New Zealand Journal of Marine and Freshwater Research abstracts

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Land-use impacts and water quality targets in the intensive dairying catchment of the Toenepi Stream, New Zealand

Robert J. Wilcock¹
Ross M. Monaghan²
John M. Quinn¹
Alan M. Campbell³
Bruce S. Thorrold⁴
Maurice J. Duncan⁵
Alec W. McGowan⁷
Keith Betteridge⁷

¹National Institute of Water and Atmospheric Research Limited
P.O. Box 11–115
Hamilton, New Zealand
²AgResearch Limited
Invermay Agricultural Centre
Private Bag 50034
Mosgiel, New Zealand
³Environment Waikato
P.O. Box 4010
Hamilton East, New Zealand
⁴Dexcel Limited
Private Bag 3221
Hamilton, New Zealand
⁵National Institute of Water and Atmospheric
 Research Limited
P.O. Box 8602
Christchurch, New Zealand
⁶AgResearch Limited
Ruakura Research Centre
Private Bag 3123
Hamilton, New Zealand
⁷AgResearch Limited
Grasslands Research Centre
Private Bag 11008
Palmerston North, New Zealand

Abstract Water quality monitoring in Toenepi Stream, New Zealand, started in 1995 in a study of dairy farming influences on lowland stream quality and has continued since then with brief interruptions. Surveys have provided information about changes in farm and soil management practices as they relate to environmental sustainability. Although average water quality in Toenepi Stream has changed little during 1995–2004, there have been some notable improvements. Water clarity measured by black disc has improved from 0.6 m to 1.5 m, and median ammonia-N and nitrate-N concentrations have declined by 70% and 57%, respectively. The frequency and magnitude of extreme concentrations have declined—most notably for nitrogen (N) forms, which also had decreased mean values. Specific yields for suspended solids (SS) and phosphorus (P) forms in 2002–04 were 47–67% of 1995–97 values, mainly because of lower water yields. Reduced specific yields for N forms in 2002–04 (34–37% of 1995–97 yields) were also attributable to lower mean concentrations in stream water. Faecal bacteria concentrations have not abated and are on average 2–3 times recommended guideline values for contact recreation. Fewer dairy farms and an increased proportion irrigating dairyshed effluent to land, rather than discharging it to the stream via two-pond systems, were likely causes of improvement in water quality. Water quality targets were developed for Toenepi Stream to achieve contact recreation criteria for the Piako River (downstream) and for intrinsic habitat values for Toenepi Stream. A range of mitigation measures has been formulated to meet these targets, but substantial uptake of sustainable farming practices is needed to improve water quality in Toenepi Stream.

Keywords land use; dairy; water quality; lowland stream; monitoring

New Zealand Journal of Marine and Freshwater Research, 2006, Vol. 40: 123–140
0028–8330/06/4001–0123     © The Royal Society of New Zealand 2006
M05036; Online publication date 9 February 2006 Received 20 June 2005; accepted 16 September 2005

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