Cycle of P by Robert M. Garrels

Transcription

1 I put some P into the sea the biomass did swell But settling down soon overcame and P went down toward Hell Cycle of P by Robert M. Garrels From Purgatory soon released it moved up to the land To make a perfect rose for thee to carry in thy hand But roses wilt and die you know then P falls on the ground Gobbled up as ferric P a nasty brown compound The world is moral still you know and Nature's wheels do grind Put ferric P into the sea and a rose someday you'll find 1

2 Phosphorus is the second most abundant mineral in the human body, surpassed only by calcium. It makes up more than 20 percent of the mineral ash in the body, about one percent of total body weight. Nearly 80 percent of the P in humans is found in bones and teeth. The remainder is widely distributed in combination with proteins, fats, and salts. Mineral supplements containing P may be prescribed by doctors when a P deficiency is diagnosed. Strong teeth and bones depend on an adequate supply of P. 2

3 The Phosphorous cycle The phosphorus cycle has no atmospheric component The phosphorous cycle is largely restricted to solid and liquid phases. Unlike N cycle, major source of reactive P is not through microbial reactions Only 10% of P from rivers to oceans is available to marine biota; rest tied to soil and deposited quickly The major sink is burial in marine sediments. Marine phosphorite deposits are mined and reintroduced to the cycle by man's activities. The phosphorus biomass reservoirs are derived from the carbon cycle and C:P ratios. 3

4 Importance of P transformations It has been suggested that the level of available phosphorus during soil development is the primary determinant in terrestrial net primary production: P is present in low concentrations in rocks. N is abundant in the atmosphere. Other essential plant nutrients (e.g., S, K, Ca, Mg) are more abundant than P. Bacteria that fix N 2 gas to biologically available N require P. 4

5 Phosphorus cycling Unlike nitrogen, phosphorus cycling includes significant inorganic (mineral) reactions that make it much more difficult to study. These reactions also tend to interfere with the availability of phosphorus in organic cycles. They also complicate the measurement of various forms of P. A second major difference is that gaseous P (phosphine, PH 3 ) is negligible in biogeochemical cycles and can be ignored. 5

6 Soil P transformations Biota BIOLOGICAL TRANSFORMATIONS Organic P Stable Organic P Soluble P Labile P Primary P minerals GEOCHEMICAL TRANSFORMATIONS Secondary P minerals Leaching loss Occluded P 6

7 Organic matter Phosphorus pools includes phosphorus in live plants and animals, P in microbes, and P in dead organic matter. Soluble and labile P P that is either in dissolved form or is readily released into solution. P in minerals and occluded P Igneous apatite (Ca 5 FP 3 O 12 ), biological forms of apatite, P coprecipitated with CaCO 3, Fe and Al-bound P, etc. 7

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10 Phosphorus Cycle The phosphorus cycle is a "sedimentary" cycle in which the earth's crust is the major reservoir. On land, phosphate rock deposits are the primary source of phosphorus. Through natural and human induced erosion processes, phosphates from these rock deposits are washed into rivers, and eventually to the oceans, where they form shallow and deep ocean phosphate rock deposits. Plants and animals play a role in the phosphorus cycle. As plant roots absorb phosphates from the soil, phosphorus is carried up through the food chain, eventually returning to the soil via animal waste and decay. However, these returns are small compared to the amount of phosphate which is continually eroding from the land to the oceans each year. Phosphorus, more than any other element, can become the limiting factor for agricultural plant growth. Many tonnes of phosphate rock are mined each year in the production of fertilizers to replace some of the phosphates lost from farmland through erosion, crop production exports and lawns, and to make phosphate 10

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13 1) Phosphate Rocks: Rocks rich in phosphate (PO4) ions are an essential part of DNA and RNA in living organisms. Phosphorus is also found in cell membranes (as fats called phospholipids). Apatite: Ca 5 (PO 4 ) 3 OH most common form of calcium phosphate 13

