CFP Water Quality & Management 3 — Questions and Answers
Question 1: Which process is primarily responsible for internal phosphorus loading in stratified, eutrophic lakes?
- Surface runoff from agricultural fields during summer
- Anoxic sediment release of phosphorus under low redox conditions (Correct answer)
- Atmospheric deposition during thunderstorms
- Macrophyte decomposition at the water surface
Correct answer: Anoxic sediment release of phosphorus under low redox conditions
Under anaerobic conditions in the hypolimnion, iron-phosphorus complexes dissolve and release phosphorus from sediments back into the water column.
Question 2: A fish hatchery is experiencing elevated CO2 (>30 mg/L) in rearing tanks. The most appropriate immediate corrective action is:
- Add sodium bicarbonate to raise alkalinity
- Increase aeration or degassing to strip CO2 (Correct answer)
- Reduce feeding rates to lower respiration
- Add potassium permanganate as an oxidant
Correct answer: Increase aeration or degassing to strip CO2
Mechanical aeration or cascade degassing rapidly strips excess CO2 from water by increasing the gas-liquid interface and driving off-gassing.
Question 3: The maximum contaminant level (MCL) for nitrate in US drinking water is 10 mg/L as nitrogen. High nitrate in aquaculture source water is most concerning for:
- Warm-water sport fish like largemouth bass
- Salmonids and sensitive cold-water species at chronic exposure levels (Correct answer)
- Marine bivalves in brackish hatcheries
- Carp and other cyprinids in pond culture
Correct answer: Salmonids and sensitive cold-water species at chronic exposure levels
Salmonids and other sensitive cold-water fish are more susceptible to chronic nitrate toxicity than warm-water generalists, with sublethal effects on growth and immune function.
Question 4: Which physical characteristic of water has the greatest influence on the concentration of dissolved oxygen at saturation?
- Turbidity
- Temperature (Correct answer)
- pH
- Hardness
Correct answer: Temperature
As water temperature increases, the solubility of oxygen (and all gases) decreases, so warmer water holds less dissolved oxygen at saturation.
Question 5: Alum (aluminum sulfate) is applied to fish ponds or lakes primarily to:
- Increase alkalinity and buffer pH
- Flocculate suspended clay particles and precipitate phosphorus (Correct answer)
- Eliminate filamentous algae
- Raise dissolved oxygen through chemical oxidation
Correct answer: Flocculate suspended clay particles and precipitate phosphorus
Alum hydrolyzes to form aluminum hydroxide floc that binds clay particles and phosphorus, settling them to the sediment and improving water clarity.
Question 6: In a recirculating aquaculture system (RAS), the biofilter converts toxic ammonia to less harmful nitrate through a two-step process. What are the two bacterial genera most associated with these steps?
- Pseudomonas and Clostridium
- Nitrosomonas and Nitrobacter (Correct answer)
- Thiobacillus and Desulfovibrio
- Bacillus and Lactobacillus
Correct answer: Nitrosomonas and Nitrobacter
Nitrosomonas oxidizes ammonia to nitrite (step 1) and Nitrobacter oxidizes nitrite to nitrate (step 2) in aerobic nitrification.
Question 7: When assessing the potential for herbicide impacts on fish in a treated water body, which measurement is most important to compare against toxicity data?
- Water hardness in mg/L CaCO3
- Measured herbicide concentration relative to LC50 values for target fish species (Correct answer)
- Secchi disk transparency
- Total dissolved solids (TDS)
Correct answer: Measured herbicide concentration relative to LC50 values for target fish species
Comparing measured herbicide concentrations to species-specific LC50 values (lethal concentration for 50% of test organisms) is the standard risk assessment approach.
CFP Water Quality & Management 3
Which process is primarily responsible for internal phosphorus loading in stratified, eutrophic lakes?