New Zealand Journal of Marine and Freshwater Research abstracts
Water quality in low-elevation streams and rivers of New Zealand: recent
state and trends in contrasting land-cover classes
Scott T. Larned1
Mike R. Scarsbrook2
Ton H. Snelder1
Ned J. Norton1
Barry J. F. Biggs1
1National Institute of Water and Atmospheric
Research Limited
P.O. Box 8602
Christchurch, New Zealand
email: s.larned@niwa.co.nz
2National Institute of Water and Atmospheric
Research Limited
P.O. Box 11 115
Hamilton, New Zealand
Abstract River water quality in New Zealand is at great
risk of impairment in low elevation catchments because of pervasive land-use
changes, yet there has been no nationwide assessment of the state of these
rivers. Data from the surface-water monitoring programmes of 15 regional
councils and unitary authorities, and the National River Water Quality Network
were used to assess the recent state (1998-2002) and trends (1996-2002) in
water quality in low-elevation rivers across New Zealand. Assessments were
made at the national level, and within four land-cover classes (native forest,
plantation forest, pastoral, and urban). Finer-scaled assessments were made
by subdividing the large number of pastoral sites into six climate classes,
and seven stream orders. At the national level, median concentrations of
the faecal indicator bacterium Escherichia coli, and dissolved inorganic
nitrogen and dissolved reactive phosphorus exceeded guidelines recommended
for the protection of aquatic ecosystems and human health. Water quality
state varied widely within land-cover classes: E. coli and dissolved
nitrogen and phosphorus concentrations in the pastoral and urban classes
were 2-7 times higher than in the native and plantation forest classes, and
median water clarity in the pastoral and urban classes was 40-70% lower than
in the native and plantation forest classes. Water quality state in the pastoral
class was not statistically different from that of the urban class, and water
quality state in the plantation forest class was not statistically different
from that of the native forest class. Significant trends in low-elevation
rivers were limited to four parameters: flow (trending down in all instances),
and temperature, clarity, and conductivity (trending up in all instances).
The trends in flow, temperature, and clarity were apparent at the national
scale, and within the pastoral class. The magnitudes of these trends were
very low, corresponding to changes of ≤0.5%/year in parameter medians.
Keywords clarity; Escherichia coli; guidelines;
land cover; land use; low-elevation; New Zealand; nutrients; state; streams
and rivers; trends; water quality
M03047; Received 13 August 2003; accepted 2 February 2004; Online publication
date 8 June 2004
New Zealand Journal of Marine and Freshwater Research, 2004, Vol. 38:
347-366
0028-8330/04/3802-0347 © The Royal Society of New Zealand 2004
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