Annual variability in heavy-metal bioconcentration in moss: sampling protocol optimization

The moss Scleropodium purum was sampled at four sampling stations, every 28 days over a period of three and a half years, and the tissue contents of Al, K, Ca, Mg, Cu, Mn, Fe, Na, Hg and Zn were determined in each of the samples. Autocorrelograms were used to study possible seasonal patterns of accumulation. A cyclic pattern of accumulation, repeated every 12 months, was revealed for Cu, K, Mg and Na, with maximum levels in winter and minimum levels in summer. The seasonal pattern of accumulation may be explained by the effect produced by desiccation of the moss during the summer months. To find the sampling design that best represents the intra-annual variability in the tissue contents of heavy metals, we proposed a series of sampling designs that combined different numbers of samplings and lag between samplings. These were then applied to the temporal series obtained and the one that best reflected the annual bioconcentration at a sampling station was selected. The proposed sampling design, recommended for application in future studies of atmospheric biomonitoring with terrestrial mosses, consists of two samplings separated by 6–7 months.