Assigning macroinvertebrate tolerance classifications using generalised additive models

1. Macroinvertebrates are frequently classified in terms of their tolerance to human disturbance and pollution. These tolerance values have been used effectively to assess the biological. condition of running waters. 2. Generalised additive models were used to associate the presence and absence of different macroinvertebrate genera with different environmental gradients. The model results were then used. to classify each genera as sensitive, intermediately tolerant or tolerant to different stressor gradients as quantified by total phosphorus concentration, sulphate ion concentration, qualitative habitat score and stream pH. The analytical approach provided a means of estimating stressor-specific tolerance classifications while controlling for covarying, natural environmental gradients. 3. Computed tolerance classification generally conformed with expectations and provided some capacity for distinguishing between different stressors in test data.