Ammonia Emissions From Seabird Colonies

Contact: Professor Sarah Wanless

Ammonia (NH3) is an important agent of environmental perturbation owing to its potential to cause both eutrophication and acidification in ecosystems. Breeding seabird populations are likely to be significant emitters of NH3 not only because they occur in high densities, but also because they import large quantities of nitrogen from their offshore feeding grounds. The excretion of these nutrients may, under suitable meteorological conditions, result in large emissions of NH3 into the atmosphere.

In a project funded under the NERC GANE (Global Nitrogen Enrichment) thematic programme, we have been studying NH3 emissions intensively from two seabird colonies in the Firth of Forth, SE Scotland – the Isle of May and Bass Rock. Various methods have been employed to measure atmospheric NH3 concentrations both on and offshore from the colonies.

The first method employed to measure atmospheric NH3 concentrations was ALPHA (Adapted Low-cost Passive High Absorption) passive samplers. The ALPHA sampler consists of a circular polyethylene tube containing an acid coated filter paper, which captures ammonia from the air which diffuses through a PTFE membrane at the open end. As the diffusion path length and area are known, in addition to the length of the exposure period, it is possible to calculate the concentration of atmospheric NH3 as an integrated average for the exposure period.

The passive sampler NH3 monitoring campaign on the Isle of May was designed to give an idea of the variability in atmospheric NH3 concentration near birds with differing nesting behaviour. Sites included those predominantly inhabited by guillemots/razorbills, puffins, gulls, kittiwakes, and shags, in addition to sampling NH3 in areas with few birds present or at significant distance from the ALPHA samplers (control sites).

The results observed so far support the hypothesis that most emissions of NH3 on the Isle of May are from areas inhabited by breeding guillemots/razorbills, as a result of their nesting behaviour. As these species breed on bare-rock cliffs, the NH3 content of the guano they deposit at the colony will remain available for volatilisation, even after their departure from the island at the end of the breeding season. Conversely, puffins spend less time above ground at the colony and are therefore less likely to deposit guano. NH3 concentrations were highest during the main period of bird occupancy at the colony (June/July) but still remained high for one month after the departure of the birds in mid July. This lag is probably due to the guano deposited at the colony retaining its NH3 content for some time until meteorological conditions are favourable for its volatilisation to the atmosphere.

Real-time atmospheric NH3 measurements were made offshore from the Isle of May and used in conjunction with a Gaussian plume dispersion model. This method gave NH3 emission estimates for the Isle of May of 3 ± 0.8 tonnes NH3 per year based on July 2000 data, and 6 ± 6 tonnes NH3 per year based on May 2000 data. These figures correlate well with those produced using data on bird numbers, colony attendance and nesting behaviour (8.67 tonnes NH3 per year for the Isle of May).

Data are also being collected on ammonia emissions from other seabird colonies around the world. Together with the intensive studies on the Isle of May, an estimate of global emissions of NH3 from seabird colonies will be made.