4. Conclusions
The results indicate that both E.coli and pathogenic bacteria, Campylobacter, continue to be detected in the groundwater, with E.coli being detected at much higher levels ranging from <1 to 2400 MPN/100ml, well above NZ drinking water guideline level of 1 MPN/100ml. There is a poor correlation between both Campylobacter and E. coli and between Campylobacter and total coliforms. This is due mainly to the relatively low number of positive Campylobacter results (9) in comparison to positive E.coli (83%) and total coliform results (almost 100%).
The selection of the wells to avoid septic tank contamination and wellhead protection issues means that the microbial contamination would be coming from dairying combined with border strip irrigation and large rainfall events. The possible exception to this is well J41-0031 where bull calves were kept in the small paddock, which houses the well. It is possible that very high concentrations (2400 MPN/100ml) of E.coli are related to the impact of the bull calves in this paddock.
There is a general trend throughout the data set of high numbers of E.coli being detected in groundwater approximately 20-25 days after a coincidence of stocking and irrigation (or a large rainfall event) in the nearby paddocks. Samples collected from well J41-0008 recorded a significant increase in E.coli concentration and the appearance of Campylobacter approximately 25 days after coincidal stocking and irrigation. This was also combined with a period of high rainfall in early February (84 mm between 25 January and 15 February 2004), so much so that most farmers did not irrigate during February 2004.
Discussions with landholders indicate that there is a concern over water quality for drinking purposes. Four out of the five wells sampled are used for household drinking purposes. One landholder indicated the occurrence of intermittent stomach complaints from a resident, and was concerned that it was related to water quality. Following an elevated E.coli count in one of the groundwater samples, the landholder was informed and has since installed a filter system on that particular well and also on a well at his other property.
Landholders were also concerned with livestock health in relation to contaminated stock water. The ANZECC & ARMCANZ (2000) water quality guidelines indicate that livestock health may be affected by water-borne microbial pathogens and parasites. Also concerns were raised over the dairy wash-down area and the use of microbial contaminated water. As E.coli counts in this study have regularly exceeded the E.coli guideline value of 1 MPN/100ml filtration systems should be considered for shallow wells used for this purpose.
The relationship between coincidal stocking and irrigation/high rainfall and high microbial counts will be further assessed in October, November and December of this year with weekly sampling of all wells. Information gained from this intensive sampling across the district will be used in conjunction with the information presented in this report to suggest farm management practices that may help mitigate microbial contamination of groundwaters.
5. Acknowledgements
This study was funded as part of the CDRP project on "Transmission pathways of pathogens from domestic livestock to water". We wish to thank Environment Canterbury for their assistance in carrying out the project, particularly Zella Smith for her assistance in sample collection and farmer liaison.
6. References
ANZECC & ARMCANZ. (2000). Australian and New Zealand guidelines for fresh and marine water quality. October 2000.
Close, M. (2000). Assessment of likely causes of microbial contamination of shallow wells in the Morven-Glenavy Area, South Canterbury. ESR Client Report CSC0204.
Close, M.; Savill, M. (2003). Transmission Pathways of Pathogens from Domestic Livestock to Water – Quantify Contamination of Groundwater. ESR Client Report CSC0302.
Contact for Enquiries
MAF Information Services
Pastoral House
25 The Terrace
PO Box 2526
Wellington, NEW ZEALAND
Fax: +64 4 894 0721
Contact this person
