Inhibition of primary production by UV-B radiation in an arctic bay – model calculations

Abstract.

Inhibition of primary production by UV-B radiation (UVBR) in Kings Bay, western Spitsbergen, was modelled using measured physical and biological data. The underwater radiation regime was modelled using continuous measurements of incoming radiation and repeated measurements of underwater attenuation of Photosynthetic Active Radiation (PAR) and UVBR. By using attenuation measurements, P/I curves and UVBR sensitivity measurements, we modelled the reduction of primary production in the photic zone for 14 days. We also calculated how the estimate was dependent on the different factors. The model showed that, on average, 2.9 % of the primary production was inhibited by UVBR, assuming that the inhibition is a function of the UVBR irradiance. If the ozone layer were reduced to 200 DU, the inhibition would increase to 4.4% using unweighted UVBR values. The model indicated that at ambient ozone levels the inhibition was practically independent of the chosen weighting function, but the choice was critical when predicting the effects of a depleted ozone layer. At 200 DU, using DNA weighting, the inhibition was 14.4% but using erythema weighting it was 6.5%. Different P/I curves did not change the estimate while changes in water attenuation gave results in the range 1.6–5.2%. The most uncertain factor in the model was the estimate of the sensitivity of primary production. Using four different in situ incubations, the estimated integrated reduction in primary production caused by UVBR ranged from 0.05–4.1%.