Biology SS 2 Week 5
Topic: Fresh Water Habitats
Introduction
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:
- 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
- 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
- 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. Temperature at the surface of the water varies slightly with that at the bottom of the water
- 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
- 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
Major Ecological Zones of Fresh Water 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 intertidal 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, duck weed, 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 lily, 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
Lotic Fresh Water Habitat
In a lotic fresh water habitat e.g. rivers, there exist two zones. These are:
- Pool zone: In 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
Some Plants and their Adaptive Features
- Water lily (Nymphae): 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 mucilaginous 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
- Hornwort (Ceratophyllum): 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
Some Animals and their Adaptive Features
- 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 float (buoyancy) in water. They also have gills for respiration
- Duck: It has webbed digit on its feet for easy locomotion and serrated beak for sieving food inwater into its mouth
- Lung fish (Protopterus): The animals obtain oxygen through the gills but when the water dries out during the dry season, they dig into the mud and breathe with lungs until the rain comes again
- Hydra: It has slippery surface, hooks and suckers for attachment to water particles
- Pond skaters (Gerris): This animal has long legs with which it skates on water surface
- 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
Factors Affecting Fresh Water Habitats
Factors which affect fresh water habitats include:
- Temperature
- Relative humidity
- Wind
- Rainfall, etc.
