The Phosphorus Cycle

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Barry Percival Wade
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1 The Phosphorus Cycle No gaseous form, present in + 5 valence state phosphate PO3 (4-) Lecture Outline Introduction Global Cycle Overview Major Forms Terrestrial Processes Freshwater Processes Ocean Processes Anthropogenic Influences 1

Introduction Phosphorus (P) is an essential nutrient

ATP DNA Phospholipids Introduction P is an essential

during photosynthesis Marine phytoplankton: 106CO 2 +

P + 106O 2 (organic matter) Terrestrial plants: 830CO 2

2 Introduction Phosphorus (P) is an essential nutrient for all life Major role in biological metabolism RNA ATP DNA Phospholipids Introduction P is an essential nutrient for plants/phytoplankton to build tissues during photosynthesis Marine phytoplankton: 106CO H 2 O + 16NH 3 + H 3 PO 4 + hv C 106 H 179 O 68 N 16 P + 106O 2 (organic matter) Terrestrial plants: 830CO H 2 O + 9NH 3 + H 3 PO 4 + hv C 830 H 1230 O 604 N 9 P + 830O 2 2

The Global Phosphorus Cycle Units: metric

3 The Global Phosphorus Cycle Units: metric tons running downhill The Global Phosphorus Cycle 4 major parts: 1) Tectonic uplift 2) Erosion and chemical weathering 3) River transport to lakes and oceans 4) Sedimentation and burial 5) Eventual uplift completes the cycle 3

4 The Global Phosphorus Cycle No significant gaseous component Atmospheric P associated with dust and sea spray Phosphorus: Terrestrial Processes From Schlesinger,

characteristics Phosphate: PO 4 3- Simplest form of phosphorus in the environment Only form that is

5 Phosphorus: forms and characteristics 1 stable isotope Main oxidation state: +5 (P 0 does not exist in nature) Dissolved Inorganic Organic Particulate Phosphate: PO 4 3- Phosphorus: forms and characteristics Phosphate: PO 4 3- Simplest form of phosphorus in the environment Only form that is readily available for biotic uptake. Highly reactive with cations (e.g. Fe, Ca) AKA: Soluble Reactive Phosphate (SRP) 5

6 Phosphorus: Terrestrial Processes Apatite mineral Ca 5 (PO 4 ) 3 OH P Crustal abundance: (0.1%) Bedrock weathering is the main P source in soils Weathered phosphate can be taken up by plants OR React with Al and Ferric oxides Phosphorus: Terrestrial Processes 6

Phosphorus: Terrestrial Processes P availability is

Ca in high ph soils 5.7 is ideal ph for P availability.

crystallization of Al and Fe hydrous oxides From Elements

with low P availability in soil: Increase root volume

7 Phosphorus: Terrestrial Processes P availability is controlled by precipitation of Al and Fe in low ph soils & Ca in high ph soils 5.7 is ideal ph for P availability. Organic acids can increase P availability by inhibiting the crystallization of Al and Fe hydrous oxides From Elements April 2008 Phosphorus: Terrestrial Processes How plants deal with low P availability in soil: Increase root volume Re-absorb P from leaves before litter fall and/or quickly recycle P in litter fall. 7

Phosphorus: Terrestrial Processes How plants deal with low P availability in soil: Mycorrhizae: Fungi that have a symbiotic relationship between them and the plant root Release enzymes and oxalic

8 Phosphorus: Terrestrial Processes How plants deal with low P availability in soil: Mycorrhizae: Fungi that have a symbiotic relationship between them and the plant root Release enzymes and oxalic acids that can: increase weathering of apatite, solubilize Fe, Al, and Ca bound P, and remove Fe, Al, and Ca from solution through chelation and precipitation. Phosphorus: Terrestrial Processes 3 locations of Terrestrial P: Bedrock, soil, living organisms. Table 1 (modified) 8

Phosphorus: Freshwater Processes-- Groundwater P

Freshwater Processes-- Rivers The main global

9 Phosphorus: Freshwater Processes-- Groundwater P in groundwater is low even in areas of high soil P it is tightly bound in insoluble minerals and/or quickly scavenged by plants Phosphorus: Freshwater Processes-- Rivers The main global flux of P is in rivers >90% of P in rivers is particle bound 9

pollution Phosphorus: Freshwater Processes-- Lakes Phosphorus is the most widely studied element in lakes major role in

