If you have an extra electron where do you put it?

Transcription

1 If you have an extra electron where do you put it? Jouni Lehtoranta Finnish Environment Institute Marine Research Center Systems Ecological Perspectives on Sustainability Conference

2 Spatial scale Redox reactions - Significance in large scales - Description of main reactions APERITIF TALK TIME Linking reactions to sediment phosphorus - Microscale processes From micro- to macroscale again Human impact on redox-reactions LUNCH

3 Sun e - Energy goes through the system (open system) Producers Consumers Life is based on electron transfer i.e. redox - reactions Inorganic nutrient pool Decomposers Nasa Nutrients cycle in the system (closed system) J. Lehtoranta

4 Transfer of electrons 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 J. Lehtoranta

5 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 - + 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) Not true in geological timescales: Long term burial of organic carbon and formation of FeS 2 (iron oxidizes J. Lehtoranta sulphur) we have free O 2 in athmosphere m

6 Biogeochemical cycles (closed system) Reservoir chemical is held for long periods of time in one place (coal and apatite deposits) Exchange pool chemical is held for only short period of time. Generally reservoirs are abiotic factors and exchange pools are biotic Residence the amount of time that a chemical is held in one place Abiotic compartments Water = hydrosphere Land = lithosphere Air = atmosphere

7 Terrestrial and aquatic systems Differences in reservoirs and exchange pools Nutrient pools a) Reactive sites b) Sites of nutrient storage Biota a) Lifespan of primary producers b) C:N, C:P of primary producers c) N-fixers d) Ratio consumers:producers Terrestrial Minerals, org. horizons, rhizosphere Soils, vegetation Long High Symbiotic with long-lived organisms Lower Lake Particles, sedim.-water Sediment, fish Short Low Free living Higher Prevalence of anoxia Rare, microsites only Sediments, hypolimnion

8 P-pools in marine and terrestrial living organisms P-pool (50 to 70 x g) in marine plankton is only 2 % of that in terrestrial living biomass However, the marine primary production incorporates 1200 x g P yr -1 is 3 to 4 times higher than the terrestrial incorporation rate

9 Turnover times ( residence ) The turnover time of living oceanic biomass is short: few days for prokaryotes week for phytoplankton few months for zooplankton In terrestrial systems the P is mainly bound to long-lived forests average turnover time for terrestrial living biomass is at least 10 years

10 What does this mean? Phosphorus cycles much faster in aquatic than terrestrial systems With a same amount of phosphorus we get more organic carbon (i.e. electron packages) into aquatic than terrestrial system

11 O 2 NO 3, Mn(IV), Fe(III), SO 4 CO 2 Seija Hällfors Photo: Ilkka Heikkinen, Inkoo

12 Energy flow goes through the system (open system) Proportion of background phosphorus Anthropogenic loading from Finland to the Baltic Sea is 30% phosphorus loading 70% Eutrophication increases amount of organic matter - Human actions have a large and growing importance on mineralization processes (redox-reactions) in aquatic systems

13 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 2-2CH 2 O + SO 4 + 2H + 2CO 2 + H 2 S + 2H 2 O m anoxic Methanogenesis CH 3 COO - + CH 4 + CO 2 HCO H 2 + H + CH 4 + 3H 2 O Canfield and Thamdrup 2009, Geobiology 7: m One element is missing Phosphorus J. Lehtoranta

14 Phosphorus: What kind of sediment we would like to have considering mineralization pathways? If you have an extra electron (organic matter) where do you put it (which electron acceptor you prefer) J. Lehtoranta

15 Pathways of organic matter oxidation Reduction reaction Formula Depth in sediment oxic Aerobic respiration Geobacter CH 2 O + O 2 CO 2 +H 2 O mm anoxic Denitrification metallireducens - 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 2-2CH 2 O + SO 4 + 2H + 2CO 2 + H 2 S + 2H 2 O m anoxic Methanogenesis CH 3 COO - + CH 4 + CO 2 Desulfovibrio vulgaris HCO H 2 + H + CH 4 + 3H 2 O Fe(III) is sensitive towards mineralization processes Phosphorus starts react on redox-reactions m J. Lehtoranta

16 Significance of sulphate Lehtoranta, Ekholm, Pitkänen Ambio 38: Lehtoranta & Ekholm 2013 Vesitalous 2: 40-42

17 Sulphate removed i.e. change in electron acceptor SO 4 2- (mg L -1 ) cores open cores closed cores open 100 A Fe(II) (mg L -1 ) cores open B Low sulphate High sulphate cores closed cores open cores open cores closed cores open DP (µg L -1 ) C Day Ekholm et al The effect of gypsum on phosphorus losses at the catchment scale. THE FINNISH ENVIRONMENT

18 Addition of organic carbon (i.e. change in electron donor) How microbial iron and sulphate reduction can be noticed after organic matter addition? 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 J. Lehtoranta Lehtoranta, Ekholm and Pitkänen 2009 Ambio 38:

19 Up-stream thinking: Soil erosion and anerobic microbial processes in brackish sediment Standard field soil Sandy clay ( mg ) 80 ml filtered Gulf of Finland water Incubation: At dark (a) +10 C, (b) +8 C (a) 308 d, (b) 745 d Natrium acetate ( mg C) Pasi Valkama 10 µl sediment Lehtoranta, J., Ekholm, P., Wahlström, S. Tallberg, P. and Uusitalo, R. Under revision

20 Mn 2+ Fe 2+ H 2 S, HS- FeS High dose of C Small amount of C

21 Laakso Johanna, Kahma Tuomas, Ekholm Petri, Lehtoranta Jouni, Uusitalo Risto, Yli-Halla Markku Constructed wetland of Ojainen in Jokioinen Black sediment indicating presence of Fe sulphides

22 Consequences of eutrophication linked to electron transfer in sediments J. Lehtoranta

23 Eutrophication associated hypoxic areas

24 Shift in microbial processes in the Baltic Sea? Shift in microbial processes 2 Anoxic sediment surfa ce SO reduction dominates 4 S. Knuuttila State indicator 1 Oxic sediment surface Microbial Fe reduction domina tes Driver Lehtoranta, Ekholm and Pitkänen 2009 Ambio 38: Threshold Flux of labile organic C J. Lehtoranta Could change in microscale processes driven by micro-organisms cause macroscale consequences?

25 phosphorus Winter surface concentration of phosphate in 2003 (µg l -1 ) Microbial iron reduction dominates? Iron oxides Tot-Fe to DIP ratio (mol:mol) ,1 0,01 State 1 State Station Eutrophy Microscale redox-processes driven by micro-organisms cause macroscale consequences phosphorus Microbial sulphate reduction dominates? Iron sulphides Lehtoranta J. Lehtoranta, Ekholm & Pitkänen (J. Mar. Syst. 74: ) J. Lehtoranta Data: PAPA Partners Figure: Mikko Kiirikki/SYKE

26 C:N:P 12/2/2014 Petri Ekholm Photos: Ekholm 26

27 Summary Eutrophication increases mineralization All terminal electron acceptors used produce CO 2 Reduced substances formed in the mineralization participate to further redox-reactions (Mn(II), Fe(II), H 2 S, CH 4 ) They have different consequences on the element cycles in the system So if you have an extra electron where do you put it, depends what you are trying to get

28 Thank you 28