The doors to our Whitianga and Paeroa offices will be closed for the summer break from 4pm on Friday, 20 December, while our Taupō and Hamilton offices will close for the summer break at 1pm on Tuesday, 24 December. All offices will reopen on Monday, 6 January 2025. To report air or water pollution, unsafe water activities in or on a river, lake or harbour, or make a general enquiry or information request during this time, call us 24/7 on 0800 800 401.

Close alert

Firth of Thames water quality and ecosystem health

TR 2015/23
  1. Services »
  2. Publications »
  3. TR2015/23

Report: TR 2015/23

Author: Malcolm Green, John Zeldis et al (National Institute of Water & Atmospheric Research Ltd (NIWA))

About this report

This technical report describes the current state of knowledge on the environmental state of the Firth of Thames and identifies information gaps. It provides critical information required for effective decision-making on the future management of the Firth of Thames. It also provides valuable, scientifically robust information for communities, stakeholders and iwi.

This technical report is divided into two parts: synthesis report and data report.

Synthesis report

The synthesis report presents key findings on water quality and ecosystem health in relation to sediment loading, nutrient loading, phytoplankton dynamics, dissolved oxygen dynamics and pH variability. It also identifies information gaps and priorities for future work that will enable more comprehensive assessments of water quality and ecosystem health of the Firth of Thames to be made in the future. All statements in the synthesis report are underpinned by data presented in the data report.

Data report

The data report describes the data underpinning the synthesis report. It presents a description of available data sets and brief descriptions of the data and analyses that support the findings presented in the synthesis report. Some additional data are presented in the data report that are not presented in the synthesis report. This is to provide additional context and a comprehensive overview of available data. The data report does not attempt to discuss the ecological significance of the data or provide detailed interpretation of the results as this is presented in the synthesis report.

Read or download the report

Firth of Thames water quality and ecosystem health [PDF, 12 MB]

Synthesis report

Contents
  Key points
  Executive summary
  Introduction
1 Geographic zones
2 Physical setting
3 Sediments
3.1 Sedimentation rates
3.2 Mangrove expansion
3.3 Sediment budget
3.4 Subtidal seabed sediments
3.5 Benthic fauna
3.6 Numerical modelling
3.7 Effects of sediments
3.8 Reversibility and remediation
4 Overview - nutrients, phytoplankton, bacteria, dissolved oxygen and pH
5 Nutrients
5.1 Data
5.2 Trends
6 Phytoplankton and bacteria
6.1 Data
6.2 Trends
7 Dissolved oxygen
7.1 Data
7.2 Patterns in DO
7.3 Causes of oxygen depletion
7.4 Trends
8 pH
8.1 Data
8.2 Results
8.3 Trends
9 Mineralisation of organic matter
9.1 Benthic mineralisation
9.2 Pelagic mineralisation
10 Water, salt and carbon/nutrient budgets
11 Assessments of water quality and ecosystem health
11.1 The current trophic state of the system
11.2 The contribution of land runoff to nutrients
11.3 Trends
11.4 The pre-development trophic state of the system
11.5 Effects of low dissolved oxygen
11.6 Effects of acidification
11.7 Reversibility and remediation
12 Overview of NWA data used in this report
12.1 Sediments
12.2 Nutrients
12.3 Phytoplankton and bacteria
12.4 Dissolved oxygen
12.5 pH
12.6 Benthic and pelagic mineralisation
13 Recommendations for further research and data collection
13.1 Trends
13.2 Sediments
13.3 Nutrients
13.4 Primary productions
13.5 Dissolved oxygen and pH
14 Data catalogue
14.1 Sediments
14.2 Nutrients
14.3 Primary production
14.4 Dissolved oxygend and pH
15 Data assessment
15.1 Sediments
15.2 Nutrients
15.3 Primary production
15.4 Dissolved oxygen and pH
  Acknowledgements
16 References
  Appendix A: Tabulation of results of trend tests
  Appendix B: Observations of depleted oxygen reported by O'Callaghan (2013)

 

Data report

Contents
1 Introduction
2 Geographic zones
3 Firth of Thames physical setting
3.1 Geology
3.2 Landcover history
3.3 Bathymetry
3.4 River inflow and catchment characteristics
3.5 Winds and circulation
3.6 Currents, waves and sea levels
3.7 References
4 Sediments
4.1 Overview of data sources
4.1.1 Subsidence
4.1.2 Mangrove forest expansion
4.1.3 Recent sedimentation history of mangrove forests
4.1.4 Unvegetated intertidal flats
4.1.5 Sediment budget for the southern Firth of Thames
4.1.6 Subtidal
4.2 Interidal-flat morphology
4.3 Subsidence
4.4 Mangrove forest expansion
4.5 Recent sedimentation history of mangrove forests
4.5.1 Data collection
4.5.2 Dating methods
4.5.3 Sediment properties
4.5.4 Sedimentation rates
4.6 Unvegetated intertidal flats
4.6.1 Data collection
4.6.2 Sedimentation rates
4.7 A sediment budget for the sourthern Firth of Thames
4.8 Subtidal region
4.8.1 Data collection and analysis
4.8.2 Sediment properties reported by Giles et al
4.8.3 Sediment properties from further datasets
4.8.4 Sediment accumulation rates
4.8.5 Subtidal benthic infauna
4.9 Satellite remote sensing of total suspended sediment
4.10 Sediment disperal and deposition modelling
4.10.1 Overview and approach
4.10.2 Deltares model
4.11 References
5 Nutrients
5.1 Overview of data sources
5.2 Data from the extended-Firth monitoring site
5.3 Trend analyses
5.4 Survey data
5.5 References
6 Phytoplankton and bacteria
6.1 Overview of data sources
6.2 Data
6.2.1 Extended-Firth monitoring site
6.2.2 Estimates of primary production
6.2.3 Chlorophyll from moored fluorometry
6.2.4 Chlorophyll from underway fluorometry
6.3 Results
6.4 Trend analyses
6.5 References
7 Dissolved oxygen
7.1 Overview of data sources
7.2 Methods
7.2.1 CTD measurements
7.2.2 Moorings
7.3 Results
7.4 Trend analyses
8 pH
8.1 Overview of data sources
8.2 Methods
8.3 Results
8.3.1 Underway surveys
8.3.2 Discrete surveys
8.3.3 Tended analyses
9 Benthic and pelagic mineralisations
9.1 Overview of data sources
9.2 Benthic mineralisation
9.3 Pelagic mineralisation
9.4 References
10 Water, salt and carbon/nutrient budgets
10.1 Introduction
10.2 Water budget
10.3 Salt budget
10.4 Carbon/nutrient budgets
10.5 Data used in budget construction
10.5.1 Ocean surveys
10.5.2 Freshwater and nutrient loadings
10.6 Results
10.7 References
 11 Acknowledgements
  Appendix A: Radioisotope dating
  Appendix B: Delft3d hydrodynamic flow and seidment transport model
  Appendix C: Accuracy and precision of nutrient budget
  Appendix D: Corrections to moored DO sensors
  Appendix E: Observations of depleted oxygen reported by O'Callaghan (2013)
  Appendix F: Carbonate Chemistry Methodology