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Trends in river water quality in the Waikato region, 1993-2012

TR 2013/20
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Report: TR 2013/20

Author: B Vant

Abstract

River water quality has been routinely monitored in the Waikato region since 1980. Monitoring at several Waikato River sites began then, with other sites being added later.

Water quality is currently monitored at monthly intervals at ten sites between Taupo Gates at the head of the river, and Tuakau Bridge, some 300 km downstream. In 1990—but particularly from 1993—monthly monitoring of the water quality of other rivers and streams in the region began. In addition to the 10 sites on the Waikato River, water quality is now measured at 104 sites on other rivers and streams, with results being reported annually.

Vant and Wilson (1998) undertook the first comprehensive analysis of trends in water quality in Waikato Regional Council’s river monitoring programmes, examining records for the period ending in 1997. This was subsequently extended at 5-yearly intervals, covering the periods ending in 2002 and 2007.

This latest report describes a further extension of the analysis, covering the 20-year period 1993 to 2012.

Trends in river water quality in the Waikato region, 1993-2012 [PDF, 1.2 MB]

Contents
1 Introduction 1
2 Methods 1
2.1 Datasets analysed 1
2.2 Statistical analyses - general approach 3
2.3 Seasonal Kendall trend slope 4
2.4 Seasonal Kendall trend test 5
2.5 Flow adjustment 5
2.6 Flow records 6
3 Results and discussion 9
3.1 Waikato River 9
3.2 Other rivers and streams 14
4 Conclusions 24
  References 26
  Appendix 1: Adusting Waikato River total P results for arsenic interference 28
  Appendix 2: Trend results for sites on the Waikato River 31
  Appendix 3: Trend results for sites on other rivers and streams 32