Lab 12: Dissolved Oxygen

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Lab 12 Dissolved Oxygen

• Ms. B

Let's begin by looking at factors that influence
the availability of oxygen
Adapted from http//www.phschool.com/science/bio
logy_place/labbench/lab12/concepts.html
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Oxygen is essential for cellular respiration in
most organisms

• factors that affect amount of dissolved O2 in
  water
• temperature
• as ?water temperature, its ability to hold O2
  decreases
• photosynthetic activity
• in bright light, aquatic plants produce more O2
• decomposition activity
• as organic matter decays, microbial respiration
  consumes O2
• mixing turbulence
• wave action, waterfalls rapids aerate H2O ?O2
• salinity
• as water becomes more salty, its ability to hold
  O2 decreases

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Primary Productivity

• Rate at which plants and other photosynthetic
  organisms produce organic compounds in an
  ecosystem.
• Gross productivity the entire photosynthetic
  production of organic compounds in an ecosystem
• Net productivity the organic materials that
  remain after photosynthetic organisms in the
  ecosystem have used some of these compounds for
  their cellular energy needs (cellular
  respiration).

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Lab 12 Dissolved Oxygen

• primary productivity
• measured in 3 ways
• amount of CO2 used
• rate of sugar (biomass) formation
• rate of O2 production

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Measuring O2 saturation Using a Nomograph

• To measure how much oxygen water can hold
  (saturation), you need to be able to read a
  nomograph.
• Many kits and testing procedures are available
  for measuring dissolved oxygen.

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Lab Procedure

• Monitor the effect of varying light levels on
  dissolved oxygen in an algae-rich water culture
• Amount of light available for photosynthesis
  drops off sharply with increasing depth in an
  aquatic environment
• Can model this condition by wrapping water-sample
  bottles with increasing layers of screen

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Lab 12 Dissolved Oxygen
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Lab 12 Dissolved Oxygen

• Conclusions
• ?temperature ?dissolved O2
• ?light ?photosynthesis ?O2 production
• O2 loss from respiration
• ?respiration ?dissolved O2 (consumption of O2)

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FRQ 2001

• A biologist measured dissolved oxygen in the top
  30 centimeters of a moderately eutrophic
  (mesotrophic) lake in the temperate zone. The day
  was bright and sunny and the wind was calm. The
  results of the observation are presented below.
• Using the graph paper provided, plot the results
  that were obtained. Then, using the same set of
  axes, draw and label an additional line/curve
  representing the results that you would predict
  had the day been heavily overcast.
• Explain the biological processes that are
  operating in the lake to produce the observed
  data. Explain also how these processes would
  account for your prediction of results for a
  heavily overcast day.
• Describe how the introduction of high levels of
  nutrients such as nitrates and phosphates into
  the lake would affect subsequent observations.
  Explain your predictions.

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FRQ 2001

• Scoring
• http//apcentral.collegeboard.com/apc/public/repos
  itory/sg_biology_01_6792.pdf
• Sample responses
• http//apcentral.collegeboard.com/apc/public/repos
  itory/sample_biology_01_q3.pdf

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Lab 12 Dissolved Oxygen

• ESSAY 2004B
• In most aquatic environments, primary production
  is affected by light available to the community
  of organisms.
• Using measurements of dissolved oxygen
  concentration to determine primary productivity,
  design a controlled experiment to test the
  hypothesis that primary productivity is affected
  by either the intensity of light or the
  wavelength of light. In your answer, be sure to
  include the following.
• A statement of the specific hypothesis that you
  are testing
• A description of your experimental design (Be
  sure to include a description of what data you
  would collect and how you would present and
  analyze the data using a graph.)
• A description of results that would support your
  hypothesis

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Eutrophication

• A nutrient overload causes an algal bloom
• Algal bloom
• Thick layer of algae growth at surface of water
• Blocks sunlight from penetrating lower levels of
  water body

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How are algal blooms harmful?

• Algae blocks out sun
• Plants dont photosynthesize
• Oxygen decreases
• CO2 increases
• Kills fish!
• Anoxia "without oxygen
• Hypoxia "low oxygen"

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• excess nutrients ? streams ponds
• Feeds algae in water, causes rapid growth (bloom)
• When the algae die, saprophytes utilize oxygen in
  water during decomposition
• Other organisms die due to low oxygen levels ?
  more decomposition
• Lake becomes shallow, build up of organic
  material at bottom of lake

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Sources of Nutrients
1 Agricultural Runoff (fertilizer)
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2 Urban Runoff
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3 Leaky septic tanks and sewage
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Over 80 billion tons of raw sewage is released
each year RIGHT back into our water systems..
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4 Stream Bank Erosion
How can an eroded stream bank allow for a
nutrient overload?
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• http//apcentral.collegeboard.com/apc/members/exam
  /exam_questions/1996.html
• http//apbio.biosci.uga.edu/exam/Essays/html/index
  .html