TO WHAT EXTEND DOES THE SULFUR-CONTENT OF FIR NEEDLES REFLECT THE SPATIAL AND TEMPORAL VARIATION OF AIRBORNE SULFUR-DIOXIDE - METHODOLOGICAL PROBLEMS IN ANALYZING BIOMONITORING NETWORKS

Since the late seventies, a biomonitoring network of firs located on a regular grid with distances 16 km (sometimes 8 km) has been operated by the Bavarian Environmental Protection Agency (LfU); the sulphur con tents in specimens of recent needles is measured every year (since 198 9 every second year). Between 1979 and 1993, sulphur levels decreased; the highest values occurred in the northeast of Bavaria. Spatial auto correlations of adjacent firs were low. We analysed to what extent thi s biomonitoring network reflects the contamination of the air with sul phur compounds by comparing the fir measurements to time series of mon thly SO2-averages from 13 air monitoring stations. High respectively l ow SO2-loads corresponded in space and time to high respectively low s ulphur levels in fir needles. Limitations in exploring quantitative do se-response-relationships resulted from missing values in the sulphur measurements and from their considerable small-scale variation. Ir is not possible to discriminate between different hypotheses concerning t he time interval during which the sulphur is deposited in the fir need les, because the corresponding aggregate variables are stochastically dependent.