The most effective additional plotline to combine with Plotlines #1 and #2 would be:
A friend of Reed’s begins to work for Reed’s father. He does not share Reed’s uncertainty about the corporation, and may end up working against Reed.
This plotline intensifies the conflict since it directly involves Reed, who is already grappling with his moral dilemma about the corporation's impact on the environment. Having a friend who is supportive of the corporation can create personal stakes for Reed, further illustrating the internal conflict and pressures he faces. Additionally, it can create tension between him and his friend, highlighting the contrasting views on corporate responsibility, and adding depth to the narrative surrounding the larger environmental fight led by Darren.