Wetland Curriculum Resource
Unit 3. Ecology - Background for Educators
Nearly 1/4 of all the world's existing wetlands lie within Canada. Although more than 14% of Canada's surface area is covered by them, it is estimated that, during the past 150 years, one-seventh of Canada's original wetland habitat, over 20 million hectares, has disappeared. In southern Ontario, this loss is even more startling. More than 75% of the wetlands that existed when the first European settlers arrived here, have vanished.
This loss continues. Each year many valuable hectares of wild life habitat disappear. Overnight, wetlands that took thousands of years to form, are transformed into parking lots, subdivisions, garbage dumps, farmlands, or shopping malls. The wetlands that remain become isolated from each other or have impaired ecological functions. With this loss of wetland habitat, there has been a decline in numbers of plant and animal species.
The main threats to wetlands include:
Wetlands are generally classed as lands that are covered with water, usually less than 2 metres deep. Each is a special ecosystem, a self-supporting community of plants and animals interacting with one another and their environment. There are five main types of wetlands:
Ponds are small wetlands with a well-defined shoreline. The water in a pond is fed mainly by rain or melted snow. Some are formed when seepage occurs from the water table, or if they are deep enough to be supplied by the underground water table. As a result, the water may be easily lost when the water table drops. Ponds are often bordered with cattails, trees, and shrubs, and contain aquatic plants such as water lilies and pondweeds.
The open water in a marsh is either standing or slow moving, and the level can fluctuate between periodic flooding, or drying. Marshes are productive and have a great diversity of plant and animal life, although there are usually no trees present. The main aquatic plants include cattails, bulrushes, arrowheads, and waterlilies.
A swamp is easily identified because it is a flooded wooded area. The most common trees in a swamp are red maple, elm, black ash, alder, and willow. A carpet of herbs and mosses is usually present. Water levels generally fluctuate (look for water marks on tree trunks which indicate high water levels), but the bottom is water-logged and does not dry out.
In a bog, low oxygen levels and the slow decomposition of plant material forms an acidic material known as peat, which accumulates in layers. These layers hold a tremendous amount of water, resulting in a high water table. The decomposition also stains the water brown, almost tea-like. Bogs have very little open water and receive most of their water from precipitation. The most common plant in a bog is Sphagnum, a moss which grows in thick carpets. Because of the lack of available nitrogen in a bog, some plants require special adaptations. Sundew and pitcher plant are carnivorous plants commonly found in a bog. They obtain nitrogen by trapping and eating insects. Other plants commonly found include Labrador tea, leatherleaf, sweet gale, and cranberry. Black spruce or tamarack are the dominant tree species.
A fen also has layers of peat, but the Sphagnum moss is usually replaced by sedges, which become the dominant plant. Better growing conditions exist because of nutrient rich ground water, and the low rate of decomposition. The soils are only slightly acidic, and as a result, a greater diversity of plants, such as reeds, grasses, and shrubs are found.
While many people thinks of wetlands as "waste land", wetlands are important:
To some people, the earth may be viewed as a system or series of systems, or simply as a living organism. This concept, known as the Gaia Theory, was first proposed in the 1970s by the British inventor and scientist James Lovelock. He named the theory after the Greek goddess of Mother Earth, Gaia.
By observing the earth's atmosphere, Dr. Lovelock discovered it was comprised of a combination of gases created by plants and animals living on the earth. He then concluded that the life processes of these plants and animals were dependant upon these gases in the atmosphere to sustain their lives.
The Gaia Theory states that the earth functions as a living organism, and not simply as an environment which supports life. The earth is a self-sustaining system that can modify its surroundings in order to maintain conditions that are favourable to life. Hence, living organisms can respond to these conditions by adapting to their environment, but are also capable of changing their environment to make it more suitable on a global perspective.
There are a number of books on the Gaia Hypothesis but one interesting resource for schools is:
Gaia: An Atlas of Planet Management (1984). Dr. Norman Myers (ed.) Anchor Press/Doubleday & Co. Inc., pp. 266
Biological diversity or biodiversity refers to incredible variety of life on earth - all species of plants, animals and microorganisms. Scientists have named about 1.4 million of these living things but it is thought that there are between 10 and 100 million different species of life on earth. But, our planet's biodiversity is disappearing at an alarming rate. Although estimates vary, many experts believe that 100 species are lost each day.
