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Scholarly Works (2 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2024)

Urban systems, or socio-ecological systems, are complex on fine and coarse scales, and are important to humans through the effects of ecological processes. Nitrogen pollution is uniquely altered by humans and variable on fine spatial scales with understudied potential sources and sinks. We found local atmospheric nitrogen pollution concertation in Riverside correlated with traffic as a pollution source, but plant canopy did not act as a significant source. Atmospheric pollution does not remain within city limits, and effects in natural systems can be observed in the air, canopy, and soil. We observed a deposition gradient, with decreased atmospheric nitrogen further from urbanization. However the pattern was not consistent for nitrogen in the canopy and the soil, highlighting a disconnect in the gradient and the complexity of teleconnections. Urban ecology affects humans in socioecological systems and plays an important role in science policy. The Salton Sea is a hyper-resilient ecological crisis that fits within the framework of wicked problems. Through research on existing government policy and interviews with key stakeholders, we identified issues that potentially keep the sea in a degraded state and recommendation via resilience theory to address the wicked problem. The dissertation as a whole seeks to improve understanding of socio-ecological systems across scales, and quantify variation in ecosystem processes and nitrogen patterns within and beyond urban areas.

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Cover page: Intraurban Nitrogen Pollution and Effects on Desert EcosystemsCreative Commons 'BY' version 4.0 license
  • Article
  • Peer Reviewed
UC Riverside Previously Published Works (2023)
Soils are the largest source of atmospheric nitrous oxide (N2O), a powerful greenhouse gas. Dry soils rarely harbor anoxic conditions to favor denitrification, the predominant N2O-producing process, yet, among the largest N2O emissions have been measured after wetting summer-dry desert soils, raising the question: Can denitrifiers endure extreme drought and produce N2O immediately after rainfall? Using isotopic and molecular approaches in a California desert, we found that denitrifiers produced N2O within 15 minutes of wetting dry soils (site preference = 12.8 ± 3.92 per mil, δ15Nbulk = 18.6 ± 11.1 per mil). Consistent with this finding, we detected nitrate-reducing transcripts in dry soils and found that inhibiting microbial activity decreased N2O emissions by 59%. Our results suggest that despite extreme environmental conditions-months without precipitation, soil temperatures of ≥40°C, and gravimetric soil water content of <1%-bacterial denitrifiers can account for most of the N2O emitted when dry soils are wetted.
    Cover page: Bacterial denitrification drives elevated N2O emissions in arid southern California drylands.
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