14 2) Mining of rocks rich in phosphorous: The polyatomic ion, phosphate, is the main source of phosphorous on Earth. The principal purpose of mining rocks rich in phosphate is for agricultural use. Phosphates are an essential ingredient in fertilizers and without it in the soil plants do not grow. 14

15 3) Fertilizers contain both nitrogen (as ammonium ion- NH4) and phosphates. Both are essential for living cells. Nitrogen is needed for proteins, DNA,RNA; PO4 for DNA, RNA. If farmers place too much fertilizer on their fields, they may alter the phosphorus cycle. Since phosphorus is a limiting factor in the living things in water, excesses entering phosphates from farmland runoff (erosion) may cause rapid growth of algae and other kinds of plants that live in water. This can cause the water to become clogged with organisms, which may change the amount of flow of water. 15

16 4) The growth of crops and plants removes phosphates and nitrogen from the soil. These go to make up amino acids, proteins, DNA and RNA which are essential for growth of the plants/crops. 16

17 5) SOIL PHOSPHATES: Soil phosphates are added to soil by fertilizers or by the excretion products of living things. 17

18 6) PLANTS: Plants (producers) are the key element to passing on phosphates to other living things. These enter the plants through the root system and become part of the plant's DNA and RNA. 18

19 7) ANIMALS: Animals receive their phosphates from producers either directly (first order consumers) or indirectly (Second, third and higher order consumers) 19

20 8) EXCRETION: Through feces and urine (and decay of dead plants and animals), phosphates return to the soil a) to be carried to other areas by erosion or b) to return to producers (plants). 5, 6, 7 and 8 are part of the land or terrestrial phase of the phosphorus cycle. 20

21 9) DISSOLVED PHOSPHATES: Phosphates are slowly leached (dissolved) from rocks by chemical weathering (see calcium cycle). This is done through rain and melting snow. The water carries it into waterways where it enters the water or aquatic phase of the phosphorus cycle). 21

22 10) PLANTS: Dissolved phosphates are first incorporated into the producers of aquatic systems (water plants, algae, etc). Just as on land, the producers are the key to sea animals receiving P04. 22

23 11) ANIMALS: Animal life in water ingest the plants. This is how these animals (first order consumers) receive their phosphate). Other sea animals receive their phosphate either directly (first order consumers) or indirectly (second or higher order consumers). 23

24 12) EXCRETION: Sea life returns phosphates as dissolved phosphates through death or through excretion of waste materials from their cells or bodies. This can return to producers or can settle to the bottom of the waterways and form hardened marine sediments. Steps 9, 10, 11 and 12 make up the water phase of the Phosphorous Cycle. 24

25 13) MARINE SEDIMENTS: Marine sediments containing phosphates can remain at the bottom of a body of water indefinitely. It comes to the surface of the earth through the process of crustal uplift. This is a process where huge forces in the earth cause bodies of land to rise. The rise can be so significant that phosphate rich rocks occur in mountainous regions or any other place on the surface of the earth (this is why scientists have found skeletons of sea life high on mountain slopes, far from any ocean). CRUSTAL UPLIFT IS CAUSED BY PLATE TECTONICS (movement of the crustal plates of the earth). 25

26 14) EROSION: Erosion is the process by which earth materials are moved from one place to another. In the case of the Phosphorous Cycle (and all other nonmetal cycles), this refers to surface runoff (water) carrying phosphates (in a dissolved form) to a water environment. 26

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29 phosphate distribution in the water column of an equatorial latitude open ocean site Ocean Note the phosphorus content is nearly zero at the surface because all phosphate is quickly used by phytoplankton. Phosphate content quickly rise below the photic zone because respiration continues without photosynthesis. Also decomposition of organic matter adds phosphate back to the water column. 29

30 At mid latitudes, there is a more marked seasonality of nutrient levels in the surface ocean. During winter time, less light reaches the photic zone and productivity goes down. Nutrient levels thus rise. During spring time, light levels increase and the added available nutrients create 'bloom' conditions. 30

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