Question

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

Explanation:

When there is an increased load of animal waste in an aquatic ecosystem, it can lead to an overgrowth of algae (eutrophication). As the algae die and decompose, bacteria consume oxygen during the decomposition process, reducing dissolved oxygen levels. Fewer pesticides would likely not reduce oxygen (pesticides are more about toxicity to organisms). Improved water health would likely not reduce oxygen. Saying there is no exact cause is incorrect as there are known factors like the one mentioned.

Answer:

an increased load of animal waste