Biodiversity conservation is one aspect of UNESCO's environmental education mandate. The world's scientists, conservationists, and government agencies have recognized the role of biodiversity in combatting poverty; addressing population issues; creating equitable social and economic conditions; and ensuring a healthy environment and sustainable use of resources to benefit present and future generations. Biodiversity cannot be preserved, utilized or fairly shared without knowledge of what exists and how it is changing.
Biodiversity conservation is more than single species conservation and includes the diversity of landscapes, ecosystems, species and genetic material, and how these change and relate to each other.
The loss of biodiversity is a concern, as is the rate of that loss. Each plant, bird, frog, snake, beetle or other living creature brings its own special beauty to the world. But, as each species disappears, we lose not only its beauty, we lose an important storehouse of genetic information. This genetic information might have provided a promising new medical cure, like the cancer treatment extracted from the Rosy Periwinkle, or it might have allowed us to breed a fungus-resistant food plant, reducing our needs for chemicals. Also, we can never fully estimate the impact of losing any individual species. The loss of one plant species might cause the unforeseen loss of an insect that feeds on it or that lays its eggs on its stem, or perhaps a bird that uses it to build a nest.
Wetlands support a wide diversity of life and as each wetland disappears, we risk the loss of the species that depend upon it for their survival. Wetland studies, either in the classroom or in an outdoor experience, are intended to foster environmental awareness leading to action at the individual and community level. Studies are best limited to linkages along, and between, watersheds. A bioregion is perhaps the largest ecological limit that promotes understanding and each has a unique and often intertwined cultural and natural history.
Plants are a key measure of biological diversity in a wetland. They provide food, water, shelter, resting places, and nesting sites for wild life and thus affect the number and kinds of animals a wetland can support. For example, an aquatic plant may provide little or no food value but its large leaves may provide excellent cover, protecting a frog from predators or the elements. Other plants are used for nesting because of their buoyancy.
Wetlands plants vary greatly and they are specially adapted for different habitats. For example, submergent plants living in the slow moving water of a marsh posses fibrous stems that to allow them to move with the flow of water. The pitcher plants is adapted for life in nitrogen-poor northern bogs. It can obtain the nitrogen it needs from the insects it traps and digests.
For Information about biodiversity contact:
These are only a few of the many groups interested in preserving biodiversity. These groups have a specific interest in the topic or have recently produced education materials about biodiversity:
Canadian Biodiversity Institute, 3351 Blanchfield Rd. Osgoode, ON K0A 2W0
Biodiversity Convention Office, Environment Canada, Ottawa, K1A 0H3
Toronto Zoo, Education Department, 361A Old Finch Ave. Scarborough, ON M1B 5K7
Sierra Club Canada, 1 Nicholas St. Ste. 620, Ottawa, ON K1N 7B7
Western Canada Wilderness Committee (WCWC), 20 Water St. Vancouver, B.C. V6B 1A4
An ecosystem consists of plants and animals interacting with their environment. It consists of two interrelated parts: the living (biotic) community including plants, animals and microscopic life, and the non-living (abiotic) environment made up of water, temperature, wind, and chemicals and nutrients like carbon dioxide and nitrogen. All ecosystems need energy and this is provided by the sun (see "Food Chain and Wetland Energy Cycle") .
Like all ecosystems, the parts of a wetland ecosystem interact and, when one part is altered, the change affects all others. In the following sections we will look at these different parts of this ecosystem and the different processes within the system to better understand this complex, interacting ecosystem. We will look at:
Every living organism interacts with other species and has a specific place in the ecosystem. This is called its niche. For example, in a marsh the niche of an adult bullfrog differs from that of the young or juvenile bullfrogs. Adults sit along the shoreline and feed on land- and water-dwelling invertebrates, such as insects. They will also eat small vertebrates, like snakes and frogs. Juvenile bullfrogs sit out in deeper water (often around lily pads) and eat invertebrates associated with this habitat. This not only reduces competition for food but it protects the smaller bullfrogs from being eaten by their larger relatives.
Within each ecosystem, each animal can be said to have its own habitat. The habitat provides for its four basic needs: food (energy), water, shelter, and space. Individual habitats can vary in size, and an ecosystem can support many different habitats.
