8 - Eutrophication

Question 1

What is eutrophication

Answer 1

The process of nutrient enrichment, increased production of organic matter, and subsequent ecosystem degradation

Question 2

What is the main effect of eutrophication?

Answer 2

Excessive plant and algal growth due to the increased availability of one or more limiting growth factors needed for photosynthesis (primary production)

Question 3

Types of productivity of lakes? What does this mean in terms of eutrophication?

Answer 3

Oligotrophic = low productivity

Mesotrophic = moderate productivity

Eutrophic = high productivity (high plant mass = high primary prod)

Question 4

What is cultural eutrophication? Sources?

Answer 4

Anthropogenic eutrophication
Increase in plant and algal growth due to anthropogenic nutrient inputs

Sources: sewage, fertilizer runoff, phosphorus-containing detergent

Question 5

Requirements for photosynthesis?

Answer 5

Light, nutrients (e.g. N, P), water, CO2

Increase in one/multiple = higher primary productivity

Question 6

What is the principle of limiting factors? AKA

Answer 6

AKA Liebig’s Law of the Minimum

Certain ecological functions are controlled by whichever environmental factor is present in the least supply relative to demand

Question 7

Nitrogen as a limiting nutrient

Answer 7

N is the main limiting nutrient in terrestrial ecosystems

Question 8

Phosphorus as a limiting nutrient

Answer 8

P is the main limiting nutrient in freshwater ecosystems

Question 9

Slide 13

Answer 9

P equilibrium

Question 10

Iron as a limiting nutrient? Experiment?

Answer 10

In the Oceans

Whole-ecosystem experiment in the Southern (Antarctic) Ocean (Fe fertilization)
Possible effects:
A) reducing availability of atmospheric CO2
B) increasing ocean pollution and little effect on atmospheric CO2

Question 11

Research in the 1960s to 1980s looked into…

Answer 11

Which nutrients are limiting? (Carbon, nitrogen, phosphorus)

Question 12

Slides 17-19

Answer 12

ELA lake 227

Question 13

Types of control on primary production

Answer 13

Top down controls (e.g. herbivores): if increased, will decrease the amount of primary production

Bottom-up controls (e.g. nutrients, water, light): addition of more elements that favour primary production = eutrophication

Question 14

Slides 25-28

Answer 14

Aquatic trophic cascades

Stressors on aquatic ecosystem

Question 15

Two issues with algae growth

Answer 15

• algae block out sunlight; no plants underneath, organisms living underneath are in the dark
• bacteria produce toxins as they grow (can kill larger mammals)

Question 16

How has the total phosphorus load of Lake Erie changed over the past 50 years

Answer 16

Amount of P in the lake has decreased, but anthropogenic sources of P are still running into the lake

Question 17

Slide 33-36

Answer 17

Look at pics/graph

Question 18

What is hypoxia?

Answer 18

When water oxygen concentration <2 mg/L O2

Reduced concentration of dissolved oxygen in a water body leading to stress and death in aquatic organisms

Question 19

What is a dead zone?

Answer 19

Hypoxic areas in aquatic ecosystems (typically a consequence of pollution, eutrophication, and high rates of decomposition) that are essentially devoid of life

Question 20

How do hypoxic zones form?

Answer 20

Nutrients enter the lake from inland rivers and streams

The nutrients cause an algal bloom. Eventually the algae die and sink to the bottom of the water column.

Bacteria decompose the algae, respiring and consuming oxygen

There is temperature stratification of the column, the oxygen depleted bottom water does not mix with the warmer, oxygenated upper water

Slides 38, 39

Question 21

How did the dead zone form in the gulf of Mexico?

Answer 21

During the spring, freshwater runoff from the Mississippi river flows into the river
Nitrogen and Phosphorus from fertilizer and sewage in the freshwater ignite algae blooms.

When the algae die, they sink and decompose, using up oxygen in deeper water

The deeper water is now a dead zone. Fish avoid the area, or die with smaller organisms. Winter brings respite, but occurs again next spring

Question 22

Slides 41-47

Answer 22

Gulf of Mexico/Mississippi water shed

Question 23

What are HABs?

Answer 23

Harmful algal blooms

Question 24

What is cyanobacteria?

Answer 24

Blue-green “algae” (eukaryotic protists)

Phylum of bacteria that can photosynthesize

Question 25

What types of toxins can cyanobacteria produce?

Answer 25

• neurotoxins
• hepatotoxins
• dermatotoxins

Question 26

What is Microcystis sp?

Answer 26

Most common bloom-causing cyanobacteria. Can produce both neurotoxins and microcystins, a type of hepatotoxins

Question 27

What is Nodularia sp.

Answer 27

Brackish genus, produces potent hepatotoxins called nodularins that can greatly harm humans

Question 28

Two types of cyanobacteria sp

Answer 28

Microcystis sp

Nodularia sp

Question 29

Microcystin limit in drinking water in Canada

Answer 29

1.5 ug/L

Question 30

Changes in N and P concentrations in Canadian waters

Answer 30

Most have no change

~25% increasing

For nitrogen, only 12% decreasing