Geography 2011A/B Lecture Notes - Lecture 17: Great Lakes Areas Of Concern, Biochemical Oxygen Demand, Algal Bloom
5 May 2018
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3 Types of Pollutants in Great Lakes
1. Non-Persistent Pollutants
2. Persistent Pollutants
3. Pollutants of Emerging Concern
1. Non-Persistent Pollutants
- Degradable: can be broken down by chemical reactions or by natural bacteria (biodegradable) into
simple, non-polluting substances that can be diluted in a big body of water.
- Examples:
- domestic sewage, fertilizers, industrial wastes (all include nutrients)
- Lake Erie = case study for non-persistent pollutants
Biological Productivity: amount of living material supported w/in a lake
- everybody of water has a natural level of biological productivity, which depends on factors such as:
a) Temperature warmer = more productive
b) Light more light = more productive
c) Depth deeper = less productive
d) Volume more volume = less productive
e) Nutrients more nutrient = more productive
- Less productivity = Oligotrophic (ex. Lake Superior = big, cold most oligotrophic)
- Intermediate productivity = Mesotrophic
- Most productivity = Eutrophic (ex. bog, den, pond = small, low influx/efflux of water, nutrients, green)
Eutrophication process of becoming more eutrophic
- Lake Erie used to be oligotrophic, but when we arrived, we made it more eutrophic by
1) increasing temperatures of tributaries (things that flow into lakes) through industrial process
like clearing land (less trees = more sunlight + higher temperatures)
2) adding nutrients (sewage, agricultural runoff like fertilizers, agricultural waste from animals,
industrial processes – phosphates from detergents)
- In Waterlife, Lake Erie was almost declared dead in 60s and 70s because of eutrophication and
oxygen depletion...
- nutrient addition algal blooms algae outcompetes other life algal dies and when it
decomposes it uses up all the oxygen causes fish to die from suffocation
- Biological Oxygen Demand (BOD) depletion of oxygen via decomposition of organic
material (the less BOD a body of water has, the healthier it is)
- Why did Eutrophication happen to Lake Erie?
- Lake Erie = shallowest, warmest, most naturally productive, furthest South (exposed to intense
agricultural + urban development...fertilizer runoff, sewage waste lead to nutrient runoff in Erie)
- 1972 Canada and the US signed the Great Lakes Water Quality Agreement
- secondary sewage treatment (taking nutrients out using filters and stuff)
- also worked w/farmers to prevent runoffs into streams and lakes (by banning
- worked b/ Erie’s retetio rate is ol 2 ears log
phosphates)
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