Question

If there are 500 units of nitrogen in a soil pool, while 10 units of nitrogen is coming into the pool (through n fixation) and 10 units of nitrogen is leaving the soil pool (through denitrification) per year, what would be the average residence time of nitrogen in this soil pool?

A. 100 years
B. 50 years
C. 5 years
D. 10 years
E. 500 years

Answer 1

The average residence time of nitrogen in a soil pool with 500 units of nitrogen and a turnover rate of 10 units per year due to nitrogen fixation and denitrification is 50 years.

Step-by-step explanation:

The average residence time of nitrogen in this soil pool is calculated by dividing the total amount of nitrogen in the pool by the rate at which it is being added to or removed from the pool. In this case, there are 500 units of nitrogen with a turnover of 10 units per year (either added through nitrogen fixation or removed through denitrification). Therefore, the average residence time is 500 units / 10 units per year = 50 years.

Given that denitrification is able to keep the nitrogen cycle in balance by removing excess nitrogen, it is important to consider the impact of human activities such as agriculture, which greatly increases nitrogen fixation rates, potentially leading to imbalances such as eutrophication.