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Kokkinos, Jason M.

Plant and Soil Science

2017

M.S.

Bioretention cells are a stormwater treatment technology that uses soil and vegetation to remove pollutants from runoff and improve downstream water quality. While bioretention has been shown to be effective at removing certain stormwater pollutants such as sediment and heavy metals, removal of nutrients has been more variable. Design components of bioretention such as vegetation and soil media amendments can influence pollutant removal performance. In my experiment, I isolate the effects of low-phosphorus compost and a Switchgrass (Panicum virgatum) monoculture on bioretention performance. In fall 2016, three bioretention cells were installed at the University of Vermont Miller Research Complex, a mixed-use research and agricultural production facility located in South Burlington, VT. Each bioretention had a unique experimental treatment that allowed for the comparison of the presence of the following design components: (1) compost with planted vegetation, (2) no compost and vegetation, and (3) no compost or vegetation. Results suggest that the presence of a low-P compost layer had a small deleterious effect on nutrient removal performance, as the bioretention cell with an added compost layer exported higher concentrations of phosphorus and nitrogen and exhibited a higher concentration of water extractable phosphorus in the bioretention media. The bioretention cell with vegetation and no compost was the only treatment to significantly reduce total nitrogen and phosphorus concentrations; however, there was no effect on media phosphorus concentration. The presence of low-P compost significantly increased the above-ground biomass growth of Switchgrass, but had no effect on the total number of plants surviving in the first year. Switchgrass proved to be a durable plant, capable of surviving in bioretention media without compost, but was slow to grow and required additional watering through droughty conditions.