Assessment, modelling and management of land use and water quality in the upper Taieri River catchment

An average of 16 years' data at sites in the upper Taireri River catchment was used to determine if water quality had changed commensurate with an increase in the irrigated area and land-use change. To help remediate perceived gaps in the nutrient modelling software Overseer (R), data was also collected from a low-intensity border dyke and high-intensity spray-irrigated property. Filterable reactive phosphorus concentrations increased over time and were attributed to the irrigation of poor anion storage capacity (ASC) soils and irrigation-return flows. Differences were noted between measured nitrogen and phosphorus loads and those predicted by Overseer (R), which were attributed to a combination of low ASC soils, spray irrigation and artificially drained soils receiving effluent. These data will be used to calibrate future versions of Overseer (R). However, with an increase in spray irrigation and land-use change forecast for the catchment, strategies should be employed to mitigate further water quality deterioration.