Seasonal Variation in the concentrations of methyl and ethyl nitrate in a shallow freshwater lake
Between February and October 2007, a time-series of alkyl nitrate concentrations in the water-column of a shallow freshwater lake, University of East Anglia (UEA) Broad, located in southeastern England was carried out to determine if methyl and ethyl nitrate are present in freshwater systems and improve understanding of alkyl nitrate production mechanisms in aquatic environments. Concentrations ranged from 4.7 (± 0.5) to 53.7 (± 4.36) pmol L-1 methyl nitrate, and 2.5 (± 0.3) to 11.1 (± 0.4) pmol L-1 ethyl nitrate, and were within the range of those measured previously in seawater. Peaks in the concentrations of methyl and ethyl nitrate were observed at 4 m in 9 and 6 of the 18 depth profiles measured, respectively. Gradients in concentrations within the hypolimnion suggest that the alkyl nitrates are produced in the bottom waters or sediments and/or are transported to the lake in groundwater. Colored dissolved organic matter (CDOM) absorbance data suggests that the penetration of ultra-violet (UV) light was limited in the lake so the deep maxima must be due to a non-photochemical alkyl nitrate source.
Limnology and Oceanography, 50, (1), 305-314
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