| Title | WATER QUALITY AND BIODEIVERSITY SURVEY OF THREE WAIOTAPU GEOTHERMAL LAKES |
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| Authors | A. Catlin, B. David, M. Hamer, M. Lake, K. Luketina, D. Özkundakci, P. Reeves, J. Smith |
| Year | 2017 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Waiotapu, Orotu, Whangioterangi, Rotowhero, geothermal lakes, water quality, aquatic ecology |
| Abstract | Waikato Regional Council undertook a comprehensive survey of water quality and biodiversity in geothermal Lakes Orotu, Rotowhero and Whangioterangi located within the Waiotapu Geothermal System. The lakes range from 2.6 ha to 4.7 ha in size. To the best of our knowledge, Lakes Orotu and Whangioterangi were surveyed for the first time by boat; previous navigation having been hindered by the terrain, accessibility and the geothermal nature of the water. As part of the survey, samples were collected for analysis of water quality (i.e. nutrient enrichment), geothermal water chemistry markers, phytoplankton and zooplankton community composition, sweep netting of the littoral zone for aquatic invertebrates, fish survey, and vertical profiles of temperature, conductivity, oxygen, chlorophyll fluorescence, pH and photosynthetically active radiation. All three lakes were acidic with the lowest pH value of 2.8 recorded in Lake Whangioterangi. Water quality assessment based on nutrient concentrations suggests that all lakes were highly nutrient-enriched but showed low primary productivity (i.e. low chlorophyll a concentrations). All lakes generally showed low species richness for all surveyed organisms. No phytoplankton and zooplankton were detected in Lake Whangioterangi using standard methodology. Only four eels in poor condition were caught in Lake Orotu with the other lakes being fishless and devoid of submerged macrophytes. Values of the geothermal water chemistry markers were consistent with geothermally influenced lakes, but concentrations of various elements varied considerably between lakes. These lakes are currently not actively managed, however, several anthropogenic pressures may pose a threat to these rare ecosystems and should thus be given more serious regard from a resource management perspective. Vertical profiles of temperature and conductivity in Lake Whangioterangi indicated weak inverse stratification. Due to this profile and its steep-sided bathymetry, we hypothesize that this lake may be classed as meromictic, a rare lake type worldwide. It is envisioned that this hypothesis can be tested with additional monitoring of key in-lake characteristics in the future. |