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LakeSPI critical appraisal for monitoring Waikato Lakes

TR 2018/14

Report: TR 2018/14

Author: March Schallenberg, Lena Schallenberg (Hydrosphere Research Ltd)

About this report

The Waikato Region has around 100 named lakes and despite water quality being routinely measured in many of them, little is known about the broader ecological health of these lakes. The LakeSPI index is an indicator of lake macrophyte community health and The Waikato Regional Council has commissioned many LakeSPI assessments on the region’s lakes since 1981. The purpose of this report is to explore whether LakeSPI is a robust ecological indicator of lake health.

LakeSPI undoubtedly has some relevance to lake functioning. However, because LakeSPI is a complex index derived from many different measurements and estimates of the macrophyte community, the specific interpretation of the functional significance of LakeSPI is complicated. When LakeSPI assessments are carried out at intervals of ≤ 5 years, LakeSPI assessments can be very useful in tracking potentially complex temporal dynamics of aspects of the macrophyte community of a lake. Important features of lake temporal dynamics such as whether the macrophyte communities show slow, rapid and/or non-linear changes over time can be shown and, thus, inferences about ecological resistance, resilience, tipping points and hysteresis in relation to pressure gradients can be made. akeSPI is not so much a robust indicator of specific pressure gradients in lakes, but is more accurately a measure of the departure of a lake’s macrophyte community from that expected to have occupied the lake prior to European arrival in New Zealand. Careful thought must be given as to whether the individual measures that contribute to LakeSPI or its amalgamated index scores are better aligned to the Waikato Regional Council’s monitoring and planning goals.

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LakeSPI critical appraisal for monitoring Waikato Lakes [PDF, 1.6 MB]

Contents

1 Introduction
2 Scope
2.1 Framework for critical appraisal of indicators
2.2 Data Sources
3 Conceptual relevance of LakeSPI
3.1 Relevance to assessment needs
3.1.1  What is LakeSPI?
3.1.2 Relationship to trophic level index (TLI)
3.1.3 The relationship between LakeSPI and TLI among Waikato lakes
3.1.4 The relationship between LakeSPI and TLI for individual Waikato lakes
3.1.5 Prediction of LakeSPI from TLI variables
3.2 Relevance to ecological function
4 LakeSPI response variability
4.1 Estimation of measurement error
4.2 Seasonal variability
4.3 Temporal variability across years
4.4 Spatial variability
4.5 Discriminatory ability
5 Interpretation and utility of LakeSPI
5.1 Data quality objectives
5.2 Assessment of thresholds
6 Conclusions and linkage to management actions
7 Critical appraisal of questions related to the LakeSPI index
8 Acknowledgements
9 References