Measuring lichen specimen characteristics to reduce relative local uncertainties for trace element biomonitoring

Local variation (within sampling sites) affects lichen air pollution biomonitoring of trace element deposition patterns. When comparing between sampling sites, global variation must be greater than local variation, thus reducing local variation is important in biomonitoring studies. To reduce local variability, sampling protocols are introduced, primarily minimum sampling height and less often sampling aspect. This study, introduces further protocols, which can help to reduce within site variation. First, the research design removed spatial variation by sampling a single tree. One–thousand and thirty–seven individual specimens of Usnea subfloridana were collected and aggregated into 97 samples based on similar collection height, aspect and mass. Samples were tested by inductively coupled plasma – atomic emission spectroscopy for total recoverable Al, As, Ba, Be, Cd, Co, Cr Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sr, Ti, Tl, V, and Zn. Fifteen of the elements tested were above minimum detection limits and their variation in concentrations were able to be partially explained with linear modeling. When explaining variation in concentrations with linear modeling, aspect was statistically significant for all of the 15 elements, height was statistically significant for 12 elements, and specimen mass was significant for 6 elements. We demonstrate that individually assessing and minimizing specimen collection aspect, height and mass prior to aggregating specimens into samples can reduce local variation, which will improve between site comparisons.