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Land-to-water transfer of nutrients: What knowledge can be gained by combined analysis of river water quality and flow records?

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Report: TR 2015/24

Author: Simon Woodward (Lincoln Agritech Ltd)

About this report

This report investigates potential advantages of establishing flow recording in parallel to an existing water quality sampling programme, in order to maximize the value of the sampling programme. Can stream flow alongside water quality enhance our understanding of water quality data and trends, particularly with regard to the transfer processes from the land to the stream monitoring site? The study focuses on the key water quality parameters associated with pastoral farming.

Waikato Regional Council collects monthly samples for monitoring of water quality at 114 sites throughout the region, both from the Waikato River and from smaller stream and rivers. This report used flow records at 26 water quality sampling sites to better understand the time series of total nitrogen (TN), nitrate-nitrite nitrogen (NNN), ammoniacal nitrogen (NH4), total phosphorus (TP), dissolved reactive phosphorus (DRP) and the non reactive phosphorus fraction (TP-DRP) collected at these sites. Silica concentration (Si) and electrical conductivity (EC) were also considered, as possible indicators of water age.

Ideally water quality sampling programmes should be accompanied by matched stream flow recording. This report proposes several additional ways in which stream flow data can be used to elucidate information from water quality sampling. When focusing on a single site, however, consideration of already available stream flow records can provide substantial additional insight gained into stream contaminant dynamics and processes.

Note: This research was primarily funded by MBIE through the “Groundwater Assimilative Capacity” programme (C03X1001), and co-funded by Waikato Regional Council.

Read or download the report

Land-to-water transfer of nutrients: What knowledge can be gained by combined analysis of river water quality and flow records?  (PDF 7MB)

Contents

  Executive summary 2
1 Introduction 6
2 Regularisation of Stream Flow Data 11
3 Water Quality Sampling Bias 17
4 Concentration-Discharge Relationships 25
4.1 Introduction 25
4.2 Nitrogen Species 30
4.3 Phosphorus Species 36
4.4 Silica 42
4.5 Electrical Conductivity 46
5 Data Stratification 48
5.1 Introduction 48
5.2 Data Stratification Approaches 48
5.2.1 Stratification based on Flow Percentiles 48
5.2.2 Stratification based on Hydrograph Separation 51
5.2.3 Discussion 68
5.3 Trend Analysis 68
5.3.1 Comparison with WRC (2013) Method 68
5.3.2 Trends in the Stratified Data 71
6 Load And Yield Estimation 77
6.1 Regression Approach 77
6.2 Beale Ratio Estimator Approach 85
6.3 Catchment Comparisons 91
  Conclusions 95
  Acknowledgments 96
  References 97
  Appendix 1: Concentration Discharge Relationships 100
  Appendix 2: Data Stratification Based on Flow 127
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