What to do with extra electrons how combating eutrophication may affect mineralization pathways

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1 What to do with extra electrons how combating eutrophication may affect mineralization pathways Jouni Lehtoranta Finnish Environment Institute Marine Research Centre

2 Sun e - Energy goes through the system (open system) Producers Consumers Nutrients cycle in the system (closed system) Life is based on electron transfer i.e. redox - reactions Inorganic nutrient pool Decomposers Life on Earth just slows down the flow of solar energy Nasa

3 Oxygen cycle Transfer of electrons from water to organic carbon Oxidation i.e. transfer of electrons from organic carbon to????? CO 2 + H 2 O [CH 2 O] + O 2 [CH 2 O] + O 2 CO 2 + H 2 O Wikipedia

4 Pathways of organic matter oxidation i.e. transfer of electrons Reduction reaction Formula Depth in sediment oxic Aerobic respiration CH 2 O + O 2 CO 2 +H 2 O mm anoxic Denitrification 5CH 2 O + 4NO H + 5CO 2 + 2N 2 + 7H 2 O mm anoxic Manganese reduction CH 2 O + MnO 2 + 4H + CO 2 + 2Mn H 2 O cm anoxic Iron reduction CH 2 O + 4FeOOH + 8H + CO 2 + 4Fe H 2 O cm anoxic Sulfate reduction 2CH 2 O + SO H + 2CO 2 + H 2 S + 2H 2 O m anoxic Methanogenesis CH 3 COO - + Η + CH 4 + CO 2 HCO H 2 + H + CH 4 + 3H 2 O Anaerobic mineralization causes indirectly O 2 consumption (reoxidation of NH 4, Mn(II), Fe(II), H 2 S, CH 4 ) O 2 is the ultimate acceptor of electrons released during mineralization In long run oxygen production = oxygen consumption (1:1) m

5 Pathways of organic matter oxidation i.e. transfer of electrons Reduction reaction Formula Depth in sediment O 2 concentration in oxic Aerobic respiration atmosphere CH 2 O + is O21% 2 CO 2 +H 2 O mm and it is stable (annual anoxic - Denitrification fluctuations 5CH 2 O are + 4NO ±0.002%) 3 + 4H + 5CO 2 + 2N 2 + 7H 2 O mm anoxic Manganese reduction CH 2 O + MnO 2 + 4H + CO 2 + 2Mn H 2 O cm anoxic Iron reduction CH 2 O + 4FeOOH + 8H + CO 2 + 4Fe H 2 O cm 2- anoxic Sulfate reduction 2CH 2 O + SO 4 + 2H + 2CO 2 + H 2 S + 2H 2 O m anoxic Methanogenesis CH 3 COO - + Η + CH 4 + CO 2 m There HCO has to 4Hbe 2 + H + CH 4 + 3H 2 O a global balance between Anaerobic mineralization primary production causes vs. indirectly O 2 consumption (reoxidation of mineralization NH 4, Mn(II), and Fe(II), burial H 2 S, CH 4 ) O 2 is the ultimate acceptor of electrons released during mineralization In long run oxygen production = oxygen consumption (1:1) Not true in geological timescales: Long term burial of carbon and formation of FeS 2 (iron oxidizes sulphur) we have free O 2 in atmosphere

6 Is marine sediment a good sink for organic matter? Organic matter is continuously degraded in sediments and carbon fixed by phytoplankton in oceans is almost completely (99.9%) oxidized back to CO 2 (Middelburg & Meusmann, Science 316: ; Hedges & Keil 1995: Mar. Chem. 49: 81-86) Eventual preservation of organic matter is closely coupled to Flux of organic carbon to sediments (compared to amount and quality of electron acceptors) Oxygen exposure time before burial To surface area of clay particles in sediments (Rothman & Forney 2007: Science 316: )

7 What kind of bottom sediment we would like to have when combating eutrophication? What to do with extra electrons (organic matter) and which electron acceptors we prefer in mineralization

8 Aquatic Ecosystems and World Wide Eutrophication problem glossary/o_r/rain_splash.html Seija Hällfors Photo library on Soil erosion processes

