30 September 2025 How Ksenia's artificial rivers could help prevent a "climate cocktail"

The Lincoln University PhD student is simulating how climate change is expected to affect our rivers by the end of the century. She aims to discover how long we have to make serious changes if we want to protect our water.

She presented her ideas and methodology at Lincoln’s Three Minute Thesis (3MT) finals and was crowned the champion. She’s now competing in the 3MT Asia-Pacific Semi-Finals, expected to conclude October 3rd.

With the help of a technician, Ksenia created nine miniature artificial rivers called mesocosms. Inside each is sediment and water from the Waikato River to maintain ecological relevance. Ksenia has control over the flow rate, temperature, oxygen and carbon dioxide levels. She’ll be observing how the sediment reacts as the water becomes more acidic, warmer, and less oxygenated.

Sediment is a humble and underappreciated player in keeping our waterways healthy. It acts as a sink for nutrients like nitrogen and phosphorus, as well as heavy metals such as arsenic amongst others.

“With growing urbanisation and agriculture, there are a lot of nutrients and potentially toxic metals going into our rivers,” Ksenia says.

“Usually, these things settle to the bottom. Sediment acts as a sink for nutrients and metals. But under certain conditions, these elements can be released back into our water.

“The increased release of these elements can fuel harmful algal blooms that poison our water and wildlife.”

Ksenia calls it a “climate cocktail”, and it poses a big issue for the security of our drinking water.

Climate change has the potential to alter oxygen penetration, oxidation reduction conditions, and microbial activity.That can alter the chemical gradients across the diffusive boundary layer where the sediment and water meet — meaning all the ingredients in the climate cocktail can escape the sediment back into the water.

It’s a serious and very real problem. In 2020 toxic algae were discovered in a Christchurch pond following the death of a dog which had entered the water.

The Waikato River is New Zealand’s longest river and acts as a major supply of drinking water in the North Island. Knowing how and when climate change will affect the river gives water managers more information to go on when making decisions about it.

As Ksenia conducts her experiments, she’ll be monitoring how much oxygen penetrates into the sediment and how many of those climate nasties are released into the water under different conditions.

“In summer, bottom water temperatures in lake Te Karapiro can get as hot as 22°C. Once I’ve done that, I’ll crank it up another 4°C to meet the IPCC’s (Intergovernmental Panel on Climate Change) predictions for climate change by 2100.

“This information helps us better understand the situation, and if we can understand, then we can better mitigate. If we know that 4°C is not a critical threshold, then we can take a breath knowing it won’t poison our water supply. But on the other hand, it might be a 1.5°C threshold, or 2°C or 3°C.

“Understanding what we’re dealing with always helps us understand our resources better, and what’s more important than fresh drinking water?”