Turbidity and mass concentration of suspended matter in lake water: A comparison of two calibration methods

Turbidity measurements by foreward scattering nephelometer have been regularly conducted on the north basin of Lake Lugano (Switzerland/Italy) since September 1992. In order to determine mass concentrations from these data, both, in-situ and laboratory calibration experiments have 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 calibrations using suspended matter originating from the water depths of interest give representative results provided that physical and chemical alterations occuring during the particle transfer process remain negligible.