DENITRIFICATION BELOW THE ROOT ZONE Vibeke Ernstsen Geological Survey of Denmark and Greenland (GEUS) Plantekongres 2006, Herning, 10. januar 2006.

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1 DENITRIFICATION BELOW THE ROOT ZONE Vibeke Ernstsen Geological 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

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4 Reduction by organic matter: 5 C + 4 NO 3 - + 2 H 2 O  2 N 2 + 4 HCO 3 - + CO 2 Reduction by pyrite: 5 FeS 2 + 14 NO 3 - + 4 H +  7 N 2 + 10 SO 4 2- + 5 Fe 2+ + 2 H 2 O Reduction by ferrous iron - N 2 : 5 Fe 2+ + NO 3 - + 12 H 2 O  5 Fe(OH) 3 + 0.5 N 2 + 9 H + Reduction by ferrous iron - NH 4 : 8 Fe 2+ + NO 3 - + 21 H 2 O  8 Fe(OH) 3 + NH 4 + + 14 H + Reduction med methane: 5 CH 4 + 8 NO 3 - + 3 H +  4 N 2 + 5 HCO 3 - + 9 H 2 O Nitratereduction - possible processes biological or abiotic process - anoxic environment

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

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8 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

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

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13 Clayey samples: 15 % clay Organic matter: 0,05 % C Pyrite: 0,003 % S Ferroous iron: 0,9 % Fe Capacity: 90-110 mol nitrate pr. m 3 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. m 3 Pr. meter: 95 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. m 3 Pr. meter: 420 - 500 years Sandy samples: 1-2 % clay Organic matter: 0,15 % C Pyrite: 0,012 % S Ferrous iron: 0 % Fe Capacity: 160 mol nitrate pr. m 3 Pr. meter: 465 years Calculation of redox capacity - exsamples THIS KIND OF CALCULATION DOES NOT TAKE INTO ACCOUNT THE REACTIVITY OF THE COMPOUNDS

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17 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.