Dg. Smith et al., TRENDS IN NEW-ZEALAND NATIONAL RIVER WATER-QUALITY NETWORK, New Zealand Journal of Marine and Freshwater Research, 30(4), 1996, pp. 485-500
An analysis of trends was made for the 14 physical/chemical determinan
ds measured monthly over the period 1989-93 at 77 river sites distribu
ted throughout New Zealand's North and South Islands. This has used no
n-parametric Kendall slope estimators and associated tests, accounting
for seasonality, which have been applied to both the raw data and to
Bow-adjusted data (flows in much of the North Island trended downward
over the period). Results indicate a general improvement in water qual
ity, particularly in the South Island. Downward national trends, for b
oth raw and flow-adjusted data, were found for water temperature, BOD5
, NH4-N, NOx-N and TP. Upward national trends, again for both raw and
flow-adjusted data, were found for dissolved oxygen, visual clarity, c
onductivity, and g(340)/g(440) (indexes of dissolved colour). No natio
nal trends are reported for pH or DRP. Downward trends for turbidity a
nd TN were seen in the raw data only. A general characterisation of th
e dependence of these determinands on river flow is presented.