9 Aquatic Ecosystems and World Wide Eutrophication problem glossary/o_r/rain_splash.html Seija Hällfors Photo library on Soil erosion processes

10 Aquatic Ecosystems and World Wide Eutrophication problem glossary/o_r/rain_splash.html Seija Hällfors Photo library on Soil erosion processes

11 Pathways of organic matter oxidation Reduction reaction Formula Depth in sediment oxic Aerobic respiration CH 2 O + O 2 CO 2 +H 2 O mm anoxic Denitrification - 5CH 2 O + 4NO 3 + 4H + 5CO 2 + 2N 2 + 7H 2 O mm anoxic Manganese reduction CH 2 O + MnO 2 + 4H + CO 2 + 2Mn H 2 O cm anoxic Iron reduction CH 2 O + 4FeOOH + 8H + CO 2 + 4Fe H 2 O cm anoxic Sulfate reduction 2CH 2 O + SO H + 2CO 2 + H 2 S + 2H 2 O m anoxic Methanogenesis CH 3 COO - + Η + CH 4 + CO 2 HCO H 2 + H + CH 4 + 3H 2 O m Mineralisation leads to formation of chemical energy in dissolved and gaseous form (NH 4, Mn(II), Fe(II), H 2 S, CH 4 ) Any favourites?

12 Utilization of chemical energy (chemolithoautotrophs) NH 4 (O 2, NO 2-, Mn) Fe 2+ (O 2, NO 3-, Mn) S, HS -, H 2 S, FeS (O 2, NO 3-, Mn, Fe) CH 4 (O 2, SO 4, Fe???NO 3???) Recent great discoveries in microbial processes Anaerobic oxidation of methane by sulphate (AOM, Hoehler et al. 1994, Hindrichs et al. 1999) Anaerobic oxidation of ammonium (ANAMMOX, van de Graaf et al. 1995, Jetten et al. 1999) Microbiologists are searching for microbes capable to oxidize methane with nitrate and Fe(III) oxides

13 Electron transfer and combating eutrophication - any links to cycling of iron bound phosphorus?

14 Pathways of organic matter oxidation Reduction reaction Formula Depth in sediment oxic Aerobic respiration CH 2 O + O 2 CO 2 +H 2 O mm anoxic Denitrification - 5CH 2 O + 4NO 3 + 4H + 5CO 2 + 2N 2 + 7H 2 O mm anoxic Manganese reduction CH 2 O + MnO 2 + 4H + CO 2 + 2Mn H 2 O cm anoxic Iron reduction CH 2 O + 4FeOOH + 8H + CO 2 + 4Fe H 2 O cm anoxic Sulfate reduction 2CH 2 O + SO H + 2CO 2 + H 2 S + 2H 2 O m anoxic Methanogenesis CH 3 COO - + Η + CH 4 + CO 2 HCO H 2 + H + CH 4 + 3H 2 O m

15 Difference between microbial and chemical Fe reduction Microbial Fe(III) oxide reduction DissFe 2+ cells DissP Chemical Fe(III) oxide reduction Geobacter metallireducens DissP FeS/FeS 2 2 FeOOH + 3 H 2 S + 4 H + 2 FeS + S H 2 O, with possibly a further reaction to pyrite (Berner 1970): FeS + S 0 FeS 2

16 Fe and P cycling Oligotrophic marine system Microbial reduction dominates Fe reduction Eutrophic marine system Chemical reduction dominates Fe reduction Water O 2 Fe(III)oxides Fe(III) bound P org-p Fe(III) Oxic sediment binds PO Anoxic sediment Burial of Fe(III) bound P Fe(III)oxides Fe(III) bound P org P 3-4 O 2 Efficient Fe and P cycling Fe(III) reduction Fe(III) reduction by H S 2 Fe:P>2 Fe(II) Solid FeS FeS 2 State 1 Low efflux of P PO 4 3- Water O 2 Anoxic sedim Fe(III)oxides Fe(III) bound P org P Fe(III) binds PO 3- partly 4 Fe(III)oxides Fe(III) bound P org P Little Fe(III) bound P buried O Inefficient Fe and P cycling Fe(III) reduction by H S 2 2 Fe(III) reduction High efflux of P Fe:P<2 Fe(II) Solid FeS 2 FeS State 2 PO 4 3- A B

