Wastewater could boost native plant growth

REDUCE, REUSE, RECYCLE: Researchers have found that treated municipal wastewater could enhance the growth of native plants. Picture supplied

Irrigating native reforestation projects with treated municipal wastewater could increase wastewater recycling and enhance the growth of native plant species, a research project has found.

After irrigating a field site on Banks Peninsula for three years, researchers found there was a negligible effect on the soil chemistry and no increase in any elements that may pose a risk to humans or ecosystems.

Researchers said that as long as the native vegetation is effective in protecting local waterways from excessive nutrient run-off from the wastewater, it poses a low risk to public health and aquatic ecosystems.

The method of reusing wastewater could help tackle multiple environmental challenges the country is facing.

“Potentially, the restoration of native ecosystems could be combined with the land application of treated municipal wastewater (TMW), reducing TMW discharge into water bodies,” a researcher said.

“High levels of nutrients, pathogens and other contaminants from TMW can degrade water quality.

“The land application of TMW on to native vegetation reduces the nutrient load in water bodies and may create zones of ecological value.”

However, establishing native plants may be challenging if the species are not adapted to highly fertile environments, such as those resulting from TMW irrigation.

The researcher said there was a critical knowledge gap about the response of native plant species to irrigation with TMW.

“We aimed to determine the distribution and specification of nutrients in the soil-plant system following application of TMW on to 11 species of native plants in a long-term field trial on Banks Peninsula.”

The researchers found no evidence of impaired soil structure following TMW irrigation.

Nitrogen did not accumulate in the soil, and it was likely to have been taken up by plants or lost through denitrification and nitrate leaching.

TMW irrigation increased plant height by 10 percent compared to the control after 3.5 years of growth.

“TMW application had negligible effects on the elemental composition of plant foliage.

“Native vegetation can facilitate the land application of TMW. Future work should elucidate the maximum rates that can be applied as well as the effect of TMW on the soil microbiota.”

This work was funded by the Christchurch City Council and by the Centre for Integrated Biowaste Research and the Native Ecosystems projects under The Institute of Environmental Science Research Strategic Science Investment Fund from the Ministry of Business, Innovation and Employment.