Over the past 60 years, the water quality has declined in many large NZ lakes, including Rotorua, Pupuke, Rotoehu, Rotoiti, Tutira and Horowhenua in the North Island, and Lakes Ellesmere (Te Waihora) and Forsyth (Wairewa) in the South Island (Rowe 2004). All of these lakes are important taonga to tangata whenua, and have served as pataka kai for many generations. These lakes have become turbid and are periodically affected by harmful algal blooms. Drinking water supplies have been reduced, culturally-significant fisheries have deteriorated, with koura and kākahi being two pertinent examples.

Concerns over the demise of these taonga lakes raises the question – what can be done? Can their deterioration be stopped? More significantly, can degraded lakes be restored? The people of Ngāti Rangiteaorere, a Te Arawa hapū centred at Waiohewa Marae on the shores of Lake Rotorua, have formed the “Roto-Ora” conglomerate, and identified an international team of researchers, innovators, and iwi to explore cutting-edge lake restoration technology.

Principal Investigator Dr Shaun Ogilvie, has whakapapa connection here, and this project will serve as an entry point for him to reconnect, and bring his expertise and experience ‘back to the people’. Modified Local Soil (MLS) technology is emerging in the global literature (Pan et al 2019) as an efficient and cost-effective method to remove harmful algal blooms from water and settle them onto sediment. MLS capping treatment will also reduce the resuspension of algae from the sediment, and convert the algal cells and excessive nutrients into fertilisers for the restoration of natural aquatic plants.

Furthermore, capping treatment using oxygen nanobubble-MLS materials can also mitigate sediment anoxia, causing a reduction in the release of internal pollutants, such as nutrients and greenhouse gases. New data obtained from field monitoring in trials in China (Pan et al 2019) showed that the algae-dominated waters transform into a macrophyte-dominated state within four months of MLS treatment.

This project will form the foundations for a larger, longer-term project aligned to mātauranga Māori relative to our lake ecosystems and their utility, past and present with an emphasis on future management.