Sirvi Autor "Deb, Sushmita" järgi

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N transformations in nitrate-rich groundwaters: combined isotope and microbial approach
(2025) Deb, Sushmita; Espenberg, Mikk; Well, Reinhard; Bucha, Michał; Jakubiak, Marta; Mander, Ülo; Jędrysek, Mariusz-Orion; Lewicka-Szczebak, Dominika
This study explores nitrogen transformations in groundwater from an agricultural area utilizing organic fertilizer (wastewater from yeast production) by integrating isotope analysis, microbial gene abundance, and the isotope FRactionation And Mixing Evaluation (FRAME) model to trace and quantify nitrogen cycling pathways. Groundwater samples with elevated nitrate concentrations were subjected to controlled laboratory incubations with application of a novel low-level 15N tracing strategy to investigate microbial processes. Isotope analyses of nitrate, nitrite, and nitrous oxide (N2O), coupled with microbial gene quantification via quantitative polymerase chain reaction (qPCR), revealed a shift from archaeal-driven nitrification to bacterial denitrification in post-incubation suboxic conditions, stimulated by glucose addition. FRAME modelling further identified bacterial denitrification as the dominant pathway of N2O production, which was supported by increased nosZI, nirK, and nirS gene abundance and observed isotope effects. Simultaneously with the intensive nitrate reduction, it was observed that the majority of nitrite is likely produced through nitrification processes linked to dissolved organic nitrogen (DON) oxidation. Nitrate reduction had a minor contribution to the total nitrite pool. The results demonstrate the efficacy of integrating multi-compound isotope studies and microbial analyses to unravel nitrogen cycling mechanisms. This approach provides a robust framework for addressing nitrogen pollution in groundwater systems and improving water quality management strategies.
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N transformations in nitrate-rich groundwaters: combined isotope and microbial approach
(2025) Deb, Sushmita; Espenberg, Mikk; Well, Reinhard; Bucha, Michał; Jakubiak, Marta; Mander, Ülo; Jędrysek, Mariusz-Orion; Lewicka-Szczebak, Dominika
This study explores nitrogen transformations in groundwater from an agricultural area utilizing organic fertilizer (wastewater from yeast production) by integrating isotope analysis, microbial gene abundance, and the isotope FRactionation And Mixing Evaluation (FRAME) model to trace and quantify nitrogen cycling pathways. Groundwater samples with elevated nitrate concentrations were subjected to controlled laboratory incubations with application of a novel low-level 15N tracing strategy to investigate microbial processes. Isotope analyses of nitrate, nitrite, and nitrous oxide (N2O), coupled with microbial gene quantification via quantitative polymerase chain reaction (qPCR), revealed a shift from archaeal-driven nitrification to bacterial denitrification in post-incubation suboxic conditions, stimulated by glucose addition. FRAME modelling further identified bacterial denitrification as the dominant pathway of N2O production, which was supported by increased nosZI, nirK, and nirS gene abundance and observed isotope effects. Simultaneously with the intensive nitrate reduction, it was observed that the majority of nitrite is likely produced through nitrification processes linked to dissolved organic nitrogen (DON) oxidation. Nitrate reduction had a minor contribution to the total nitrite pool. The results demonstrate the efficacy of integrating multi-compound isotope studies and microbial analyses to unravel nitrogen cycling mechanisms. This approach provides a robust framework for addressing nitrogen pollution in groundwater systems and improving water quality management strategies.
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Transitional hypoxia during peatland water table fluctuations drives high N2O fluxes via shifting microbial pathways
(Volume 305, Part 1, 2026) Masta, Mohit; Ali Kazmi, Fahad; Espenberg, Mikk; Visnapuu, Triinu; Sennett, Louise B.; Eving, Lauri; Lewicka-Szczebak, Dominika; Deb, Sushmita; Khanongnuch, Ramita; Kuusemets, Laura; Kupper, Priit; Butterbach-Bahl, Klaus; Mander, Ülo
Nitrogen (N) cycling in peatlands is sensitive to variations in water table, temperature, and soil moisture. Water table fluctuations in peatlands can trigger the formation of transitional oxic and hypoxic zones within the peat and influence N2O fluxes. However, studies exploring these transitions by combining isotopic and microbial analyses are rare. This study assessed the impact of oxic-to-hypoxic transitions on N dynamics in drained peat soil. Birch-planted mesocosms were treated with 15N-NO3- and 15N-NH4+ tracers, while artificial fog generation allowed for the quantification of N2O exchange between the soil surface and the atmosphere. Rewetting reduced soil oxygen levels, significantly increasing N2O fluxes; peak value (162 ± 22.80 μg N m−2 h−1) was recorded under hypoxic conditions. During the transition, the abundance of nirK-type denitrifiers increased. N2O was initially enriched by the 15N-NH4+ tracer, followed by the 15N-NO3- tracer, which contributed significantly to the N2O flux under hypoxic conditions. The 3D FRAME isotope model attributed early N2O production to nitrification (Ni) and nitrifier denitrification (nD); however, it identified a dual contribution from nitrification (Ni) and bacterial denitrification (bD) during the later phases. NosZ genes were detected in birch leaf samples, suggesting a potential aboveground microbial N2O sink. 15N tracer also confirmed the solubility of soil N2O in fog droplets during the experimental period, but the fraction of dissolved N2O was found to be very low (<0.2%). Nonetheless, these findings warrant further research.