Published on February 7, 2008
Biogeochemistry of Phosphorus: Biogeochemistry of Phosphorus Carlo Heip & Jack Middelburg Netherlands Institute of Ecology Yerseke History of Phosphorus (1): History of Phosphorus (1) Discovered in 1669 by Hennig Brand: P is a white solid that not only glows in the dark, but also spontaneously ignites in air. Greek: Phos (light) and Phorus (bearing). Mid-1800s: P is a nutrient. Thereafter: P production from phosphorites Ca-PO4-minerals: reaction with sulfuric acid Still used today, but Cd, U, acid, gypsum sewage History of Phosphorus (2): History of Phosphorus (2) After 1900: role of P in energy transfer 1930-50-ies: discovery of adenosine triphosphate (ATP); recognition role of phosphate esters and elucidation structure of DNA 1970-ies: recognition role of P in eutrophication of lakes and coastal systems Inorganic Chemistry of P (1): Inorganic Chemistry of P (1) Isotopes: 31P: stable (15 protons + 16 neutrons) 32P: 14.3 days half-life (from nuclear reactions with Ar) 33P: 25.3 days half-life (from nuclear reactions with Ar and from 32Si decay) White phosphorus: P4 molecule Phosphine: PH3 (very small amounts due to pollution and microbial formation under anoxic conditions) Inorganic Chemistry of P (2): Inorganic Chemistry of P (2) Minerals: Apatite: Ca10(PO4)6X2 where X=OH-, F-, Cl- 95 % of all P in earth’s crust main constituent of phosphorites main P bearing mineral in igneous rocks teeth, bones, scales Vivianite: Fe3(PO4)2·8H20 in reducing fresh-water sediments Inorganic Chemistry of P (3): Inorganic Chemistry of P (3) Solution chemistry: dissociated anions of H3PO4 : H2PO4- HPO42- PO43- depends on pH and salinity freshwater: H2PO4- sea: HPO42- Inorganic Chemistry of P (4): Inorganic Chemistry of P (4) Speciation of phosphate in seawater at pH 8 Inorganic Chemistry of P (5): Inorganic Chemistry of P (5) Polyphosphates: P-O-P bonds: reactive: concentrations are low energy storage by organisms industrial and commercial applications: water softeners Organic Chemistry of P (1): Organic Chemistry of P (1) DNA and RNA contain and transfer genetic information Organic Chemistry of P (2): Organic Chemistry of P (2) ATP: for transmission and control of energy Organic Chemistry of P (3): Phospholipids are structural component of cell membrane Organic Chemistry of P (3) Proteins Phospho-lipid Biogeochemical Pools (1): Biogeochemical Pools (1) Size fractionation Dissolved: < 0.2 to 0.7 m filter Particulate: particles retained on filter Colloid problem Particulate Colloids Dissolved Biogeochemical Pools (2): Biogeochemical Pools (2) Dissolved Inorganic Phosphate (DIP): dissolved P pool that reacts with molybdate reagents under acidic conditions some problems: side reactions: Si, As, Ge acidification causes hydrolysis organic-P; serious problem: soluble reactive phosphorus or SRP Biogeochemical Pools (3): Biogeochemical Pools (3) Total Dissolved Phosphate (TDP): dissolved P pool that reacts with molybdate reagents under acidic conditions after conversion of all dissolved P into phosphate. Dissolved Organic Phosphorus (DOP): Is calculated by difference: DOP = TDP-DIP Some the term Soluble Non-reactive P (SNP) is used. Biogeochemical Pools (4): Biogeochemical Pools (4) Particulate P (PP): Total P of particulates retained on filter Particulate Organic P (POP): Organic P of particulates retained on filter: (450 oC heating to convert to inorganic P). Total P (TP): Total P without filtration. Biogeochemical Pools (5): Biogeochemical Pools (5) Particulate P is operationally defined into: Iron associated P Apatite-P Organic-P Detrital-P (from rocks) P Sorption (1) : P Sorption (1) Phosphate in solution interacts with a number of solid phases: Fe-oxides CaCO3 P Sorption (2) : P Sorption (2) Redox Processes and P : Redox Processes and P P has no significant redox chemistry but PH3: contrast with C, O, N and S However, it is indirectly affected by redox processes through its