The study looked at how different tiny organisms in water, like bacteria and small plankton, are affected by pollution and too many nutrients. In clean water, bacteria and small plankton are important for moving carbon around. But when there's too much food for them, their role becomes less important. Heavy metals can harm the smallest plankton more than other tiny organisms. Changes in these tiny organisms can have big effects on the whole water ecosystem, including the bottom of the water. The way these tiny organisms work is similar in oceans, brackish water, and freshwater.