How Matter and Nutrients Cycle Biogeochemical Cycle - recycle nutrients through the earth’s air, land water, and living organisms Complete path moves through four major components (reservoirs) Atmosphere Hydrosphere Lithosphere Biosphere

Biogeochemical Cycles 3 types Hydrologic (water) – water moves through spheres, most found in hydropshere Atmospheric – large portion of a given element exists in gaseous form (nitrogen, carbon) Sedimentary – most found in lithosphere, generally very slow (phosphorus,sulfur)

The Nitrogen Cycle

What happens to atmospheric nitrogen in the nitrogen cycle? Atmospheric Nitrogen (N2) N N Bacteria (cyanobacteria in soil and water or rhizobium bacteria on the roots of plants) Lightning Nitrogen Fixation Nitrates (NO3) Nitrogen combines with Oxygen to make Nitrates Ammonia (NH3) Nitrogen combines with Hydrogen to make Ammonia

Nitrogen Fixation N2 + 3H2 → NH3 → (dissolves) → NH4+ the process that causes the strong two-atom nitrogen molecules found in the atmosphere to break apart so they can combine with other atoms. Nitrogen gets “fixed” when it is combined with oxygen or hydrogen. N2 + 3H2 → NH3 → (dissolves) → NH4+ (ammonia) (ammonium)

But…… Very few plants can use NH3 (ammonia) or NH4+ (ammonium) Nitrification can help

Nitrification NH4+→NO2-→NO3- Nitrifying bacteria in the ground first combine ammonia or ammonium with oxygen to form nitrites. Then another group of nitrifying bacteria convert nitrites to nitrates which green plants can absorb and use! NH4+→NO2-→NO3- [nitrite (toxic)] [nitrate (nutrient)]

How do plants and animals get the nitrogen they need? Assimilation

Assimilation Roots: absorb NH3, NH4+, NO3- to make DNA, amino acids, proteins Animals: eat plants or plant-eating animals to make DNA, amino acids, proteins

How does the nitrogen return to the atmosphere? 2 more steps! Ammonification Denitrification

Ammonification Decaying organisms→NH3 → NH4+ What happens to the NH4+? Bacteria and fungi decomposers break down amino acids from dead animals and wastes into ammonium Decaying organisms→NH3 → NH4+ dissolves What happens to the NH4+?

Denitrification NH3 → NO2- → N2 and N2O (nitrous oxide) Atmosphere Denitrifying bacteria live deep in soil and in aquatic sediments where conditions make it difficult for them to get oxygen. The denitrifying bacteria use nitrates as an alternative to oxygen, leaving free nitrogen gas as a byproduct. They close the nitrogen cycle! NH3 → NO2- → N2 and N2O (nitrous oxide) NH4+ NO3- Atmosphere Soil

How are humans affecting the nitrogen cycle? Use of nitrogen-rich fertilizers can cause eutrophication Burning fossil fuels and forests Releases solid forms of nitrogen Farming Livestock wastes release nitrogen into soil and water