interaction with Fe redox dependent retention by bacteria: P storage aerobic bacteria >> anaerobic bacteria Atmospheric P: Atmospheric P The atmospheric part of the P cycle is very limited: mainly P associated with dust. Contrast with C and in particular N and S P during weathering : P during weathering P contained in apatite is readily released. P contained in xenotime, monazite (Ce/YPO4) does not become available Funghi attack, some say eat, P-minerals (symbiosis with plants) Liberated P can be re-adsorbed to Fe-oxides Aquatic P cycle: Aquatic P cycle Uptake by algae Uptake by bacteria Regeneration by bacteria Regeneration by other heterotrophs Interaction with solid phases PO4 uptake kinetics: PO4 uptake kinetics Uptake V = S * Vmax/ (Ks + S) PO4 distribution in ocean: PO4 distribution in ocean Stoichiometry: Redfield: Stoichiometry: Redfield C:N:P = 106:16: 1 Redfield, Ketchum & Richards (1963) Based on: Composition of marine particulate matter and algae Ratio during regeneration Ratio during uptake Redfield ratio concept works (1): Redfield ratio concept works (1) Redfield ratio concept works (2): Redfield ratio concept works (2) Redfield: one of the basic tools : Redfield: one of the basic tools Extended Redfield ratio: 138 O2: 106 C: 16 N: 1 P: 0.000x Trace element P or N can be used to quantify C-flux: P *106 = C-flux or N * 106/16 = C-flux GCM model Carbon Uptake of ocean is based on difference of PO4 in surface layer vs. subsurface layer times Redfield ratio: IPCC estimate is as good as Redfield ratio. Limiting nutrient assessment Slide32: Total N vs. Total P Inorganic N vs. Inorganic P N = 0 & P > 0: N is limiting P = 0 & N > 0: P is limiting Slide33: N-limiting ? P-limiting ? Inorganic Pools Total Pools Dissolved Organic Pool is N rich: Dissolved Organic Pool is N rich Redfield N vs. P limitation (1): N vs. P limitation (1) Oceanographers/Biogeochemists: P limits primary production on the longer term because N2 fixation can balance N shortage given time Marine Biologists: N is limiting because DIN:DIP ratio is lower than 16 and high turnover rate of N (based on 15N methods) N vs. P limitation (2): N vs. P limitation (2) Time scale: limiting nutrient may alternate with time (season, years, kyears) There is more: Si, Fe, …… Organic nutrient pools should be included Fluxes are more relevant than stocks (concentration) because of high turnover: yet this information usually is lacking Organic P pools do matter: Organic P pools do matter P pools turnover (days): P pools turnover (days) P balance of the ocean (1010 mol P): P balance of the ocean (1010 mol P) Atmospheric Input: 1 River Delivery: 3-15 Ocean Inventory 32,000 Hydrothermal: 0.4-0.65 Phosphorite: >8 Fe-oxide-P: 1.5-5.3 Organic: 1.1-4.1 Residence time of P in ocean: Residence time of P in ocean Residence time = stock/source or stock/sink Stock = 32,000 1010 mol P sinks = 11-34 1010 mol P yr-1 sources = 4-16 1010 mol P yr-1 Residence time: sinks: 9,300-29,100 year sources: 20,000-80,000 year Ocean P budget: steady-state? Pertubations in ocean P budget: Pertubations in ocean P budget Non-steady state vs. Mass balance error? Recovering from ice-ages? Time scale P turnover is similar to ice-age: causal relationship? River input during anthropocene = 3 times pristine input Ocean anoxic event: major role of P? Anoxia and P cycling: complex feedbacks (1): Anoxia and P cycling: complex feedbacks (1) Anoxic conditions in water causes more P regeneration: Fe-oxide-P is liberated anaerobic bacteria store less P More dissolved P results in more production More production sustains/enhances anoxic conditions A positive feedback! Anoxia and P cycling: complex feedbacks (2): Anoxia and P cycling: complex feedbacks (2) Negative feedbacks operate via oxygen and carbon dioxide in the atmosphere and their effect on weathering, hence riverine P fluxes. Negative feedbacks also operate via nitrogen cycle: denitrification/nitrogen fixation.