Push-pull tracer studies for in-situ measurement of denitrification rates in stream sediments

Burgin, A.J., and S.K. Hamilton

Presented at the All Scientist Meeting (2003-09-12 )

Streams receive many anthropogenic sources of pollution, including increased nitrogen loading from agricultural areas. Denitrification, the conversion of nitrate (NO3-) to dinitrogen gas (N2), represents the only permanent loss of nitrogen from these systems. Nitrous oxide (N2O), a potent greenhouse gas, is also produced during denitrification in an intermediary step. The ratio of N2 to N2O produced during denitrification is unknown in many aquatic systems. Denitrification in streams occurs mainly in benthic substrata (organic matter accumulations) that vary in abundance between streams and are heterogeneously distributed within a stream. Denitrification has been measured using push-pull methods in groundwater and wetlands. Water containing a conservative solute plus nitrate is injected into the sediments, and then the injectate is withdrawn over time to quantify the rate of reactant uptake. Using 15N-labeled nitrate, we can measure its uptake as well as 15N2 and 15N2O production. This poster presents a proposed push-pull method to obtain in situ nitrate uptake rates and estimates of denitrification products within the microhabitats characteristic of stream systems.

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