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What are the three main zones of a freshwater lake?
What are the three main zones of a freshwater lake?
The three main zones of a freshwater lake are the littoral zone, the limnetic zone and the profundal zone.
What is the name of the process where fragmental material originates from the disintegration of rocks and other sources, is transported, and is deposited in layers or remains suspended in the water?
What is the name of the process where fragmental material originates from the disintegration of rocks and other sources, is transported, and is deposited in layers or remains suspended in the water?
Thermal stratification is most pronounced during the summer in lakes of the warmer latitudes.
Thermal stratification is most pronounced during the summer in lakes of the warmer latitudes.
True
What is the primary cause of the aging and extinction of lakes?
What is the primary cause of the aging and extinction of lakes?
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Lakes can be classified according to the degree of enrichment of nutrient and organic matter. Which of the following is a recognized classification of lakes?
Lakes can be classified according to the degree of enrichment of nutrient and organic matter. Which of the following is a recognized classification of lakes?
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What is the term for the natural aging process of a lake, which may take thousands of years?
What is the term for the natural aging process of a lake, which may take thousands of years?
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Cultural eutrophication is a rapid process that can take only decades to happen and ultimately pollutes the water.
Cultural eutrophication is a rapid process that can take only decades to happen and ultimately pollutes the water.
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What are the effects of eutrophication? (Select all that apply)
What are the effects of eutrophication? (Select all that apply)
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What is the primary objective of controlling cultural eutrophication?
What is the primary objective of controlling cultural eutrophication?
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What are the main sources of phosphorus that can enter a lake and cause eutrophication?
What are the main sources of phosphorus that can enter a lake and cause eutrophication?
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What is the commercially available form of phosphate rock called?
What is the commercially available form of phosphate rock called?
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Plants need phosphate as a fertilizer or nutrient.
Plants need phosphate as a fertilizer or nutrient.
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Why is the nitrogen cycle important for life?
Why is the nitrogen cycle important for life?
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What are the four main processes that participate in the cycling of nitrogen through the biosphere?
What are the four main processes that participate in the cycling of nitrogen through the biosphere?
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What is the most inert form of nitrogen?
What is the most inert form of nitrogen?
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Which of the following is NOT a type of nitrogen fixation?
Which of the following is NOT a type of nitrogen fixation?
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Biological nitrogen fixation requires a complex set of enzymes and a huge expenditure of ATP.
Biological nitrogen fixation requires a complex set of enzymes and a huge expenditure of ATP.
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What is the process called where ammonia is converted into nitrates?
What is the process called where ammonia is converted into nitrates?
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What is the process called where nitrates are reduced to nitrogen gas?
What is the process called where nitrates are reduced to nitrogen gas?
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What are the main inorganic compounds that are part of the sulphur cycle?
What are the main inorganic compounds that are part of the sulphur cycle?
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The environmental sulphur cycle involves many physical, chemical and biological agents.
The environmental sulphur cycle involves many physical, chemical and biological agents.
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What is the most common form of sulphur in mineral form?
What is the most common form of sulphur in mineral form?
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What is the name of the bacteria that is involved in the oxidation of ferrous to ferric iron?
What is the name of the bacteria that is involved in the oxidation of ferrous to ferric iron?
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The metabolic activity of T. ferrooxidans is temperature independent.
The metabolic activity of T. ferrooxidans is temperature independent.
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What are the two main groups of sulphate reducing bacteria (SRB)?
What are the two main groups of sulphate reducing bacteria (SRB)?
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SRB activity in natural wetlands is capable of metal sulfide precipitation from acid rock drainage.
SRB activity in natural wetlands is capable of metal sulfide precipitation from acid rock drainage.
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What are the two main types of mineralization of sulfur?
What are the two main types of mineralization of sulfur?
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What are the three categories of oxidation-reduction reactions for minerals with micro-organisms?
What are the three categories of oxidation-reduction reactions for minerals with micro-organisms?
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Oxidation of sulphur or sulphides for energy production is restricted to the bacteria genera: Thiobacillus, Thiomicrospira and Sulfolobus.
Oxidation of sulphur or sulphides for energy production is restricted to the bacteria genera: Thiobacillus, Thiomicrospira and Sulfolobus.
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Acid rock drainage is the product formed by the atmospheric oxidation of pyrite and pyrrhotite.
Acid rock drainage is the product formed by the atmospheric oxidation of pyrite and pyrrhotite.
