科研之友
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摘要
Levels of nitrate in Malta's groundwater are high. Median concentrations in the main sea-level aquifers of Malta and Gozo are 14 and 10 mg NO3-N L-1, respectively, and even higher in the younger groundwaters of the perched aquifers on Malta (37 mg NO3-N L-1). The wide variations in groundwater nitrate concentration are not due to denitrification, as N-15/N-14 and O-18/O-16 analyses of 47 samples from the three aquifer types found clear evidence for this process in only one sample. 90% of the groundwater nitrate samples had delta O-18 values in the range +3.1 to +6.1 parts per thousand which correspond exactly to those expected for nitrate formed by microbial processes in the presence of Maltese surficial waters (delta O-18 of H2O typically -5.3 to -4.3 parts per thousand). The delta N-15 values of these groundwater nitrate samples, +7.7 to +11.77 parts per thousand were compared with those of a wide variety of potential nitrate sources in Malta (fertilizers, sewage, manure and soils). The closest correspondence was found for the organic N in cultivated soils (+6.0 to +11.2 parts per thousand). These relatively high delta N-15 values for soils may reflect greater fluxes of N from soils with a low C/N ratio and a long history of cultivation. While the isotope data support soil nitrification as the source for nitrate in the groundwaters, they do not rule out direct leaching of manure-derived nitrate as a source.
- 出版日期2012-1-11
