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Abstract. Dissolved CH 4 was measured in coastal waters of the southern North Sea, in two adjacent U.K. estuaries with well-defined turbidity maxima (Humber and Tyne) and in their associated river catchments, during a series of campaigns covering the period 1993-1999. In general, samples from all three environments were significantly to highly CH4 enriched relative to atmospheric air. Observed river water concentrations,-33-152 nmol L -• (940-4305% saturation) for the Humber river catchment and ---3-62 nmol L '• (86-1754% saturation) in the river Tyne, were within but toward the low end of the range of CH4 concentrations in river waters world wide. In sea waters from the outer Wash estuary (U.K. coast) and adjacent to the Dutch coast, CH4 was highly but nonlinearly correlated with salinity, consistent with strong CH 4 removal from river and/or estuarine CH4 sources influencing these locations. In transects along the Humber and Tyne estuaries, CH4 was highly negatively nonconservative, confirming the estuarine removal hypothesis. lost globally to gas exchange in estuaries, increasing previous such estimates by-8-50 %. However, as it is based on data that exclude the possibility of elevated CH 4 levels at estuarine turbidity maxima, even this revision is likely to be conservative. Detailed studies of CH4 distributions in major world estuaries would now be required in order to successfully reevaluate the CH4 budget of the coastal marine atmosphere.

+ derived from internal resuspension and/or ammonification, or external inputs and were independent of river-borne NO 3 − . We reevaluated total UK and European estuarine N 2 O emissions using these and published data, based on an aerially weighted approach that separately identified inner and outer estuaries, and a downward revision of the total European estuarine area used in a recent synthesis. Our revised estimates, ∼1.9 ± 1.2 × 10 9 g N 2 O yr −1 for the UK and 6.8 ± 13.2 × 10 9 g N 2 O yr −1 for Europe (including UK) are dominated by large (area ∼200-500 km 2 ) anthropogenically impacted macrotidal inner estuaries. By contrast large pristine macrotidal systems, small inner estuaries, and large outer estuaries appear to be comparatively minor N 2 O sources. The UK estuarine N 2 O source is <2% of the UK N 2 O budget. Our revised European estuarine N 2 O emission is around 2 orders of magnitude smaller than a recent previous estimate that set this equivalent to ∼26% of the global estuarine total. We contend that this is an overestimate due to biases in the flux calculations resulting from likely overestimates of the mean N 2 O saturation and mean wind speed for European estuaries, and the European estuarine area. Taking this into account reduces this estimate to be more in line with our revised synthesis.Citation: Barnes, J., and R. C. Upstill-Goddard (2011), N 2 O seasonal distributions and air-sea exchange in UK estuaries: Implications for the tropospheric N 2 O source from European coastal waters,

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