8 - Eutrophication Flashcards
What is eutrophication
The process of nutrient enrichment, increased production of organic matter, and subsequent ecosystem degradation
What is the main effect of eutrophication?
Excessive plant and algal growth due to the increased availability of one or more limiting growth factors needed for photosynthesis (primary production)
Types of productivity of lakes? What does this mean in terms of eutrophication?
Oligotrophic = low productivity
Mesotrophic = moderate productivity
Eutrophic = high productivity (high plant mass = high primary prod)
What is cultural eutrophication? Sources?
Anthropogenic eutrophication
Increase in plant and algal growth due to anthropogenic nutrient inputs
Sources: sewage, fertilizer runoff, phosphorus-containing detergent
Requirements for photosynthesis?
Light, nutrients (e.g. N, P), water, CO2
Increase in one/multiple = higher primary productivity
What is the principle of limiting factors? AKA
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
Nitrogen as a limiting nutrient
N is the main limiting nutrient in terrestrial ecosystems
Phosphorus as a limiting nutrient
P is the main limiting nutrient in freshwater ecosystems
Slide 13
P equilibrium
Iron as a limiting nutrient? Experiment?
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
Research in the 1960s to 1980s looked into…
Which nutrients are limiting? (Carbon, nitrogen, phosphorus)
Slides 17-19
ELA lake 227
Types of control on primary production
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
Slides 25-28
Aquatic trophic cascades
Stressors on aquatic ecosystem
Two issues with algae growth
- algae block out sunlight; no plants underneath, organisms living underneath are in the dark
- bacteria produce toxins as they grow (can kill larger mammals)
How has the total phosphorus load of Lake Erie changed over the past 50 years
Amount of P in the lake has decreased, but anthropogenic sources of P are still running into the lake
Slide 33-36
Look at pics/graph
What is hypoxia?
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
What is a dead zone?
Hypoxic areas in aquatic ecosystems (typically a consequence of pollution, eutrophication, and high rates of decomposition) that are essentially devoid of life
How do hypoxic zones form?
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
How did the dead zone form in the gulf of Mexico?
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
Slides 41-47
Gulf of Mexico/Mississippi water shed
What are HABs?
Harmful algal blooms
What is cyanobacteria?
Blue-green “algae” (eukaryotic protists)
Phylum of bacteria that can photosynthesize
What types of toxins can cyanobacteria produce?
- neurotoxins
- hepatotoxins
- dermatotoxins
What is Microcystis sp?
Most common bloom-causing cyanobacteria. Can produce both neurotoxins and microcystins, a type of hepatotoxins
What is Nodularia sp.
Brackish genus, produces potent hepatotoxins called nodularins that can greatly harm humans
Two types of cyanobacteria sp
Microcystis sp
Nodularia sp
Microcystin limit in drinking water in Canada
1.5 ug/L
Changes in N and P concentrations in Canadian waters
Most have no change
~25% increasing
For nitrogen, only 12% decreasing
