Impacts of Sodium Chloride on Nutrient, Heavy Metals, and Total Suspended Solids Removal by Bioretention Mesocosms with Varied Vegetation and Saturation
Restricted (Penn State Only)
- Author:
- Brown, Alexander
- Graduate Program:
- Environmental Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 13, 2023
- Committee Members:
- Patrick Fox, Program Head/Chair
Lauren Mc Phillips, Thesis Advisor/Co-Advisor
Nathaniel Richard Warner, Committee Member
Margaret Crowley Hoffman, Committee Member - Keywords:
- bioretention
deicing salt
stormwater
green infrastructure
bioinfiltration
heavy metals
nutrients
nitrogen
phosphorus
copper
zinc
stormwater control measure
best management practice
sediment
internal water storage
vegetation
removal efficiency
water quality
loading
urban
runoff
nonpoint pollution - Abstract:
- Salt, which is known to alter soil properties, affect microbial communities, and damage ecosystems, enters bioretention basins in large quantities after winter application to roads and walkways. This affects the performance of these bioretention basins, which are a crucial part of efforts to remove pollutants and attain water quality criteria, but more work is needed to quantify and understand these impacts. 48 6-inch diameter bioretention mesocosms were built in a greenhouse and regularly dosed with synthetic stormwater throughout 2022 and in early 2023. NaCl was added in the late winters of both years, and effluent was monitored over the spring, summer, and fall of 2022 and early spring of 2023. A factorial experimental design was used to determine the effects of a high or low salt concentration; the presence of Panicum virgatum, Eupatorium purpureum Euphoria™ Ruby PPAF, or no vegetation; and the presence of an internal water storage zone or free-flowing design on contaminant removal. Testing revealed generally good removal of nitrogen and total suspended solids (TSS) and excellent removal of total phosphorus, copper, and zinc throughout the experiment; but deicing salt application significantly reduced the spring removal of phosphorus, copper, TSS, and zinc, resulting in major, though brief, export of zinc. The effects of salt on performance, while relatively short, exceeded natural contaminant concentrations and acute toxicity limits, posing risks to aquatic ecosystems. Internal water storage (IWS) and vegetation were generally found to positively affect or have no influence on performance, varying with analyte, although both were important in nutrient removal. Good annual removal was demonstrated despite the effects of salt, especially when vegetation and IWS were included. This indicates that bioretention can successfully operate in cold climates, although effective design and regular maintenance are crucial, and NaCl application should be reduced where possible.