How do organisms get Nitrogen?

Turn and Talk: Compare and contrast the nitrogen cycle on land and in the water. 

Essential Question: Why does increasing nitrogen cause algae populations to grow while aquatic plant populations grow at first but then decline? 

How Are Humans Disrupting the Nitrogen Cycle?

Nitrogen is essential for life. Plants need nitrogen to grow, but they cannot use nitrogen directly from the atmosphere. Instead, bacteria convert nitrogen into a usable form that plants absorb through their roots. Animals obtain nitrogen by eating plants or other animals.

Too Much of a Good Thing

Farmers use fertilizers containing nitrogen to help crops grow. However, when it rains, extra fertilizer can be carried by runoff into rivers, lakes, and oceans.

Extra nitrogen causes algae to grow rapidly, creating an algal bloom. Too much algae can block sunlight from reaching underwater plants, causing them to die. When algae and plants die, decomposers break them down and use up dissolved oxygen in the water. Without enough oxygen, fish and other aquatic organisms may die.

Restoring the Balance

Humans can reduce nitrogen pollution by using less fertilizer, planting vegetation to absorb runoff, and improving wastewater treatment.

Although nitrogen is necessary for life, too much nitrogen can disrupt ecosystems and harm living organisms.

Why does increasing nitrogen cause algae populations to grow while aquatic plant populations eventually decline? How does this cause fish to suffocate? 

Construct a scientific explanation using evidence from both graphs and scientific reasoning from the reading.