Interactions of treated municipal wastewater with native plant species
Potentially, the restoration of native ecosystems could be combined with the land application of treated municipal wastewater (TMW), reducing TMW discharge into waterbodies. High levels of nutrients, pathogens, and other contaminants from TMW can degrade water quality. The land application of TMW onto 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. There is a critical knowledge gap about the response of native plant species to irrigation with TMW. We aimed to determine the distribution and speciation of nutrients in the soil-plant system following application of TMW onto 11 species of native plants in a long-term field trial on Banks Peninsula, New Zealand (NZ). TMW was irrigated at a rate of 1000 mm per annum, equivalent to N, and P loading rates of 194 and 110 kg ha yr−1, respectively. We determined physicochemical properties from soil profiles (0–65 cm) under selected species as well as the growth and chemical composition of the plants. Despite the site receiving 950 kg ha−1 yr−1 of Na, there was no evidence of impaired soil structure following TMW irrigation. Nitrogen did not accumulate in the soil, and it is likely to have been taken up by plants or lost through denitrification and nitrate leaching. The accumulation rate of P indicated that soil P concentrations will remain within the range found in NZ agricultural soils for at least 50 years. TMW irrigation increased plant height by 10% compared to the control after 3.5 years of growth. Plant species significantly affected the concentrations of total C, total N, nitrate (NO3−), and Na in the soil. TMW application had negligible effects on the elemental composition of plant foliage. NZ 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.