Fluorometer measurements and transmission of light in different parts of Lake Ladoga

A fluorometer and multispectral underwater photodetector was used in different parts of Lake Ladoga during a joint Russian-Finnish expedition in 1995 to measure in vivo fluorescence and the intensity of solar and sky radiation. The spectral distribution of radiation at various depths in the water column and penetration of photosynthetically active radiation (PAR) were measured using an underwater multispectral photodetector (420–670 nm). The results were compared with Secchi disk and temperature measurements. The fluorometer values were highest in the pelagic zone of the lake and smallest in areas close to the Burnaya River and in the Volkhov Bay. Light absorption by algae and other suspended matter effectively reduced light penetration especially in the Volkhov Bay. Deepest transmission of light in water and relatively low fluorometer values were found in the western areas of the lake, where light (at 1% level of surface radiation) was transmitted more than six metres. Pulp mill waste waters seemed to decrease the photosynthetic activity in the NE part of the lake.