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/biology_place/labbench/lab12/concepts.html

• 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

Oxygen is essential for cellular respiration in most organisms

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).

Lab 12: Dissolved Oxygen

• primary productivity– measured in 3 ways:

• amount of CO2 used

• rate of sugar (biomass) formation

• rate of O2 production

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.

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

Lab 12: Dissolved Oxygen

Lab 12: Dissolved Oxygen• Conclusions

temperature = dissolved O2

light = photosynthesis = O2 production

– O2 loss from respiration

respiration = dissolved O2

(consumption of O2)

FRQ 2001A 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.

a. 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.

b. 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.

c. Describe how the introduction of high levels of nutrients such as nitrates and phosphates into the lake would affect subsequent observations. Explain your predictions.

hour 6am 8am 10am noon 2pm 4pm 6pm 8pm 10pm mid

[O2] mg/L 0.9 1.7 3.1 4.9 6.8 8.1 7.9 6.2 4.0 2.4

FRQ 2001

• Scoring: – http

://apcentral.collegeboard.com/apc/public/repository/sg_biology_01_6792.pdf

• Sample responses:– http://apcentral.collegeboard.com/apc/public/r

epository/sample_biology_01_q3.pdf

Lab 12: Dissolved OxygenESSAY 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

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

How are algal blooms harmful?

• Algae blocks out sun• Plants don’t

photosynthesize• Oxygen decreases

• CO2 increases

• Kills fish!

• Anoxia: "without oxygen”• Hypoxia: "low oxygen"

• 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

#1: Agricultural Runoff

(fertilizer)

Sources of Nutrients…

#2: Urban Runoff

#3 Leaky septic tanks and sewage

Over 80 billion tons of raw sewage is released each year RIGHT back

into our water systems..

How can an eroded stream bank allow for a nutrient overload?

#4 Stream Bank Erosion

• http://apcentral.collegeboard.com/apc/members/exam/exam_questions/1996.html

• http://apbio.biosci.uga.edu/exam/Essays/html/index.html