Applying the (15)N labelling technique to material derived from a landfill simulation experiment to understand nitrogen cycle processes under aerobic and anaerobic conditions

Reactive nitrogen (N) species, such as ammonium (NH(4)(+)), nitrate (NO(3)) and gaseous nitrous oxide (N(2)O), are released into the environment during the degradation of municipal solid waste (MSW), causing persistent environmental problems. Landfill remediation measures, such as in-situ aeration, may accelerate the degradation of organic compounds and reduce the discharge of ammonium via leachate. Nonetheless, the actual amount of N in the waste material remains relatively constant and a coherent explanation for the decline in leachate ammonium concentrations is still lacking. Hence, the present study aimed to elucidate the dynamics of N and its transformation processes during waste degradation. To this end, the gross rates of organic N mineralization and nitrification were measured using (15)N pool dilution in waste material derived from a landfill simulation reactor (LSR) experiment. The results revealed a high potential for N mineralization and nitrification, the latter of which declined with the diminishing amount of extractable ammonium (after aeration). The analysis of the concentration and isotopic composition of N(2)O formed confirmed incomplete denitrification as the main source for N(2)O. Moreover, the natural abundance of (15)N was investigated in various waste N pools to verify the conclusions drawn from the (15)N tracing experiment. δ(15)N values of total waste N increased during aeration, indicating that nitrification is the major driver for N losses from aerated waste. The application of stable isotopes thereby allowed unprecedented insights into the complex N dynamics in decomposing landfill waste, of their response to aeration and their effect on hydrological versus gaseous loss pathways. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10532-022-10000-7.