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Water quality and sources of nitrogen and phosphorus in the Hauraki rivers, 2006–15


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Report: TR 2016/17

Author: Bill Vant

About this report

Major rivers in the Hauraki area flow in a generally northerly direction into the Firth of Thames. Water quality has been monitored monthly at 19 sites on these rivers since 1990–94. Information is also available for the 24 moderate-to-large discharges of sewage or industrial wastewaters into the rivers. This report describes the current water quality of the rivers—as indicated by conditions during the past decade—and the changes observed since the records began. It also describes the loads of the plant nutrients nitrogen (N) and phosphorus (P) that are carried by the rivers into the nutrient-sensitive Firth of Thames; various different sources contribute to the loads, and these are quantified.

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Water quality and sources of nitrogen and phosphorus in the Hauraki rivers, 2006-15 [PDF, 1.5 MB]



  Abstract iii
1 Introduction 1
2 Water quality of the Hauraki rivers 3
2.1 Current condition: WRC guidelines 3
2.2 Current condition: NOF requirements 7
2.3 Long-term changes 8
3 Sources of nitrogen and phosphorus in the rivers 11
3.1 Loads carried by the rivers 11
3.2 Loads from point sources 15
3.3 Components of the total loads in rivers 20
4 Summary and conclusions 21
  References 23