Spotlight on health of our lakes
Scientists starting $12m check of 380 bodies of water around the country
Scientists have begun a sprawling health-check of hundreds of New Zealand lakes, at a time where monitoring data shows more North Island spots are graded bad than good.
In a five-year, $12 million project, led by GNS Science and the Cawthron Institute, researchers will try to find out how 380 lakes have changed over the past 1000 years.
Dubbed Lakes 380, and supported by the Government’s Endeavour Fund, the ambitious study will offer a snapshot of around 10 per cent of New Zealand’s lakes larger than 1ha.
“Currently there is limited data on the health of only 5 per cent of these lakes, and this only monitors water quality over the past decade,” said a study co-leader, GNS paleoclimate scientist Dr Marcus Vandergoes.
That meant there was scant evidence to show when and why changes happened, with the natural condition of lakes largely unknown.
“This limits our ability to set realistic restoration aspirations and meet ecosystem health limits.”
But Vandergoes and his team could still draw on lake sediments — or what he called “geological whakapapa” — which were stacked year upon year, preserving indicators of lake life, water quality and the surrounding catchment.
Fellow programme leader and Cawthron scientist Dr Susie Wood said the sediments provided the equivalent of centuries of monitoring.
“These natural archives will provide the knowledge we need to understand the drivers of environmental change and restore the ecological vitality of our lakes.”
The team will travel from lake to lake, using small boats to collect up to four sediments from each site.
The samples will be analysed using methods that could pin-point the time when surrounding land and bush was cleared.
Cawthron social scientist Dr Charlotte Sunde said the project would also work with iwi and hapu. “The study will provide knowledge on how divergent lake health is from its natural pre-human condition and highlight what variables have caused this change,” Vandergoes said. “For example, it might show that the presence of native aquatic species like plants and fish has varied, or the effect of introduced species on native biodiversity.” Some lakes had changed little, but others had undergone “significant” transformation. “As far as we know, this study will be the first national-scale quantification of human impact on lake health globally, providing a unique opportunity to . . . explore how lake health has changed regionally and nationally.” The findings will be used to predict future changes and inform protection and restoration efforts, on a national scale.
HFor a quick check of lake quality see nzherald.co.nz
The study comes as more than 50 lakes monitored through the jointly run Land Air Water Aotearoa (LAWA) website are graded either very poor or poor for water quality.
Among the worst were Lake Rototuna in Northland, Lake Waikopiro in Hawke’s Bay, Lake Horowhenua, Lake Wairarapa, and Lake Ellesmere and Lake Rotorua in Canterbury.
Others ranked “poor” included Lake Tutira in Hawke’s Bay, Lake Rotorangi in Taranaki, and Lake Hayes in Central Otago.
The best-rated included Lake Waikaremoana, Lake Ohau, Lake Tekapo, Lake Manapouri and Lake Te Anau.
NZ’s largest, Lake Taupo — recently hit by algal bloom — was “good”, as were Lake Tarawera, Lake Okataina, Lake Dunstan and Lake Wanaka.
Lakes rated good or very good tended to be clear, with low levels of nutrients and algae, while the poor or very poor were typically turbid, with high concentrations of nutrients that fuelled frequent algal blooms.
These lakes were rarely suitable for swimming and some could not support native freshwater species.
The gradings were based on the Trophic Level Index (TLI), using four water quality indicators to signify a lake’s life-supporting capacity.
Of 65 lakes monitored between 2009 and 2013, 24 had median TLI scores of very good or good, 17 were moderate and 24 poor or very poor.
Over the same period, 12 sites had phosphorus levels too high to meet national bottom lines for ecosystem health, 11 had too much nitrogen, and 11 had excessive algae biomass.
Such lakes were at high risk from nutrients causing algal blooms, or from not enough oxygen.
Long-term data showed nitrogen, phosphorus, algal indicator chlorophyll-a and visual clarity were generally improving at lakes from 2004 to 2013, but bottom-water dissolved oxygen and nitratenitrogen were worsening. How clean is that lake? Go to lawa.org.nz