MICROBIAL CONTROLS ON NITROGEN POLLUTION MITIGATION WITHIN STORMWATER BASINS
Morse, Natalie Rose
When considering sustainable urban development, trade-offs between water quality and greenhouse gas emissions exist. Therefore, this study examined the nitrogen (N) cycling dynamics, water quality treatment, and greenhouse gas emissions from stormwater basins located on Cornell University’s campus. Stormwater basins that were often saturated ("Wet Basins") had a greater abundance of denitrification genes, and denitrified a greater proportion of incoming N. However, overall N treatment (measured as the difference between incoming N and N leaving the basin underdrains) was greater in quick draining "Dry Basins" likely due to the large volume of infiltrated stormwater. Rain events did not create hot-moment emissions of N2O or CH4 from these basins. Using EPA calculations, stormwater sent to a WWTP would produce 7X more CO2-eq per L than if it were sent to a Dry Basin. Conversely, stormwater sent to a Wet Basin instead of the WWTP would lead to an approximately 8X increase in CO2. These results suggest that stormwater basins with saturated conditions are likely doing a better job of completely removing N via denitrification, but are also emitting greater quantities of GHGs. Thus, the tradeoff between better N water quality treatment and greater GHG emissions must be considered when designing stormwater basins. In an effort to understand how increased urbanization will influence the soil microbial community, we examined the soil microbiome in stormwater basins after 2-months and 2-years of exposure. Overall, the microbial communities did not shift dramatically within the stormwater sites. Microbial sub-pathways of methanogenesis and V-ATPase were increased within the Wet Basin treatment, likely due to excess Na and soil moisture. While denitrification is also an anaerobic process like methanogenesis, the denitrification genes did not increase within the often saturated Wet Basin treatment. This indicates that denitrification may take longer than 2-years to adjust to new environments, and practices like stormwater basins that rely on denitrification to remove nitrogen and improve water quality may be initially limited. In addition to these field studies, a lab-scale mesocolumn study done in collaboration with Monash University examined the plant-microbe interactions and their impact on N treatment within stormwater basins. We conducted N water quality, N partitioning, soil metagenomics and 16S profiling across 7 unique plant species and 1 soil control over the 2-year experiment. Plant species with greater root volume, plant and microbial assimilation, and NOx removal, had lower denitrification genes and rates. Our hypothesis that greater denitrification would lead to better NOx removal was not supported by these data, because plant species with high NOx removal depressed denitrification genes and rates, but led to a better ‘treatment’ rate as a larger proportion of incoming N was assimilated and did not directly exit the column drainage. This aligns with the other projects where increased denitrification did not necessarily lead to higher N treatment, unless the ultimate fate of N is considered, and then the amount denitrified is more critical. Overall, anaerobic conditions in stormwater basins promoted denitrification and complete removal of N from downstream waters. However, because of excess greenhouse gas emissions, designers should consider the tradeoffs when installing these stormwater treatment technologies.
Supplemental file(s) description: AppendixA_EFFECTS OF BLACK CARBON ON CU AVAILABILITY, MICROBIAL UPTAKE AND DENITRIFICATION
Environmental engineering; metagenomics; microbial community; nitrogen; denitrification; stormwater; Microbiology; Biogeochemistry
Walter, Michael Todd
Shapleigh, James P.; Ahner, Beth A.
Biological and Environmental Engineering
Ph. D., Biological and Environmental Engineering
Doctor of Philosophy
dissertation or thesis