Land management effects on in-situ denitrification and N2O emission in natural and semi-natural land use types in two UK catchments.

Fotis Sgouridis1, Sami Ullah1
1 School of Physical and Geographical Sciences, Keele University

O 3.1 in Fluxes between the atmosphere and ecosystems

17.07.2014, 11:00-11:20, H17

Soil denitrification activity and the subsequent emission of N2O can be highly variable both spatially and temporally due to the effects of varied land use management practices within catchments on the biogeochemical regulators of denitrification. Whilst data and understanding of the controls of denitrification process at microbial and plot scale exist, quantification of in situ annual denitrification rates at catchment scales is scarce particularly in natural and semi-natural land use types in the UK. In situ denitrification (DNT) was measured monthly (April 2013-2014) in organic (peat bog, heathland, and acid grassland), forest (coniferous and deciduous), and grassland (improved and semi-improved) rural land use types in the Ribble-Wyre and Conwy River catchments in the UK. A static chamber technique according to the 15N-Gas Flux method1 was employed for quantifying the fluxes of 15N-N2 and 15N-N2O gases with the aim of attaining more accurate and wider spatio-temporal coverage of DNT measurements. Land use type significantly (p<0.05) influenced DNT rates, which ranged between 0 and 2.3 mg N m-2 h-1. The mean annual denitrification rates of organic and forest soils (0.04 mg N m-2 h-1) was 5 and 10 times less than that of semi-improved (0.2 mg N m-2 h-1) and improved (0.4 mg N m-2 h-1) grassland soils, respectively. The N2O emission followed a similar trend with lower fluxes from organic soils and higher from improved grasslands (range: 0 – 0.04 mg N m-2 h-1), whilst the N2O:N2 ratio was highest in the nitrate rich land uses (grasslands: 4%) and lowest in the nitrate poor soils (organic soils: 0.2%). The results suggested a difference in DNT rates between unmanaged/ low nitrate content versus managed/ high nitrate content land use types. This was further supported by the significant positive correlation between DNT and soil nitrate content, whilst the relative importance of other controlling factors (e.g. organic carbon, moisture, bulk density and pH), as these are influenced by the relative degree of land management within each land use type, exerted additional controls on DNT rates. Therefore, land management practices can have significant impacts on the biogeochemical controls of denitrification, and thus need consideration when modelling denitrification across large spatio-temporal scales and/or predicting the response of denitrification to land use change.

1R. Stevens and R. Laughlin, Nutr. Cycling Agroecosyst., 1998, 52, 131-139.

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last modified 2014-03-28