APES Biogeochemical Cycles

biogeochemical cycle

a cycle of matter through an ecosystem (between organisms and the abiotic environment); the cycle involves biological, geologic and chemical interactions

carbon cycle

During photosynthesis, plants remove carbon from the air and store it as chemical compounds such as sugar, the carbon will be released back into the atmosphere through cellular respiration. Sometimes plants or animals with carbon trapped in their body will get buried before fully decaying; over millions of years the heat and pressure will turn them into fossil fuels containing carbon. This carbon is then released back into the atmosphere through combustion.

nitrogen cycle

Consists of five steps: nitrogen fixation, nitrification, assimilaton, ammonification, and denitrification.

nitrogen fixation

First step of nitrogen cycle. The conversion of gaseous nitrogen to ammonia, a form that organisms can use.

nitrification

Second step of the nitrogen cycle. Conversion of ammonia or ammonium to nitrate; performed by soil bacteria. First they turn it into nitrite, then oxidize it to form nitrate.

assimilation

Third step of the nitrogen cycle. Plants absorb nitrate, ammonia, or ammonium and incorporate them into plant proteins.

ammonification

Fourth step of the nitrogen cycle. The conversion of biological nitrogen compounds back into ammonia and ammonium. Nitrogen-containing waste products of organisms as well as nitrogen compounds in dead organisms are decomposed, releasing ammonia into the abiotic environment.

denitrification

Final step of the nitrogen cycle. The reduction of nitrate to gaseous nitrogen, returning nitrogen to the atmosphere.

phosphorus cycle

A sedimentary cycle. Water erodes phosphorus-containing minerals and releases phosphorus into soil, where plant roots absorb it and incorporate it into biological molecules. Dead organisms decompose and release phosphorus back into the soil to be reused. Phosphate is often carried by water into the ocean where it remains on the sea floor for millions of years until uplift eventually exposes the sea floor sediments as new land surfaces, where the phosphate will be eroded again.

sulfur cycle

Most sulfur is underground in sedimentary rocks and minerals, which eventually erode and release sulfur compounds into the ocean. Many natural abiotic occurrences release sulfur into the atmosphere, where it combines with oxygen and hydrogen to form sulfuric acid. Plant roots absorb sulfate from soil and incorporate it into plant proteins. Dead organisms then release it back into the soil.

hydrologic cycle

Water moves from the atmosphere to the land and ocean through precipitation. Water evaporates from the ocean, streams, soil, etc. to form clouds in the atmosphere. Transpiration (the loss of water vapor from land plants) also adds water to the atmosphere. Plants and animals absorb or consume water, then decompose and release it back into the abiotic environment.