Humans can alter the phosphorus cycle in many ways, including in the cutting of tropical rain forests and through the use of agricultural fertilizers. Rainforest ecosystems are supported primarily through the recycling of nutrients, with little or no nutrient reserves in their soils. As the forest is cut and/or burned, nutrients originally stored in plants and rocks are quickly washed away by heavy rains, causing the land to become unproductive.
Phosphorus is naturally weathered out of rocks and slowly gets transported to the oceans. Mining phosphate rock can accelerate this process and also leave scars on the landscape if the mining companies don't do reclamation. Exposed phosphate rock will also weather and erode more quickly, again speeding up the delivery of phosphorous to the oceans.
Exposed and eroding phosphate rock and fertilizer run-off, can also cause a bloom of bacteria along the coastlines, leading to "dead zones," where very little, if any, life is found. Agricultural runoff provides much of the phosphate found in waterways. Crops often cannot absorb all of the fertilizer in the soils, causing excess fertilizer runoff and increasing phosphate levels in rivers and other bodies of water. At one time the use of laundry detergents contributed to significant concentrations of phosphates in rivers, lakes, and streams, but most detergents no longer include phosphorus as an ingredient.
