National Environmental Research Institute

Denitrification from the root zone to streams

Gitte Blicher-Mathiesen

NERI

Department of Freshwater Ecology

Plant Congress 2006 January 10 and 11, 2006

National Environmental Research Institute

Nitrate reduction from the root zone to the sea

• Nitrate reduction: about 100.000 tonnes N/year

• Nitrate leaching from the root zone: 168.000 tonnes N/year

• N run off to the sea: 67.000 tonnes N/year

National Environmental Research Institute

Nitrate reduction occurs

• in aquifers• in wetlands and riparian areas• in the stream bottom• during water transport in streams and

lakes

National Environmental Research Institute

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National Environmental Research Institute

% N-retention

n_ret_1dec

< 20.0

20 - 25

25 - 30

30 - 35

35 - 40

40 - 45

45 - 50

50 - 55

55 - 60

60 - 63

N-retention (%) i 26 catchments

FromFYNS AMT

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Measured N-reduction inRiparian Areas

Study site Reduction(kg N/ha/year)

N-retention(%)

River Stevns 57 97

Rabis brook 398 56

River Gjern,4 meadows and fen 42 – 2,179 67-99

River Brede 92 71 (Hoffmann, 1998)

National Environmental Research Institute

Measured N-reduction i Riparian Areas, irrigated with drain - or stream water

Study site Reduction(kg N/ha/year)

N-retention(%)

Glumsø, reed forest* 520-2,725 54-65

River Stevns 350 99

Syv brook 300 72

River Store 530 48

River Gjern* 30-196 90-98

* Study with variable hydraulic load (Hoffmann, 1998)

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Outline of groundwater flow through riparian areas

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Riparian area

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Conclusion• N-reduction for DK about 100.000 tonnes N per y

• N-retention between root zone and streams

– sandy catchments 38 - 89 %

– loamy catchments 12- 47 %

– geology, discharge, tile drainage, lakes and wetlands/riparian areas

• Riparian areas

– reduction 32 - 2,100 kg N/ha/year

– N-load, geology, groundwater flowpath