This document discusses the relationship between water quality and populations in an ecosystem. It provides examples of different types of population changes, such as seasonal, short-term, and long-term changes. Water quality can significantly impact populations - for example, acidic water from volcanic activity can make a pond "dead". Algal blooms from excess nutrients like fertilizers entering bodies of water can also negatively impact populations by blocking sunlight and reducing oxygen levels. Salmon runs and sardine migrations are important population events that support other species.

1. Populations & Water
Quality

2. Population
Population: is a group of organisms of the same species that live in a
particular area.
Example: Population of clown fish

3. Population
Populations can experience different types of changes:
Seasonal - Yearly cycles in population.
ex: Mosquito eggs in water
Short term - Small, non-repeating change.
ex: Dry spring -> low water levels ->
insect population off to a slow start.
Long term - Large, non-repeating change.
ex: Zebra mussels introduced to
N. America from Europe

4. Population
Water quality can have a
significant effect on populations
within the ecosystem.
This pond has been made very
acidic by the nearby volcanic activity.
It is considered "dead" water.

5. Population
algal blooms - rapid increases in the
population of algae and
phytoplankton.
The following can cause algal blooms:
• increases in nutrients from
fertilizers and sewage
• increases in temperature from
industrial runoff (thermal
pollution)

6. Eutrophication
Eutrophication is excess algae growth caused by
fertilizers leaching into ponds, lakes, rivers, and
streams. The nutrients in the fertilizer cause larger
amounts of algae to grow in an algal bloom
The excess algae float on the surface of the water
and block sunlight from reaching plants that grow in
the water.
This kills these plants which means that they no
longer put oxygen into the water. Because there is
less oxygen in the water, other aquatic life like fish
suffocate leading to the collapse of the ecosystem.

7. Salmon Run
Salmon are unique species of fish. They are born in
freshwater streams, but then live their lives in
saltwater oceans. Every fall, mature salmon return to
the freshwater streams where they were born to
spawn the next generation of their species. This
event is called a salmon run.
Salmon runs are not only incredibly important to the
survival of salmon, they are also key to the survival of
a large number of species who benefit directly or
indirectly from these yearly events.

8. The Greatest Salmon Run

9. The Sardine Run
Sardines live in large shoals (schools) to protect
themselves from predators. Sardines need cool
waters and ample food (plankton) in order to spawn.
Most years, billions of sardines migrate from the
open ocean, up the coast of South Africa to spawn.
This migration is an important event for many
predators and can mean life or death for them.
Unfortunately, climate change is making the sardine
run less predictable and some years it doesn’t occur
at all.

10. Sardine Run