Mock Exam: Water Quality

1

Which lake zone is characterized by rooted aquatic macrophytes, high invertebrate diversity, and receives both light and sediment nutrients?

A. Profundal zone
B. Limnetic zone
C. Littoral zone
D. Epilimnion

2

Total Suspended Solids (TSS) is measured by:

Turbidity & Suspended Solids intermediate

A. Filtering a known volume of water and weighing the dried residue
B. Comparing light transmission to a calibration standard
C. Counting particles under a microscope
D. Measuring electrical conductivity

3

Acid mine drainage (AMD) primarily causes water quality problems through:

pH & Acid/Base Chemistry advanced

A. Adding heavy metals and lowering pH to toxic levels through sulfuric acid production
B. Increasing nutrient loads causing eutrophication
C. Adding organic matter that raises BOD
D. Increasing turbidity through fine sediment addition

4

Diatoms are a major group of algae. As a result, diatoms are considered:

Aquatic Ecology & Food Webs intermediate

A. Zooplankton
B. Microplankton
C. Phytoplankton
D. Bacterioplankton

5

The Secchi disk is used to measure water transparency. At what depth does a 'Secchi depth' reading occur?

Turbidity & Suspended Solids beginner

A. When the disk reaches the bottom of the water body
B. When the disk first disappears from view while being lowered
C. At exactly 1 meter depth for standardization
D. When the disk's white and black quadrants are no longer distinguishable

6

What is the boundary score between "Good" and "Medium" water quality in the NSF WQI system?

WQI Interpretation medium

A. 70 (scores ≥70 = Good)
B. 71 (scores ≥71 = Good, 70 and below = Medium)
C. 75 (scores ≥75 = Good)
D. 65 (scores ≥65 = Good)

7

How does increasing salinity affect dissolved oxygen saturation?

DO saturation — temp, salinity, altitude intermediate

A. It increases DOsat by providing additional ionic binding sites for dissolved oxygen
B. It has no measurable effect on DOsat in natural water bodies
C. It decreases DOsat because dissolved salt ions interact with water molecules and reduce available sites for dissolved gas
D. It increases DOsat at low temperatures but decreases it at high temperatures

8

A pristine mountain stream would be expected to score HIGH on which WQI parameter?

Water Quality Index (WQI) beginner

A. Fecal coliform (needs to be high for good score)
B. BOD (needs to be high for good score)
C. Dissolved oxygen (near saturation = high score)
D. Nitrates (high concentrations needed)

9

In aquatic food webs, allochthonous organic matter refers to:

Aquatic Food Webs & Trophic Structure intermediate

A. Organic material produced within the aquatic system by photosynthesis
B. Organic material originating outside the aquatic system (e.g., leaf litter, terrestrial insects)
C. Organic matter from decomposition of aquatic macrophytes only
D. Dissolved inorganic nutrients carried by precipitation

10

List the MCLs for the following parameters and indicate the units: (a) nitrate, (b) arsenic, (c) total coliform, (d) turbidity in filtered systems. For lead, state the action level and explain why it differs from an MCL.

11

What is the MCL for nitrate in drinking water, and how is it expressed?

Common MCLs to know (nitrate, arsenic, lead, coliform) beginner

A. 10 mg/L expressed as nitrogen (mg/L-N)
B. 10 mg/L expressed as nitrate ion (mg/L-NO₃⁻)
C. 44.3 mg/L expressed as nitrogen
D. 1 mg/L expressed as nitrogen

12

Which group of organisms is responsible for re-mineralizing organic nutrients back to inorganic forms usable by primary producers?

Aquatic Food Webs & Trophic Structure beginner

A. Herbivores (primary consumers)
B. Apex predators
C. Decomposers (bacteria and fungi)
D. Phytoplankton

13

According to SOINC water quality standards, what is the normal pH range for rivers in the United States?

pH easy

A. 6.5 to 8.5
B. 5.0 to 7.0
C. 7.5 to 10.0
D. 4.0 to 9.0

14

Looking at the dragonfly nymph image, what is the most distinctive feature that separates it from a damselfly nymph?

macroinvertebrates medium

15

Which stream habitat type is characterized by shallow, fast-flowing water tumbling over coarse substrate (gravel, cobble, boulders) with high turbulence?

Stream ecology — riffles, runs, pools beginner

A. Pool
B. Run
C. Riffle
D. Glide

16

A BOD₅ test is conducted at a wastewater treatment plant. The initial DO is 9.0 mg/L and the final DO after 5 days at 20°C is 2.5 mg/L. What is the BOD₅?

Dissolved Oxygen advanced

A. 2.5 mg/L
B. 6.5 mg/L
C. 9.0 mg/L
D. 11.5 mg/L

17

Which of the following describes the correct sequence of oxygen zones in the 'oxygen sag curve' downstream from an organic pollution source?

