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Global models have indicated agriculturally impacted rivers and streams may be important sources of the greenhouse gas nitrous oxide (N2O). However, there is significant uncertainty in N2O budgets. Isotopic characterization can be used to help constrain N2O budgets. We present the first published measurements of the isotopic character of N2O emitted from low (2-4) order streams. Isotopic character of N2O varied seasonally, among streams, and over diel periods. On an annual basis, δ 18O of emitted N2O (+47.4 to +51.4‰; relative to VSMOW) was higher than previously reported for larger rivers, but δ 15N of emitted N2O (-16.2 to +2.4‰ among streams; relative to atmospheric N2) was similar to that of past studies. On an annual basis, all streams emitted N2O with lower δ 15N than tropospheric N2O. Given these streams have elevated nitrate concentrations which are associated with enhanced N2O fluxes, this supports the hypothesis that streams are contributing to the accumulation of 15N-depleted N2O in the troposphere. [ABSTRACT FROM AUTHOR]

In this article the author discusses eutrophication, which is a process leading to increased algal productivity in lakes through time, and why nutrient control in aquatic ecosystems requires asking the right questions. Topics include the impact of eutrophication on key ecosystem services, the importance of preventing a state shift into an undesirable state via nutrient control, and the role of nitrogen (N), and N control, in eutrophication.