Groundwater biogeochemistry Dr. Christof Meile University of Georgia

Dept. of Marine Sciences University of Georgia Athens Georgia 30602-3636 USA

cmeile@uga.edu http://www.marsci.uga.edu/directory/christof-meile https://orcid.org/0000-0002-0825-4596 Dr. Samantha B. Joye University of Georgia

Dept. of Marine Sciences University of Georgia Athens Georgia 30602-3636 USA

mjoye@uga.edu http://www.marsci.uga.edu/directory/samantha-b-joye Georgia Coastal Ecosystems LTER Project

Dept. of Marine Sciences University of Georgia Athens Georgia 30602-3636 USA

gcelter@uga.edu https://gce-lter.marsci.uga.edu/ Dr. Christof Meile University of Georgia

Dept. of Marine Sciences University of Georgia Athens Georgia 30602-3636 USA

cmeile@uga.edu http://www.marsci.uga.edu/directory/christof-meile https://orcid.org/0000-0002-0825-4596 Principal investigator 2001-01-01 2006-12-31 Dr. Samantha B. Joye University of Georgia

Dept. of Marine Sciences University of Georgia Athens Georgia 30602-3636 USA

mjoye@uga.edu http://www.marsci.uga.edu/directory/samantha-b-joye Principal investigator 2001-01-01 2006-12-31 Dr. Willard S. Moore University of South Carolina

Department of Geological Sciences University of South Carolina Columbia South Carolina 29208 USA

moore@geol.sc.edu http://www.geol.sc.edu/billy.htm Co-investigator William P. Porubsky University of Georgia

Dept. of Marine Sciences University of Georgia Athens Georgia 30602-3636 USA

newcastl@uga.edu Graduate research assistant 2026

Field measurements were used to characterize the biogeochemistry of groundwater along a shallow monitoring well transect on a coastal hammock. Radium isotope data indicate considerable discharge of groundwater into the river bordering the hammock. Nutrient measurements indicated a switch in the redox status of the dissolved inorganic nitrogen (DIN) pool in the well closest to the upland/saltmarsh transition over the spring-neap tidal cycle. The DIN pool was dominated by NOx (NO2- + NO3-) during spring tide and by ammonium (NH4+) during neap tide. A two dimensional density-dependent reaction-transport model was employed to investigate the processes responsible for the observed redox switch. The model represents a saturated vertical plane from the upland to the upland/saltmarsh transition; measured pressure heads were used to constrain transport over spring and neap tides. Using process parameterizations derived from laboratory experiments, the observed N redox-switch was evaluated with regard to the relative roles of denitrification (DNF), dissimilatory nitrate reduction to ammonium (DNRA), ammonium adsorption, and variations in flow regime between spring and neap tides. The spring tide flow was found to cause increased intrusion of sea water into the near marsh zone and promote higher NOx concentrations under spring conditions. Additionally, the impact of increased dissolved organic matter and DIN loading was evaluated by the inclusion of septic effluent simulations which indicated that while the DNF rate increased ~95%, the increased rate could not keep pace with the increase in DIN loading, removing only ~40% of the NO3- load, resulting in export of DIN.

Question 2: How do the spatial and temporal patterns of biogeochemical processes, primary production, community dynamics, decomposition, and disturbance vary across the estuarine landscape, and how do they relate to environmental gradients? (more information)

dissolved inorganic nitrogen LTER NSF Georgia GCE biogeochemistry groundwater radium isotope salt marsh upland wells Overall geographic extent of the research project -81.295506 -81.258908 31.497026 31.462320 2001-01-01 2006-12-31

National Science Foundation grant number OCE-9982133. Additional funding by the Georgia Sea Grant: 'Assessing the impact of residential development and recreational land use on shallow groundwater quality in coastal environment'; separate awards to S.B. Joye and C.D. Meile.

estuary marsh complex Hunt Camp - Barrier island/marsh site on western Sapelo Island. This site is located at the upper reaches of the Duplin River, and is within the Sapelo Island National Estuarine Research Reserve. Existing well fields border small marsh area to northwest, some wells have been installed to south end of hammock where marsh is more extensive and permanent plots are located. Two existing hydrographic sondes and weather stations within this site are operated by SINERR (Hunt Camp dock) and UGAMI (flume dock). -81.295506 -81.258908 31.497026 31.462320 Porubsky, W.P., Joye, S.B., Moore, W.S., Tuncay, K. and Meile, C. 2011. Field measurements and modeling of groundwater flow and biogeochemistry at Moses Hammock, a backbarrier island on the Georgia coast. Biogeochemistry. 104:69-90. (DOI: 10.1007/s10533-010-9484-8) http://www.springerlink.com/content/t18x02358tt6x123/ Meile, C., Porubsky, W.P., Walker, R.L. and Payne, K. 2009. Natural Attenuation Of Nitrogen Loading From Septic Effluents: Spatial And Environmental Controls. Water Research. 44(5):1399-1408. (DOI: 10.1016/j.watres.2009.11.019) Porubsky, W.P. and Meile, C. 2009. Controls on groundwater nutrient mitigation: Natural attenuation of nitrogen loading from septic effluents. In: Hatcher, K.J. (editor). Proceedings of the Georgia Water Resources Conference. Athens, Georgia. Porubsky, W.P., Meile, C. and Joye, S.B. 2007. Presentation: Using field measurements, laboratory assays and modeling to examine flow conditions and variations in groundwater biogeochemistry. Estuarine Research Federation 2007 Annual Meeting, 4-8 November 2007, Providence, Rhode Island. Porubsky, W.P., Meile, C. and Joye, S.B. 2007. Poster: Variations in groundwater biogeochemistry and flow on Moses Hammock (Sapelo Island, GA): Field measurements, laboratory assays, and modeling. American Society of Limnology and Oceanography 2007 Aquatic Sciences Meeting, 4-9 February 2007, Santa Fe, New Mexico. Joye, S.B., Weston, N.B. and MacAvoy, S.E. 2001. Presentation: Groundwater inputs and sediment biogeochemical processes in Georgia and South Carolina coastal ecosystems. Biannual Meeting of the Estuarine Research Federation. Estuarine Research Federation, November, 2001, St. Petersburg, Florida.