1. 31. Which may cause scientist to be concerned about the quality of lake water?
A. low levels of salt
B. low levels of arsenic
C. high levels of oxygen
D. high levels of nitrates

2. A. pH B. salinity C. temperature D. turbidity
32. Which MOST directly affects the amount of dissolved oxygen in a body of water?
A. pH
B. salinity
C. temperature
D. turbidity

3. A. acidity/alkalinity B. dissolved oxygen C. nutrient level
33. What does pH measure?
A. acidity/alkalinity
B. dissolved oxygen
C. nutrient level
D. turbidity

4. A. lower temperatures B. fertilizer runoff C. overfishing
34. Which causes a decrease in the amount of dissolved oxygen in a lake?
A. lower temperatures
B. fertilizer runoff
C. overfishing

5. 35. Which nonpoint pollutants are MOST LIKELY linked to agriculture?
A. oil spills and motor oil
B. road salt and pet waste
C. acid rain and lawn runoff
D. bacteria and excess nutrients

6. A. bacteria B. mercury C. nitrates D. sodium
36. Which groundwater contaminant contained in fertilizers and pesticides comes from farms?
A. bacteria
B. mercury
C. nitrates
D. sodium

7. 37. Which is a bio-indicator?
A. current
B. insect
C. rock
D. water

8. 38. Which is the BEST example of point source pollution?
A. runoff from fields
B. pesticides sprayed from the air
C. oil spill from a boat in the ocean
D. smoke from factories in a large city

9. 39. Which would be the MOST LIKELY cause of large numbers of fish dying in a stream?
A. a lack of nitrogen
B. high levels of mercury
C. decreased carbon dioxide
D. low dissolved oxygen concentration

10. B. fertilizing a cornfield C. watering a flowerbed
40. Which human activity would MOST LIKELY increase the nutrients in an ecosystem?
A. building a rock wall
B. fertilizing a cornfield
C. watering a flowerbed
D. pulling weeds from a garden

11. A. turbidity B. temperature C. nutrient level D. dissolved oxygen
41. Which water quality indicators can be determined by measuring how light travels through water?
A. turbidity
B. temperature
C. nutrient level
D. dissolved oxygen

12. 42. Which is an accurate prediction of the pH of a lake that receives large amounts of acid rain?
B. 6-7
C. 8-9 D

13. A. algal blooms B. greater salinity C. decreased turbidity
43. Which is the MOST LIKELY effect of too much nitrogen and phosphorus flowing into a lake?
A. algal blooms
B. greater salinity
C. decreased turbidity
D. lower temperatures

14. 44. Why do biologists use indicator species?
A. to compare freshwater and ocean ecosystems
B. to count the number of organisms present
C. to monitor water quality and biodiversity
D. to analyze the dominant species

15. 45. Which will BEST show lakes, rivers, and streams are healthy?
A. large amounts of algae
B. large amounts of nitrates
C. large amounts of decomposers
D. large amounts of dissolved oxygen