1 Introduction
1.1 Background
New Zealand's lakes are the 'crown jewels' of our country. We swim in them, fish in them, boat on them and enjoy looking at them. They provide water for drinking and hydroelectric power, reduce the effects of floods, and support diverse communities of plants and animals. However, lakes are vulnerable to activities within their catchments. This has been highlighted in recent years with political recognition of the threats facing Lake Taupo and the Rotorua lakes and the initiation of efforts to protect or restore these water bodies.
This report was prompted by the fact that we have no recent national picture of lake water quality and the concern that many of our lakes may be facing water quality pressures. The last comprehensive national monitoring programme of New Zealand lakes was carried out by NIWA between 1992 and 1996 (Burns and Rutherford 1998). Furthermore, the New Zealand State of Environment (SoE) Report published by the Ministry for the Environment in 1997 gave no overall perspective of lake water quality.
This report focuses on lake water quality monitoring undertaken by regional councils in the last 10 years, particularly the smaller, less iconic lakes. While other organisations monitor and investigate lake water quality, the bulk of the monitoring for state and trends is currently done by regional councils, or in association with regional councils. This report is not an inventory of New Zealand lakes such as that produced by Livingston et al (1986); it is not comprehensive and there will be information on other lakes, not covered by the Livingston report. Instead, this report provides a snapshot of current lake water quality monitoring by councils in New Zealand - its scope, extent and results. Additional information will be available from university research, Crown Research Institutes such as NIWA, one-off surveys or resource consent investigations.
Several important tools have been developed in the last 10 years to help with lake management. These include:
- the protocol for monitoring lake trophic levels and assessing trends in trophic state (Burns et al 2000)
- development of a method for using submerged aquatic macrophytes to assess lake condition, called LakeSPI (Clayton et al 2002)
- the publication of an update to the Lake Managers' Handbook (Elliott and Sorrell 2002; Mark and Single 2002; Champion et al 2002; Rowe and Graynoth 2002).
Also, a lake classification system is currently being developed by NIWA and the Department of Conservation and this is likely to provide a useful tool for prioritising lakes for more intense management intervention.
1.2 Snapshot survey method
This snapshot survey of lake water quality is a desktop assessment drawing together information from regional councils and published reports which describes lake monitoring programmes and their results. All regional councils and unitary authorities were contacted by letter and phone and asked to provide information on their lake monitoring programmes and results. This information was recorded in a template to improve consistency (see Appendix 1 and 2). Information in published reports was used to elaborate on the monitoring information supplied by councils. Many of these reports were supplied by the regional councils and others identified through a literature search. Actual water quality data was also requested from councils, primarily to assist with a parallel project being undertaken by NIWA to organise, classify and map information where available. This data was used to fill gaps where there was no recent published report describing lake water quality, or where insufficient details were provided to assess lake trophic status.
This survey identifies lakes as being monitored only if samples are collected from the lake itself, in contrast to samples from the rivers flowing out of the lakes. This is particularly the case with hydroelectric lakes on the Waikato River where water quality samples are collected downstream of the tailrace of several lakes as part of the river water quality monitoring network.
The trophic state for each lake is described using the most recent published results. Where no published results are available, a Trophic Level Index has been calculated from the data using the most recent 10-year period available (generally 1995-2005). The data has not been analysed for trends. The trends observed in this report are based on the results of published reports (primarily using methods in Burns et al (2000)) or, where not available, from comparative changes in the trophic state since the New Zealand Lake Water Quality Monitoring Programme (NZLMP) (Burns and Rutherford 1998).
1.3 Structure of report
This report is presented in six sections:
- an introduction
- a general overview of New Zealand lakes and factors affecting their water quality
- a snapshot of lake water quality monitoring
- a snapshot of lake water quality and trends identified by this monitoring
- a discussion of gaps for national reporting of lake water quality
- recommendations for further work to address gaps.
The key issues and themes are drawn together in the discussion and conclusions. Details of regional council monitoring programmes and the monitoring of individual lakes are provided in Appendix 1 and Appendix 2 respectively.
