# Lesson 8: Water Quality

## Activities

### Activity 1: Evaluating Graphics

Materials: colored pencils, ruler or straight edge
For the first part of the activity, you will use the information in Table 1 to develop a graph. Use the top half of the "Graphs" page to create your graph. For the graph, you will provide the following information:
• Title ("Fresh Water and Salt Water")
• A label for the x-axis (Temperature) and the y-axis (mg/L oxygen)
• A key showing the color or line style used for fresh water and salt water (see note below)
Because you have two different measurements for the y axis (fresh water and salt water) you will want to provide a way to know the difference between the two. There are two ways to do this: 1) use different colored pencils or ink for each component or 2) use a different style line for the fresh water (—f-f-f-f-f-f—) and salt water (-s-s-s-s-s-s-).
 TABLE 1: FRESH WATER AND SALT WATER Temp (Celsius) mg/L oxygen fresh water mg/L oxygen salt water 0 14.6 11.7 5 12.8 10.4 10 11.3 9.3 15 10.1 8.5 20 9.1 7.8 25 8.2 7.1 30 7.5 6.5
After you complete your graph, answer the questions below based on the information in the graph:
• Based on the need for oxygen, at what temperature would you expect to find the greatest number of organisms?
• What would possibly limit the number of organisms at 0(degrees)C?
• Compare fresh water and salt water. What do you notice?
• Assuming that dissolved oxygen remains at a steady state, why does salt water have lower concentrations of dissolved oxygen then fresh water at the same temperatures?
For the second part of this activity, look at the graph called "Dissolved Oxygen and Pollutants" found at the bottom of the "Graphs" page. Answer the following questions about the graph:
• Briefly describe what the graph is saying.
• What do you think could be the cause of the increased level of pollutants?
• Based on your understanding of steady states and equilibrium, what do you think will happen?
Student Activity Page
In this activity, your child will first generate a graph ("Fresh Water and Salt Water") using raw data from a table. The graph should have two different lines (one for fresh water, one for salt water). The x-axis should be used to record the numbers for temperature and the y-axis should be used to record numbers for dissolved oxygen. Numbers on the x-axis should increase from left to right and numbers from the y-axis should increase as you move from the bottom to the top. The lines should descend from the left to right. As temperature increases (x-axis), dissolved oxgyen content decreases (y-axis). The lines should basically slope downward from left to right, but should not be overlapping.

Your child's graph should look something like this:
Answer Key - Water Quality (Graph 1)
• Based on the need for oxygen, at what temperature would you expect to find the greatest number of organisms? Based on oxygen only, 0(degrees)C.
• What would possibly limit the number of organisms at 0(degrees)C? Water temperature is at freezing, and not all organisms are adapted to temperatures at this level.
• Compare fresh water and salt water. What do you notice? At the same temperatures, fresh water has a higher concentration of dissolved oxygen. While subtle, the rate of decrease in the concentration of dissolved oxygen is quicker in fresh water than in salt water.
• Assuming that dissolved oxygen remains at a steady state, why does salt water have lower concentrations of dissolved oxygen than fresh water at the same temperatures? Salt water contains other components in the form of dissolved elements and ions, such as salts. While fresh water also has dissolved minerals and elements, the amounts are greater in salt water, making for decreased capacities to carry dissolved oxygen. CHALLENGING ANSWER: Just by sheer volume, the amount of water in the oceans is also much greater than that of fresh water. The volume, coupled with the lack of photosynthesis at great depths, will limit the production of oxygen.
Next, your child will look at a second graph to interpret the role of pollutants on dissolved oxygen. The goal with this graph is to encourage your child to begin to understand the relationships among pollutants, whether naturally or humanly introduced. As your child views the graph, encourage her to understand that the relationship communicated in the graph is common. There are often inverse relationships in the hydrosphere among the abiotic factors and the biotic factors.
The questions and answers for the second graph ("Dissolved Oxygen and Pollutants") are as follows:
• Briefly describe what the graph is saying. The graph is tracking the level of dissolved oxygen and pollutants over the course of an undisclosed amount of time. The graph shows that dissolved oxygen is decreasing as time passes and that pollutants have increased as time has passed. The graph also shows a significant relationship between the level of pollutants and dissolved oxygen, and this relationship is an inverse relationship (one variable decreases when the other increases). As pollutants increase in the water source being tracked, the amount of dissolved oxygen decreases.
• What do you think could be the cause of the increased level of pollutants? Because pollution is the unnatural increase or introduction of a contaminant into the water, there are two possibilities: natural disaster (earthquake, volcanic eruption) or human introduction via point or non-point source pollution.
• Based on your understanding of steady states and equilibrium, what do you think will happen? The reservoir of water that is being tracked should eventually return to normal levels of dissolved oxygen as the pollutants reduce or are removed by either natural process or human intervention.

### Activity 2: Investigating Oil Seepage

There have been many well-known oil spills throughout the world. Memories are still fresh with regards to the Deep Water Horizon spill in the Gulf of Mexico, yet few people focus on the natural occurrence of organisms that help clean this up. In order to understand more, you will read and consider how marine ecosystems are both challenged by and able to overcome oil spill disasters as well as naturally occurring releases of oils from the depths of the oceans.