Effect of ultraviolet radiation on phytoplankton primary production in Lake Balaton

Abstract

The aim of the present study was to assess the effect of ultraviolet radiation (UVR, 280–400 nm) on phytoplankton primary production in Lake Balaton, a shallow lake with the largest surface area in Central Europe possessing unique optical properties. The experiments were performed in situ in summer 1999 in the western basin with generally higher primary production rates and light attenuation coefficient due to higher algal biomass and in the eastern basin of the lake. Primary production was measured using 14C-technique, samples collected on-site were incubated at different depths for 4 h centred around noon. Underwater photosynthetically active radiation (PAR, 400–700) was measured prior to incubation. The incubation was carried out in three treatments using cut-off filters to exclude various portions of the UVR spectrum. Surface photoinhibition reached 72–78% in the samples exposed to PAR and UVR as compared to the control treatment from which UVR was excluded, however, areal primary production showed only an 8–14% decrease in the presence of UVR. Although the filters applied absorb ca. 15% PAR as well, comparison of the treatments pointed out that it was UVAR (320–400 nm), and not UVBR (280–320 nm) that predominantly inhibited photosynthesis.