A population is a group of individuals of the same species living together in the same area. For example, one pond may have a large population of green frogs, meaning that many individuals live there. When several populations of different organisms are present, a community exists. For example, a marsh community would include individual populations of green frogs, Great Blue Herons, snapping turtles, dragonflies, and cattails, as well as numerous other species. A community is a naturally occurring group of different organisms living together in the same area.
The soils in wetlands are full of organic matter. The amount of organic matter increases as succession advances in a wetland (See "Processes in the Wetland Ecosystem: Wetland Succession"). Organic levels increase as the annual level of accumulation of dead plant and animal material exceeds the annual decomposition of these materials. The rate of decomposition is slowed because of relatively low temperatures (especially in cool regions), an increase in pH or low oxygen, and the saturated conditions.
Drainage in wetlands is usually restricted by an underlying impermeable layer of soil, bedrock or hardpan (a cemented or compacted layer of soil, usually clay). Although water levels fluctuate in a wetland (usually decreasing during the summer months from evapotranspiration), by late fall the water levels are restored. The ability to support such high water levels is important, especially in the spring when wetlands receive meltwater and run-off.
Soil pH values vary with the amount of organic matter present. Wetlands in the early stages of succession typically display a neutral or basic environment. As succession advances and the amount of organic matter increases, acidic conditions develop because of decomposition and the resulting carbon dioxide that is produced.
Individual soil types vary from region to region. Along with organic matter, soils also contain mineral matter which varies between soil types. These include sand, silt, and clay. The factors which determine the formation and characteristics of soil are:
Plants form the basis of all life on earth. Without the energy that they provide, no other life could exist. Wetland plants serve many other functions beyond that of being a food or energy source. Floating mats of cattails provide safe nesting sites for many marsh birds, and muskrats make their homes of cattails and other marsh plants. The broad leaves of emergent plants shelter tiny frogs from predators and fish hide in the thick growth of aquatic plants. Insects lay their eggs on their stems and leaves and amphibians may use the shelter of plants to harbour their eggs. The Redwing Blackbird and Yellowthroat stake their territories and sing their mating songs from a cattail perch. Floating lily pads and cattail mats are used by some animals as a platform for drinking or sunning, or as a pathway for moving quickly over water. Underneath, an aquatic predator may use the lily pad as shade, or as hiding place while it searches for its next meal.
In pond and marsh ecosystems, aquatic plants tend to grow in distinct zones. Emergent plants are rooted in or near water, with the main stem and leaves growing above the water. Submergent plants grow entirely below the water surface, often forming dense masses. Floating plants have leaves which float on the surface of the water. They may have roots or they may float freely.
Wetlands burgeon with animal life; from the tiny microorganisms that live in their water and soil to permanent mammal residents, like the beaver and muskrat, or even larger mammals, like moose and deer, that come to drink or feed at the water's edge.
Most wetland-dwelling animals have special adaptations such as long legs, webbed feet, bills for straining small plants and animals from water, or waterproof fur. As wetlands disappear, animals that depend upon wetland habitats also disappear.
Succession is a natural process describing the sequential changes in plant and animal communities. Succession may be affected by external processes, such as a change in water levels, or internal processes in which each new community creates an environment favourable for colonization by other plant and animal species.
The pioneer stage of wetland succession begins with a pond bottom without plant life. The earliest life forms to inhabit the pond are plankton, which include plant and animal life. They arrive by insects or by the wind which deposit them in the water. The high light levels and nutrient levels favour algal growth. When plankton dies, it sinks to the bottom and decomposes to form a layer of muck. This layer of muck provides a growing medium where deep water submergent plants can take root. At this time, fish and other large organisms may arrive, migrating by way of inlets, or brought in by other animals (birds have been known to drop their prey while carrying it). As the surrounding land begins to erode, sediments begin to deposit on the bottom of the pond. The improved conditions now give rise to other plants groups such as floating pond lilies.
Pond lilies prevent light from reaching the bottom of the pond and eventually the submergent plants begin to die off. The bottom slowly rises as more sediments and organic material accumulate. This process can take anywhere from a few years to thousands of years, determined primarily by climate, but also influenced by soil, topography and drainage. As the water becomes shallower, the shoreline plant community spreads inward. Eventually, grasses, other plants, small shrubs and trees move in. Depending upon the ecosystem, this may be the start of a new forest. Like wetlands, forests are dynamic, and the new forest will continue to go through a series of changes that lead to a mature climax forest.
