Monitoring temporal trends of air pollution in an urban area using mosses and lichens as biomonitors.

Monitoring air quality by using living organisms as biomonitors has received increasing attention in recent years. However, rather few studies were based on the concomitant use of passive biomonitoring (based on the different sensitivity of living organisms to air pollution) or active biomonitoring (based on their capacity to accumulate pollutants in the tissues). We carried out a repeated survey of an urban area in Northern Italy, with the objective of comparing temporal trends of different kinds of air pollutants with bioindication (passive biomonitoring) and bioaccumulation (active biomonitoring) techniques. During a five-year interval, temporal patterns of moss metal concentrations underwent significant changes probably due to intercurring variations in the importance of different pollution sources. Nitrogen (N) concentration in moss tissues also decreased and was paralleled by increasing diversity of epiphytic lichens. Increasing δ15N in moss tissues suggested a higher contribution of oxidized N species compared with reduced N species