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Lesson Note

Subject: Biology
Topic: Aquatic Habitat
Subtopic: Fresh Water Habitat
Lesson Objectives: At the end of the lesson, learners should be able to:

  1. Define fresh water Habitat;
  2. State the characteristics of fresh water habitat;
  3. Identify the Zones in fresh water habitat;
  4. State some adaptive features of the plants and animals in the fresh Water habitat;
  5. Construct a food chain of the organisms in fresh water habitat;
  6. Mention the factors affecting fresh water habitat.

Lesson Summary/Discussion

FRESH WATER HABITATS

Definition: Fresh water habitat is a body of water formed mainly from inland waters and contain very low level of salinity. Examples of fresh water habitats are rivers, ponds, streams, springs and lakes.

Types of Fresh Waters
Fresh waters are classified on the basis of their mobility. Based on this, two types are identified.
These are:

1. Lotic fresh waters: These include all running waters which can flow
continuously in a specific direction. In
other words, these are flowing or running waters, e.g.rivers, springs and streams.

2. Lentic fresh waters: These include
standing or stagnant waters. These waters do not flow nor move. Examples of lentic fresh waters are lakes, ponds, Swamps and dams.

Characteristics of Fresh Water Habitats
The following characteristics are associated with fresh water habitats:

  • Low salinity: Fresh water habitats normally contain very low level of salts, It has about 0.5% of salt compared to about 3.5% for sea water.
  • Seasonal variation: Some fresh water habitats like streams and rivers normally dry up during the dry season while others have their volume reduced. The volume of water in rivers also increases during the rainy season. Turbidity and fast flow of rivers are also high during the rainy season than in dry season.
  • Currents: Currents can affect the distribution of gases, salts and small organisms in fresh water habitats such as rivers and streams.
  • Small in size: Fresh water habitat is usually very small compared to the ocean water which is about 75% of the earth surface.
  • Variation in temperature: The temperature of fresh water habitat usually varies with season and depth.
  • High concentration of oxygen content: Oxygen is usually available in all parts of the fresh water especially in the surface of the water.
  • Shallowness of water: Most fresh water habitats are very shallow hence sunlight can easily penetrate through the water to the bottom.

Major Ecological Zones of Fresh Water

a. Habitats: The zones of a lentic fresh water habitat, e.g. lake are similar to those of the marine habitats but there are no supratidal and inter-tidal zones.

There are two major zones in a lentic fresh water
habitat. These are littoral and benthic zones.

  • Littoral zone: Littoral zone is the shallow part of fresh water habitat. It contains several plants and animals. The littoral zone has rooted vegetation at its base. It has the highest level of primary production because sunlight can easily penetrate the zone. hence photosynthetic activities are common. Plants associated with this zone include Spirogyra, Chlamydomonas, water lettuce, water fern, duckweed, diatoms and sedges. Animals associated with this zone include water fleas, water snails, flatworms, frogs, toads, water skaters, ducks, snakes, crocodiles, tadpoles, Hydrae, and hippopotamus.
  • Benthic zone: Benthic zone is the deepest parts of the lentic fresh water habitat. The benthic zone does not have rooted vegetation like the littoral zone although flowering plants may occur at its surface. Plants associated with the benthic zone have well developed root system in the mud. These plants include water Iily, water arum, ferns, crinum lily, commelina and grasses. Animals associated with the benthic zone include protozoa, rotifers, Hydrae, Tilapia fish, mud fish, cat fish, leeches, caddish fly larvae, larvae and pupae of mosquito, water snail, water Spider, crayfish, water scorpion, water boatman and water bugs

b. Eutrophication: Eutrophication is the excessive growth of plant life or algae in water course or bodies caused by increase in organic nutrients or minerals leading to the death of aquatic organism.
Causes: (i) overuse of fertilizers which chain into water bodies (ii) sewage discharge from fish farming

Zones in Lotic Fresh Water Habitat
In a lotic fresh water habitat e.g. rivers, there exist two zones. These are:

  • Pool zone: ln this zone, water is relatively slow and calm.
  • Rapid zone: In this zone, water is very fast. The lotic fresh water habitat is not as stratified as the lentic fresh water habitat.

