Optical properties of coastal waters of northwestern Estonia: in situ measurements

A field study of optical properties of the coastal waters of northwestern Estonia was performed from 29 July to 3 August 2002. It was the relaxation period of extensive cyanobacterial bloom in the Gulf of Finland. The concentrations of optically active substances (chlorophyll a, coloured dissolved organic matter, suspended matter) and spectrometric light attenuation coefficients were determined from water samples. In addition, continuous measurements of attenuation and absorption coefficients were performed using a flow-through system based on the ac-9 device. The results show that variations of the optical properties of the water masses in the coastal sea of northwestern Estonia are mainly due to changes in the concentration of coloured dissolved organic matter. Water turbidity is well characterized by the slope factor of the scattering coefficient spectrum that is approximated by the power law.