Water quality and public health

Swimming, fishing, boating and generally playing around in water is an important part of New Zealand culture. Yet these activities, along with drinking water supplies and shellfish gathering, could be risky if the water contains the pathogenic organisms that can make us sick. Some of those microorganisms (called zoonoses) are spread into the environment from animal faeces. Zoonotic pathogens are the leading cause of human infectious disease in New Zealand.

AgResearch’s Dr Richard Muirhead is leading some of the research to understand and mitigate the spreading of faecal microorganisms from farms. In the faecal-oral cycle of zoonotic diseases the animal acts as an amplifier that boosts the numbers of zoonotic pathogens so that their faeces contain very high numbers.  The research is focusing on modelling the numbers of microorganisms transferred to surface waters via different pathways and identifying appropriate mitigation options.  The numbers of microorganisms discharged from farms is highly variable and we are using Monte Carlo simulation techniques to help model and understand this variability.  The results from these model simulations are used to develop simpler risk indices that can be incorporated into decision support tools for land managers.

Fences and bridges keep stock out of streams and minimise faecal microbial transfer to water. Current good environmental practice of matching the farm dairy effluent management system to the farm landscape and using storage to avoid irrigation to wet soils are also effective for microbes. These mitigations will improve microbial water quality during base-flow conditions such as the stream flow between storm events. Future research is focusing on options to reduce faecal contamination during storm events and risk assessment of downstream effects.