Dissolved Oxygen advanced

A. Clean zone → Recovery zone → Active decomposition → Septic zone → Degradation zone
B. Clean zone → Degradation zone → Active decomposition → Septic zone → Recovery zone
C. Septic zone → Degradation zone → Active decomposition → Recovery zone → Clean zone
D. Degradation zone → Clean zone → Septic zone → Active decomposition → Recovery zone

18

The herbicide atrazine is particularly concerning for aquatic ecosystems because:

Pesticides/herbicides — types, runoff pathways intermediate

A. It is highly lipophilic and bioaccumulates to toxic concentrations in top predators
B. At concentrations as low as 0.1 μg/L it acts as an endocrine disruptor, causing feminization in male frogs
C. It inhibits acetylcholinesterase in aquatic invertebrates at concentrations above 10 mg/L
D. It irreversibly binds to sediment and permanently contaminates wetland soils

19

In a lake, "bottom-up control" of food web structure means:

Aquatic Food Webs & Trophic Structure intermediate

A. Deep-water predators control shallow-water organisms
B. Nutrient and primary producer availability drives population sizes at higher trophic levels
C. Top predators regulate the entire food web through predation
D. Sediment nutrients control planktonic food webs from the lake bottom up

20

The addition of excess nitrogen and phosphorus to aquatic systems will:

Nutrient Cycles & Eutrophication intermediate

A. Increase algae and decrease O₂
B. Increase O₂ and decrease algae
C. Increase the number of fish
D. Decrease productivity

21

Which term describes the process by which a stream ecosystem gradually changes from a disturbed state to a complex biological community over time?

Aquatic Ecology & Food Webs intermediate

A. Eutrophication
B. Ecological succession
C. Biomagnification
D. Stratification

22

In the Strahler stream order diagram, when two first-order streams join, what order is the resulting stream segment?

stream_order easy

23

A sample contains 200 total macroinvertebrates. Of these, 60 are EPT individuals representing 6 different EPT taxa. What are the EPT richness and % EPT, respectively?

EPT richness and EPT index intermediate

A. EPT richness = 60; % EPT = 6%
B. EPT richness = 6; % EPT = 60%
C. EPT richness = 6; % EPT = 30%
D. EPT richness = 200; % EPT = 30%

24

Zebra mussels (Dreissena polymorpha) are invasive in the Great Lakes. Which of the following is a primary ecological impact?

Invasive Species intermediate

A. They increase turbidity by stirring sediments
B. They filter massive quantities of phytoplankton, increasing water clarity but depleting food for native species
C. They produce toxins that kill native fish directly
D. They parasitize native bivalves, causing their shells to dissolve

25

Which statement best describes the relationship between streamflow and precipitation in a hydrograph?

Hydrologic Cycle intermediate

A. Peak streamflow occurs simultaneously with peak precipitation
B. Peak streamflow always occurs before peak precipitation due to groundwater pressure
C. Peak streamflow occurs after peak precipitation due to travel time through the watershed
D. Streamflow is not related to precipitation events

26

A wastewater effluent with TAN = 2.0 mg/L is discharged into a warm, algae-rich lake at pH 9.0 and 25°C, where the un-ionized NH₃ fraction is 25%. What is the approximate un-ionized NH₃ concentration?

Ammonia toxicity (un-ionized vs. ionized) intermediate

A. 0.004 mg/L
B. 0.05 mg/L
C. 0.5 mg/L
D. 2.0 mg/L

27

What does MPN stand for in water quality microbiology?

MPN Method beginner

A. Maximum Pathogen Number
B. Most Probable Number
C. Minimum Positive Numerator
D. Mean Plate Number

28

In which type of aquatic sediment does mercury methylation (conversion to toxic methylmercury) most actively occur?

Biomagnification & Contaminants advanced

A. Highly oxygenated, coarse sandy sediment
B. Anaerobic, fine-grained, organic-rich sediment
C. Alkaline, calcareous sediment in clear lakes
D. Acidic, nutrient-poor sediment in mountain streams

29

Why do turbulent streams recover from organic pollution faster than sluggish, slow-moving rivers?

DO sources and sinks intermediate

A. Turbulent streams receive more solar radiation, boosting photosynthetic DO production
B. Turbulence continuously renews the water surface, dramatically accelerating atmospheric reaeration
C. Turbulence physically breaks apart organic matter, directly reducing BOD
D. Slow-moving rivers have more nitrification, which consumes additional oxygen

30

What is the EPA nitrate Maximum Contaminant Level (MCL) in drinking water, and why is it important for infants?

groundwater hard

A. 10 mg/L as N; above this level causes blue-baby syndrome (methemoglobinemia) in infants under 6 months
B. 50 mg/L as N; above this level causes kidney failure in adults
C. 1 mg/L as N; any nitrate is harmful to all humans
D. 25 mg/L as NO3; above this level causes liver toxicity

💧 Water Quality Mock Exam