Dissolved Oxygen and Aquatic Life
Estimated Time of Activity: 1.5 hrs
Goals: Process Skills and Content Knowledge:
- Students will explain why dissolved oxygen is important in aquatic ecosystems.
- Students will evaluate the optimal dissolved oxygen levels for living organisms.
- Students will explain the relationship between oxygen levels, time of day, bacteria and the breakdown of organic matter.
- Dissolved oxygen PPT.
- Water from different sources: Classroom tank, tap water, water from a local pond.
- Dissolved oxygen kits.
- Ask students “Where do we get our oxygen from?” (Slide 1)
- Review Photosynthesis: Plants combine CO2, water and sunlight to produce glucose (for energy) and oxygen. (Slide 2)
- CO2 – comes from the air
- Water – from the ground
- Carbohydrate stored in plant
- O2 – released into air
- Ask students “How does Oxygen get into aquatic ecosystems?” (Slide 3)
- Aquatic plants and phytoplankton (single cell floating plants) release oxygen into the water as a product of photosynthesis
- phytoplankton (single cell plants) – are the base of the aquatic food web and provide most of the aquatic oxygen. (Slide 4).
- Tell students
- Amount of oxygen present in water.
- Test will measure the amount of free oxygen “gas” dissolved in your water sample in mg/L (ppm)
- In addition to providing oxygen for aquatic life, submerged aquatic plants can provide shelter for young fish as well as house an abundant food supply (Slide 5).
- Ask students: “What is dissolved oxygen?” (Slide 6).
- “Why do we measure dissolved oxygen?” (Slide 7)
- Dissolved oxygen is one of the best indicators of the health of a water ecosystem.
- Aquatic animals such as fish and zooplankton, cannot use the oxygen in the water molecules (H2O) to breathe.
- They rely on "free" molecules of oxygen gas (O2) dissolved in the water, without sufficient levels of which they would suffocate.
- Dissolved oxygen levels (Slide 8)
- Dissolved oxygen can range from 0 – 18 ppm (parts per million).
- Dissolved oxygen levels of at least 5 - 6 ppm (mg/L) are usually required for growth and to support a diverse population.
- Dissolved oxygen levels of below 3 ppm are stressful to most aquatic organisms.
- Reiterate points (Slide 9)
- Oxygen in
- CO2 and H2O out
- Carbohydrates in à
- Energy out
- Why does the amount of DO increase from sunrise to sunset?
- Sunlight is necessary for photosynthesis à increase in sunlight, increase in photosynthesis à increase in O2
- Respiration: How we, the animals, use oxygen (and plants too!) Slide 10
- Ask someone to describe the diagram.
- Why does the pH level increase from sunrise to sunset?
- Ask someone to describe the diagram (Slide 11).
- Slide 12 – Tell students that CO2 is also a gas that is soluble in water.
- Slide 13 – How does CO2 affect aquatic ecosystems?
- Slide 14 – Biological influences and dissolved oxygen
- As photosynthesis increases, oxygen levels increase:
- CO2 + H2O Biomass + O2
- As respiration increases due to decay or organic materials, oxygen levels decrease:
- Biomass + O2 CO2 + H2O
- Slide 15 – Decomposition – Not good for DO
- Decomposer organisms (mainly bacteria) consume oxygen
- Sometimes consume oxygen faster than plants can produce it, even during the middle of the day!
- A sudden increase in organic matter (think leaf litter) can create a spike in decomposition activity – especially if it is hot
- Hurricanes not only add organic matter to our waterways, but also stir up the sediment.
- Can cause fish kills!!
- Slide 16: When organic matter such as animal waste or improperly treated wastewater enters a body of water, algae growth increases and the dissolved oxygen levels decrease as the plant material dies off and is decomposed through the action of the aerobic bacteria.
- Water Clarity
- Cloud Cover
- Current Flow (Velocity)
- The warmer water is, the less DO it can hold.