During succession, the following progressional changes occur within the ecosystem:
Wetlands are dynamic with species and community composition reflecting changing water levels. Part of the diversity of wetlands is dependent upon this dynamic change.
Wetlands provide varied and diverse habitats and support a wide range of food chains and predator-prey relationships. While the sun is the primary source of energy, the different plants and animals must convert the energy into different forms in order to use it.
The transfer of energy within a community occurs at different levels in the food chain. There are three levels: producers, consumers, and decomposers.
Plants are the primary producers of an ecosystem. Plants make their own food by capturing and using the sun's energy during photosynthesis. All life in an ecosystem depends directly or indirectly on the initial energy produced by plants.
Organisms that obtain their food by eating plants or other organisms are called consumers. There are three types of consumers: herbivores (plant-eaters), carnivores (meat-eaters) and omnivores (all-eaters). We also refer to animals as predators, those carnivores that feed on live animals (prey) and as scavengers, animals that feed on dead plants and/or animals.
In a wetland, typical herbivores would include a moose, beaver, muskrat, and duck. Wetland carnivores include the Great Blue Heron, trout, Bullfrog, Snapping Turtle, Marsh Hawk (Northern Harrier), and weasel. Omnivores found in a wetland would include a Painted Turtle, Red Fox, Raccoon, and Striped Skunk. Snapping Turtles, snails, and crayfish are wetland scavengers.
Decomposers are organisms which break down non-living organic matter (tissue and wastes), and recycle valuable nutrients in the ecosystem. The most common decomposers are bacteria and fungi. Decomposers are very important to an ecosystem. Without them, nutrients could not be recycled.
Organisms found in an ecosystem are all linked together through predator-prey relationships, commonly referred to as a food chain. A food chain shows the transfer of energy from one trophic level to the next. The energy produced and stored by plants is passed along through the ecosystem in a series of successive eat and be eaten processes. The first trophic level in a food chain begins with plants as producers. When a herbivore feeds on a plant, it becomes a first-order consumer. When a carnivore feeds on the herbivore, the carnivore becomes a first-order carnivore and second-order consumer. When that carnivore is preyed upon, the predator becomes a second-order carnivore and third-order consumer. The following diagram illustrates a typical food chain:
Every organism requires energy to maintain its life processes. A considerable amount of potential energy is lost as heat energy or unconverted waste in the movement through each level. About 85% of the energy transferred from each trophic level to the next is lost to growth, respiration, movement and similar processes. The remaining 15% is accumulated in the ecosystem and only this accumulated energy is available to the organisms at the next trophic level. Eventually, the amount of energy at the top of the food chain is so small, that only a few organisms can be supported. The loss of energy at each trophic level limits the number of steps in a food chain to four or five, and the number of organisms found at each trophic level decreases as you go up a food chain. Energy flow in an ecosystem is one-way. Once lost, it must re-enter the ecosystem from the outside (the sun).
No one organism survives wholly on another. Food chains are interconnected, because many organisms will eat more than one type of food. As a result, organisms can occupy a trophic level in more than one food chain. When food chains interconnect, a food web is formed.
Green plants are unique in that they have the ability to produce their own food using energy from the sun. This process is called photosynthesis (photo - light, synthesis - putting things together). The key component in this process is chlorophyll. Chlorophyll is a green pigment found in plants which functions as a catalyst in the photosynthetic process. It does not become involved in the chemical reactions, but rather, captures energy. Chlorophyll is found in the chloroplasts of the leaves and stem of the plant.
All organisms depend upon photosynthesis. They rely on the food produced by plants either directly or indirectly. Plants require four materials for photosynthesis, including chlorophyll, light energy from the sun, water, and carbon dioxide. The following equation outlines photosynthesis:
light energy carbon dioxide + water --------> glucose + oxygen 6 CO2 + 6 H20 -------> C6H12O6 + O2
Photosynthesis occurs in two stages. Light is required for the first stage, or light phase. During this stage, the chlorophyll traps the light energy from the sun and this energy splits the water molecule. The hydrogen atom remains in the chloroplasts, and the oxygen atom passes out of the leaf through the stomates (tiny openings in the leaf by which oxygen, carbon dioxide, and water vapour enter and exit the leaf). During the second stage or dark phase (because light is not needed), the hydrogen atoms combine with carbon dioxide that has entered through the stomates, producing a new glucose (sugar) molecule. The glucose molecule stores the chemical potential energy which will be released during respiration.
