Phosphorus Cycle - Human Interference

Human Interference

Nutrients are important to the growth and survival of living organisms, and hence, are essential for development and maintenance of healthy ecosystems. However, excessive amounts of nutrients, particularly phosphorus and nitrogen, are detrimental to aquatic ecosystems. Natural eutrophication is a process by which lakes gradually age and become more productive and may take thousands of years to progress. Cultural or anthropogenic eutrophication, however, is water pollution caused by excessive plant nutrients, which results in excessive growth in algae population. Surface and subsurface runoff and erosion from high-P soils may be major contributing factors to fresh water eutrophication. The processes controlling soil P release to surface runoff and to subsurface flow are a complex interaction between the type of P input, soil type and management, and transport processes depending on hydrological conditions.

Repeated application of liquid hog manure in excess to crop needs can have detrimental effects on soil P status. In poorly drained soils or in areas where snowmelt can cause periodical waterlogging, Fe-reducing conditions can be attained in 7–10 days. This causes a sharp increase in P concentration in solution and P can be leached. In addition, reduction of the soil causes a shift in phosphorus from resilient to more labile forms. This could eventually increase the potential for P loss. This is of particular concern for the environmentally sound management of such areas, where disposal of agricultural wastes has already become a problem. It is suggested that the water regime of soils that are to be used for organic wastes disposal is taken into account in the preparation of waste management regulations.

Human interference in the phosphorus cycle occurs by overuse or careless use of phosphorus fertilizers. This results in increased amounts of phosphorus as pollutants in bodies of water resulting in eutrophication. Eutrophication devastates water ecosystems.

Total excess input from 1600 to 3600 AD is 1860 Tg (teragrams) of phosphorus. Given that, in the marine environment, between 106 and 170 units of carbon are buried per unit of phosphorus one can predict that excess phosphorus would effectively bury 76,000 to 123,000 Tg carbon. In essence, this burial removes carbon from the atmosphere through the biological fixation of carbon dioxide during photosynthesis. The present annual rate of anthropogenic carbon addition to the atmosphere is 7900 Tg carbon, so the phosphorus eutrophication effect would only account for about 10–15 years of anthropogenic carbon emissions to the atmosphere over the next 2000 years (i.e. only 0.6% of total projected carbon emissions, if emissions stay constant).

Although the net effect as a carbon sequestration mechanism is minimal, the ecological impact of phosphorus fertilization to the ocean could be extreme. Given the other assaults on marine ecosystems, including warming, and acidification of surface ocean waters from higher carbon dioxide levels, it would be pure speculation to project how P eutrophication would affect ecosystem structure and distribution in the future. However, those who have witnessed local eutrophication in ditches, streams, ponds, and lakes can attest to the ecological devastation that excess nutrients and the proliferation of monocultures can cause in such isolated environments. The eutrophication of coastal and open-marine ecosystems would result in a grim future for ecological diversity.