No abstract

The industrial complex Neot Hovav, in Israel, is situated above an anaerobic fractured chalk aquitard, which is polluted by a wide variety of hazardous organic compounds. These include volatile and non-volatile, halogenated, organic compounds. In this study, we characterized the indigenous bacterial population in 17 boreholes of the groundwater environment, while observing the spatial variations in the population and structure as a function of distance from the polluting source. In addition, the de-halogenating potential of the microbial groundwater population was tested through a series of lab microcosm experiments, thus exemplifying the potential and limitations for bioremediation of the site. In all samples, the dominant phylum was Proteobacteria. In the production plant area, the non-obligatory organo-halide respiring bacteria (OHRB) Firmicutes Phylum was also detected in the polluted water, in abundancies of up to 16 %. Non-metric multidimensional scaling (NMDS) analysis of the microbial community structure in the groundwater exhibited clusters of distinct populations following the location in the industrial complex and distance from the polluting source. Dehalogenation of halogenated ethylene was demonstrated in contrast to the persistence of brominated alcohols. Persistence is likely due to the chemical characteristics of brominated alcohols, and not because of the absence of active de-halogenating bacteria.

<p>Measuring soil dinitrogen (N<sub>2</sub>) emissions is notoriously challenging under field conditions. Hence, N<sub>2</sub> emissions represent a significant uncertainty in the nitrogen mass balance of terrestrial ecosystems. The <sup>15</sup>N gas flux (<sup>15</sup>NGF) method is the only method currently available for directly quantifying N<sub>2</sub> emissions in situ. However, this method has rarely undergone independent validation under field conditions. In this study, our objectives were to: (1) Quantify N<sub>2</sub> emissions and their role in the fertilizer N mass balance of a wheat rotation using the <sup>15</sup>NGF method (2) Verify the obtained quantities of N<sub>2</sub> emissions using a mass balance approach and (3) Verify the temporal N<sub>2</sub> emission dynamics at the soil-atmosphere interface using vertical soil profiles of <sup>15</sup>N<sub>2</sub> enrichment.</p><p>To achieve these objectives, we grew winter wheat in lysimeters and applied <sup>15</sup>N enriched mineral fertilizers via fertigation in three doses (sum 170 kg N ha<sup>-1</sup>). We then analyzed gaseous (NH<sub>3</sub>, N<sub>2</sub>O, N<sub>2</sub>) and hydrological N losses, as well as fertilizer N fates in plant and soil, and <sup>15</sup>N<sub>2</sub> enrichment in soil air.</p><p>Our results showed that N<sub>2</sub> emissions directly measured using the <sup>15</sup>NGF method amounted to 30 ± 4 kg N ha<sup>-1</sup>, which was equivalent to 18 ± 3 % of the applied fertilizer N. These measurements agreed with unrecovered fertilizer N obtained from the <sup>15</sup>N fertilizer mass balance, although the latter had large inherent uncertainty (21 ± 21 kg N ha<sup>-1</sup>). N<sub>2</sub>O emissions, however, were negligible (0.14 ± 0.02 kg N ha<sup>-1</sup>). The temporal variability of measured N<sub>2</sub> emissions after fertilizer additions was generally well explained by <sup>15</sup>N<sub>2</sub> enrichment in soil gas.</p><p>Overall, we provide independent validation of the <sup>15</sup>NGF method in measuring N<sub>2</sub> emissions in the field and highlight the significant role of these emissions in the nitrogen balance of crop systems. Our data also suggest that soil gas measurements in combination with diffusion modeling could serve as an alternative method for quantifying N<sub>2</sub> emissions. These results should encourage a wider application of the <sup>15</sup>NGF method in order to improve our understanding of N<sub>2</sub> emissions and reduce the current uncertainties in estimates of these emissions.</p>