17 Fe and P cycling Oligotrophic marine system Microbial reduction dominates Fe reduction Eutrophic marine system Chemical reduction dominates Fe reduction Water O 2 Fe(III)oxides Fe(III) bound P org-p Fe(III) Oxic sediment binds PO Anoxic sediment Burial of Fe(III) bound P Fe(III)oxides Fe(III) bound P org P 3-4 O 2 Efficient Fe and P cycling Fe(III) reduction Fe(III) reduction by H S 2 Fe:P>2 Fe(II) Solid FeS FeS 2 State 1 Low efflux of P PO 4 3- Water O 2 Anoxic sedim Fe(III)oxides Fe(III) bound P org P Fe(III) binds PO 3- partly 4 Fe(III)oxides Fe(III) bound P org P Little Fe(III) bound P buried O Inefficient Fe and P cycling Fe(III) reduction by H S 2 2 Fe(III) reduction High efflux of P Fe:P<2 Fe(II) Solid FeS 2 FeS State 2 PO 4 3- A B

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19 Regional pattern in Fe to P ratio can be explained with microbial processes Intensive monitoring of water quality Monitoring of harmful substances in tissues of fish and evertebrates Zoobenthos monitoring Microbial iron reduction dominates 1000 State 1 Fe to P ratio 2:1 moles State State N km Tot-Fe to DIP ratio (mol:mol) ,1 0,01 State Station Microbial sulphate reduction dominates Lehtoranta, Ekholm & Pitkänen (J. Mar. Syst 2008)

20 In freshwater systems Oxygen exposure time before burial is short for org. C What is the importance of anaerobic pathways in mineralization? Flux of organic carbon compared to amount of electron acceptors in specific system can be high: inhibition of coupled nitrification/denitrification? large sulphide formation, blocking of Fe cycle resulting in high release of P? effective methane production?, efficient C burial? How we affect the flux of electron acceptors when combating eutrophication?

21 Amendment of electron acceptor Positive Negative Nitrate Inhibition of Fe, SO 4 reduction and CH 4 formation Acts as nutrient Iron oxides Coupled Fe and P cycling, inhibition of SO 4 reduction and CH 4 formation Increase of Fe causes problems for water purification Sulphate Inhibition of methane formation and oxidation of methane Formation of toxic H 2 S and blocking of Fe cycling

22 Summary Micro-organisms are main drivers in biogeochemical cycles and they control global redox state Consequences of amendments have to be understood in a wide perspective: they may have an effect on fundamental biogeochemical cycles in recipient aquatic systems (i.e. cycling of C, Mn, Fe, S, N, P)

23 Photo Petri Ekholm

24 Artificial oxygenation (PROPPEN-project) Delivery of oxygen to near-bottom water in order to trigger preferable mineralization pathway (Pitkänen, Lehtoranta) Shift in microbial processes State indicator 2 Anoxic sediment surface SO reduction dominates 4 Thresholds B 1 Oxic sediment surface Microbial Fe reduction dominates Flux of labile organic C

25 MYTVASII Coastal sediment manipulation with organic matter/electron acceptors to control the anaerobic mineralization processes (MYTVASII, Ekholm) Fresh sample Anoxia, No carbon addition Anoxia, Carbon addition 300 Cores open Cores closed Fe:P < 2 (C+) Cores open 0.02 Concentration (µmol l -1 ) Fe(II) C+ Fe(II) C- DP C+ DP (C-) Fe:P < 2 (C-) Days 1.6 2B Lehtoranta, Ekholm and Pitkänen. Thresholds in coastal regions a matter of sediment microbial processes, AMBIO 2009

26 Application Up-stream thinking: Soil erosion from a point of view of processes in marine sediment (MYTVAS, Ekholm, Lehtoranta) Day 16: Clay+ labile C + sulphate + Baltic sediment microbes Day 23: Clay+ labile C + sulphate + Baltic sediment microbes Photo: Pasi Valkama

27 Wauer et al Wat. Res.39:

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