OBJECTIVE: To determine the effects of phosphates on water quality
Detergents contain phosphates which are chemicals that allow detergents
to clean in all kinds of water, hard or soft. Phosphates act as fertilizers
and stimulate aquatic plant growth. This stimulation makes algae multiply
rapidly. They use up large quantities of oxygen, depleting the supply for
other plants and animals thus causing them to die. In this kind of situation
the pond will slowly change into a decaying swamp. This final stage is called
eutrophication. To see the effects of phosphates on aquatic life, find a
pond and collect water, some algae, daphnia, and elodea. If this is not
possible, pet stores sell these aquatic organisms. While collecting the
organisms pay close attention to the pond. Does it look viable and healthy
or does it look like it is being taken over by algae and slowly dying? Fill
each jar 3/4 full of pond water, equal numbers of daphnia, elodea plants,
and algae. Buy a detergent that is not low in phosphates. Mix a cup
of detergent to a pint of water and using an eye dropper, put ten drops
of the mixture in the first jar, twenty drops in the second jar, thirty
drops the third jar, fourty drops in the fourth jar, fifty drops in the
fifth jar, and none in the sixth jar, because it will be the control jar.
Label each jar accordingly. Place the jars in the same sunny location and
make daily observations.
MATERIALS: Elodea (aquatic plant), daphnia (water fleas), 6 jars (2-quart
or 1-gallon size), pond water, detergents, eye dropper
SETTING: Pond and classroom
TIME ALLOTMENT: 45 minutes to set up the jars and unlimited time to collect
pond water and aquatic organisms
VOCABULARY: Phosphates, aquatic, pollutants, eutrophication
Since many plant fertilizers contain phosphates, do the same experiment
using fertilizers instead of detergents. Using either liquid fertilizer
or, making a mixture of fertilizer and water as above, put the same number
of drops of liquid fertilizer in the jars. Compare your results with those
from the first experiment with detergent.
1. Did the daphnia die at equal rates in all of the jars? Explain the differences.
2. Did the algae grow equally well in all of the jars or better in some
than in others? Why?
3. What happened to the elodea plants as the algae began to grow better
4. What happens to an aquatic ecosystem when large amounts of detergents
are added to it?
5. What were the similarities and the differences between the experiment
with the detergent and the experiment with the fertilizer?
6. What happens to aquatic ecosystems when both detergents and phosphates
are added to them? Does this double their chances of decaying and becoming
an eutrophic ecosystem?
7. If the daphnia and the elodea were killed by the phosphates, how would
this affect the other organisms in the food chain?