A NIWA research project has come up with an ingenious method to make restoring degraded freshwater lakes easier and more likely to succeed by using biodegradable mats.
The solution has been dubbed RotoTurf, and comprises a mat made from natural fibres on which aquatic plants can be grown and nurtured, and then the whole lot rolled out on to the bottom of a lake or waterway.
The RotoTurf project addresses one of the issues facing many of New Zealand's shallow lakes – permanently turbid water leaving plants with insufficient light to grow. And without plants, wave action creates a feedback loop trapping a lake in a degraded state.
Action is required on several fronts to reverse the process, including reducing sediment and nutrient inputs, but RotoTurf project lead and NIWA Principal Scientist, Dr Deborah Hofstra says even when that is addressed, it can be difficult for plants to re-establish themselves.
“That’s where our research with mats can help.”
The team trialled a range of biodegradable mats, including hessian, coconut fibre, muka (flax) and wool, using different plants and densities. The matting needed to support large-scale plant cultivation and be able to be easily relocated to a lakebed. Over time the mat breaks down naturally while the plants anchor themselves into the lakebed.
Wool and muka were the longest-lasting mats in outdoor culture tanks and were both subsequently trialled in a lake. Plant selection is also crucial for success, with the research having looked at a range of natives, including milfoils, pondweeds, charophytes and isoetes.
RotoTurf is a NIWA-led Smart Ideas project funded by the Ministry of Business, Innovation and Employment. The project infused scientific research with mātauranga Māori to ensure the best outcomes.
From the research two tools were developed that can be used to help decide whether RotoTurf can help with a restoration project:
- The RotoTurf suitability decision tool – guides the decision-making process and identifies areas that may be improved before using RotoTurf
- The RotoTurf Macrophyte Species Selector – helps select species of aquatic plants that will thrive in different conditions.
Both are available on the NIWA website along with a guide on growing and translocating aquatic plant mats for freshwater restoration.
“The goal is to be able to grow enough plants and have a mass planting event that reaches a threshold where the plants are self-perpetuating, the water becomes clearer and the ecosystem is in much better health,” Hofstra says.
