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 %.

Influence of water mixing on the inhibitory effect of UV radiation on primary and bacterial production in Mediterranean coastal water

“…In our case, the relationship between phytoplankton productivity and UVR sensitivity can be complicated by the addition of the acclimation processes (Banaszak 2003) or by a change in phytoplankton community structure that can occur during UVR stress (Sommaruga 2003). Changes in phytoplankton sensitivity towards UVR within small temporal or spatial scales has been shown earlier (Wängberg et al 2006 and references herein). Over the 3 days, we observed a good agreement between the changes in the UVR inhibition of the integrated PP measured with fixed and moving incubations.…”

Mercury photochemistry in snow and implications for Arctic ecosystems

“…Abiotic photoproduction of MeHg has been observed in the upper sunlit portions of some temperate lakes, in the presence of DOM (Siciliano et al 2005). Degradation of MeHg occurs through microbial action (Compeau and Bartha 1984;Oremland et al 1991) but can also occur through photochemical reaction (Constant et al 2007), which is induced primarily by UV radiation (Lalonde et al 2001;Wängberg et al 2006). MeHg has been detected in snow (Lahoutifard et al 2005;Constant et al 2007;Dommergue et al 2010), and up to 7.6% of the total Hg in an Arctic snowpack may be MeHg, based on one study area in the low Arctic tundra (Constant et al 2007).…”

“…Methylmercury (MeHg, CH 3 Hg(I)), a toxic and bioaccumulative organic ion of Hg (Fitzgerald and Clarkson 1991), is also not simply a Hg reaction endpoint, with bioaccumulation a foregone conclusion. Rather, MeHg is a photoreactive species itself and also has the ability to be bound by particulates and organic matter, which will affect MeHg bioavailability (Sellers et al 2001;Wängberg et al 2006;Skyllberg et al 2006;Skyllberg 2008).…”

Chemical characterization of dissolved organic matter (DOM): A prerequisite for understanding UV-induced changes of DOM absorption properties and bioavailability

“…Aquatic organisms that play important roles in carbon cycling such as phytoplankton, bacterioplankton, and coral reefs are damaged by UV radiation. The biological processes known to be affected by UV-B are primary production (Beardall and Raven, 2004;Leu et al, 2007;Wangberg et al, 2006), bacterioplankton growth (Hernµndez et al, 2007;Herndl et al, 1993;Jeffrey et al, 1996;Langenheder et al, 2006), and coral bleaching Anthony and Kerswell, 2007), enhancing the warming-related stress on corals Rodriguez-Roman et al, 2006). UV-B damages on algal photosynthesis include inhibitory effects on nutrient uptake and damage to DNA (Beardall and Raven, 2004 and refs.…”