Ecology Biogeochemical Nutrient Cycles 3 — Questions and Answers
Question 1: Eutrophication of lakes most commonly results from excess input of which two nutrients?
- Carbon and sulfur
- Nitrogen and phosphorus (Correct answer)
- Iron and manganese
- Calcium and potassium
Correct answer: Nitrogen and phosphorus
Excess nitrogen and phosphorus from agricultural runoff fuel algal blooms that lead to eutrophication and oxygen depletion.
Question 2: In the global carbon cycle, which process represents the largest annual flux of carbon from the land surface to the atmosphere?
- Fossil fuel combustion
- Soil respiration and decomposition (Correct answer)
- Deforestation
- Cement production
Correct answer: Soil respiration and decomposition
Soil respiration and decomposition release more CO₂ annually than any other land-based process, though it is balanced by photosynthesis.
Question 3: Which form of nitrogen is directly assimilated by most plants from the soil?
- N₂ gas
- Nitrite (NO₂⁻)
- Ammonium (NH₄⁺) and nitrate (NO₃⁻) (Correct answer)
- Urea
Correct answer: Ammonium (NH₄⁺) and nitrate (NO₃⁻)
Plants primarily absorb nitrogen in the inorganic forms of ammonium and nitrate through their roots.
Question 4: The Haber-Bosch process has dramatically altered the nitrogen cycle by:
- Accelerating denitrification in soils
- Industrially fixing atmospheric N₂ into ammonia for fertilizer (Correct answer)
- Increasing biological nitrification rates
- Converting nitrate to nitrous oxide
Correct answer: Industrially fixing atmospheric N₂ into ammonia for fertilizer
The Haber-Bosch process uses high pressure and temperature to convert N₂ and H₂ into ammonia, enabling mass fertilizer production.
Question 5: What is the primary fate of phosphorus that erodes from land into the ocean over geological timescales?
- It evaporates back to land as rain
- It is fixed by marine bacteria into organic forms
- It settles into marine sediments and eventually forms rock (Correct answer)
- It is returned to land by seabirds immediately
Correct answer: It settles into marine sediments and eventually forms rock
Phosphorus carried to the ocean by rivers eventually settles into marine sediments, where it is incorporated into sedimentary rock over millions of years.
Question 6: Which ecosystem type typically has the highest rate of decomposition and nutrient cycling?
- Arctic tundra
- Temperate grassland
- Tropical rainforest (Correct answer)
- Desert scrubland
Correct answer: Tropical rainforest
Tropical rainforests have the highest decomposition rates due to warm temperatures, high moisture, and abundant decomposer organisms.
Question 7: Acid rain is primarily caused by atmospheric reactions involving which two pollutants?
- CO₂ and CH₄
- SO₂ and NOₓ (Correct answer)
- O₃ and NH₃
- H₂S and CO
Correct answer: SO₂ and NOₓ
Sulfur dioxide and nitrogen oxides react with water vapor in the atmosphere to form sulfuric and nitric acids, producing acid rain.
Ecology Biogeochemical Nutrient Cycles 3
Eutrophication of lakes most commonly results from excess input of which two nutrients?