Question

1. high levels of nitrogen and phosphorus can enter rivers as rainwater carries excess fertilizer from agricultural areas. therefore, the mississippi river often carries unnaturally high levels of nitrogen and phosphorus into the gulf of mexico, where the river meets the ocean. each summer, phytoplankton, photosynthetic bacteria, and algae grow rapidly because of the increased amount of nutrients, which alters the food chain and depletes the dissolved oxygen in the water. when the level of dissolved oxygen in the water is low, large marine dead zones can form. organisms that depend on dissolved oxygen to survive are unable to live in these areas, hence the term \dead zone.\ scientists tracked the flow of the mississippi river into the gulf of mexico from 2008 to 2016. they observed a large decrease in flow in 2012, which the scientists attributed to decreased rainfall. the scientists observed a gradual increase in rainfall each year after 2012 until 2016. as a result of the change in river flow during 2008 and 2016, which of the following graphs best shows the predicted relative size of the dead zone as a result of the change in river flow between 2008 and 2016?

Explanation:

Step1: Understand the relationship

High - nutrient runoff (from nitrogen and phosphorus) carried by the Mississippi River to the Gulf of Mexico causes dead zones. Lower river flow (in 2012 due to decreased rainfall) likely led to less nutrient runoff and a smaller dead zone. After 2012, as rainfall and river flow increased gradually, nutrient runoff increased and the dead zone size should increase gradually.

Step2: Analyze the graphs

The first graph shows a large decrease in 2012 and then similar levels after 2012 which doesn't match the gradual increase in river flow and dead - zone size after 2012. The second graph shows a peak in 2012 which is incorrect as river flow decreased in 2012. The third graph shows a large peak in 2012 which is wrong for the same reason. The fourth graph shows a decrease in 2012 and then a gradual increase after 2012 which is consistent with the described relationship.

Answer:

The fourth graph (the one with a decrease in 2012 and a gradual increase after 2012) best shows the predicted relative size of the dead zone as a result of the change in river flow between 2008 and 2016.