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Regional estuary monitoring programme: April 2001 to April 2006 - Southern Firth of Thames and Raglan (Whaingaroa) harbour

TR 2008/48
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Report: TR 2008/48

Author: Malene Felsing and Nathan Singleton

Abstract

Environment Waikato is responsible (with other agencies) for managing about 1150 km of open coast and estuarine shoreline, extending 12 nautical miles seawards of mean high water springs. Estuaries have been identified in the Waikato State of the Environment Report as one of the coastal areas within the Waikato Region most at risk from human activities (Environment Waikato, 1999). They are important areas for people culturally, commercially and recreationally; and are highly productive ecosystems that provide important habitats for many fish, shellfish and bird species. Estuaries receive and accumulate sediment, nutrients and contaminants from the surrounding catchment. What happens on land can directly or indirectly affect the health of an estuary. Monitoring will allow early detection of any adverse environmental changes, and as such provide a trigger for assessing land management practices.

Environment Waikato's Regional Estuary Monitoring Programme was initiated in April 2001, to determine the current status and monitor the temporal changes in the state of the Region’s estuaries. The monitoring programme samples sediments and associated macro-invertebrate communities at five permanent sites in each of two estuaries: the Firth of Thames, and Raglan (Whaingaroa) Harbour. Sampling is undertaken quarterly at two sites in each estuary, and twice a year at three sites.

The findings from a pilot study undertaken in April 2001 were presented in Turner et al. (2002). Results from the monitoring have beenpublished in three data reports to date (Turner & Carter, 2004; Felsing et al., 2006; Singleton & Pickett, 2006). These reports presented the findings from one or two years, including the species present and the sediment characteristics at the different sites in each estuary. The current report aims to bring together the data for the five years of monitoring from April 2001 to April 2006, to assess:

  • the current status of health of the estuaries, based on invertebrate community and
    sediment characteristics; and
  • temporal changes in the health of the estuaries over the duration of the monitoring
    to date.

The report also recommends where changes should be made to the estuary monitoring programme.

Regional Estuary Monitoring Programme: April 2001 to April 2006 [PDF, 813 KB]

Contents
  Acknowledgement iii
  Executive summary v
1 Introduction 1
2 Methods 1
2.1 Field sites and sampling regime 2
2.2 Sample collection and processing 3
2.2.1 Benthic macrofauna 3
2.2.2 Sediment characteristics 5
2.3 Statistical analysis 5
2.3.1 Sediments 5
2.3.2 Macrofauna 6
3 Results 8
3.1 Benthic macrofauna community structure 8
3.1.1 Southern Firth of Thames 8
3.1.2 Raglan (Whaingaroa) Harbour 10
3.2 Macrofaunal changes over time 12
3.2.1 Southern Firth of Thames 12
3.2.2 Raglan (Whaingaroa) Harbour 16
3.3 Sediment characteristics 20
3.3.1 Southern Firth of Thames 20
3.3.2 Raglan (Whaingaroa) Harbour 27
3.4 Linking assemblage composition to sediment characterics 35
3.4.1 Southern Firth of Thames 35
3.4.2 Raglan (Whaingaroa) Harbour 36
4 Discussion 37
4.1 Firth of Thames 37
4.1.1 Sediment characteristic 37
4.1.2 Macrofaunal assemblages 38
4.2 Raglan (Whaingaroa) Harbour 40
4.2.1 Sediment characteristics 40
4.2.2 Macrofaunal assemblages 40
4.3 Comparison of the southern Firth of Thames and Raglan (Whaingaroa) Harbour 42
4.3.1 Sediment characteristics 42
4.3.2 Macrofaunal assemblages 43
4.4 Recommendations for future monitoring 44
4.4.1 Macrofauna 44
5 Conclusions 45
  References 47
  Appendix 1: Most abundant indicator species 49
  Appendix 2: Abundance of indicator species Firth of Thames 51
  Appendix 3: Abundance of indicator species Raglan (Whaingaroa) Harbour