	Knotweed Rushes

Submerged Plants
These plants are also rooted in the silt and mud of the wetland but their stems, leaves and flowers are underwater. Submerged plants have a number of adaptations which makes them different from other water plants, such as; Stems which are long enough to allow for changes in water levels, Photosynthesis is possible in poorly lit waters, Water movement does not damage the submerged leaves and Oxygen, released during photosynthesis, is reused through the plant’s roots. Examples of submerged plants are; Hornwort, Pondweed and Watermilfoil.	Hornwort

Floating Attached
While these plants are also rooted at the bottom of the wetland, their long stems reach the water’s surface and their leaves float on the water. Although some leaves may be under water, the flowers are always protruding above or floating on the surface of the water. Examples of such plants are Waterlilies, Nardoo and Crassula.	Crassula

Free Floating

Not rooted in the ground, these plants float unattached in the water, usually floating on the surface. Some species become dormant when water levels drop and others are able to drop their roots in the drying mud. Common examples of these plants are Azolla and Duckweed. Azolla is often seen as a green cover on still waters, however in full sunlight it can be pink or red in colour. Duckweed appears as a green cover on still water. It is an important food source for some birds and aquatic animals.

Azolla

Eutrophication

Eutrophication is a problem commonly found in wetlands, dams and reservoirs due to an increase of nutrients in the water, especially phosphorus. In particular, phosphorus from sewage treatment works, and run-off of nitrates from farming zones in catchment areas.
The increase in nutrients causes problems such as increased plant growth. In an urban wetland system, algal blooms are detrimental to the ecosystem in a number of ways:

• Algae uses oxygen, which would normally support fish and invertebrates, causing these organisms to die when algal populations are very dense.
• Algae can grow in such abundance that they can change the colour of the water to red, brown or green!
• Some algae species can grow in such abundance they can kill fish by clogging their gills.
• Blue-green algae can produce toxins. The toxins are released with the death of these algal cells or when consumed.
• Some algae can make water taste like cucumbers! They can also make filtration difficult and costly by clogging filters and pipes.
• Other plants can choke a waterway, growing 2 metres thick, when exposed to high levels of nutrients such as phosphorus and nitrates. Image: bluegreen algae2

Plant Invasion !
Hardy, fast growing plants such as Willows, Water Hyacinth, Salvinia, Bulrushes, Common
Reeds and Pond weed can dominate and choke a waterway, given the right conditions. Although the last three plants are native, under conditions of high nutrient levels, they become invasive and difficult to control. Blue-green algae, also native, can be the most sinister invasive plant as it contains toxins which can impact on the health of fish, livestock and humans.