Which layer will become saturated first when rain falls?

The correct answer is: SOIL.

Explanation:

The very first layer that gets rain is the soil.

poor water quality affects most estuarine organisms, including commercially important fish and shellfish. the pollutants that have the greatest impact on the health of estuaries include toxic substances like chemicals and heavy metals, nutrient pollution (or eutrophication), and pathogens such as bacteria or viruses.

a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.