Phosphorus Cycle
Lake Superior and all the other great lakes have been greatly affected by fluctuating Phosphorus levels in the last hundred years. Before the turn of the 20th century, the lakes were clear, cool bodies of water. After people starting inhabiting the areas around the lakes, the combination of synthetic fertilizers, organic pollutants, human waste and phosphate detergents. This combined with a increase of natural phosphorus run of because of the increase in agriculture caused the production of massive algae blooms that depleted oxygen in the center of the lake taking away the homes of many organisms. So right now there is a lot more phosphorus going into Lake Superior than there is going out since the start of the 20th century. Although it is not as much as there was in the mid 1900's thanks to efforts to decrease phosphorus output.
Carbon Cycle
Logging in the Lake Superior area affects the carbon cycle because once the trees are cut down, they cannot absorb any more carbon. This increases the carbon levels in the surrounding atmosphere. Forests converted for agriculture use cannot absorb as much carbon dioxide in the atmosphere, also raising carbon dioxide levels. There is also short-term storage of carbon in terrestrial organisms in the lake. Also when animals living on surrounding land die, their carbon is absorbed into the ground which eventually would turn into sediment. Carbon is also cycled through the Lake Superior ecosystem by photosynthesis (taking carbon away from the atmosphere) of plants and algae, cellular respiration (putting carbon back into the atmosphere) from animals like bears, deer, and rabbits, and decomposition of dead organisms.
Nitrogen Cycle
Nitrogen-fixing bacteria in the root nodules of legumes convert nitrogen gas into ammonium. Also, nitrifying bacteria in the soil converts ammonium into nitrates and nitrites. Plants receive this usable form of nitrogen through uptake. Animals then eat these plants and absorb their nitrogen. When these animals die, their bodies decompose and their nitrogen is recycled back into the soil. Cyanobacteria in the Lake convert nitrogen gas into complex ions like ammonium and release it into the water, which the fish then can absorb. Also the odd lightning storm over the lake can convert nitrogen gas to form nitrate and ammonium ions. Lastly, the burning of fossil fuels increases nitrogen in the atmosphere which can lead to acid rain.
Human Impact
Humans have impacted Lake Superior and the other lakes greatly since the urbanization of the area surrounding them. Lake Superior has had fluctuating nutrient levels making it hard for many organisms to survive and adapt in this changing ecosystem they live in. Building of dams on US-Canadian borders have prevented salmon and sturgeon in rivers from reaching their spawning grounds. Over-fishing is also a problem in the great lakes. Between 1979 and 1999 whitefish harvests declined from 24 million pounds to just 9 million pounds. Logging in the Lake Superior region removed tree cover over spawning grounds that provided shade. This affected temperature conditions in the spawning grounds and disrupted reproduction cycles of fish.