Relative Response of Biological and Non-Biological Monitors in a Coastal Environment

A field study was carried out in the spring and summer of 2003 (2 months each), to assess the efficiency of alternative exposure modes of biological monitors – lichen biomass and tree-bark biomass – together with prospective, non-biological monitors – cellulose acetate and Chelex-100 resin – versus conventional transplants of the same species. After exposure to the marine atmosphere of Sines (SW Portugal), saline elements (Cl, Na, K, Mg) contents were determined in all samples by instrumental neutron activation analysis (INAA). Manganese was used as the crustal reference for data normalisation. As a whole, the results pointed to a consistent elemental accumulation regardless of the season (spring, summer), and to some fair reproducibility of data. There were good correlations between Cl and Na in terms of both raw and normalised data, for either the biomonitors or the cellulose acetate. Elemental ratios generally agreed with the average relative composition of bulk seawater. The degree of association between Cl and Na appeared rather unaffected by the normalisation procedure, which suggests that (i) both elements most likely had an almost exclusive marine origin; and (ii) accounting for crustal inputs via Mn did not bias the results. Other sources than the sea-spray might contribute to the Mg levels, though, as only Mn-normalised data showed intrinsic (correlation) and extrinsic (ratio) consistency. The performance of the Chelex-100 resin was rather disappointing when compared to the other monitors.