Zooplankton monitoring for TLI and lake health assessment of the Waikato lakes : 2016-2017 / prepared by: Ian C. Duggan (Environmental Research Institute, School of Science, Faculty of Science and Engineering, The University of Waikato) For: Waikato Regional Council.

Includes bibliographical references.

Traditional inference of lake trophic state typically relies on monthly sampling of a variety of indicators (e.g., Secchi transparency, chlorophyll a concentrations, nutrients), but for lakes that are isolated or have difficult access such fine-scale monitoring is difficult or unfeasible. Also, in areas with at least moderate numbers of lakes, regular monitoring of many water bodies is not always practically or financially possible.

Biotic indices are commonly used in such circumstances, as they integrate biological, physical and chemical factors over time, allowing for less fine-scale monitoring than traditional methods.

A number of studies globally have found good relationships between zooplankton communities and trophic state, and the potential utility or actual development of bioindicator schemes using zooplankton is increasing. Duggan et al. (2001a, b) found that trophic state was the major determinant of rotifer distribution among lakes in North Island, New Zealand, and based on these responses developed a quantitative bioindicator index using rotifer community composition for inferring Trophic Lake Index (TLI) values (sensu Burns et al. 1999).

In New Zealand, Waikato Regional Council and Auckland Council have undertaken the only long-term water quality monitoring programs oflakes utilising zooplankton globally, based on the Rotifer inferred TLI of Duggan et al. (2001).

This report aims to:

1) Examine rotifer inferred TLI assessments for 2016 and early 2017 for the WaikatoRegional Council lakes, and compare these to assessments made previously.

2) Examine changes in the proportions of native versus non-native zooplankton species,and crustacean versus rotifers, in 2016 and early 2017 relative to earlier monitoring.

3) Examine the zooplankton of three geothermally influenced lakes, which have limited data.