10 Phosphorus: Freshwater Processes-- Rivers Phosphate buffering mechanism- Suspended sediments can act as a source/sink for dissolved inorganic P (DIP) This maintains near constant levels of DIP in rivers Protects against P depletion and excess pollution Phosphorus: Freshwater Processes-- Lakes Phosphorus is the most widely studied element in lakes major role in biological metabolism Often in limited supply, but too much can cause problem eutrophication Reliant on watershed inputs 10

11 Phosphorus: Freshwater Processes-- Lakes P is a good measure of lake productivity: <5 ug/l = low productivity it >100 ug/l high productivity. Phosphorus: Freshwater Processes-- Lakes 11

12 Phosphorus: Freshwater Processes-- Lakes Much of the hypolimnetic increase in P is near the sediments Phosphorus: Freshwater Processes-- Lakes Under oxic conditions the P exchange equilibrium is unidirectional towards the sediments P concentration in sediments is much greater than overlying water and is bound with ferrous iron, If the sediment micro-zone is oxic then the If the sediment micro-zone is oxic, then the release of P is prevented. When it is anoxic, P is released due to ferric oxide reduction 12

During summer soluble P accumulates in the hypolimnion with fall turnover,

13 LAKES Phosphorus: Freshwater Processes-- Lakes Seasonal effect: Summer higher temperatures, more OM loading, more microbial activity = anoxic conditions During summer soluble P accumulates in the hypolimnion with fall turnover, ferrous iron is oxidized and precipitates out most of the P as ferric phosphate. 13

Phosphorus: Ocean Processes River inputs are the main source of P to the oceans

certain conditions (anoxic) Some is take up by algae and some is directly deposited

stimulates primary productivity in oceans Seawater: C:N:P CNP- 1,000:15:1 15 1

14 Phosphorus: Ocean Processes River inputs are the main source of P to the oceans Some particulate t bound P released as ph of water changes or if deposited under certain conditions (anoxic) Some is take up by algae and some is directly deposited Ocean sediments are the largest store of global P Phosphorus: Ocean Processes P stimulates primary productivity in oceans Seawater: C:N:P CNP- 1,000:15: Marine phytoplankton: C:N:P - 106:16:1 N and P are closely limiting N most but varies spatially 14

15 Phosphorus: Ocean Processes Global Warming The limiting nature of P links it to climate change C and P cycles linked through photosynthesis Marine phytoplankton: 106CO H 2 O + 16NH 3 + H 3 PO 4 + hv C 106 H 179 O 68 N 16 P + 106O 2 Terrestrial plants: 830CO H 2 O + 9NH 3 + H 3 PO 4 + hv C 830 H 1230 O 604 N 9 P + 830O 2 Phosphorus: Ocean Processes Global Warming P limits primary productivity, which influences atmospheric CO 2 levels Interesting feedback to consider. During cold periods, sea level drops, exposing coastal sediments (high in P) to erosion remobilizing P, enhancing productivity and reducing CO2 and enhancing cooling trends. 15

16 Phosphorus: Anthropogenic impacts Major use of P is in agriculture Alexander & Smith, USGS Also use in home lawn/gardens Phosphorus: Anthropogenic impacts Most P mined from marine sedimentary rocks. Biggest P mine in the US is in Florida 16

Nature v461- Estimate reserves will last 125 years at our

igneous and weathering products and guano Phosphorus:

to streams can cause eutrophication Since no major

and erosion then the land can become infertile Almost all

17 Nature v461- Estimate reserves will last 125 years at our current rate 80% comes from sedimentary deposits Rest igneous and weathering products and guano Phosphorus: Anthropogenic impacts Deforestation increases P loading to streams can cause eutrophication Since no major atmospheric source of P, once it is removed in biomass and erosion then the land can become infertile Almost all P in rainforest is in living material Dams have stopped transport to oceans 17

Phosphorus: Anthropogenic impacts P from domestic sewage,

Historically in the US 2 million tons of P in detergents

Anthropogenic impacts Many other anthropogenic sources:

pesticides, food processing, garbage leachate, livestock

18 Phosphorus: Anthropogenic impacts P from domestic sewage, human waste and detergents. Historically in the US 2 million tons of P in detergents annually (7-12% of weight of detergent was P) Phosphorus: Anthropogenic impacts Many other anthropogenic sources: plasticisers, flame-retardants, corrosion inhibitors, pesticides, food processing, garbage leachate, livestock industries--feedlots Overall: 3X increase in ocean P loading above pre industrial levels 18

Phosphorus and Sulfur

Global Change Instruction Program Phosphorus and Sulfur The Important Nutrient Phosphorus Phosphorus is a key nutrient, fueling organic productivity on land and in water. A portion of its cycle is shown