Nitrogen biogeochemistry of groundwater fluxes to the estuaries in the northern Gulf of Mexico

• Applicant: Dr. Dini Adyasari
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management ; Microbial Ecology and Applied Microbiology
• Term: from 2020 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 446330207

• Final Report Year: 2024

Final Report Abstract

Mobile Bay, located in the northeastern part of the Gulf of Mexico, has experienced longterm coastal hypoxia, resulting in fish kills and negative economic impacts on the region. This condition is exacerbated by submarine groundwater discharge delivering high concentrations of ammonia (NH4+) and dissolved organic matter into coastal waters. Combining geochemical and molecular biology analyses, this study addresses biogeochemical transformations of nitrogen (N) and carbon (C) in the coastal aquifer and investigates potential ecological shift under future climate and land use change scenarios. These scenarios include increasing anthropogenic nitrate (NO3-) input, saltwater intrusion, and changing groundwater residence time due to increasing frequency of drought or intense rainfall. The findings of this study suggest that elevated NH4+ and organic matter in coastal groundwater originate from internal carbon cycling in sediments, derived from the degradation of vascular plants. Terrestrial anthropogenic NO3- is attenuated in coastal sediments by denitrification; however, laboratory experiments show that this process is negatively affected by increasing ionic strength in groundwater. Additionally, this study found that aquifer salinization, likely to occur in the near future due to sea level rise, results in the mobilization of NH4+, phosphate (PO43-), and refractory, highly unsaturated organic matter from sediments. Highly unsaturated organic matter can be resistant to heterotrophic reworking in coastal water, and its combination with elevated nutrient concentrations will likely exacerbate hypoxic events in Mobile Bay and other Gulf of Mexico estuaries. Longer groundwater residence times, typically occurring during extended periods of drought, allow sufficient time for microbes to degrade refractory organic matter, promoting the re-release of buried solid-phase organic matter into the active carbon cycle. Microbial assessments suggest that sediment communities are resilient to increasing terrestrial NO3- input; however, their diversity and metabolic function are negatively affected by changes in ionic strength and residence time. In the context of global climate change, the results of this study illustrate the sensitivity of nitrogen and carbon cycling, as well as the microbial communities that mediate those processes, in coastal sediments to salinization and altered residence times, consequently affecting coastal aquatic ecosystems and health.

Publications

• Open access R script of radon mass balance [script].
  Adyasari, D., Dimova, N. T., Dulai, H., McKenzie, T. & Fuleky, P.
  
• Anthropogenic impact on Indonesian coastal water and ecosystems: Current status and future opportunities. Marine Pollution Bulletin, 171, 112689.
  Adyasari, Dini; Pratama, Mochamad Adhiraga; Teguh, Novi Andriany; Sabdaningsih, Aninditia; Kusumaningtyas, Mariska Astrid & Dimova, Natasha
  
• Storm-Driven Fresh Submarine Groundwater Discharge and Nutrient Fluxes From a Barrier Island. Frontiers in Marine Science, 8.
  Adyasari, Dini; Montiel, Daniel; Mortazavi, Behzad & Dimova, Natasha
  
• Nitrogen biogeochemistry in the subterranean estuaries affected by submarine groundwater discharge [oral abstract]. Ocean Science Meeting 2022, online.
  Adyasari, D. & Dimova, N.
  
• Nitrogen sources and sinks in subterranean estuaries affected by submarine groundwater discharge [oral abstract]. Radium and Radon Meeting 2022, online.
  Adyasari, D. & Dimova, N.
  
• Dissolved organic matter and nutrient processing in organic-rich subterranean estuaries: Implications for future land use and climate scenarios. Geochimica et Cosmochimica Acta, 362, 65-76.
  Adyasari, Dini; Dimova, Natasha; Waska, Hannelore & Ni, Chadhain Sinead
  
• Geochemical and microbial community dynamics in subterranean estuaries under salinization and changing groundwater residence times [poster abstract]. American Geophysical Union Fall Meeting 2023, 11-15 December 2023, San Francisco, USA.
  Adyasari, D., Dimova, N. T., Ní Chadhain, S. M. & Waska, H.
  
• Radon-222 as a groundwater discharge tracer to surface waters. Earth-Science Reviews, 238, 104321.
  Adyasari, Dini; Dimova, Natasha T.; Dulai, Henrietta; Gilfedder, Benjamin S.; Cartwright, Ian; McKenzie, Tristan & Fuleky, Peter
  
• Microbial assemblages and functional predictions in organic-rich subterranean estuaries [Online Dataset]. Hydroshare.
  Adyasari, D., Dimova, N., Sinead Ni, C. & Hannelore, W.
  
• Microbial Assemblages and Metabolic Activity in Organic‐Rich Subterranean Estuaries: Impact of Climate and Land Use Changes. Journal of Geophysical Research: Biogeosciences, 129(3).
  Adyasari, Dini; Dimova, Natasha T.; Ní, Chadhain Sinéad M. & Waska, Hannelore