Lake Ecology and Chemistry

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Questions and Answers

Which zone of a dimictic lake is the warmest during the midsummer stratification?

Aphotic

Metalimnion

Epilimnion (correct)

Hypolimnion

The hypolimnion is warmer than the epilimnion during the summer.

False

What is the term for the rapid vertical change in water chemistry?

Chemocline

Lake Karachay in Russia is known as a dumping spot for __________ waste.

nuclear Signup and view all the answers

Match the following pollutants with their descriptions:

Point Source = Pollution that can be traced to a single identifiable source Non-Point Source = Pollution that comes from multiple, diffuse sources Cumulative = Pollution that accumulates over time from various sources Signup and view all the answers

What is a common consequence of heavy metal pollution in lakes?

Bioaccumulation in aquatic webs Signup and view all the answers

Acid rain is primarily caused by the release of sulfur dioxide.

True Signup and view all the answers

What are the two nutrients mentioned that can impact lake chemistry?

Nitrogen and Phosphorus Signup and view all the answers

___________ conditions can occur in deep water layers where there is no oxygen.

Anoxic Signup and view all the answers

Which factor does NOT impact lake chemistry?

Water temperature Signup and view all the answers

Which lake is known for its exploding phenomenon due to carbon dioxide belching?

Lake Nyos Signup and view all the answers

Eutrophication is solely induced by natural processes.

False Signup and view all the answers

What is the primary limiting factor for growth in oligotrophic lakes?

Nutrients Signup and view all the answers

Lake Kivu contains _______ million tons of carbon in the form of methane and CO2.

500 Signup and view all the answers

Match the type of lake with its characteristics:

Oligotrophic = Clear, low nutrients, deep Mesotrophic = Moderate nutrients, moderate plant growth Eutrophic = High nutrients, turbid, rich plant growth Signup and view all the answers

What is the primary color of the waters in eutrophic lakes?

Turbid green/yellow Signup and view all the answers

Lake Kivu is home to over 2 million people living in its basin.

True Signup and view all the answers

Name one of the two main nutrients that act as limiting factors for growth in lake ecosystems.

Nitrogen or Phosphorous Signup and view all the answers

Cultural eutrophication is primarily caused by human-generated _______ of water bodies.

fertilization Signup and view all the answers

What classification of lakes has the Secchi disk depth of greater than 15 m?

Oligotrophic Signup and view all the answers

Study Notes

Dimictic Lakes

Summer Stratification
- Epilimnion: Warm upper layer
- Metalimnion (Thermocline): Transition zone with rapid temperature change
- Hypolimnion: Cold, deeper layer
Fall overturn
- Water becomes isothermal (same temperature)
Winter Stratification
- 4°C at bottom, 0°C at top
Early Spring
- Isothermal
Early Summer
- Water warms and stratifies

Lake Chemistry

Factors that influence lake chemistry:
- Size of watershed
- Climate
- Geology (e.g., karst)
Concerns:
- pH: Too acidic or too basic
- Sulfates and Nitrates (SO4-2 & NO3): Acid rain (sulfur dioxide)
- Heavy metals (e.g., Mercury (Hg))
  - Bioaccumulation in aquatic webs
- Oil spills
- Salt (NaCl) concentrations
- Nutrients (N & P)
Pollutants:
- Point Source: Specific, identifiable source
- Non-Point Source: Diffuse, widespread source
- Cumulative: Effects of multiple sources

Chemical Zonation

Horizontal Variations:
- Concentrations higher near shorelines
- Algal blooms, plant and animal concentrations
- Wave action mixes sediments and erodes shoreline
- Overland flow and groundwater bring nutrients from:
  - Weathering, landslides, fires
  - Fertilizers, land clearing, urbanization
Vertical Variations:
- Chemocline: A rapid vertical change in water chemistry
  - Examples: Salts in Summit Lake and Kitlope Lake
- Annoxic Conditions: Example: Saanich Inlet (225 m deep)
- Purple sulfur bacteria: Need both sunlight and H2S produced by anaerobic bacteria (Example: Mahoney Lake)

Stratification and pH

Stratification can cause pH levels to differ above and below the thermocline.

Laguna Verde and Licancabur Volcano, Bolivia

Sediments contain copper minerals.

Laguna Colorada, Bolivia

Shallow salt lake with red sediments and red algae contrasted with white islands.

Exploding Lakes

Lake Nyos, Cameroon (August 21, 1986): Belched carbon dioxide killing 1,700 people and 3,500 livestock.
- Surface area: 1.58 km2
- Depth: 208 m
- Active volcanic crater, 500 years old

Lake Kivu, Cameroon

Contains methane and CO2 (500 million tons of carbon)
- Represents 2% of human annual emissions
2 million people live in the basin

Nutrient Supply

Nutrients: N (nitrogen) and P (phosphorous)
Low nutrient levels:
- Limiting factors for growth of algae, phytoplankton, zooplankton, and fish
Nutrient Retention Time:
- How long a nutrient is held in a lake
- Often reflects hydraulic retention time
- Nutrients can be consumed or changed in form by organisms

The Phosphorus and Nitrogen Cycles

Phosphorus and Nitrogen are key nutrients in aquatic ecosystems and are cycled through complex processes involving organisms and the environment.

Oligo-Eutro Classification Scheme

Succession of Lakes: Oligotrophic > Mesotrophic > Eutrophic > Marsh > Land
Oligotrophic Lakes:
- Poorly supplied with nutrients
- Support little plant growth
- Biological productivity is low
- Clear, blue-green waters
- Secchi disk depth of 15 m or more
- Large, deep, cold, steep
- Lots of dissolved oxygen (DO) at deepest layers throughout the year
Mesotrophic Lakes:
- Moderately well supplied with plant nutrients
- Support moderate plant growth
- Secchi disk depth of 7.5 - 15 m
Eutrophic Lakes:
- Richly supplied with nutrients
- Abundant plant growth
- High biological productivity (plankton, algae, macrophytes)
- Turbid green/yellow waters
- Secchi disk depth less than 7.5 m
- Small, shallow, warm lakes
- Reduced DO during stratification

Eutrophication

Natural Eutrophication:
- Slow and gradual process
- Occurs over centuries
- Production and consumption out of balance
- Lake slowly becomes over fertilized
Cultural Eutrophication:
- Green algae and other microorganisms
- Human-generated fertilization of water bodies
- Nitrates and phosphates from:
  - Treated sewage
  - Runoff from farms and urban areas
- Eventually lake dies

Kootenay Lake Classification

Based on the information provided, it is unclear how to classify Kootenay Lake without additional information on its nutrient levels, productivity, and other characteristics.

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Description

Explore the fascinating dynamics of dimictic lakes, including their seasonal stratification and the impact of environmental factors on lake chemistry. This quiz covers important concepts such as the layers of lake water, factors affecting chemistry, and common pollutants. Test your understanding of these critical ecological systems.