Exploring the past and present health and biodiversity of Lake Wairarapa
A new Ngāti Kahungunu ki Wairarapa-led initiative is bringing together kairangahau (Māori researchers) and freshwater scientists from GNS Science and the Cawthron Institute, to better understand the health and biodiversity of Lake Wairarapa.
Ra Smith, Kaiwhakahaere Taiao (Environmental Manager) for Kahungunu ki Wairarapa, says the Te Raranga Māramatanga me Ngā Tipu project will use a combination of scientific techniques and mātauranga Māori to gain a deeper understanding of current water quality and biodiversity, and how the ecosystem has changed throughout history.
“Our goal is to restore the lake, but the question is, ‘to what?’ To answer that question, we approached scientists at Cawthron Institute and GNS Science, who we’ve previously worked with through the national Lakes380 Programme, to help us enrich our understanding.”
The Lakes380 Programme assessed the health of more than 10% of Aotearoa New Zealand’s lakes, including Lake Ōnoke(external link), Lake Pounui(external link), Lake Rototawai(external link) and Lake Nganoke(external link) in the Wairarapa rohe (regional) part of the programme. Lake Wairarapa was not included as part of the programme because lakes that were not routinely monitored were prioritised.
“We now know some of the drivers of environmental degradation in lakes in the wider Wairarapa rohe and have a great picture of what they used to be like before human arrival. We want to have the same understanding of Lake Wairarapa that goes beyond water quality, starting with aquatic plants as they are a key component of lake ecosystems,” Smith says.
The project will use cutting edge techniques, including hyperspectral scanning and environmental DNA analysis of sediment cores – long tubes of mud taken from the bottom of the lake. Lake sediment is laid down year by year, and the layers preserved in the cores are like the pages of a history book, providing a natural archive of the lake’s life.
Science co-leader Marcus Vandergoes from GNS Science, says the analysis of sediment cores provides rich, time-stamped data including which animals, plants, algae, and insects were present in and around the lake in each time period, and how changes in land use around the lake might have impacted the water quality.
“One example of the kind of insight we have gained through core sampling of Ōnoke (Lake Ferry) is that post-European settlement there was widespread burning of beech and podocarp forest. You can see the layers of charcoal in the sediment core from that time period.”
Katie Brasell, science co-leader from Ngāti Kahungunu and Cawthron Institute, will use eDNA analysis of sediment cores and water and surface sediment samples to explore the biodiversity, with a focus on macrophytes (aquatic plants).
“All living things leave traces of their DNA behind them in the environment, even long after they have died. We can extract it from the samples and identify which species were present in the past, and which are there today,” Brasell says.
“In Lake Pounui, eDNA analysis revealed that the introduction of perch and trout after European settlement had caused a big shift in the communities of bacteria that lived in the lake, and this was a major driver of the severe cyanobacterial blooms the lake now experiences most summers.”
For Ra Smith and Kahungunu ki Wairarapa, it is hoped that similar insights into the drivers of declining health in Lake Wairarapa will enable successful restoration.
Our ultimate goal is to draw support for Lake Wairarapa to obtain its own tino rangatiratanga – or flourishing growth within its own ecosystem. If we help the lake to recover by restoring some of the aquatic plants it has lost, we support it to heal itself.