TRENDS IN NEW-ZEALAND NATIONAL RIVER WATER-QUALITY NETWORK

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.