Photosynthesis only occurs in plant cells in the presence of chlorophyll. Even if the plant is not green photosynthesis still occurs as these plants still possess chlorophyll in their cells. The green pigment is masked by other pigments such as xanthophylls (yellows) and carotenes (oranges). These pigments also capture energy from the sun, and may assist in the transfer of energy to chlorophyll molecules.
The presence of other pigments in a plant may function to trap different wavelengths of light energy. The various colours contained within the visible spectrum of light, possess different wavelengths. The darker colours (green, blue, and violet) have shorter wavelengths, while the lighter colours (red, orange, and yellow) have longer wavelengths. The shorter the wavelength, the more energy the light contains, and vice versa. Most land plants absorb violet and blue rays.
Some green and yellow rays are absorbed, but most are reflected, or pass through the plant. That is why most plants are green, because the rays that are reflected are the rays that are seen. Very little orange or red rays are absorbed. In oceanic conditions, as depth increases, light intensity decreases, allowing only certain pigments to absorb wavelengths. Water absorbs most of the red and violet rays. Brown shallow water plants absorb blue, green, and yellow rays, while deeper red plants absorb blue and green rays.
All living organisms require a continuous energy supply to maintain their life functions. Organisms are able to maintain this supply of energy through a process called respiration. Respiration occurs in the cytoplasm and mitochondria of cells in all living organisms. It is a series of chemical reactions where energy is released from the breakdown of glucose molecules produced during photosynthesis. Plants store this energy in roots, stem, and leaves. Eventually, the plant uses stored energy or it is passed on to the animal that eats the plant.
Although we often use the words breathing and respiration interchangeably, they are different. Breathing is an exchange of gases between the body and the environment, where oxygen is transported by the blood to cells, and carbon dioxide is removed. Breathing does not involve chemical reactions but respiration does. In respiration, chemical reactions occur that break down glucose molecules and transfer energy. Respiration requires oxygen which combines with the atoms in the glucose. The glucose molecule oxidizes releasing the heat energy. The following equation outlines respiration:
glucose + oxygen -----> carbon dioxide + water + energy C6H12O6 + O2 CO2 + H2O
Respiration is similar to photosynthesis, in respect that they both require the same four basic materials to occur. Though similar, they are opposite reactions. The following describes their differences:
Photosynthesis and respiration are the two basic life processes responsible for maintaining the recycling of carbon and oxygen in nature. During photosynthesis, plants obtain water and carbon dioxide from the atmosphere. As the plant absorbs the sun's energy, the water molecules split. The hydrogen atoms combine with the carbon dioxide to form carbohydrates (glucose). When this occurs, oxygen is released into the atmosphere. During respiration, the glucose molecules, which contain carbon, are oxidized and carbon dioxide is released into the atmosphere. The atmosphere normally contains 21% oxygen and 0.04% carbon dioxide and 78.09% nitrogen.
Another important factor in the carbon-oxygen cycle is the production of organic compounds. These are produced from the carbohydrates formed during photosynthesis. Organic compounds are essential in the formation of protoplasm, a complex system of substances that establishes the living condition through chemical activity. All organic compounds contain carbon. When the initial carbohydrates are consumed by a plant-eating animal, the carbon-containing organic compounds are passed on to other organisms in the food chain. When the organisms die, the carbon in the decaying bodies is released into the atmosphere as carbon dioxide. Plants and animals are essential in the carbon-oxygen cycle. Producers, consumers, scavengers, and decomposers all recycle carbon dioxide and oxygen into the atmosphere. Rocks and mineral fuels also contribute to the level of carbon dioxide in the atmosphere. Coal, natural gas, and oil all contain carbon, since they are transformed remnants of plant life that existed in the geologic past. The burning of these fuels releases carbon dioxide into the atmosphere. Because coal, oil, and gas are the preserved remains of plants and/or animals, they are often referred to as "fossil fuels". The oceans serve as a valuable storage area for most of the earth's carbon, capable of holding 50 times the amount of carbon that is found in the atmosphere. Oceans absorb excess amounts of carbon from the atmosphere and then slowly release it again. With the excess burning of fossil fuels today, carbon dioxide is being produced at a greater rate than the oceans can absorb it. This is a problem that is contributing to global warming.
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