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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

Biology Field Trip

Freshwater stream

  • 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
Physical factors
  • Light intensity
  • Temperature
  • Current speed
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.

  • 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

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

Chemical factors
  • pH value
  • Dissolved oxygen
  • Phosphate content
  • Ammonia content
  • Conductivity
  • Total suspended solids
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)

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
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)

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

  • 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.

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

Adaptation of freshwater animals
  • Mayfly nymph
  • Goby
  • Blood Worm
  • Mosquito
  • Pond skater
  • Dragonfly Nymph
  • water cricket
  • Damselfly nymph
  • Water skater
mayfly nymph
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”
  • 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.
blood worm
Blood Worm
  • Red colour
  • Blood gills
  • Some have green blood

Water skater

  • Long, thin legs
  • hair on legs
  • thin, flattened body
water cricket
Water cricket
  • strong & thick body
  • dark brown with 2 orange lines down the back
  • orange abdomen
  • About 2mm in length
damselfly nymph
Damselfly nymph
  • 3 terminal caudal gills
  • No rectal gills
  • Large, mask-like labium
  • More slender than dragonfly nymph
dragonfly nymph
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.
  • 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

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
the end

~The End~

From: Lingnan Hang Yee Memorial Secondary School