Quantifying Dry NH3 Deposition to an Ombrotrophic Bog from an Automated NH3 Field Release System

Abstract

Providing an accurate estimate of the dry component of N deposition to low N background, semi-natural habitats, such as bogs and upland moors dominated by Calluna vulgaris is difficult, but essential to relate nitrogen deposition to effects in these communities. To quantify the effects of NH 3 inputs to moorland vegetation growing on a bog at a field scale, a field release NH 3 fumigation system was established at Whim Moss (Scottish Borders) in 2002. Gaseous NH 3 from a line source was released along of a 60 m transect, when meteorological conditions (wind speed >2.5 m s −1 and wind direction in the sector 180-215 • ) were met, thereby providing a profile of decreasing NH 3 concentration with distance from the source. In a complementary study, using a NH 3 flux chamber system, the relationships between NH 3 concentrations and cuticular resistances were quantified for a range of NH 3 concentrations and micrometeorological conditions for moorland vegetation. Cuticular resistances increased with NH 3 concentration from 11 s m −1 at 3.0 µg m −3 to 30 s m −1 at 30 µg m −3 . The NH 3 concentration data and the concentration-dependent canopy resistance are used to calculate NH 3 deposition taking into account leaf surface wetness. The implications of using an NH 3 concentration-dependent cuticular resistance and the importance for refining critical loads are discussed.

The relationship between NH<sub>3</sub> emissions from a poultry farm and soil NO and N<sub>2</sub>O fluxes from a downwind forest

“…Similar elevated NH 3 concentrations and relatively fast decay rates over a short distance (<300 m) have been observed at several woodlands downwind of intensive poultry and pig farms (e.g. Theobald et al, 2004;Spangenberg and Kölling, 2004) and also downwind of an artificial NH 3 release source over an ombrotrophic bog (Leith et al, 2004). Thus a tree shelterbelt can be ideal in not only screening an unsightly animal farm from the public, but also by creating a biological filter, which contains the pollution to a small local area.…”

Early effects of atmospheric ammonia deposition on Calluna vulgaris (L.) hull growing on an ombrotrophic peat bog

“…AMMONIA TREATMENTS NH 3 gas is released over a 60 m transect of degenerate phase C. vulgaris from a 10 m line source with multiple release points. Details and a description of this dry deposited N simulation are given in Leith et al (2004). Monthly NH 3 concentrations (average exposure concentration), N deposition and cumulative N deposition, for five distances along the transect, and a control position that receives ambient dry and wet deposition only, are given in Table I.…”

“…This type of exposure mimics local releases from point sources such as the poultry farms studied by Sutton et al (1998). NH 3 deposition has been calculated using a concentration dependant R c and V d based on the NH 3 concentration 0.1 m above the vegetation (Leith et al (2004)). A characteristic of this experimental system is the irregular nature of the exposure regime, which can often give rise to both periods of intensive exposure and long periods with no exposure.…”

An automated wet deposition system to compare the effects of reduced and oxidised N on ombrotrophic bog species: Practical considerations

“…Monitoring at Whim Moss over the first year of wet treatment, July 2002 to June 2003, recorded 850 mm of precipitation which provided an annual wet N deposition, calculated from the sum of weekly measured deposition of NH + 4 and NO − 3 , of 5.8 kg N ha −1 y −1 . The annual dry NH 3 deposition for the same period was 4.0 kg N ha −1 y −1 (Leith, et al, 2004). Taking the deposition of "other" N forms (NH + 4 particles, nitric and nitrous acid and NO x ) as measured at Auchencorth Moss, the maximum annual N deposition (excluding organic inputs) to the vegetation at Whim was 1.2 other + 4.0 NH3g + 5.8 wet = 11 kg N ha −1 yr −1…”

“…Wind speed and direction are measured every minute with a sonic anemometer. Solar radiation, net radiation, air and soil temperature (10 and 20 cm) and the level of the water table are also measured (see Leith et al, 2004). Ambient NH 3 concentrations are measured over a month using passive diffusion to alpha samplers and are converted to monthly N deposition using an inferential method (see Leith et al, 2004).…”