Abstract
Denitrification in floodplain soils is one key process that determines the buffering capacity of riparian zones in terms of diffuse nitrate pollution. One widely used approach to measure the denitrification potential is the acetylene inhibition technique that requires fresh soil samples. We conducted experiments with air-dried soils using a time series analysis to determine the optimal rewetting period. Thus, air-dried soil samples from six different floodplain areas in Germany were rewetted for 1 to 13days to 100% water-filled pore space. We analyzed nitrogen accumulated as N2O in the top of anaerobic flasks with and without acetylene by gas chromatography after four hours of incubation. We observed an overall optimal rewetting of at least seven days for complete denitrification. We also saw the strong influence of pH and field capacity on the denitrification product ratio; in soils with pH < 7, we hardly assumed complete denitrification, whereas the treatments with pH > 7 achieved stable values after seven days of rewetting. This advanced method provides the opportunity to carry out campaigns with large soil sample sizes on the landscape scale, as samples can be stored dry until measurements are taken.
Highlights
Floodplains that link the aquatic and terrestrial environment range from low-water to high-water levels and are characterized by floods and changing groundwater levels [1]
The subset of the 12 soil samples ranged from a pH of 5.15 to 8.66, whereas Nmin ranged from 0.21 mg/100 g dry matter (DM) to
In group I and II nitrous oxide (N2 O) emissions continued to rise over the rewetting period in some cases (e.g., #1 and #2), whereas in others they decreased after an initial increase (#3) and in others, we hardly found any N2 O emissions over the entire rewetting period (e.g., #4: mean N2 O emission rate 1.6 ± 0.9 ng N2 O-N g−1 h−1 )
Summary
Floodplains that link the aquatic and terrestrial environment range from low-water to high-water levels and are characterized by floods and changing groundwater levels [1]. They make a significant contribution to the biodiversity of landscapes and serve as important nutrient traps [2]. N2 helps to reduce the effects of mineralized nitrogen pollution [3,4]. It has long been considered as the most important process of removing nitrate permanently from soils. Further it is possible that ammonium produced via DNRA pathways is Geosciences 2020, 10, 431; doi:10.3390/geosciences10110431 www.mdpi.com/journal/geosciences
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