New Zealand Journal of Agricultural Research abstracts
Attenuation of effluent-derived faecal microbes in grass buffer
strips
R. Collins
National Institute of Water and Atmospheric Research Ltd
Gate 10, Silverdale Road
P.O. Box 11 115
Hamilton, New Zealand
A. Donnison
C. Ross
AgResearch Limited
Ruakura Campus
Private Bag 3123
Hamilton, New Zealand
M. McLeod
Landcare Research Limited
Private Bag 3127
Hamilton, New Zealand
Abstract A series of field experiments assessed
the ability of sloping (8°) 5-m-long by 2-m-wide grass buffer
strips to trap the faecal microbes Escherichia coli and
Campylobacter. The microbes, applied within dairy-farm effluent, were
washed into the strips by surface runoff generated at rates of 4–13
litres/min using a water sprinkler system. The effluent and surface and
subsurface outflows at the lower end of each plot were sampled for
microbial analysis. Flow rate influenced the timing of peak microbial
concentration in outflow and the recovery of both microbes. Under high
flow, recovery rates varied from 15–100%, and hence entrapment was
often minimal. Under the slowest rate of water application, entrapment
was much greater (≥95%), at least over the 40 min of
water application.
During large runoff events, and where preferential flowpaths occur,
buffer strips need to exceed 5 m in length in order to markedly
reduce the delivery of faecal microbes to waterways. Of those microbes
trapped in the grass strips under fast flow rates, some were
remobilised and washed out following a subsequent runoff event, 5 days
later. On occasion, a considerable volume of flow was observed
to bypass beneath the subsurface collecting troughs, probably reducing
the effectiveness of the buffer strips.
Keywords effluent; faecal microbes; buffer strips;
attenuation; flow rate; remobilisation
A04026; Received 19 April 2004; accepted 16 August 2004; Online
publication date 15 December 2004
New Zealand Journal of Agricultural Research, 2004, Vol. 47:
565–574
0028–8233/04/4704–0565 © The Royal Society of New Zealand 2004
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