New Zealand Journal of Marine and Freshwater Research abstracts
Short communication
Water quality impact of a dairy cow herd crossing a stream
Rob J. Davies-Colley
John W. Nagels
National Institute of Water and Atmospheric
Research Limited
P.O. Box 11 115
Hamilton, New Zealand
email: r.davies-colley@niwa.cri.nz
Rob A. Smith
Tasman District Council
Private Bag 4
Richmond, New Zealand
Roger G. Young
Cawthron Institute
Private Bag 2
Nelson, New Zealand
Chris J. Phillips
Landcare Research
P.O. Box 69
Lincoln, New Zealand
Abstract The water quality impact of a herd of 246 dairy
cows crossing a stream ford was documented. Two cow crossings produced plumes
of turbid water associated with very high concentrations of faecal indicator
bacteria (Escherichia coli) and high suspended solids (SS) and total
nitrogen (TN). On the first crossing, towards the milking shed, the cows
were tightly-bunched and produced a sharp spike of contamination (E. coli
peaking at 50 000 cfu/100 ml). After milking, the cows wandered back across
the stream as individuals or small groups, and contaminants were less elevated,
albeit for a longer period. Light attenuation, measured continuously by beam
transmissometer, correlated closely with E. coli, SS, and TN, permitting
the total yield of these contaminants to be estimated. Contaminant yields
for the two crossings were very similar, suggesting that time taken and whether
or not cows are herded may not greatly influence water quality impact. The
cows defecated c. 50 times more per metre of stream crossing than elsewhere
on the raceway. This study has shown that cattle accessing stream channels
can cause appreciable direct water contamination, suggesting that excluding
cattle from streams will have major water quality benefits.
Keywords bacteria; Escherichia coli; environmental
management; indicators; livestock; water quality
M04005; Received 26 January 2004; accepted 20 May 2004; Online publication
date 5 August 2004
New Zealand Journal of Marine and Freshwater Research, 2004, Vol. 38:
569-576
0028-8330/04/3804-0569 © The Royal Society of New Zealand 2004
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