Detection of pulses of atmospheric mercury deposition with extensive surveys and frequently sampled stations: A comparison

We present the results of the analysis of several datasets corresponding to the mercury contents of moss tissues. Some of the data were collected in regional surveys devised to study the atmospheric deposition of pollutants in Galicia (Spain). The surveys were carried out with low frequency (usually biennially) and the data obtained were compared with similar data collected with high frequency (monthly or bimonthly) at several locations in the same area. The temporal series of data demonstrated the existence of strong pulses of mercury deposition of small duration. They caused dramatic increases in the Hg contents in the samples from some localities and, sometimes, modified the Hg contents of the mosses in the complete study area. Our results demonstrate the low probability of detecting pulses in surveys separated so widely in time. This suggests that the information obtained in regional surveys should be complemented with data collected with high frequency.