Stormwater pollution, green infrastructure, heavy metals, nitrogen cycling
Arturo Keller, Josh Schimel
Dissertation Title & Abstract
N treatment in stormwater biofilters: Relationships between sequestered pollutants, environmental conditions, and N cycling soil bacteria
Urban stormwater runoff contains high levels of nitrogen (N) and other pollutants that may disrupt stream, lake or coastal ecosystems. To mitigate these disruptions, runoff can be captured and treated with stormwater biofilters. Yet, biofilters variably remove N, and sometimes N export as nitrate or trace gases could occur. Nitrate is formed through transformations that are mediated by N cycling bacteria, but these bacteria have been minimally studied. How N cycling bacteria interact with other contaminants that are retained in biofilter soils, such as metals, is also uncertain, and may be a concern for long-term sustainability. Further, due to a lack of studies performed in full-scale biofilters under intermittently wet and dry conditions, how N cycling bacteria respond to dynamic conditions is insufficiently understood. In my dissertation work, I address these knowledge gaps with a series of studies on field-scale biofilters and show that metal accumulation in soils is proportional to the ratio of impervious drainage area to biofilter area. Results also indicate that gene abundances of N cycling bacteria are influenced by soil properties and metal concentrations, with potential implications for N treatment outcomes. I also show that typical biofilter designs perform poorly to high N loading, behaving as persistent N sources in subsequent storms. I propose an alternate design consisting of a stormwater capture system, followed by a fast- and slow-draining cell, to improve N treatment and minimize N export.
MESM UC Santa Barbara
BS Chemical Engineering, Buenos Aires Technological Institute