.[1] Any change in the ability of northern peatlands to act as a sink for atmospheric CO 2 will play a crucial part in the response of the Earth system to global warming. We argue that a true assessment of the sink-source relationships of peatland ecosystems requires that losses of C in drainage waters be included when determining annual net C uptake, thus connecting measurements of stream C fluxes with those made at the land surfaceatmosphere interface. This was done by combining estimates of net ecosystem exchange (NEE) with stream water measurements of TOC, DIC, and gaseous C loss, in a 335-ha lowland temperate peatland catchment (55°48.80 0 N, 03°14.40 0 W) in central Scotland over a 2-year period (1996)(1997)(1998). Mean annual downstream C flux was 304 (±62) kg C ha À1 yr À1 , of which total organic carbon (TOC) contributed 93%, the remainder being dissolved inorganic carbon (DIC) and free CO 2 . At the catchment outlet evasion loss of CO 2 from the stream surface was estimated to be an additional 46 kg C ha À1 yr À1 . Over the study period, NEE of CO 2 -C resulted in a flux from the atmosphere to the land surface of 278 (±25) kg C ha À1 yr À1 . Net C loss in drainage water, including both the downstream flux and CO 2 evasion from the stream surface to the atmosphere, was therefore greater or equal to the net annual C uptake as a result of photosynthesis/respiration at the land surface. By combining these and other flux terms, the overall C mass balance suggests that this system was either acting as a terrestrial C source or was C neutral.

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5Potatoes are an important staple crop, grown in many parts of the world. Although ozone 6 deposition to many vegetation types has been measured in the field, no data have been 7 reported for potatoes. Such measurements, including the latent heat flux, were made 8 over a fully-grown potato field in central Scotland during the summer of 2006, covering a 9 4-week period just after rainfall and then dry, sunny weather. The magnitude of the flux 10 was typical of many canopies showing the expected diurnal cycles. Although the bulk-11 canopy stomatal conductance declined as the field dried out (~300 mmol-O 3 m -2 s -1 to 12 ~70 mmol-O 3 m -2 s -1 ), the total ozone flux did not follow the same trend, indicating that 13 non-stomatal deposition was significant. Over a dry surface non-stomatal resistance (R ns ) 14 was 270-450 s m -1 , while over a wet surface R ns was ~50% smaller and both decreased 15 with increasing surface temperature and friction velocity. From the variation with relative 16 humidity (RH) it is suggested that three processes occur on leaf surfaces: on a very dry 17 surface ozone is removed by thermal decomposition, possibly enhanced by photolytic 18 reactions in the daytime and so R ns decreases as temperature increases; at 50-70% RH a 19 thin film of liquid blocks the "dry" process and resistance increases; above 60-70% RH 20 sufficient surface water is present for aqueous reactions to remove ozone and resistance 21 decreases. 22Keywords: eddy-correlation; surface conductance; ozone critical levels; AOT40, AFst6; 23 stomatal uptake; non-stomatal; dry deposition 24 Capsule: Ozone deposition to a potato crop depends not only on stomatal uptake but is 25 enhanced by increasing surface temperature or the presence of water. 26

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