Human Influence On Biogeochemical Cycles


Human activities have increased atmospheric carbon dioxide by about 40% over pre-industrial levels and more than doubled the amount of nitrogen available to ecosystems. Similar trends have been observed for phosphorous and other elements and these changes have major consequences for biogeochemical cycles and climate change.
HUMAN INFLUENCE ON BIOGEOCHEMICAL CYCLES
 
ON NITROGEN CYCLE
  • The nitrogen cycle has been dramatically altered by human activity, especially by the use of nitrogen fertilizers, which have increased agricultural production.
  • Reactive nitrogen is any nitrogen compound that is biologically, chemically, or radiatively active, like nitrous oxide and ammonia, but not nitrogen gas (N2).
  • Once created, it can, in sequence, travel throughout the environment (for example, from land to rivers to coasts, sometimes via the atmosphere), contributing to environmental problems such as the formation of coastal low-oxygen “dead zones” in marine ecosystems in summer.
  • The nitrogen cycle affects atmospheric concentrations of the three most important human-caused greenhouse gases: carbon dioxide, methane, and nitrous oxide. Increased available nitrogen stimulates the uptake of carbon dioxide by plants, the release of methane from wetland soils, and the production of nitrous oxide by soil microbes.UPSC Prelims 2024 dynamic test series
  • The strongest direct effect of an altered nitrogen cycle is through emissions of nitrous oxide (N2O), a long-lived and potent greenhouse gas that is increasing steadily in the atmosphere.
  • Emissions of nitrogen oxides (NO x) increase the production of tropospheric ozone, which is a greenhouse gas. Elevated tropospheric ozone may reduce CO2 uptake by plants and thereby reduce the terrestrial CO2 sink.
 
ON PHOSPHOROUS CYCLE
  • Changes in the phosphorus cycle have no direct effects on climate, but phosphorus availability constrains plant and microbial activity in a wide variety of land- and water-based ecosystems
  • In land-based ecosystems, phosphorus availability can limit both CO2 storage and decomposition, as well as the rate of nitrogen accumulation.
  • In turn, higher nitrogen inputs can alter phosphorus cycling via changes in the production and activity of enzymes that release phosphorus from decaying organic matter.

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