Assessment of excess N₂ and groundwater N₂O emission factors of nitrate-contaminated aquifers in northern Germany

D. Weymann (1) , R. Well (1) , H. Flessa (1) , C. von Der Heide (2) , M. Deurer (3) , K. Meyer (4) , C. Konrad (5) , W. Walther (5)

1 Soil Science of Temperate and Boreal Ecosystems
2 Inst. for Soil Science
3 HortResearch
4 Geries Ingenieure
5 Inst. for Groundwater Management

We investigated the dynamics of denitrification and nitrous oxide (N₂O) accumulation in 4 nitrate (NO₃^?) contaminated denitrifying sand and gravel aquifers of northern Germany (Fuhrberg, Sulingen, Thülsfelde and Göttingen) to quantify their potential N₂O emission and to evaluate existing concepts of N₂O emission factors. Excess N₂-N₂produced by denitrification ? was determined by using the argon (Ar) concentration in groundwater as a natural inert tracer, assuming that this noble gas functions as a stable component and does not change during denitrification. Furthermore, initial NO₃^? concentrations (NO₃^? that enters the groundwater) were derived from excess N₂ and actual NO₃^? concentrations in groundwater in order to determine potential indirect N₂O emissions as a function of the N input. Median concentrations of N₂O and excess N₂ ranged from 3 to 89 ?g N L^?1 and from 3 to 10 mg N L^?1 respectively. Reaction progress (RP) of denitrification was determined as the ratio between products (N₂O-N + excess N₂) and starting material (initial NO₃^? concentration) of the process, characterizing the different stages of denitrification. N₂O concentrations were lowest at RP close to 0 and RP close to 1 but relatively high at a RP between 0.2 and 0.6. For the first time, we report groundwater N₂O emission factors consisting of the ratio between N₂O-N and initial NO₃^?-N concentrations (EF1). According to denitrification intensity, EF(1) was smaller than the ratio between N₂O-N and actual NO₃^?-N concentrations EF(2). In general, these emission factors were highly variable within the aquifers. The site medians ranged between 0.00043?0.00438 for EF(1) and 0.00092?0.01801 for EF(2), respectively. For the aquifers of Fuhrberg and Sulingen, we found EF(1) median values which are close to the 2006 IPCC default value of 0.0025. In contrast, we determined significant lower EFs for the aquifers of Thülsfelde and Göttingen.

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]; Interfaces continentales, environnement; Océan, Atmosphère; Sciences de la Terre

D. Weymann, R. Well, H. Flessa, C. von Der Heide, M. Deurer, et al.. Assessment of excess N₂ and groundwater N₂O emission factors of nitrate-contaminated aquifers in northern Germany. Biogeosciences Discussions, 2008, 5 (2), pp.1263-1292. ⟨hal-00297988⟩