A note on abiotic factors that constrain periphyton growth in alpine glacier streams

Periphyton growth limitation experiments were conducted in five glacier streams during the main ice melt period in late summer using nutrient diffusing substrata (NDS) that contained nitrate and/or phosphate. Periphyton net growth was determined as chlorophyll a accrual after an exposure time of 4 weeks. In addition, primary water chemistry and physical parameters of the study streams were measured. These chemical and physical parameters characterised the sites as kryal (glacial) systems. Neither nutrient limitation nor a significant correlation between water chemistry and physical data and chlorophyll a values were apparent. A comparison between current velocity and ln-transformed chlorophyll a values revealed a typical optimum curve with highest periphyton accrual at 0.5 m s–¹ on NDS. During the summer ablation period, the net growth of periphyton in these glacial streams appeared to be controlled primarily by current velocity.