Wairarapa Moana may take generations to recover. PHOTO/FILE
Despite being granted Ramsar status as an internationally important wetland last year, Wairarapa Moana’s water quality is likely to get worse before it begins to mend.
Niwa’s chief freshwater scientist Scott Larned said contaminants that were entering lake Wairarapa right now were most likely generated many decades ago.
Nitrogen and phosphorus contaminants entering the lake would only reflect land use from the 1960s, he said.
“The contaminants that are being generated in the 2020s is just now getting into the groundwater system.
It’s going to take contaminants another 20 or 30 years of travel through the groundwater system before they get to the lake.”
Larned said the travel time was prolonged from the land where these contaminants had been generated, to getting into the lake itself.
“We haven’t even seen the signal of current land use in Wairarapa on Lake Wairarapa,” he said.
According to Ramsar, Wairarapa Moana is the largest wetland complex on the southern part of the North Island.
The lake is a shallow, 2.5m at its deepest point, and suffers from two layers of sediment, which cause some of the most significant issues with water quality.
More than a century of development, including drainage and flood control schemes, has left the lake in a “highly modified state”, a Greater Wellington Regional Council report said.
The lake is classified as “supertrophic”, meaning it has very high levels of nutrients such as nitrogen and phosphorus in its waters, Land Air Water Aotearoa said.
The supertrophic rating of the lake is the last step before it is deemed dead.
Larned said that even if we massively changed how we use our land immediately, we would not see any benefits for decades.
He said central government was ambitious with some regulations they were trying to bring in, including the national policy statement for freshwater management.
He said the policy was “by far the most far-reaching piece of environmental regulation in New Zealand”.
The policy provides updated guidelines to local authorities on how they should manage freshwater under the Resource Management Act. The RMA is also under reform.
On top of the NPS-FW, Larned said Three Waters reform would also produce new freshwater regulations.
Three Waters reform seeks to change the management of stormwater, wastewater, and drinking water from the hands of councils to fewer, centralised entities.
“If you think about all the possible improvements that come from all of these ambitious regulations, some of them can happen very fast, which will hopefully keep people happy, but some of them will take a long time,” he said.
He said that although some water quality improvement would take a long time to see, people shouldn’t lose heart.
Larned said the slow change in the lake’s water quality was simply down to the physical process, which means water takes a long time to move a long distance.
He said the water that was making the trip from the land to the lake was carrying the contaminants with it.
Larned said the best attitude towards the slow change in the lake’s health was the Maori concept of kaitiakitanga [guardianship of natural resources].
Larned said that if we did manage to make these changes, it would be ground-breaking not only for New Zealand, but for the world.
