Impact of Autumn Olive Nitrogen-Fixation on Groundwater Nitrate Concentration

Autumn olive (Elaeagnus umbellata) is an exotic and invasive species that was used extensively as an erosion control plant along many highways in the Midwestern United States during the last century. Due to its invasive and strong nitrogen-fixing abilities, it aggressively spread outside its intended use area. Unfortunately, control management programs by many organizations have failed to control its spread. Currently, it exists in dense patches over vast areas in the Midwest. A by-product of its nitrogen-fixing is nitrate. Nitrate is regulated in drinking water for its known toxicity to human and animal infants. This study assesses the leaching of nitrate from autumn olive infested areas into its surrounding environment. Soil and groundwater samples were collected from areas infested with autumn olive and from paired nearby grass plots in Indiana and Michigan between 2009 and 2014. The samples were analyzed for nitrate, ammonia, and total nitrogen in addition to other relevant chemical and physical soil and water parameters.A matched pairs t-test indicates that the concentration of nitrate is significantly higher (p-value=0.0002) in the soil and groundwater beneath the autumn olive infested areas compared to their control areas. The nitrate concentrations in soil water of many infested areas exceeded the EPA’s MCL of 10 mg/L and were over ten times higher compared to their control areas. The data also showed varying seasonal nitrate leaching levels.