OBJECTIVE DERIVATION OF MACROINVERTEBRATE FAMILY SENSITIVITY GRADE NUMBERS FOR THE SIGNAL BIOTIC INDEX - APPLICATION TO THE HUNTER RIVER SYSTEM, NEW-SOUTH-WALES

Chessman's SIGNAL-95 biotic index was modified on the basis of data fr om spring and autumn surveys of macroinvertebrates at 42 sites in the Hunter River and tributaries. An iterative algorithm was used to deriv e improved grade numbers reflecting the pollution sensitivities of ind ividual families of river macroinvertebrates. The new grades were used to calculate values of the modified index (SIGNAL-HU97). These values were highly correlated with SIGNAL-95 values but were more widely spr ead, giving better discrimination between the sites of higher environm ental quality and the more degraded sites. SIGNAL-HU97 values were als o more highly correlated than were SIGNAL-95 values with environmental variables such as the conductivity of the water and a riparian, chann el and environmental inventory. There was little difference in values between spring and autumn, but riffles consistently had higher mean va lues than other habitats.