Excessive nutrients from fertilizer in runoff often cause excessive growth of which can lead to the creation of dead zones in aquatic ecosystems.​

Nutrient pollution is the process where too many nutrients, mainly nitrogen and phosphorus, are added to bodies of water and can act like fertilizer, causing excessive growth of algae. Nutrients can run off of land in urban areas where lawn and garden fertilizers are used

Explanation:

One half

Explanation:

The question is asking how  much of the oxygen we breathe is produced from algae. Algae is a plant which uses photosynthesis to produce oxygen, like many other species of plants. Scientists have estimated about 50-80% of our air to be produced from algae. The only closes answer of your options is one half, because 1/2=50%