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Biology Field Trip. Freshwater stream. Introduction. Field site location: Freshwater stream habitat at Ho Chung Date: 10 th May 2004 Time: 1:00 pm – 4:00 pm Weather: sunny, hot and windy. Physical factors. Light intensity Temperature Current speed. Light Intensity.

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Biology field trip l.jpg

Biology Field Trip

Freshwater stream

Introduction l.jpg

  • Field site location: Freshwater stream habitat at Ho Chung

  • Date: 10th May 2004

  • Time: 1:00 pm – 4:00 pm

  • Weather: sunny, hot and windy

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Physical factors

  • Light intensity

  • Temperature

  • Current speed

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Light Intensity

  • In still water, there are many suspended solids and the turbidity is relatively high, which prevent the penetration of sunlight

  • In running water, the slope is steeper which limits the penetration of sunlight

    Result: the light intensity in the stagnant water is higher than that of the running water.

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  • In running water, rapid pool avoid and reflects sunlight from direct penetration

  • As light can only penetrate to a limited distance, so light intensity increases and temperature increases

    Result: the temperature in still water is higher than that of running water

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Current Speed

  • The freshwater bed is not a smooth surface rock layer.

  • Rocks and sand sink to the freshwater bed. increases the contact area of water and the friction is present.

  • more rocks and sand, increases the friction of the water and thus the current speed decreases.

  • Gradient of freshwater bed is also a factor affecting the current speed, but it is not included in our investigation.

    Result: the current speed in running water is

    higher than that of still water

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Chemical factors

  • pH value

  • Dissolved oxygen

  • Phosphate content

  • Ammonia content

  • Conductivity

  • Total suspended solids

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pH value

  • Decomposer in muddy area of the station might cause decomposition at the pond bottom, lead to production Carbon dioxide(rocky in nature might not be suitable for decomposers to grow)

  • Erosion of minerals from stones and decomposition of detritus

  • Acid rain & carbon dioxide dissolved in water.

Result: pH value in running water is higher than that of stagnant water

( both value are lower than 7)

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Dissolved oxygen

  • Dissolved oxygen in running water is higher than in stagnant water. Since animal found in still Water current is more than in running water

  • Water current is faster in running water than in still water

  • Fast flow of water can replenish the oxygen content quickly

  • Result: more D.O. in running water

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Phosphate content

  • The phosphate in stream is came from the erosion of the stone or came from fertilizers & detergent

  • Phosphate is washed away because the current speed of water is high

    Result: thus, still water contains more phosphate than running water (lower than the government standard)

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Ammonia content

  • Comes from dead body of plants & animals & their metabolic wastes

  • as the current speed in running water is higher, it washes away the ammonia content, so it decreases

    Result: The ammonia content in still water is higher than that of running water

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  • Due to the presence of charged ions from mineral concentration in still water , the decomposition and dilution effect decrease

  • Ions accumulated in slow current zone, so concentration of ions increases and the conductivity increases.

    Result: the conductivity of still water is higher than the running water.

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Total suspended solids

  • The current speed of running water is high, so it washes away the suspended solids

  • The still water is muddy and also the human disturbance, so the current speed is slower and the solids remain at the slow current zone.

    Result: the suspended solids in still water is

    higher than running water

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Adaptation of freshwater animals

  • Mayfly nymph

  • Goby

  • Blood Worm

  • Mosquito

  • Pond skater

  • Dragonfly Nymph

  • water cricket

  • Damselfly nymph

  • Water skater

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Mayfly nymph

  • herbivores and detritivores

  • Flattened body & legs for dripping on to the surface of stones

  • have three ‘tails’ for possessing a long central filament

  • grow slowly

  • They are found in fast-moving water and slow-moving water

    Body Characteristics:

  • 5-28 mm long

  • 6 legs

  • gills present on the abdomen

  • 2 or 3 long thin “tails”

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  • Depressed head with a wide mouth

  • The mouth is large

  • Pelvic fins fused to form pseudosucker

  • It feeds on smaller fish, shrimps, insect larve, and aquatic insects

  • 10—14 cm in length.

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Blood Worm

  • Red colour

  • Blood gills

  • Some have green blood

    Water skater

  • Long, thin legs

  • hair on legs

  • thin, flattened body

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Water cricket

  • strong & thick body

  • dark brown with 2 orange lines down the back

  • orange abdomen

  • About 2mm in length

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Damselfly nymph

  • 3 terminal caudal gills

  • No rectal gills

  • Large, mask-like labium

  • More slender than dragonfly nymph

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Dragonfly Nymph

  • pond species with long thin and rather delicate legs

  • opposed to the common torrent stream species

  • has a flatted body and stout flattened legs.

  • the mask is very large and can be seen covering the front of the face.

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  • large anterior ends formed by head and thorax

  • a part of plates at the end for swimming

  • Larva: bearing 9 abdominal segments

  • bearing and gill at the 9th segment

  • dark brown to black in colour

  • 6-9mm long

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From the investigation, we found out that the water is clean from all factors (lower than the government standard)

Both water zone are scored for 2 marks

  • Learn different kinds of species

  • Physical and chemical factors in a habitat

  • There are interaction between matters

  • Protect our environment

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~The End~

From: Lingnan Hang Yee Memorial Secondary School