Data visualisation using Partial Least Squares Regression models shows derivation of local or site-specific assessment values is warranted for the AMD-impacted Callide Creek Catchment, Central QLD, Australia

Acid mine drainage from the historic Mount Morgan Au-Cu-Ag mine is a legacy issue impacting waters of the Callide Creek catchment, Fitzroy Basin, Central Queensland. Water quality objectives used to assess these surface waters were scheduled in 2011. Long-term water quality monitoring data (2010-2020) were examined to better understand the associated waterways and to investigate the suitability of these catchment-wide assessment values. Partial Least Squares Regression (PLS) models showed differences between samples from the Dee and Don Rivers versus those from Callide creek. Broad segregation of samples by land use (grazing, cropping, mining) or groundwater zone (dominant major ions) were also observed. In the Callide subset, turbidity, TN and TP were the variables where median concentrations were greater than current assessment values. Whereas, in the Dee-Don subset, median EC, SO4 and (0.45 μm field filtered) Cd, Cu, Zn and Co were (1.3, 23, 5.3, 27, 13 and 5.6 times, respectively) greater than their respective assessment values. A 2-factor PLS model of the Dee-Don subset (24 variables, n=30-575) explained 82% of the variation in the data. Samples further grouped at the individual site level. Variables with correlation loading >|0.7| in Factor-1 (72%) were pH, Al, Cu, Fe, Ni, Zn, Co and Mn. Turbidity and TP were important to Factor-2. Recent data (2021-22) from two Dee-Don River locations were examined at the site level. Median EC, TN, TP, Al, and SO4, differed significantly. Median sulfate sampled from one site (374 mg/L) was greater than the other (13 mg/L) (n=6, Kruskal-Wallis, P=0.02). Sulfate results from that site consistently exceeded the current catchment-level assessment value (<20 mg/L). Overall, this analysis demonstrated multi-variate water quality differences within the rivers and creeks of the Callide Creek Catchment. PLS was used as a visualisation tool and confirmed that where possible, site-specific assessment is merited.