An Examination of Stream Water Quality Data from Monitoring of Forest Harvesting in the Eastern Highlands of Victoria

A large data set measuring surface stream turbidity, dissolved oxygen levels, and water temperature was developed by sampling 32 rivers and streams with forested catchments at weekly intervals for between two and three years. This was in response to allegations of possible water quality impairment by forest harvesting (“logging”). Additionally, nine rivers or streams external to the forests were sampled to form a “reference set”; concern was expressed that the water quality of these may be impaired by upstream forest harvesting. An unlogged forested control catchment was selected from the data set and used as a comparator to help reduce seasonal variation. Division of the data into “logged forested catchments” and “unlogged forested catchments” allowed for us to test the null hypothesis. The null hypothesis was that there was no difference between the means of the logged and unlogged sets by a “Student’s t test of difference between means”. The null hypothesis was supported for the three parameters. There was no discernible deterioration in water quality associated with the presence of logging in the stream catchments. It was concluded that logging in this environment was not a determinant of water quality, and that the presence or absence of logging in these catchments did not affect the measured water quality. Spearman rank correlation analysis was unable to detect any statistically significant correlations between the water quality parameters, suggesting they are substantially independent measures of water quality. The monitoring showed that the small upland streams had generally good-to-excellent water quality. The water quality in these was generally better than the “reference set”—this probably reflected agriculture and cultivation in the proximity of their sampling points.