Humans impact this cycle because we are removing so much of the photosynthetic efforts of the plants in order to support our enterprises, we are diverting 40% of the photosynthetic productivity of land plants to support human enterprises, (pg 67). Two examples of our harmful tendencies are burning fossil fuels which has increased atmospheric carbon dioxide 35% over preindustrial levels, (pg. 67) and logging. These both are being used naturally by the ecosystem and the lack of these resources causes stress and strain to keep the balance.
At the rate it is going carbon to complete its cycle from the atmosphere through one or more living organism and back to the atmosphere happens about every 6 years. The phosphorus cycle includes the cycle of all the biologically important nutrients found in the natural minerals. These elements include iron, calcium, potassium found in the rock and soil minerals in the lithosphere. Over time a rock breaks down and releases phosphate (PO43-) and other ions which replenish phosphorus that is lost due to runoffs and leaching.
The phosphate is absorbed by plants and turned into compounds that are moved through the food chain. Humans impact this cycle because we are using the phosphorus to make fertilizers, animal feeds, detergents or other products and mining these locations. Our water systems are being damaged because human applications have tripled the amount of phosphorus making it to the oceans, (pg 68). This is a problem because it causes over fertilization or eutrophication of the aquatic ecosystem.
The waterborne phosphorus cannot be returned to the soils this causes too much bacteria or algae in the water and kills of the fish and other water mammals. The nitrogen cycle is similar to the carbon and phosphorus cycles; because it has a gas phase like carbon and can also be a limiting factor such as phosphorus. The main form of nitrogen is in the air which is about 78% nitrogen gas (N2), (pg 68). The plants change the nitrogen into organic compounds which are necessary like proteins and nucleic acids.
Humans impact this cycle because many of our crops are legumes or nonleguminous. Legumes like peas, beans provide the bacteria a place to live and a source of food and receive nitrogen in exchange, where it enters the food web. Nonleguminous crops such as corn, wheat, potatoes and cotton have to be heavily fertilized with nitrogens from industrial fixations. The over fertilization of nitrogen into the soils are destroying lakes, ponds and forests.
However our actions are more than doubling the rate which nitrogen is moved from the atmosphere to the land, nitric acid has destroyed thousands of lakes and ponds and caused extensive damage to forests, (pg 70). Humans have a great impact on all three cycles. If it continues the way that we are using fossil fuels, and destroying the land as we are currently are. We are depleting our resources at a faster rate than we can sustain naturally which is causing harmful living conditions which we may not necessarily feel the repercussions of immediately.