Human Impact on the Phosphorus Cycle
Like other biogeochemical cycles, human activities have altered the phosphorus cycle. Human beings mine phosphate rocks and guano deposits to make phosphorus available for production of fertilisers, detergents, animal feed, medicines, pesticide: and numerous other products. This mining exposes phosphate deposits made over millions of years. Phosphates are removed from soil through cropping of vegetation and to replace it phosphate fertilisers have to be added. Because of the abundance of calcium, iron and aluminium in the soil much of the phosphates get immobilised as insoluble salts. Thus more fertilisers have to be added. This results in high concentration of phosphates in agricultural runoffs. Similarly concentration of phosphorus in detergents, wastes of food processing plants, animal feed lot, sewage, etc., add to a considerable quantity of phosphorus poured in natural waters.
This problem becomes acute in urban areas. As said earlier, in aquatic ecosystems the phosphorus is taken up rapidly by the vegetation resulting in a sudden explosive growth of algae. Like nitrogen, this leads to cultural eutrophication of the water body. The producers cloud the water and forms a scum on the surface, blocking sunlight for the submerged plants. This is one example of the result of accumulation of nutrients at one stage of the nutrient cycle. It is important to note that the means of returning phosphorus to the cycle are inadequate to compensate for the loss. Sea birds have traditionally played-an important part in returning phosphorus to the cycle via their droppings (for example guano deposits off the coast of Peru) but apparently not at the rate at which it has occurred in the past. Unfortunately human activities appear to hasten the rate at which phosphorus is lost and thus make the cycle 'less perfect'. You could think our present use of phosphorus which is washed out into the rivers and finally into the oceans as an accelerated 'pouring' of phosphorus from the source to the sink.