Question

what can cause a reduction in dissolved oxygen levels in an aquatic ecosystem? fewer pesticides in the water improved water health there is no exact cause an increased load of animal waste

Explanation:

Fewer pesticides and improved water health generally increase dissolved - oxygen levels. There are known causes for dissolved - oxygen reduction. An increased load of animal waste can lead to higher biological oxygen demand as bacteria decompose the waste, consuming oxygen and reducing dissolved - oxygen levels in the aquatic ecosystem.

Answer:

an increased load of animal waste