Drones to monitor NZ lakes

Drone flying over water. Photo / Getty Images.

Colour-coded lakes, drones and satellites to gather accurate picture of our lakes' water quality.

Drones measuring the colour of our lakes could become a regular part of the battle to assess and improve the water quality of New Zealand lakes.

The drones are part of a three year study which aims to use satellite data to more effectively show mechanisms affecting water quality in New Zealand lakes, to better understand the end result.

Professor Ian Hawes, a freshwater ecologist at the University of Waikato, and his research are particularly interested in lakes which can be affected by growth of blue-green algae, or cyanobacteria, often resulting in health warnings being issued.

Tracking years of changes in freshwater bodies is often attributed to algal blooms being caused by a mix of different issues, he says. These include nutrient loading from agriculture (horticulture, viticulture, deer, pigs, dairy and beef and sheep) on surrounding land. Often exotic species, such as koi carp, have been introduced and disturb the lake floor during their feeding activities.

Another prime driver is the suspended sediment drawn into lakes by river flow which can cause a chronic increase in the algal blooms but he says it is easy to underestimate the amount of waterway pollutants contributed by urban sources.

"But there are some urban issues, and they're easy to underestimate," he says. "They might seem relatively minor but they need to be taken into account. Anything that adds nutrients has an effect."

Only a small proportion of lakes around the country are monitored for algal blooms at present, due to it being an expensive exercise where council staff collect water samples, then taken to laboratories for testing.

This leads to a suspicion that algal bloom problems could be more widespread than previously realised and modelling work, while providing a good overall picture, can give a misleading result for a specific water body.

But with the use of satellite images it's hoped changes in lake water colour caused by the blooms will be more quickly identified and appropriate interventions planned and put in place.

Much of the data which will be used is already freely available, Hawes says, but the first challenge was to decide on the size of the water bodies to be studied. A medium size was established and now work has moved on to developing techniques to identify water quality variables which satellites would need to able to distinguish.

The task is made all the harder because this country's freshwater bodies are very different to each other, with a wide range of lake types which look different from space due to the country around them.

So the solution scientists are working on is an optical classification system, which means they don't need to visit each lake separately. Instead similar freshwater bodies will be grouped together based on their colour. Some of the factors being used in their classification include the area's geography and the impact surrounding vegetation may have.

Hawes' hope is that the country's lakes will be classified into between five and seven different categories over the second year of the project.

"We want to keep it to a small number because if there are too many categories it's pointless," he says. "You can't treat every lake as being individual."

Once this work is completed, the scientists will look at how algal abundance and sediment loading can be estimated by satellite. As these involve different forms of cyanobacteria, scientists need to be able to differentiate between their two colour signals.

That will involve the colour of each lake's water being measured with either boat or drone-mounted instruments.

"The research drones will allow us to the get the most acceptable use of satellites," Hawes says.

He's confident cyanobacteria and other algae will be able to be detected by use of the high-resolution images which the drones will produce. From this data, satellite-based measurements will be able to be developed and enhanced as improvements in satellite imagery are made in the future.

Once further refinement has taken place, it's hoped the final part of project will be a web-based tool able to compare the present state of a particular water body with that shown in historical data.

"So people will potentially be able to look at a body of water of interest," he says.

His project is not funded to develop the tool itself but he hopes this will happen within three years, depending on the investment interest from groups such as councils: "Some areas are under much more stress than others."

It's hoped the completed tool will be able to be used to highlight significant problems affecting the growth of algae with this surveillance showing the lakes that are most affected by catchment activities. They could then be prioritised for more investigation.

And potentially, as water quality improves, the tool could be used to document accurately what's happening so there's no dispute about water quality management methods.