Bay of Islands Sedimentation Report

The Northland Regional Council commissioned NIWA to analyse and report on sediment and benthic ecological data collected as part of the 2010 LINZ Oceans 20/20 Bay of Islands (BOI) survey.

These data provide:

  • Detailed and robust information on the state of the environment; and 
  • An opportunity to inform the future management of the catchment and the receiving coastal marine environment of the BOI system.

This report provides a detailed account of how the BOI system has been impacted by catchment land-use changes over the last ~700 years following the arrival of people.  

Due to the size of the document it has been broken into the following sections

Sections 1-2

Executive summary

1 Introduction
1.1 Background
1.2 Study objectives
1.3 Recent sedimentation in NZ estuaries and coastal marine environments
1.4 Study area
1.5 History of the Bay of Islands: deforestation and settlement

2 Methods
2.1 Strategy
2.2 Sediment core collection
2.3 Radioisotope dating and sediment accumulation rates
2.4 Sediment core composition
2.5 Sediment deposition in the BOI system
2.6 Sediment accommodation capacity of fringing estuaries
2.7 Sediment source determination
2.8 Landcover history for sediment-source modelling
2.9 Benthic ecology and sensitivity and vulnerability to sedimentation
2.10 Estimation of benthic community vulnerability to sedimentation
2.11 Recent changes in mangrove and saltmarsh-habitat extent

Section 3

3 Results
3.1 Sedimentation patterns
3.2 Estimating the surface mixed layer and recent sediment accumulation rates
3.3 Spatial variations in recent sediment accumulation rates
3.4 Long-term sediment accumulation rates
3.5 Influence of land-use changes on sedimentation
3.6 Particle size
3.7 Recent sedimentation in the BOI system
3.8 Comparison of recent and prehistoric sediment budgets
3.9 Comparison with sedimentation rates in other North Island estuaries
3.10 Sediment accommodation capacity of fringing estuaries
3.11 Present-day sources of Bay of Islands sediments
3.12 Past sources of Bay of Islands sediments
3.13 Present-day deposits – recent or historical sediments?
3.14 Benthic ecology
3.15 Recent historical changes in mangrove and salt marsh-habitat extent
3.16 Potential for future mangrove-habitat expansion

Sections 4-Appendices

4 Summary and conclusions
4.1 Catchment history
4.2 Sedimentation
4.3 Sediment sources
4.4 Macro-benthic communities
4.5 Changes in mangrove and saltmarsh-habitats extent

5 Acknowledgements

6 References

Appendix A Radioisotope dating
Appendix B Compound Specific Stable Isotopes