Periphyton pigment shifts in lakes with varying water colour: a possible monitoring method for freshwater Browning

Despite several negative effects of browning, there are no sufficient bioindicators to monitor it. In this study, the effects of water quality on the photosynthetic pigment content of periphyton grown on artificial substrata in different depths were examined. The study was conducted in June–July 2024 in southern Finland. The accrual of periphyton fresh mass was on average 50 μg cm2. The chlorophyll a:b ratio (Chl a:b) of periphyton decreased with increasing water colour at 80 cm incubation depth. The ratio of Chl a to carotenoids (Chl a:Car) increased with increasing water colour at 20 cm incubation depth. No effect of total phosphorus or water Chl a concentration on the periphyton pigment content was observed. The results suggest that Chl a:b and Chl a:Car of periphyton are potential new indicators of browning in lakes due to their specific response to browning.