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 Saturated zone - potentiale for reduction The water flowpattern and distribution of nitrate

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

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

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

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.

Clayey samples: 15 % clay Organic matter: 0,05 % C Pyrite: 0,003 % S Ferroous iron: 0,9 % Fe Capacity: mol nitrate pr. m 3 Pr. meter: 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: % clay Organic matter: 0,10 % C Pyrite: 0,005 % S Ferroous iron: 1,2 % Fe Capacity: mol nitrate pr. m 3 Pr. meter: 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

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