Seasonal fluctuations of the airborne pollen spectrum in Murcia (SE Spain): Some peculiarities in the pollen calendar

During six consecutive years (1993-1998), a Burkard volumetric pollen trap was continuously operated to sample pollen from the air of the city of Murcia. The aim of the study was to elucidate the spectra of airborne pollen and the variations during the year, and to elaborate a pollen calendar. This time span includes the end of the period with severe drought from 1990-1995, which particularly affected the south-eastern region of Spain. The total sum of daily average pollen concentrations amounted to 148,645 pollen grains belonging to 93 different taxa. A daily average of 74 pollen grains/m super(3) and 11 taxa were recorded, with maxima of 1157 and 27 respectively. The total pollen amount registered in a year correlated with yearly rainfall, but there was no relation with mean annual temperature. As for annual fluctuations, there seemed to be no influence by total rainfall or temperature. Spring and winter were the seasons with the highest pollen counts and pollen diversity. From the 93 identified taxa, 36 are included in the pollen calendar. Noteworthy findings are: (i) the presence of Thymelaeaceae, Robinia, Betula, Castanea, Zygophyllum, Caryophyllaceae and Cannabis, (ii) a long pollen season of Chenopodiaceae/Amaranthaceae, Urticaceae, Poaceae, Arecaceae and Plantago, (iii) the occurrence of summer, autumn and winter flowering of Artemisia, (iv) the late appearance of Corylus pollen, and (v) the minor presence of Casuarina pollen during the mid winter and late spring.