- Explains how wind and current velocity affects DO
- Slide 17: ABiotic factors that affect DO
- Slide 18: Ask students to explain the relationship between temp and DO using the graph
- Ask a student to explain how the amount of sunlight reaching the plants would affect DO.
- Sediment would block amount of Sunlight à decrease photosynthesis à decrease amount of O2 produced
- Slide 19: Explain Diffusion of O2 into and out of water column
- Slide 20: Wind stirs in atmospheric oxygen à diffusion
- Slide 21: Current à the faster water flows, the more atmospheric O2 is mixed into the water viagra naturel
- Slide 22: Explain the water clarity diagram.
- Slide 23: Ask a student to explain how cloud cover would affect DO. (same reason as water clarity
- Slide 24: Warning signs of pollution.
|Type of Land Use||Warning Signs of Pollution|
|Forests||Cloudy or muddy water may be signs of sedimentation from logging, road building or clear cutting trees and vegetation.|
|Agricultural||Algal blooms are normally associated with the misuse or overuse of fertilizers and manure runoff from pastures, feedlots or compost piles.|
|Urban||Surface sheen, low pH levels and the absence of pollution intolerant macroinvertebrates may indicate urban runoff such as metals, salts, chemicals and oils.|
|Industries||Stream discoloration, odors, low pH levels, excessive algal growth and the absence of pollution intolerant macroinvertebrates and fish may indication the deposit of unnatural materials by industry.|
|Sewage Treatment Plants and Septic Systems||Excessive algal growth is an indication of the release of organic matter. An absence or a decrease in macroinvertebrate levels may indicate high levels of chlorine in the water.|
|Sanitary Landfills||Rusty streaks and signs of runoff from landfills may be indicated by excessive algal growth and the absence of pollution-intolerant macroinvertebrates.|
|Construction||Cloudy or muddy water may be signs of sedimentation which may occur around construction sites if proper barrier structures are not in place.|
|Residential||Algal blooms, the absence of aquatic life and a colored sheen on the water may indicate the dumping of automobile oil, poor fertilizing practices and defective septic systems.|
Lab activity – students will practice using Dissolved oxygen kit and test different types of water.
- Water of Classroom tank
- Water taken from a local park
- Tap water
Students will create a lab report to report their findings.
- Where do we get our oxygen from? Draw and label a diagram.
- Read Hypoxia Fact Sheet
- Write a 200 word essay on how the most recent BP oil spill in the Gulf of Mexico, which occurred on April 20th 2010, will contribute to hypoxic conditions already seen in this area. Use terms learned in your reading.
- Remind students to bring in digital cameras for field trip.
- Have students choose which water quality parameter they would like to measure for the remainder of the course. (Salinity, Dissolved Oxygen and pH).
- Quality of Essay
- Lab report
Testing Dissolved Oxygen of pond water – Field Trip #3
Estimated Time of Activity: 1.5 – 2 hrs
Goals: Process Skills and Content Knowledge:
- Students will learn different methods for finding out about a study site.
- Students will conduct a visual survey of study site to discover information about local land cover, water quality and document their findings.
- Students will test the dissolved oxygen of the water found in a local park.
- Lamotte D.O. testing kit
- Digital water quality meter
- Digital cameras.
- Water monitoring sheet
- Hand out Water Monitoring Sheet and give the students 10 – 15 minutes to complete.
- Place water quality meter in pond water and take a digital reading of the dissolved oxygen of the water.
- Repeat in different areas of the pond if possible.
- Hand out materials for dissolved oxygen testing (might be best to prepare ahead of time in plastic baggies for distribution to individual groups)
- Have students collect the salinity at 3 different locations, 3x at each location.
- Have students’ record data in their appropriate data sheets.
- Remind students to take pictures with their digital cameras of the field site and the act of performing the salinity test.
Start lab report for the days activities by asking students to hypothesize the dissolved oxygen of the water body that you will be testing. (Students should have researched this for last lessons H.W.)
- Have students email pictures taken on today’s field trip – at least three of the field site and two of sampling.
- Have students complete a lab report. Students should hand in a copy of the Water Monitoring Form per pair/team.