The Missoula Poplar Project: Utilizing Poplars to Enhance Wastewater Treatment

Wastewater treatment plants rank second to agricultural runoff in the top ten major pollution sources to U.S. surface waters. Such nutrient-rich inputs can degrade aquatic ecosystems by accelerating eutrophication events, especially in summer months when surface water flows are low. Alternative treatment practices, modeled after natural ecosystem processes, could reduce nutrient inputs to surface waters while accumulating biomass and sequestering atmospheric carbon dioxide. I designed and implemented an alternative treatment strategy, using effluent to fertilize trees at the Missoula Wastewater Treatment Facility. The objectives of this work were to assess: 1) environmental impacts of effluent application; 2) tree survivorship; and 3) growth effects. A two acre plantation was established in May 2009 by planting 316 dormant, unrooted stem cuttings of two hybrid poplar species, Populus deltoides X Populus trichocarpa and Populus deltoides X Populus nigra, and the native Black Cottonwood, Populus balsamifera ssp. trichocarpa. The effects of effluent fertilization on poplar growth, soil and ground water nutrient contents were monitored throughout the first growing season of this pilot project. Effluent fertilization nearly doubled poplar growth, and as suspected, had no major impacts on soil or ground water nutrient concentrations. Continued research at this site is necessary to observe environmental impacts as effluent loading rates increase. Our initial results suggest that surface application of wastewater effluent offers a valuable strategy for decreasing effluent input rates to the Clark Fork River. Moreover, this project offers smaller communities a blue print from which to design similar projects that remediate nutrient-rich effluent in a cost-effective way