Monitoring station to provide real time water quality data

From the surface, it just looks like an array of yellow buoys in the centre of Lake Pearson, visible from State Highway 73.

A custom-made buoy hosts a range of sensors that measure the water quality

A custom-made buoy hosts a range of sensors, transmitting water quality data

But below the surface, it’s a complex device containing a range of sensors that are constantly transmitting all sorts of data about lake water back to land.

On a crisp August morning, a team of our scientists and technicians, with help from the Harbourmaster’s Office and Fish & Game, anchored the custom-made buoy in the northern half of the hourglass-shaped lake.

In early September, the final recorders were installed and the monitoring station became fully operational, generating data that will provide a better picture of the health of one of the region’s emblematic high-country lakes.

Measuring the health of a lake

The water quality in Canterbury’s high-country lakes is tested seasonally. Samples are collected by helicopter, which are then analysed to give a picture of the lakes’ health.

Anchoring the buoy was a collaborative effort

Anchoring the buoy was a collaborative effort

But to get a fuller picture of what’s happening below the surface, continuous water quality recording at different depths is necessary.

The Lake Pearson monitoring station is now providing that picture. It measures dissolved oxygen, turbidity, algal biomass and conductivity at two metres depth.

Near the bottom of the lake it also measures dissolved oxygen, and water temperature is measured at 1.5 metre intervals between the buoy and bottom sensors.

A weather station measuring air temperature, relative humidity, global radiation, barometric pressure and wind speed and direction is also included, as well as a water level recorder on the shore.

Putting all this together was a collaborative effort, with NIWA providing the telemetry and datalogging systems, Limnotrack providing the buoy hull and Fish & Game aiding with installation.

Getting information in real time

In an area with poor mobile cellphone reception, getting data from the logger is a challenge.

Powered by a solar panel, the buoy senses and records water quality and meteorological data, which it transmits by radio to a small tower installed by the lake edge. This tower, in turn, sends the data, together with lake level information, out to the world using satellites.

An on-shore tower transmits data in real time

An on-shore tower sends out data in real time

Changing land use brings challenges

Lake Pearson was chosen for continuous monitoring as it faces many of the same stresses as other lakes in the region.

Hugging the state highway as it winds towards Arthur’s Pass, Lake Pearson is a recreational hotspot, with a picnic area and walking trails nearby. It’s also a popular fishing lake, and recreational users have raised concerns about degradation in its water quality.

Over the past decade the water has become noticeably less clear.

Land-use intensification in the high-country, as well as a changing climate, have been suggested as likely causes for declining water quality in the lake.

A pilot study over the past two years discovered oxygen loss deep in the lake over summer, which may have been linked to fish deaths in the past.

Future plans for monitoring stations

We plan to install a similar buoy in Lake Benmore in 2021.

It is hoped these monitoring stations will give scientists better information that can be used in making decisions on how to best protect Canterbury’s high-country lakes.