AMES, Iowa – Hardwood tree species have traditionally been used as a source of wood chips for bioreactors, but could conifers be used, as well?
Cesar Martinez, a senior in forestry, posed this question to Billy Beck, associate professor of natural resource ecology and management, last summer at a conference. Martinez was specifically interested in exploring eastern redcedar’s potential as a bioreactor wood chip source, since some consider the species invasive.
A bioreactor is an edge-of-field water-treatment technology used to remove nitrate nitrogen in tile water that drains from crop fields. The water is piped into a plastic-lined trench where it interacts with a high-carbon material, such as wood chips. The bioreactor environment supports microbes that transform nitrate into harmless nitrogen gas. This process results in cleaner water leaving the bioreactor before entering nearby waterways or ditches.
Martinez said existing literature does not address how wood chips from specific conifer species perform in bioreactors, so he took it as an opportunity to fill the gap.
Partnering with Nora Conzemius, a senior in chemistry, Martinez set up an experiment to test wood chips from 13 different conifers to see how effective they were in removing nitrate from tile water. The species represented trees found throughout the United States. The effectiveness of the conifers was compared with that of hardwood tree wood chips from two companies often used as bioreactor wood chip sources.
Martinez filled 1-liter mason jars with wood chips, microbes and tile water and let the jars sit for 48 hours before adding a nutrient solution. After another nine hours, he tested the nitrate levels of the water in each jar.
The following is the nitrate removal rate for each tested species:
- Scots pine – 57%
- White cedar – 56%
- Norway spruce – 48%
- Colorado Blue spruce – 46%
- Jack pine – 45%
- Western larch – 45%
- Eastern redcedar – 32%
- White pine – 32%
- Ponderosa pine – 24%
- Douglas fir – 22%
- Red pine – 20%
- European larch – 18%
- Cypress mulch (since a cypress tree could not be sourced in time) – 7%
The hardwood wood chips from one of the companies had a 51% nitrate removal rate and the other company’s had a 22% removal rate.
These rates align with the 9-54% average nitrate removal rates seen by Iowa State researchers over the years.
“White cedar’s high nitrate removal rate was surprising because there is nothing in the literature that said it would be so effective,” Martinez said.
Conzemius is beginning to dig into the data and analyze why some species are better at removing nitrate than others. She is excited to see what the data reveals.
“It’s been nice to explore the research process throughout this project, especially since it’s preparing me for the type of work I’ll be doing in graduate school,” Conzemius said.
The graduating seniors aim to publish a paper about their findings. Martinez also hopes the project will encourage states with large conifer populations to consider using those species as a source of carbon for nitrate removal from agricultural tile water.
“Results of the project will have on-the-ground impact across Iowa and nationally, as forest products markets often drive sustainable woodland stewardship,” Beck said. “A new market for coniferous bioreactor carbon media may enhance water quality while simultaneously incentivizing critical conservation activities that generate conifer logs, such as windbreak renovation and oak regeneration efforts.”
Funding for this project came from the USDA Forest Service and the USDA National Institute of Food and Agriculture.
Contacts
Cesar Martinez, Natural Resource Ecology and Management, cm45012@iastate.edu
Nora Conzemius, Chemistry, nconz22@iastate.edu
Billy Beck, Natural Resource Ecology and Management, 515-294-8837, wjbeck@iastate.edu
Whitney Baxter, Agriculture and Life Sciences Communications, 515-294-2314, wjsager@iastate.edu