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