How Matter and Nutrients Cycle Biogeochemical Cycle recycle

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) 1. 2. 3. 4. Atmosphere Hydrosphere Lithosphere Biosphere

Biogeochemical Cycles • 3 types 1. Hydrologic (water) – water moves through spheres, most found in hydropshere 2. Atmospheric – large portion of a given element exists in gaseous form (nitrogen, carbon) 3. Sedimentary – most found in lithosphere, generally very slow (phosphorus, sulfur)

The Nitrogen Cycle

What happens to atmospheric nitrogen in the nitrogen cycle? Atmospheric Nitrogen (N 2) N N Bacteria (cyanobacteria in soil and water or rhizobium bacteria on the roots of plants) Ammonia (NH 3) Nitrogen combines with Hydrogen to make Ammonia Lightning Nitrogen Fixation Nitrates (NO 3) Nitrogen combines with Oxygen to make Nitrates

Nitrogen Fixation • 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. • N 2 + 3 H 2 → NH 3 → (dissolves) → NH 4+ (ammonia) (ammonium)

But…… • Very few plants can use NH 3 (ammonia) or NH 4+ (ammonium) • Nitrification can help

Nitrification • 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! • NH 4+→NO 2 -→NO 3[nitrite (toxic)] [nitrate (nutrient)]

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

Assimilation • Roots: absorb NH 3, NH 4+, NO 3 - 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 • Bacteria and fungi decomposers break down amino acids from dead animals and wastes into ammonium • Decaying organisms→NH 3 → NH 4+ dissolves What happens to the NH 4+?

Denitrification • 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! • NH 3 → NO 2 - → N 2 and N 2 O (nitrous oxide) NH 4+ NO 3 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