dc.description.abstract | This study evaluates, for the first time, the influence of biofilms on single and double optical window (SOW and DOW, respectively) fast repetition rate fluorometer (FRRF) measurements of microalgal photosystem-II initial fluorescence (F<sub>0</sub>), maximum fluorescence (F<sub>m</sub>), variable fluorescence (F<sub>v</sub>= F<sub>m</sub> – F<sub>0</sub>), quantum yield(F<sub>v</sub>/F<sub>m</sub>) and functional absorption cross section (σPSII)]. Biofilms with chlorophyll > 0.1 μg cm<sup>-2</sup> and > 0.3 μgcm<sup>-2</sup> on SOW and DOW, respectively, produced a substantial increase in fluorescence. However, the relative magnitude of biofouling effects depended on sample chlorophyll concentrations, being more critical at concentrations < 1 mg m<sup>-3</sup>. In DOW-FRRF, biofilms affected F<sub>0</sub> (increased) and F<sub>v</sub>/F<sub>m</sub>) (decreased) but not F<sub>v</sub> and σPSII, whereas in SOW-FRRF, biofilms increased fluorescence and showed a variable effect on F<sub>v</sub> F<sub>m</sub> and σPSII, because only biofilms on SOW attained actual F<sub>m</sub>. As a result, the biofilm effect was substantial on SOW-FRRF measurements. On the other hand, the neutral-density filters (representing non-chlorophyll containing biofilms) with different transmission levels reduced the fluorescence signal. Correction procedures for the above photosystem-II parameters are proposed here. | |