Baltimore Ecosystem Study Institute of Ecosystem Studies

2015 BES Annual Meeting Presentation and Poster Abstracts

Denitrifying microbes and nitrous oxide yields from urban water bodies across the United States
Blaszczak, Joanna
Co-Authors: Blaszczak, J.R., Steele, M., Badgley, B., Hobbie, S., Heffernan, J., Bernhardt, E.S., & Groffman, P.

Abstract: Numerous stormwater retention ponds are built in US cities to manage storm flows; however, their effect on biogeochemical cycles, specifically denitrification, is largely unknown. The low oxygen and high nitrate typical of these urban water bodies should provide ideal conditions for denitrifying microbial communities, and as a result, stormwater ponds may be major sources of both N2O and N2 fluxes within urban landscapes. Here we ask the question: Which conditions in sediments from ponds across 8 US cities best explain the variation in potential N2O and N2 production? To address this question, during the summer of 2014 we collected sediments from 4 highly urban and 4 ‘green space’ ponds within 8 USA metropolitan statistical areas (MSAs). We measured potential N2O and N2 production, porewater chemistry, sediment chemistry, and heavy metal concentrations for each pond. Our findings show no consistent categorical differences in sediment chemistry or rates of denitrification between urban and green space ponds. However, there was significant variability among cities and N2O accounted for as little as 0.01% to as much as 99% of total gaseous N fluxes. Through a comparison of multivariate linear regression models we also found that a substrate model and a stressor model explain approximately the same (R2=0.12 and R2=0.11, respectively; p<0.05), but different parts of the variation in total denitrification rates. In addition, the stressor model explained more of the variation in N2O production (R2=0.31), indicating that stressors may play a more important role in determining the importance of the N2O reduction pathway.