Benthic primary production 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. 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 2003-01-01 William P. Porubsky University of Georgia

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

newcastl@uga.edu Graduate research assistant Liliana E. Velasquez University of Georgia

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

lilianav@uga.edu Graduate research assistant 2026

Dissolved organic carbon (DOC) flux dynamics were examined in the context of other biogeochemical cycles in intertidal sediments inhabited by benthic microalgae. In August 2003, gross oxygenic photosynthetic (GOP) rates, oxygen penetration depths, and benthic flux rates were quantified at 7 sites along the Duplin River, GA. Sediments contained abundant benthic microalgal (BMA) biomass with a maximum chlorophyll a concentration of 201 mg chl a m-2. Oxygen microelectrodes were used to determine GOP rates and O2 penetration depth, which were tightly correlated with light intensity. Baseline and 15N-nitrate amended benthic flux core incubations were employed to quantify benthic fluxes and to investigate the impact of BMA on sediment water exchange under nitrogen (N) limited and N replete conditions. Unamended sediments exhibited tight coupling between GOP and respiration and served as a sink for water column dissolved inorganic nitrogen (DIN) and a source of silicate and dissolved inorganic carbon (DIC). The BMA response to the N addition indicated sequential nutrient limitation, with N limitation followed by silicate limitation. In light incubations, biological assimilation accounted for 86 to 142 % of the nitrate uptake while denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) accounted for < 7 %; in contrast, under dark conditions DNF and DNRA accounted for > 40 % of the NO3- uptake. The N addition shifted the metabolic status of the sediments from a balance of autotrophy and heterotrophy to net autotrophy under light conditions, and the sediments served as a sink for water column DIN, silicate, and DIC, but became a source of DOC, suggesting that BMA production was decoupled from sediment bacterial consumption of DOC.

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)

LTER NSF GCE benthic biogeochemical denitrification DIC dissolved organic carbon DOC microalgal microelectrodes primary production Overall geographic extent of the research project -81.295506 -81.258908 31.497026 31.462320 2003-01-01 2006-05-01

National Science Foundation grant numbers OCE-9982133 and OCE-0620959

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., Velasquez, L.E. and Joye, S.B. 2008. Nutrient replete benthic microalgae as a source of labile dissolved organic carbon to coastal waters. Estuaries and Coasts. 31(5):860-876. (DOI: 10.1007/s12237-008-9077-0) http://www.springerlink.com/content/j6531n2472m364u4/?p=4887a9488d8a46098b68a028eafc3b71&pi=0 Porubsky, W.P., Weston, N.B., Lee, R. and Joye, S.B. 2003. Poster: Diel and seasonal patterns of benthic fluxes of nutrients, gases, and dissolved organics from temperate intertidal sediments of Georgia and South Carolina. Long Term Ecological Research All Scientists Meeting. September 2003, Seattle, WA.