Otago University Researchers Lauded for World Leading Freshwater Study

Otago University Researchers Lauded for World Leading Freshwater Study

​​​​​​​ Otago University students and staff have set up a world leading system for testing freshwater in a "real" rather than laboratory situation.


On Otago's Kauru River, the researchers can test for a variety of indicators to see how freshwater ecosystems respond to multiple agricultural stresses, including high and low flows, the presence of pesticides, nitrogen, and phosphate.

They have also designed it to study what happens to the water under a climate warming scenario - a world first.

The ExStream system set up at the Kauru River in Otago.

The ExStream system set up at the Kauru River in Otago.


The researchers won the "stories" section of the New Zealand River Awards for their ExStream project, which has now been established in Germany, Ireland, China and Japan.

Associate Professor Dr Christoph Matthaei said the idea came to him more than 10 years ago.

ExStream developer Jay Piggot addresses school children about rivers.

ExStream developer Jay Piggot addresses school children about rivers.


"I got the idea about this in 2004 at a conference in the United States, and Jay Piggot and I sat down and designed it together. Jay really was the person who did most of the engineering."

Piggot, 34, who is now an assistant Professor at Trinity College Dublin, was fresh out of completing a BSc when he started on the project, and it became part of his study towards a PhD.

"The research has supported the academic development, life experience and scientific discovery of more than two dozen other students and interns from more than a dozen countries while also engaging local communities and schools under the 'Linking Landscapes Project' - connecting rural communities with their waterways," Piggot said.

Matthaei said the system could manipulate up to four factors, mainly related to agriculture, such as nutrient enrichment, sedimentation or reduced flow.

"We found that these interact together so two together are much worse than you would expect from just one stressor."

Researchers know that agriculture and forestry lead to nutrient enrichment from run-off, with sedimentation smothering stream beds. They also know that water abstracted for irrigation results in changed water quantity. As stresses happen simultaneously, it's difficult to work out which one causes the effects and – importantly – how to prioritise mitigation.

A project was established to disentangle these effects. Initially a BSc graduate student worked with academic staff as part of an honours project. As funding allowed–and people became interested in the research–other Masters and PhD students joined.

Collaborating institutions have included Cawthron Institute and the National Institute of Water and Atmospheric Research (NIWA).

Kauru River was chosen to conduct field work because its water quality was relatively good. This project wasn't about improving Kauru River water quality specifically, but was about how to conduct the research needed to find out the answers to real problems; and applying findings to rivers elsewhere.

Where deposited fine sediment smothers habitat, invertebrates often respond by drifting downstream from an affected area. A complex interplay between the effects of sediment, increased temperatures and increased nutrients occurs.

Research was aided by a piece of equipment called ExStream (experimental stream mesocosm system). Water from the Kauru River is piped to dozens of mesocosms, which are ring-type cake tins with a central overflow hole.

The ExStream is open to the air and exposed to the same weather and light conditions that the river experiences, which means a much more realistic experimental set-up than one in a laboratory. Substrates in the mesocosms reflect natural substrates seen in rivers.

Stream variables can be manipulated, including water flow, grades and amounts of fine sediment, incoming water temperature, nutrients plus commonly used agricultural chemicals. The technology allows measurement of these impacts on algal and invertebrate communities and ecosystem function, such as leaf decomposition.

The team produced more than thirty scientific publications documenting results and implications for freshwater management. The latter includes developing assessment tools used by regional councils around New Zealand for monitoring sedimentation in streams. Fine sediment is now an attribute for consideration under the National Objectives Framework for the National Statement of Freshwater Management.

Research that started with students on the Kauru River is now being used in Asia and Europe. Through developing new technology in a university setting, emerging researchers were involved in a project that has been commercialised and is resulting in improved freshwater management.