Question

after the elwha and glines canyon dams were built, areas downstream saw a change in the river environment. select the events and drag them into the correct order to show how building the dams affected the elwha river habitat.
the elwha river dams were built.
mud deposits and clay that normally washed out to sea became trapped behind the dams.
chinook salmon and trout increased; pink salmon decreased.
the river downstream from the dam became more rocky.

Explanation:

1. First, after the dams were built, the immediate effect on sediment is that mud and clay (which normally go to sea) get trapped behind the dams. So the second event is "Mud deposits and clay that normally washed out to sea became trapped behind the dams."
2. Next, because the sediment (mud, clay) is trapped, the river downstream loses that sediment input, so the river downstream becomes more rocky (since the sediment that would have smoothed it or added silt is gone). So the third event is "The river downstream from the dam became more rocky."
3. Finally, the change in the river's physical environment (more rocky) affects the fish species. So the last event is "Chinook salmon and trout increased; Pink salmon decreased."

Answer:

First empty box: Mud deposits and clay that normally washed out to sea became trapped behind the dams.
Second empty box: The river downstream from the dam became more rocky.
Third empty box: Chinook salmon and trout increased; Pink salmon decreased.