Adaptive Features of Some Organisms in Fresh Water Habitat

Adaptive Features of Fresh Water Plants

  • Water lily (Nymphaea): The plant has air bladders, expanded shape and light weight which keep it afloat. It has long petioles attached at the centre of leaf blade which prevent them from being drawn under water by the current.
  • Water Hyacinth (Ipomea grassipis): They have cavities and intercellular air spaces which give them the ability to float or maintain buoyancy on water.
  • Spirogyra: The plant has mucilagenous cover which protect them in water.
  • Water lettuce (pistia): Water lettuce has hairs on their leaves which help them to trap air and enable them to float.
  • Hormwort (Ceratophylum): The plants have submerged or thin dissected leaves which increase their surface area to sunlight and gaseous exchange.
  • Water weed (Elodea): The plant has a long and flexible submerged petiole which enables it to swing with water currents.

Adaptive Features of Fresh Water Animals

  • Hydra: It has slippery surface, hooks and Suckers tor attachment to water particles.
  • Pond skaters (Gerris): This animal has long legs with which it skates on water surface.
  • Protozoa: These animals possess contractile vacuoles which enable them to carry out osmoregulation in water.
  • Tilapia fish: They have swim bladders which enable them to stay (buoyancy) in water. They also have grills tor respiration
  • Duck: It has webbed digit on its feet for easy locomotion and serrated beak for sieving food in water into its mouth.
  • Lung fish (Protopterus): The animals obtain oxygen through the gills but when the water dries out curing the dry season, they dig into the mud and breathe with lungs until the rain comes again.
  • Water boatman: This animal can carry bubbles of air with it as it goes below the water surface to the bottom and use these as their air supply (respiration) under water.

Food Chain In Fresh Water Habitats

Diatoms, Spirogyra, detritus, water lily and most of the flowering plants are the major producers in fresh water habitat. Some examples of food chains are:
1. Diatoms >Fish fry >Tilapia
2. Detritus > Worm > Shrimps > Birds
3. Spirogyra >Tadpoles >Carps > King

Energy Flow In Freshwater Habitat

  • Energy from sun radiant energy/solar energy is received.
  • It is then absorbed/trapped by green plants/algae/phytoplanktons of fresh water/pond/stream river.
  • This is used in photosynthesis, to manufacture organic substances.
  • Zooplankton/fish/animals of the pond would now depend or feed on the green plants for food.
  • The feeding is direct if they are herbivores as the plants are eaten by herbivores.
  • The feeding is indirect if they are carnivores as herbivores are eaten by carnivores.
  • When plants or animals/organisms die or when animals discharge their droppings wastes, they are decomposed via the action of saprophytes/fungi/bacteria-
  • decomposers/micro-organisms.
  • By so doing, energy is lost.

Factors Affecting Fresh Water Habitats
Factors which affect fresh water habitats are both biotic and abiotic factors.

1. Biotic Factors

  • plants/producers
  • animals/consumers
  • parasites
  • decomposers/saprophytes/micro organisms
  • predators

2. Abiotic Factors

  • temperature
  • Sunlight
  • wind
  • inorganic compound
  • turbidity/suspended transparency
  • topography
  • dissolved oxygen
  • pH/dissolved
  • water current/currents particles
  • rainfall/precipitation

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Done studying? See previous Lessons in Biology

  1. Define fresh water Habitat.
  2. What are the characteristics of fresh water habitat?
  3. Mention the Zones in fresh water habitat.
  4. State some adaptive features of the plants and animals in the fresh Water habitat.
  5. Construct a food chain of the organisms in fresh water habitat.
  6. What are the factors affecting fresh water habitat?

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