Digging into lakes’ histories
ROTORUA: Obtaining vital clues to the health and history of lakes in New Zealand is the focus of research being carried out on three Rotorua lakes.
Scientists from GNS
Science, the Cawthron Institute, Victoria University of Wellington and the University of Otago in conjunction with Te Arawa Lakes Trust are taking both sediment and water samples from lakes Rotorua, Okataina and Okareka to provide a full 1000year history.
It is part of a project called ‘‘Lakes 380 — Our lakes' health — past, present, future’’ which aims to find out about the health, wellness and history of about 10% of New Zealand's 3800 lakes which are greater in size than a hectare.
The team of scientists first visited the Rotorua region in 2019 and have returned to collect longer core samples from the bottom of the lakes.
Project coleader Marcus Vandergoes, of GNS Science, said the team was using a unique type of lake sediment corer, called a Mackereth corer.
It is 12m long and uses a compressed air system. It is lowered over the side of a boat and settles on the bottom of the lake and sucks up the samples in a tube.
It is then hauled back to the surface and the core sample is taken off and the process is then repeated.
It allows them to collect samples up to 6m, which equates to a 1000year history.
‘‘These are 2m long tubes of mud in most cases and we try and capture the history of the lake and how it is has changed over time by analysing indicators of lake health and water quality change trapped in the mud over time.
‘‘The mud at the bottom of a lake layers year by year and accumulates over time, so we can take the mud cores and basically use them in a way to go back in time.''
He said it would provide information from before humans arrived in New Zealand and any changes that had occurred as a result of human interaction with lake systems and landscape changes.
‘‘Prehuman is sort of a reference state of its natural condition and how a lake has changed in response to a volcanic event, so the historic component gives us a reference baseline condition of what the lake was like.''
Dr Vandergoes said the Rotorua lakes were of particular interest because of local volcanic activity.
‘‘We can investigate how some of those naturally occurring events have impacted on the lakes in their history.’’
Water samples taken at the same time as the core samples provide information on water conditions, including algae and bacteria which are often a problem in lakes.
Te Arawa Lakes Trust said the research was an exciting opportunity to see how factors such as human arrival and the 1886 Mt Tarawera eruption had impacted on lake ecosystems.
Trust strategic manager Mariana Te Rangi said it would help identify what the lakes and their surroundings were once like and to where they were today.
She said iwi would need to decide if they wanted the lakes returned to how they were before human arrival and the introduction of pests, farming and forestry.
‘‘A wider discussion will need to be had.
Lakes 380 — Our lakes' health — past, present, future is a fiveyear project which will be completed by the end of 2022. — RNZ