Question

list the order of events which lead to a dead zone.

first thing that happens

1 an algal bloom forms

2 waterways move excess nutrients into a large body of water where it collects

3 excess nutrients enter the waterways.

4 as algae in algal bloom decomposes, it takes out all of the oxygen in the water

5 algal bloom uses up all of the nutrients in the area, and then dies off

6 excess nutrients feed aquatic plants and algae

last thing that happens

Explanation:

Identify the initial nutrient input

Using the Eutrophication knowledge point
The process begins when excess nutrients (such as nitrogen and phosphorus from agricultural runoff or wastewater) first enter local freshwater systems.

• First Event: "Excess nutrients enter the waterways."

Trace nutrient transport to larger basins

Using the Eutrophication knowledge point
These local streams and rivers flow downstream, carrying the dissolved nutrients into larger coastal waters, lakes, or gulfs where they accumulate.

• Second Event: "Waterways move excess nutrients into a large body of water where it collects"

Analyze the biological response to nutrients

Using the Algal Blooms knowledge point
The high concentration of nutrients acts as a fertilizer, rapidly accelerating the growth of primary producers in the water column.

• Third Event: "Excess nutrients feed aquatic plants and algae"

Determine the resulting population explosion

Using the Algal Blooms knowledge point
This rapid growth leads to a dense, visible accumulation of algae at the surface of the water.

• Fourth Event: "An algal bloom forms"

Identify the depletion of nutrients and die-off

Using the Ocean Dead Zones knowledge point
The massive algal population quickly consumes the available nutrient supply until it is exhausted, causing the algae to die.

• Fifth Event: "Algal bloom uses up all of the nutrients in the area, and then dies off"

Determine the final oxygen depletion stage

Using the Ocean Dead Zones knowledge point
Aerobic bacteria decompose the dead organic matter, consuming dissolved oxygen in the process and creating hypoxic conditions.

• Sixth Event: "As algae in algal bloom decomposes, it takes out all of the oxygen in the water"

Answer:

The correct chronological order of events leading to a dead zone is:

1. Excess nutrients enter the waterways.
2. Waterways move excess nutrients into a large body of water where it collects.
3. Excess nutrients feed aquatic plants and algae.
4. An algal bloom forms.
5. Algal bloom uses up all of the nutrients in the area, and then dies off.
6. As algae in algal bloom decomposes, it takes out all of the oxygen in the water.