Dead zones are areas along the coasts where rivers spill excess nutrients into the oceans. microorganisms feed on these nutrients, which in turn causes them to use up all the in the water and kill larger organisms like fish.
1. sediments
2. phosphorus
3. oxygen
4. nitrogen

3. oxygen

Explanation:

Dead zones are hypoxic (lacking oxygen) water bodies (oceans, lakes, rivers) where there is an increase in nutrients (generally nitrogen and phosphorous) that lead to an excessive population of algae that lowers oxygen levels. These conditions make life impossible in these areas, therefore, their name.

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