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Content: Nitrate reduction and the aquatic environment The processes

DENITRIFICATION BELOW THE ROOT ZONE Vibeke Ernstsen Geological Survey of Denmark and Greenland (GEUS) Plantekongres 2006, Herning, 10. januar 2006. Content: Nitrate reduction and the aquatic environment The processes The unsaturated zone - distribution, and potential for reduction

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Content: Nitrate reduction and the aquatic environment The processes

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  1. DENITRIFICATION BELOW THE ROOT ZONEVibeke ErnstsenGeological Survey of Denmark and Greenland (GEUS)Plantekongres 2006, Herning, 10. januar 2006

  2. Content: • Nitrate reduction and the aquatic environment • The processes • The unsaturated zone - distribution, and potential for reduction • Saturated zone - potentiale for reduction • The water flowpattern and distribution of nitrate

  3. Reduction by organic matter: • 5 C + 4 NO3- + 2 H2O  2 N2 + 4 HCO3- + CO2 • Reduction by pyrite: • 5 FeS2 + 14 NO3- + 4 H+ 7 N2 + 10 SO42- + 5 Fe2+ + 2 H2O • Reduction by ferrous iron - N2: • 5 Fe2+ + NO3- + 12 H2O  5 Fe(OH)3 + 0.5 N2 + 9 H+ • Reduction by ferrous iron - NH4: • 8 Fe2+ + NO3- + 21 H2O  8 Fe(OH)3 + NH4+ + 14 H+ • Reduction med methane: • 5 CH4 + 8 NO3- + 3 H+ 4 N2 + 5 HCO3- + 9 H2O • biological or abiotic process - anoxic environment Nitratereduction - possible processes

  4. Reduce compounds: • bioavailable organic matter • reduced sulfur (pyrite & hydrogen sulphide) • available ferrous iron (exchangeable/structural) • manganese • methane • ? SOME ARE USED UP - OTHER ARE RENEWABLE

  5. Nitratreduction - unsaturated zone • biological or abiotic process - anoxic environment • potential of nitrate reduction relates to the regeneration • of reduced compounds - the inherited pools are used up • Vegetation - renewable source of organic matter • leaching from the surface • in the root zone - roots etc. • fauna and flora incl. bacteria • Organic matter retension: • sorption • compleks-binding • used up • precipitate • etc. Maximum 3 meters

  6. Nitrate reduction - below the usaturated zone Ramsømagle SBIV SBI SBIII SBV SBVI SBXII SBIV SBVIII SBVII GWT SBIII SBIX Ramsølille SBVI SBXI Viby SBV SBX SBI SBXII SBVIII SBIX SBX SBXI Kristiansen et al., 1991 SBVII Reduction in anoxic environments by the inherited reduced compunds at different depths. Considerable differences related to geology.

  7. Calculation of redox capacity - exsamples • Sandy samples: 1-2 % clay • Organic matter: 0,15 % C • Pyrite: 0,012 % S • Ferrous iron: 0 % Fe • Capacity: 160 mol nitrate pr. m3 • Pr. meter: 465 years • Clayey samples: 30-40 % clay • Organic matter: 0,10 % C • Pyrite: 0,005 % S • Ferroous iron: 1,2 % Fe • Capacity: 150 -180 mol nitrate pr. m3 • Pr. meter: 420 - 500 years THIS KIND OF CALCULATION DOES NOT TAKE INTO ACCOUNT THE REACTIVITY OF THE COMPOUNDS • Clayey samples: 15 % clay • Organic matter: 0,05 % C • Pyrite: 0,003 % S • Ferroous iron: 0,9 % Fe • Capacity: 90-110 mol nitrate pr. m3 • Pr. meter: 250 - 300 years • Sandy samples: 1-2 % clay • Organic matter: 0,03 % C • Pyrite: 0,005 % S • Ferrous iron: 0 % Fe • Capacity: 30 mol nitrate pr. m3 • Pr. meter: 95 years

  8. LITERATURE: • Miljøstyrelsen. 2001. Arbejdsrapport nr. 24 • Miljøstyrelsen. 2005. Miljøprojekt nr. 1023, 1024 og 1025 • Ernstsen, V., H.J. Henriksen og F. von Platen. 2001. Principper for beregning • af nitratreduktion i jordlagene under rodzonen. Arbejdsrapport nr. 24. • Ernstsen, V. 2005. Nitratreduktion i den umættede zone. Miljøprojekt 1023. • Ernstsen, V., Jørgensen, N., og Lynge, C.R. 2005. Metode til analyse af • reducerende stoffer i sedimenter. Miljøprojekt 1024. • Ernstsen, V. 2005. Undersøgelse af reaktiviteten af reducerende stoffer i nogle • danske sedimenter - et pilotstudie. Miljøprojekt 1025.

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