Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Watershed Sciences

Committee Chair(s)

Erin Rivers


Erin Rivers


Ryan Dupont


Sarah Null


Joan McLean


Low impact development (LID) systems are practices that use natural elements, such as soils and vegetation, to absorb and filter stormwater to protect water quality and aquatic habitats. Many LID designs use native soils; however, urban soils typically have a limited potential for infiltrating and treating stormwater. Incorporation of soil amendments, such as compost and biochar, into LID soils can improve the physical properties of soil. However, soil amendments may increase or decrease pollutants in the water leaving the site. A comparison of the effects of different types and application rates of amendments on water quality is necessary to determine the appropriate use of amendments in LID systems. The objective of this study was to evaluate the use of soil amendments in LID systems by examining the effects of sources and amendment rates on soil properties and water quality. Water draining from soils amended with three types of compost and one type of biochar at different amendment rates (0, 5, 10, 25, and 50% by volume) were monitored during five simulated storm events. Results showed that compost treatments increased nitrate and phosphate concentrations, with higher concentrations occurring with higher amendment rates. Nitrate was flushed from the soils within the first storm events, and phosphate was released steadily across all five storms. Biochar exported less nutrients than the compost treatments, and ammonium, copper, lead, and zinc were removed in all treatments. The export of dissolved arsenic resulted from the addition of all amendments to the control soil and was closely linked to dissolved organic carbon. The chemistry and amendment rates of compost and biochar were the primary drivers of pollutant export. Overall, biochar improved water quality and soil physical properties to a greater degree than compost. This study shows that amendment type and amendment rate can affect water quality when utilized in LID. Biochar was shown to outperform compost in water quality treatment and may be an optimal soil amendment source where available. The results of this study will help inform guidelines in statewide design standards for LID practices using soil amendments to improve stormwater capture and treatment.