Composite samples with a small sample size reflect mean element concentrations in three lichens differing in element-specific concentrations

The biomonitoring of atmospheric element deposition often uses a single composite sample to test the local mean lichen element concentrations, so as to reduce the expenditure. However, further study is needed to test the composite sample representativeness on the mean element concentration (CSRMC) and its lichen species specificity and element specificity. In this study, we compare the concentration differences of 55 elements between three lichens (Evernia mesomorpha Nyl., EVM; Usnea aciculifera Vain., UAC; Ramalina sinensis Jatta., RSI) from a remote forest site of Hebei, northern China. The results show that the differences of element concentrations between lichens have strong element specificity. Composite samples can well represent the local mean element concentrations in three lichens. CSRMC is the highest in RSI in comparison with EVM and UAC. It is usually ranking 1 for most elements in three lichens except Al, Ca, Hg, P and Si. Therefore, when we use the composite samples with a small sample size for lichen biomonitoring, it is necessary to carefully select lichen species and the number of composite samples according to the CSRMC of the elements of interest. This method is especially suitable for sites with small spatial heterogeneity in atmospheric element depositions.