Contents
| AIR HYGIENE REPORT no. 10 | |
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Contents |
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Burton (1986) was sceptical towards the use of algae as biomonitors other than as an indicator of urban boundaries. Although literature on the use of algal biomonitoring of air pollution is rare, some recent developments have occurred in this area.
An increase in epiphytic algal growth usually coincides with a reduction or disappearance in epiphytic lichens (Hanninen et al., 1993; Brakenhielm and Qinghong, 1995). Green algae respond positively to increased nitrogen deposition (Bates et al., 1990). Algae have been included in epiphyte recolonisation studies (Bates et al., 1990), where Desmococcus viridis decline was postulated to be a consequence of decreasing SO2 levels in London, UK.
The use of epiphytic algae as bioindicators of air quality has been hindered by the lack of a non-destructive, non-laborious sampling method. Hanninen et al. (1993) proposed a reliable, replicable method, which overcomes these obstacles and allows time series analysis. This method was based on photography and digital image processing used to estimate the chlorophyll density of the algal layer. Detailed methodology along with calibration and testing aspects are outlined in the paper.
Since 1986 aerial green-algal monitoring has been carried out annually in about twenty reference sites as part of the National Swedish Environmental Monitoring Programme (PMK). The abundance and colonisation of mainly Pleurococcus vulgaris (Protococcus viridis) growing on needles of Norway Spruce (Picea abies) were related to atmospheric deposition. Detailed methodologies are found in Brakenhielm (1996), Brakenhielm and Qinghong (1995) and Bernes (1990), and are summarised in the following paragraphs. References
In a study of spatial and temporal patterns of epiphytes in relation to low level, long-range pollutant deposition in Sweden (Brakenhielm and Qinghong, 1995), spatial distribution of algal colony thickness and colonisation rate correlated well with climatic conditions and pollutant deposition gradients in the country. However, the statistical analysis was not capable of distinguishing between the natural and anthropogenic effects. The four-year algal data set from 1989 to 1993 was not sufficient to draw conclusions about temporal variations. Colonisation rate was thought to be a more reliable and objective sampling tool than colony thickness.
Brakenhielm (1996) obtained comparable results with the above study. Refinements such as partial Redundancy Analysis (RDA) and modeling were applied to the data in an attempt to clarify signal and noise relationships. The author concluded that climatic factors were of primary importance in green-algal distribution and deposition of S and N were of secondary importance. However under similar climatic conditions, epiphytic green algae are potentially good bioindicators of S and N deposition.
UN ECE (1993) prescribed sampling methods for aerial green algae in their manual for integrated monitoring programme phase 1993 to 1996. The basis is similar to the Swedish format but the following modifications/additions are provided: precise details on tree selection; a four point scale is used in assessing algal thickness; the type of annual shoots to be used in the assessment, and recommended sampling time is July to September. All of this information is used in the assessment. References
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