January 2020 Update
Lake Taupo Water Quality
Lake Taupō has an area 620km² being the largest lake in New Zealand. It has a mean depth 97m. Lake Taupō fills the caldera left by massive volcanic eruptions approximately 26,500 years ago; volcanic activity has also occurred in the recent past; the last eruption happened about 1,800 years ago.
Taupō gets its name as the shortened version of its correct name, Taupō-nui-a-Tia. This translates from Maori as "the great cloak of Tia."
Lake Taupō is an oligotrophic lake, i.e., nutrient concentrations are relatively low. Therefore, plants, such as algae, also occur in low concentrations because they require nutrients (nitrogen and phosphorus) to grow.
This in turn means that Lake Taupō water is particularly clear and blue, and dissolved oxygen levels are not seriously depleted (through decaying plant matter). The residence time of water in the Lake is 11 years meaning that changes in lake water chemistry happen slowly.
Background
Lake Taupō is valued for its deep, clear blue waters, stunning scenery and recreational values. However, as far back as the 1950s, contamination of the lake and in-flowing streams from rural and urban activities were of concern. Initiatives to protect Lake Taupō and near-shore areas were undertaken through the Lake Shore Reserves Scheme. Although not fully completed, over 18,000 ha of reserves were set aside as a buffer to protect water quality and preserve the natural character of the environment.
Much of the remaining near-shore land is owned by Ngati Tuwharetoa and is still undeveloped to meet the intent of the scheme. In the 1960s, iwi decided that the East Taupō Forest would be established to further protect the lake.
In 1973, Lake Taupō Catchment Control schemes were developed to protect erodible stream banks and steep land in pastoral areas. The schemes were designed to control erosion and prevent soil nutrient loss, especially phosphorus.
The DSIR Lake Taupō Freshwater Laboratory measured elevated nitrogen concentrations in Lake Taupō foreshore areas providing evidence of the impact of urban sewage from septic tanks. These observations prompted Taupō District Council to begin, in the 1980s, upgrades of sewage treatment systems. Today, this system removes all Taupō and Waitahanui sewage from the Lake Taupō catchment.
Since the 1990s, connections between land use and water quality have become increasingly evident. Development and intensification of rural and urban land was increasing the amount of nitrogen entering the lake through groundwater and rivers, promoting the growth of algae and phytoplankton.
In 2000, based on water quality monitoring, and with a strong mandate from the community, the Waikato Regional Council initiated an ambitious project to protect Lake Taupō water quality and maintain it at 2001 levels. The Lake Taupō Protection Project’s (LTPP) long-term objective is to maintain water quality at these levels; the Project includes regional council policy that aims to reduce manageable loads of nitrogen to Lake Taupō by 20%.
“Since the legislation was put in place, nitrogen has increased due to historical loads in the system. However the long-term goal of reaching, by 2080, 2001 water quality levels are currently believed to be on track. This means that the processes aimed at protecting water quality are seen to be working ten years on from the implementation of the Lake Taupo Protection Project.”
Lakes and Waterways Science Engagement
Through the development of the LTPP, to today, LWAG united the people behind the protection of Lake Taupō. We also support sound science in Lake Taupō and its catchment.
The Lake Taupō Protection Project has specific numerical targets for water quality parameters in place. These have been set for total nitrogen, total phosphorus, chlorophyll and water quality. Waikato Regional Council has a deep water buoy measuring these. Installed by NIWA, the buoy monitoring station delivers continuous data on lake water quality parameters. Near-shore monitoring of five sites over the summer months is also carried out to test for bacteria levels (E.coli).
As well as hearing presentations from Waikato Regional Council, NIWA and GNS scientists on their Lake Taupō-related science programmes, LWAG had an opportunity to become actively involved in a then state-of-the-art BioFish monitoring system between 2004 -2006. Unlike the deep water buoy, the BioFish was towed across the lake profiling water quality in the summer and autumn months.
LWAG, in conjunction with students from the University of Waikato under Professor David Hamilton, undertook this water quality monitoring programme measuring water temperature, dissolved oxygen and biological activity, (growth of algae). The data from this project aimed to track long-term trends and was used for the assessment of options aimed at the maintenance and protection of water quality in the Lake Taupō Catchment.
LWAG also supported the collection of water samples at the Waikato River mouth to calculate the amount of nitrogen exiting the Lake via its only outlet.