Standardised Grasses as Biomonitors of Ammonia Pollution Around Agricultural Point Sources

The use of standardised plant species as biomonitors of air pollution has been a recognised technique for a number of years (De Temmerman et al. 2004). Grass species have been used extensively in a number of biomonitoring studies (Sant' Anna et al. 2004). These standardised grasses can be used as passive biomonitors, but are more effectively used as active bioaccumulators of a range of gaseous and particulate pollutants (Scholl 1971). The advantage of these standardised plants as bioaccumulators is their ability to accumulate a variety of inorganic and organic air pollutants without showing symptoms of visible injury. Standardised plants can also provide an indication of air pollution impacts over a short time period and are independent of the habitat substrate. Although the use of standardised biomonitors is extensively reported in the literature for the bioaccumulation of sulphurous compounds, heavy metals and trace elements (Klumpp et al. 2004) they have not been widely used as active bioaccumulators of N pollution.

Sommer (1988) exposed barley (Hordeum vulgare var. Harry) plants as a bioindicator of ammonia (NH₃) deposition along a 0–300 m transect from a dairy farm for 1 month. The tissue N content of the barley plants was increased closer to the farm reflecting the increased N deposition from ammonia. In a subsequent study, Sommer and Jensen (1991) exposed Lolium multiflorum Lam. along 0–130 m transects away from a dairy farm. Tissue N concentration was found to increase closer to the farm. Dry matter was also increased in close proximity to the farm but did not decrease significantly with distance from the farm. Hicks et al. (2000) used two graminiod species Deschampsia flexuosa (L.) and Nardus stricta L. as potential biomonitors of wet N deposition in upland areas.