Dairying and water-quality issues in Australia and New Zealand

Field: Environmental Science (Physical Sciences)

The scale and intensity of dairy farming can place pressure on our freshwater resources. These pressures (e.g. excessive soil nutrient concentrations and nitrogen excretion) can lead to changes in the levels of contaminants in waterways, altering the state and potentially affecting the uses and values society ascribes to water. Resource management involves putting in place appropriate responses to address water-quality issues. In the present paper, we highlight trends in the scale and extent of dairying in Australia and New Zealand and describe water-quality pressures, state, impacts and responses that characterise the two countries. In Australia and New Zealand, dairy farming has become increasingly intensive over the past three decades, although the size of Australia’s dairy herd has remained fairly static, while New Zealand’s herd and associated excreted nitrogen loads have nearly doubled. In contrast, effluent management has been improved, and farm waterways fenced, in part to reduce pressure on freshwater. However, both countries show a range of indicators of degraded water-quality state. Phosphorus and nitrogen are the most common water-quality indicators to exceed levels beyond the expected natural range, although New Zealand also has a significant percentage of waterways with faecal contaminants beyond acceptable levels for contact recreation. In New Zealand, nitrate concentrations in waterways have increased, while phosphorus and suspended sediment concentrations have generally decreased over the past decade. Water quality in some coastal estuaries and embayments is of particular concern in Australia, whereas attention in New Zealand is on maintaining quality of high-value lakes, rivers and groundwater resources, as well as rehabilitating waterbodies where key values have been degraded. In both Australia and New Zealand, water-quality data are increasingly being collated and reported but in Australia long-term trends across waterbodies, and spatially comprehensive groundwater-quality data have not yet been reported at national levels. In New Zealand, coastal marine systems, and particularly harbours and estuaries, are poorly monitored, but there are long-term monitoring systems in place for rivers, groundwater and lakes. To minimise pressures on water quality, there is a high reliance on voluntary and incentivised practice change in Australia. In New Zealand, industry-led practice change has been important over the past decade, but regulated environmental limits for dairy farmers are increasing. Dairy industries in both countries have set targets for reducing pressures through sustainability frameworks and accords. To address future drivers such as climate change and increasing domestic and international market demand for sustainability credentials, definitions of values and appropriate targets for waterbodies draining agricultural landscapes will be required. Environmental limits (both natural and societal) will constrain future growth opportunities for dairying and research into continued growth within limits remains a priority in both countries.