Answer:
Reducing the use of fertilizers on land.
Step-by-step explanation:
Dead zones are areas in lakes or oceans where there is not enough oxygen to support marine life. These dead zones can occur when excessive nutrients, such as nitrogen and phosphorus, enter the water from human activities like using fertilizers in agriculture, sewage-treatment plants, and burning fossil fuels.
When fertilizers are used on land, rain or irrigation water can wash away the excess nutrients, carrying them into nearby lakes and rivers. These nutrients act as food for algae, causing them to multiply rapidly, leading to algae blooms. However, when the algae eventually die, they sink to the bottom and undergo decay. During the decay process, bacteria consume oxygen to break down the dead algae, resulting in a depletion of oxygen in the water. To decrease the size and number of dead zones, we need to reduce the amount of excess nutrients entering the water. One effective way to do this is by reducing the use of fertilizers on land. By using fertilizers more carefully and only applying the necessary amounts, we can prevent excessive nutrients from reaching the lakes and rivers. This would help to limit the occurrence of algae blooms and the subsequent oxygen depletion caused by bacterial decay.
It's important to note that addressing dead zones requires a combination of efforts, including better wastewater management, reducing fossil fuel emissions, and implementing sustainable agricultural practices. However, reducing the use of fertilizers is a significant step toward improving water quality and protecting aquatic ecosystems from the harmful effects of nutrient pollution, ultimately decreasing the size and number of dead zones in large lakes.