Biogeochemical Cycles (Water, Carbon, Nitrogen, Phosphorus, Sulfur)

What is a biogeochemical cycle? A biogeochemical cycle is the continual recycling of nutrients through the air, water, rock, soil, and living organisms. All of these nutrients are essential to life. No new molecules are created – what we have is what was here at the beginning.

The Water Cycle

The Water Cycle Groundwater is water that sinks into the soil and is stored in aquifers. An aquifer is a groundwater storage area.

Humans alter the water cycle by… Withdrawing large quantities of freshwater for agriculture leading to groundwater depletion. Clearing vegetation for agriculture, roads, building, and mining. Covering land with buildings and concrete which increases runoff, and prevents water from becoming ground water. Altering the quality of the water by the addition of nutrients from chemicals and pollutants.

The Carbon Cycle

Humans alter the carbon cycle by… Clearing trees therefore, the trees cannot remove the carbon dioxide from the air Burn fossil fuels which release a large amount of carbon into the air

The Phosphorous Cycle

Humans alter the phosphorus cycle by… Mining for phosphate rock to make inorganic fertilizers Cutting down tropical trees reduces the amount of phosphorus in the tropical soil Runoff from animal wastes, fertilizers, and sewage add phosphorus to aquatic systems

The Sulfur Cycle

Acidic fog and precipitation Water Air Pollutant Acidic fog and precipitation Sulfur trioxide Sulfuric acid Ammonia Ammonium sulfate Oxygen Sulfur dioxide Hydrogen sulfide Plants Volcano Dimethyl sulfide Industries Animals Combustion of Fossil Fuels Ocean Sulfate salts Decaying matter Metallic sulfide deposits Sulfur Hydrogen sulfide Industry, burning fossil fuels add sulfur to atmosphere

Humans alter the sulfur cycle by… Burning coal and oil to create electricity which releases sulfur into the air Refining petroleum to create gasoline Creating metals from ores

The Nitrogen Cycle

The Nitrogen Cycle Nitrogen in the air is in the form of N2 which is unusable to plants and animals. The N2 needs to be converted to a useable form – this is done by 1) lightening and 2) bacteria in the water and soil. Nitrogen fixation – bacteria in the soil convert N2 to NH3 so that plants can use it Nitrification – bacteria take the NH3 and turn it into nitrite (NO2 - toxic) and nitrate (NO3) ions Assimilation – Plants absorb the ammonia and nitrate; animals get nitrogen by eating plants Ammonification – decomposer bacteria take animal and plant wastes and turn it into ammonia Denitrification – ammonia is converted into nitrites and nitrates and then to N2 where it is released into the air

The Nitrogen Cycle Plants need nitrogen in the form of nitrates to make nucleic acids (DNA) and amino acids.

Humans alter the nitrogen cycle by… Burning fuel releases nitric oxide (NO) which converts to (HNO3) in the atmosphere and falls back to the earth as acid rain Using inorganic fertilizers which releases N2O (nitrous oxide) into the atmosphere which depletes the ozone layer Destroy forests, grasslands, and wetlands which releases the N in the soil and the plants Agricultural runoff and sewage goes into waterways and the nitrates disrupt the aquatic ecosystems When working with crops (irrigating, harvest, burn to create room for) nitrogen is taken from the topsoil.