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An important reaction involving Thiobacillus ferrooxidans is the oxidation of ferrous to ferric iron (Fe²⁺ to Fe³⁺).
An important reaction involving Thiobacillus ferrooxidans is the oxidation of ferrous to ferric iron (Fe²⁺ to Fe³⁺).
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What is the typical habitat pH of Thiobacillus ferrooxidans?
What is the typical habitat pH of Thiobacillus ferrooxidans?
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Study Notes
Learning Objectives
- Students should be able to describe the major zones of a lake.
- Students should be able to state different classes of lakes.
- Students should be able to explain and distinguish the types of eutrophication.
- Students should be able to explain the factors that control the eutrophication process.
- Students should be able to discuss ways to control eutrophication.
- Students should be able to explain the nitrogen, phosphorus, and sulfur cycles.
Introduction to Lakes
- Lakes are described by physical properties (light penetration, temperature, sediment, and morphology), chemical properties (chemical constituents, plant nutrients, and dissolved gases), and biological properties (plankton, benthos, and nekton).
- These properties are interconnected and crucial for assessing water quality.
Introduction to Lakes (Light Penetration)
- The littoral zone is the shallow-water area where light reaches the bottom.
- Wave action can cause shoreline erosion and bring materials into suspension, potentially causing turbidity and reducing light penetration.
- The limnetic zone is the open-water area extending from the surface to the depth where light intensity is reduced to one percent of surface light.
- The compensation level marks the depth where oxygen uptake equals photosynthetic oxygen release by plants, influenced by light.
- The limnetic zone encompasses free-floating and swimming organisms like plankton and fish.
- The euphotic zone encompasses both the littoral and limnetic zones. It is the area with sufficient light for photosynthesis.
- The profundal zone is the deep-water area where only respiration and decomposition occur, as light intensity is too low for photosynthesis here.
Introduction to Lakes (Temperature)
- Lake thermal properties are determined by sunlight exposure, water composition, and wind mixing.
- Thermal stratification is most prominent in summer, particularly in warmer latitudes.
- Water's greatest density is at 4°C. Density decreases above or below this temperature.
- This temperature-dependent density variation causes seasonal mixing and stratification patterns in many lakes.
Photosynthesis and Respiration in Lakes
- Photosynthesis is carried out by green plants and some bacteria. Respiration is carried out by plants and animals.
- These processes impact dissolved oxygen and carbon dioxide levels in lakes, which can be out of balance.
- Excessive photosynthesis, in the presence of sufficient sunlight and nutrients, can lead to phytoplankton blooms (e.g., "algal bloom").
- Respiration consumes dissolved oxygen. In thermally stratified lakes during summer, bacterial respiration can deplete bottom water oxygen to dangerous levels.
Eutrophication
- Eutrophication is the enrichment of lakes due to nutrient and sediment input, which, while natural, can accelerate due to human activities.
- The aging process of a lake begins with plant formation in a basin followed by increased nutrient accumulation and sediment deposits, leading to plant production increase and shoreline vegetation encroachment.
- Decreased water depth and higher emergent vegetation conversion transforms the lake into a bog or dystrophic system. Eventually the lake will become land.
The Biogeochemical Cycle
- Materials entering a lake from tributaries or the atmosphere may settle in the basin, be removed through the outlet, or remain in solution. Those necessary for plant production are incorporated into living tissue.
- Sedimentation is the major pathway for nutrient input & flow in a lake.
- This involves the disintegration of rocks, transportation, and either deposition or suspension in the water.
- Lakes receive sediment from wind and inflowing water.
Processes in Lakes (Sedimentation; Nutrient Cycling)
- Lakes trap incoming sediment, which affects plant nutrient availability in the lake.
- Sediment absorbs plant nutrients, making them more soluble in the different chemical environment of the lake.
- Some elements, like phosphorus, nitrogen, and silicon, may become limiting nutrients reducing plant production.
Processes in Lakes (Nutrient Recycling)
- Many elements cycle through several chemical forms. For example, nitrogen cycles through forms like nitrates, nitrites, ammonia, etc.
- Similarly, phosphorus cycles through inorganic phosphate, organic phosphorus, and associated compounds.
Classification of Lakes
- Oligotrophic lakes are nutrient-poor, with low algae and organic matter, great clarity, and abundant oxygen.
- Eutrophic lakes are nutrient-rich, with high algae and organic matter, poor clarity, and often depleted oxygen.
