2021 Virtual Undergraduate Research Symposium

2021 Virtual Undergraduate Research Symposium

Biomat Resilience to Desiccation in a Laboratory Scale, Engineered Unit Process Open Water Wetland

Biomat Resilience to Desiccation in a Laboratory Scale, Engineered Unit Process Open Water Wetland

PROJECT NUMBER: 31 | AUTHOR: Kimberly Riddle​, Civil and Environmental Engineering

MENTOR: Josh Sharp and Adam Brady, Civil and Environmental Engineering

ABSTRACT

Unit-process open water (UPOW) wetlands contain a photosynthetic biomat that attenuates nitrate; however, reliability concerns limit their widespread implementation. Further understanding of the processes affecting UPOW wetlands could contribute to increased widespread use in water treatment. One major concern is how increased hydrological extremes due to climate change will impact UPOW efficiency. To expand upon this knowledge, system resilience to a desiccation event was tested. System resilience was determined by developing flow-through cells in a moderated water bath of desiccated and undisrupted biomat, and comparing the physical characteristics, nitrate removal, photosynthetic activity, and microbial ecology over time. The pH and dissolved oxygen in each cell were measured at the start and end of each twelve-hour photoperiod (simulating nocturnal and diurnal activities) serving as a proxy for photosynthesis. Rehydrated biomat that had been naturally dried through drainage and evaporation reestablished nitrate removal consistent with undisrupted biomat in less than a week. However, a pulse of nitrogen and carbon was released upon rehydration; the microbial community within the rehydrated biomat was also significantly impacted. The results of this experiment suggested that UPOW wetlands have the potential for intermittent or seasonal use due to the ability of the rehydrated mat to return quickly to previous nitrate removal performance, as long as the nitrogen pulse is mitigated upon rehydration.

PRESENTATION

AUTHOR BIOGRAPHY

Kimberly Riddle is a senior in Environmental Engineering with a minor in Economics. She conducted research for one and a half years with Dr. Josh Sharp’s research group in the Civil and Environmental Engineering Department on the applications of engineered passive treatment systems to impaired water supplies. She worked on three main projects for research relating to amendments that improve microbial activity in wetlands, resiliency of wetlands during hydrologic extremes, and the use of woodchip bioreactors to remove contaminants of concern. Kimberly looks forward to starting her career in environmental engineering after graduation.

8 Comments

  1. Why aren’t plants growing in UPOW?
    How did you create the biomat in the lab?

    • Hi Shaked,

      UPOW wetlands are lined with a weed barrier (similar to those used in gardens) to prevent plants from growing. The fresh and desiccated biomats were both real samples transferred to the lab from our field-scale UPOW wetland (Orange County Water District’s Prado wetland) in Corona, California.

  2. Great presentation, Kim. Well done!

    • Thank you, Adam!

  3. Very nice work, Kim. What does the alpha diversity measure indicate? Do larger or smaller values suggest more or less microbial diversity? What microbial species and concentrations of those species are indicators of wetland health and suitability for use as biological filters?

    • Thank you, Nick!

      The alpha diversity numbers, specifically the observed number of amplicon sequence variants (ASVs), demonstrates the number of separate microbes that are in the system. Higher values indicate that there is a more diverse population of microbes.

      Although the fresh and desiccated systems had significantly different diversity, the performance of the biomat was not significantly different. The range of ASVs in the rehydrated samples demonstrates the microbial community likely underwent random selection due to the desiccation and rehydration process.

      For determining if a wetland was suitable for use as a biological filter, operational measurements such as nitrate removal would be taken first to see if the wetland/biomat was functioning. Then, 16S rRNA sequencing, metagenomics, and metatranscriptomics could be used to determine which microbial species were there and what they were doing. For this particular project, we were not looking for the wetland health or biofiltering abilities, and instead focused on the impacts of desiccation on a community that had previously been healthy and filtering in the field-scale system.

      Please do not hesitate to reach out to me if you have any further questions!

  4. Hi Kimberly, this presentation was incredible! There’s a lot of varying levels of difficulty within this project and I feel as though you clearly explained all of them. Nice job!

    • Thank you so much, Nazim! It was a fun project, and I am thankful to have had the opportunity to work on it!

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