TURBIDITY AND MASS CONCENTRATION OF SUSPENDED MATTER IN LAKE WATER - A COMPARISON OF 2 CALIBRATION METHODS

Turbidity measurements by foreward scattering nephelometer have been r egularly conducted on the north basin of Lake Lugano (Switzerland/Ital y) since September 1992. In order to determine mass concentrations fro m these data, both, in-situ and laboratory calibration experiments hav e been performed in November and December 1992 on suspended matter of the hypolimnion. Results show: 1. Mass concentration/turbidity ratios are different in the two turbidity zones examined due to variation in the optical signature of the suspended matter.2. Laboratory calibratio ns using suspended matter originating from the water depths of interes t give representative results provided that physical and chemical alte rations occuring during the particle transfer process remain negligibl e.