Weather maps for water
Measuring water quality
The system aims to use oceanographic forecasting to produce a map of changes in water quality in Tasman and Golden bays, similar to a weather map. It’s one of eight scientific research projects that have recently received funding as part of the Sustainable Seas National Science Challenge.
The Sustainable Seas innovation fund offers up to NZ $1.5 million a year to support projects, each up to a value of $150,000 per year for two years.
The project developed from a similar one on the United States’ Columbia River, in the Pacific Northwest. Updated several times a day, it takes into account tides, wind and rainfall.
“If you’re harvesting fish or shellfish, you can see how the water quality changes,” Cawthron ecologist and project leader Jonathan Banks says. “It’s coloured, like a heat map. It’s also animated, so you can see the river plume going in and out with the tide and how the predicted wind will affect it.”
Handy for council and mussel farmers after heavy rain
The water quality maps would come in handy after heavy rain, when rivers flush sediment and other contaminants out to sea. They would show river plumes, their predicted path, and information about the risk of bacterial contamination. That sort of information is important to local councils to manage beach closures, as well as the shellfish industry whose harvest depends on water quality. Because most shellfish are filter-feeders, a high level of contaminants in the water can mean harvest is delayed until the water clears.
“What we want is for mussel farmers to be able to look at this map and for example say ‘There’s a storm coming and water quality will go down’. They could then harvest two days’ worth of stock, bring it in, and keep the processing plant going while waiting for the waters to clear,” Dr Banks says.
Current estimating too conservative
Currently, water quality is managed by ‘trigger points’ driven by flow rate in the Motueka River. Once the river flow goes over a certain volume for a certain length of time, the area is shut for harvest.
“That works well, but it’s conservative – because if you have a southerly blowing hard, the river plume might miss the farms completely,” Dr Banks says. “Whereas if you have the same amount of water coming down the river, and the wind is coming from the opposite direction, the wind hits the farm. We think we can produce higher-resolution models.”
Better predictions and harvests
Colin Johnston is the technical director of Aquaculture New Zealand and Executive Officer of Marlborough Shellfish Quality Programme. He says the programme will help industry better understand and predict the impacts of rivers affected by climate and terrestrial activities, and their plumes where they meet productive seas.
“Not only will this help us ensure that we can harvest shellfish, it may help us expand our harvest windows. This is through both a better understanding of the dynamics of the rivers and seas, and through the encouragement of catchment management techniques that address any adverse impacts of climate or terrestrial activity on the rivers feeding into our coastal waters.”