- Mesotrophic lakes are intermediate between oligotrophic and eutrophic, having moderate nutrient levels and adequate oxygen.
Eutrophication (Natural and Cultural)
- Eutrophication, a natural aging process in lakes, can be accelerated by human activities (e.g., wastewater discharge), known as cultural eutrophication.
- Cultural eutrophication progresses more quickly and may have negative effects on water bodies compared to natural eutrophication.
Effects of Eutrophication
- Nutrient buildup leads to excessive plant growth, primarily algae.
- Algae blooms deplete oxygen levels and disrupt environments, leading to fish and other organism deaths.
- Excessive decomposition further depletes oxygen, worsening the situation.
The Different Stages of the Life Cycle of a Lake
- Describes the progressive changes from oligotrophic to eutrophic to senescent lake stages.
Principle Factors Controlling Eutrophication
- Availability of sunlight affects water transparency and eutrophication levels.
- Nutrient concentrations (especially nitrogen and phosphorus) are critical factors in eutrophication.
- Euphotic zone (top water layer), and profundal zone (bottom water layer) important for water quality.
Case Study - Red Tides or Harmful Algae Bloom
- High concentrations of algal toxins can cause massive fish kills.
Simplified Representation of Algal Photosynthesis
- The balanced chemical equation for photosynthesis in algae is simplified.
- Factors affecting algal blooms (minimum N/P ratio, P and N concentrations).
Phosphorus Model for Lakes
- Phosphorus is a crucial factor in eutrophication. It enters lakes via streamflow, runoff, and point sources (e.g., industry). Sedimentation and outflow are key removal processes.
Thermal Stratification and Its Impact on DO
- Thermal stratification, distinguishing epilimnion, thermocline, and hypolimnion layers, impacts oxygen distribution.
- Summer stratification often results in less oxygen in the deeper water layers.
- Winter stratification can cause adverse effects.
Thermal Stratification and Its Impact on DO (Continued)
- During summer stratification, decreased oxygen in the deeper layers (hypolimnion) can cause fish death.
- The reduced oxygen availability in the hypolimnion is directly related to the decomposition of organic matter.
- Winter stratification has a less negative influence on conditions, due to decreased metabolic rate.
Water Quality Management in Lakes
- Managing cultural eutrophication involves controlling phosphorus input.
- Steps include limiting fertilizers, sewage treatment, and sediment management techniques (e.g., dredging).
Phosphorus Cycle
- Phosphorus enters the environment from rocks and sediments.
- Weathering and erosion release inorganic phosphorus.
- Organic phosphorus enters the soil from dead vegetation.
- In plants and animals, phosphate is essential for energy storage, DNA, and RNA.
Human Inputs to the Phosphorus Cycle
- Commercial fertilizers introduce phosphorus into the environment, potentially accelerating eutrophication.
- Manure and other animal wastes can also contribute to phosphorus runoff.
- Sewage treatment plants, untreated or inadequately treated, release phosphorus.
Nitrogen Cycle
- Nitrogen is a crucial element for life, found mostly as N2 in the atmosphere.
- Fixation processes make nitrogen usable by living organisms.
- Nitrogen fixation occurs through atmospheric fixation, biological fixation, or industrial fixation, in order of lowest to highest input.
- Decay converts organic nitrogen into ammonia.
- Nitrification converts ammonia to nitrites and nitrates, which can be taken up by plants.
- Denitrification returns nitrogen to the atmosphere as nitrogen gas.
Sources of Sulphur
- Inorganic sulfur (e.g., sulfates, sulphites).
- Organic sulfur from plant and animal matter (e.g, amino acids).
Sulphur Cycle
- The environmental sulfur cycle involves numerous physical, chemical, and biological processes.
- Mineral sulfur can be present as sulfides or sulfates.
- Microorganisms play critical roles in sulfur transformations, including oxidation (creating sulfate) and reduction (to produce hydrogen sulfide).
- Acid rock drainage (ARD) is an example of sulfur oxidation.
Sulfur Reduction
- The reduction of sulfur forms from sulfate to hydrogen sulfide is key in the sulfur cycle.
- Chemical activities in natural and constructed wetlands are examples of such processes.
Mineralization of Sulphur
- Aerobic conditions lead to the formation of sulphates.
- Anaerobic conditions result in the formation of hydrogen sulfide.
Summary
- This summary covers the fundamental processes and interactions related to lakes, eutrophication, and nutrient cycling.
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