Optimization of the Biomonitoring Technique with the Aquatic Moss Fontinalis antipyretica Hedw.: Selection of Shoot Segment Length for Determining Trace Element Concentrations

Abstract

Bryophytes, including Fontinalis antipyretica Hedw., are widely used for biomonitoring aquatic environments. However, some methodological aspects, such as the fraction of shoot analysed, have not yet been standardized. The main objective of this study was to establish the length of segments of F. antipyretica shoots that should be used for trace element determination in monitoring studies. For this purpose, we determined the concentrations of 12 different trace elements (11 metals and one metalloid) in five successive 1 cm-long segments of the shoots of F. antipyretica collected from four different locations. We found that the concentrations of most elements increased steadily towards the basal part of the shoots without becoming stable. Sometimes, these increasing trends were concealed by another underlying trend of increasing dry/fresh weight ratios, caused by morphological changes (leaf density, shoot thickness) related with shoot development. The concentration trends were due to factors such as the deposition of Mn oxides on the moss surface. This element showed the largest increases in concentration towards the basal part of the shoot and its concentrations were closely correlated with those of most of the other elements. Considering the results obtained, we recommend the use of 3 cm-long apical segments for determining trace element concentrations in F. antipyretica. This recommendation is based on the following: (1) The change in dry weight beyond this length of segment is small; (2) the workload and the quantity of material to collect in the river is acceptable; (3) Most previous studies have used shoot segments of similar lengths.