CLUES model calibration and its implications for estimating contaminant attenuation

Catchment water quality models are essential for freshwater management; however, their value is dependent on their performance and level of uncertainty. Here we present the latest calibration of the Catchment Landuse for Environmental Sustainability model (CLUES) and examine the implications of the calibration for estimating in-stream contaminant attenuation. CLUES estimates catchment mean annual loads of Total Nitrogen, Total Phosphorus and E. coli and is widely used in New Zealand for both catchment planning and policy development. We found that CLUES gives reasonable load estimates at the catchment scale. However, there was significant uncertainty in the SPARROW parameterisation. We conclude that while CLUES can be used to estimate catchment contaminant loads, it cannot adequately estimate instream attenuation. Improved representation of lower order streams in the calibration data would allow us to evaluate the source yields from each of the model components to better estimate attenuation.