Diurnal patterns of N2O and NO emissions from soils are linked to diurnal oscillations of the soil temperature. Soil temperature diurnal oscillations dampen with increasing soil depth. Comparison of diurnal patterns of temperature at a range of depth with diurnal patterns of N2O or NO emissions may be used to locate the depth of maximum denitrification or nitrification activity. In a well-drained soil, denitrification occurs at deeper soil layers and nitrification in the upper soil layers.
In aquatic systems, very different diurnal denitrifica-tion patterns are reported. In shallow streams, lakes, or estuaries with good light penetration, the diurnal pattern ofbenthic microalgal production and associated rise in O2 concentration at the sediment surface, during the day inhibits denitrification. Consequently, larger denitrifica-tion rates can be observed at night. For rivers, however, the opposite was observed. Denitrification rates were higher during the day than night, in spite of maximum O2 concentrations during the day. It has been suggested that diurnal denitrification patterns are controlled by the nitrification cycling driven by diurnal variations in water pH and temperature.
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