1. Examining the Effects of Seasonal and Salinity Variations on Satilla River Sediments (Georgia, U.S.A.) Using In Situ Voltammetric Depth Profile Measurements EAS Graduate Student Symposium November 2 nd, 2007 Presented By: Deidre Meiggs Advisor: Dr. Martial Taillefert

2. Carbon Remineralization Heterotrophic respiratory processes are responsible for the oxidation of natural organic matter (NOM) in marine sediments (Froelich et al., 1979). Heterotrophic respiratory processes are responsible for the oxidation of natural organic matter (NOM) in marine sediments (Froelich et al., 1979). Rates of NOM oxidation are highest in continental margin sediments but quite difficult to quantify (Burdige, 2006). Rates of NOM oxidation are highest in continental margin sediments but quite difficult to quantify (Burdige, 2006). Attempts to quantify respiration assume O 2(aq) as the ultimate oxidant Attempts to quantify respiration assume O 2(aq) as the ultimate oxidant Current total (TOU) and dissolved (DOU) oxygen uptake methods generally underestimate NOM oxidation rates because reduced metabolites are not always oxidized by oxygen (Glud and Gundersen, 2002). Current total (TOU) and dissolved (DOU) oxygen uptake methods generally underestimate NOM oxidation rates because reduced metabolites are not always oxidized by oxygen (Glud and Gundersen, 2002). Individual terminal electron accepting processes must be considered simultaneously Individual terminal electron accepting processes must be considered simultaneously The impact of microbial iron reduction has been underestimated in areas of high bioturbation and tidal fluctuation (Kostka et al., 2002). Tidally driven advection can enhance the supply of dissolved oxygen to recycle microbially produced Fe +2 (Taillefert et al., 2007). The impact of microbial iron reduction has been underestimated in areas of high bioturbation and tidal fluctuation (Kostka et al., 2002). Tidally driven advection can enhance the supply of dissolved oxygen to recycle microbially produced Fe +2 (Taillefert et al., 2007).

3. Our Goals: Demonstrate that the recycling of iron in these sediments is fast and due to dissolved oxygen in the surficial sediment provided by strong tidal flux. Quantify benthic fluxes as well as the chemical composition of pore waters and combine the information into a diagenetic model to obtain more information about carbon remineralization rates. Accomplished by construction and testing of a free benthic lander to study these redox processes in situ Accomplished by construction and testing of a free benthic lander to study these redox processes in situ Also optimize a voltammetric technique to obtain high resolution depth profiles and benthic chamber measurements autonomously Also optimize a voltammetric technique to obtain high resolution depth profiles and benthic chamber measurements autonomously

4. The Satilla River The Satilla River is located 15 miles north of GA state border with Florida. The Satilla River is located 15 miles north of GA state border with Florida. SAT 2 is located farthest from the river mouth (about 20km upstream). SAT 2 is located farthest from the river mouth (about 20km upstream). SAT 1 SAT 2 SAT 3 SAT 4 SAT 5

5. The Benthic Lander Remotely operated micromanipulator Potentiostat: ISEA (from AIS) Multiplexer: for up to 4 working electrodes KI Tracer Injector Benthic Chamber with Seabird pump

6. DOU Measurements DOU is calculated from ex-situ core data. DOU is calculated from ex-situ core data. Sample is from SAT 3 in May 2007 Sample is from SAT 3 in May 2007 Requires high resolution Requires high resolution Flux = D 0 (dC/dz) Flux = D 0 (dC/dz) D 0 = (4.72*10 -9 ) *T*(  V b 0.6 ) -1 D 0 = (4.72*10 -9 ) *T*(  V b 0.6 ) -1 T = Temperature (K) T = Temperature (K) V b = 27.9cm 3 mol -1 V b = 27.9cm 3 mol -1  = 0.01poise  = 0.01poise D 0 = cm 2 s -1 D 0 = cm 2 s -1 dC/dz =  Mcm -1 dC/dz =  Mcm -1 Flux = 5.652+/-1.070 mmol*m -2 *day -1 Flux = 5.652+/-1.070 mmol*m -2 *day -1

7. Flux Trends

8. Average flux decreases toward the river mouth Average flux decreases toward the river mouth Due to changes in biogeochemical processes Due to changes in biogeochemical processes Indirectly related to the salinity gradient. Indirectly related to the salinity gradient.

9. Biogeochemical Processes SAT 2SAT 4 Plots display yearly trends for SAT 2 (upriver) and SAT 4 (downriver) Plots display yearly trends for SAT 2 (upriver) and SAT 4 (downriver) Iron reduction is more prevalent in SAT 2 (freshwater) sediment Iron reduction is more prevalent in SAT 2 (freshwater) sediment Sulfate reduction is more prevalent in SAT 4 (saltwater) sediment Sulfate reduction is more prevalent in SAT 4 (saltwater) sediment

10. The Drought SAT 2Salinity Apr-050 Jul-050 Sep-050 Oct-050 Dec-0510 Jan-060 Jun-0622.5 Aug-0624.36 Oct-0625 Nov-0623 Jan-0722 May-0721 Jul-0725 Sep-0715

11. Conclusions Addressing the stated goals: Addressing the stated goals: Lander has been successfully tested along river sediments. Lander has been successfully tested along river sediments. A voltammetric sequence optimal for benthic chamber measurements as well as sediment profiles has been developed. A voltammetric sequence optimal for benthic chamber measurements as well as sediment profiles has been developed. Sediment profiles have been used to calculate DOU fluxes. Sediment profiles have been used to calculate DOU fluxes. Next Steps: Next Steps: A model for TOU calculations is in the final stages of editing. A model for TOU calculations is in the final stages of editing. A diagenetic model to ascertain the impact of iron oxidation in these sediments is currently being developed. A diagenetic model to ascertain the impact of iron oxidation in these sediments is currently being developed.

12. Conclusions Unexpected Findings: Unexpected Findings: A total of 69 deployments have been completed over three seasonal cycles. A total of 69 deployments have been completed over three seasonal cycles. Seasonal fluctuations are evident. Seasonal fluctuations are evident. An increase in sulfate reduction is noticed during dryer years because saline waters reach further up river. An increase in sulfate reduction is noticed during dryer years because saline waters reach further up river. Drought conditions are leading to salt water intrusion upriver, leading to significant changes in the biogeochemical processes occurring in these sediments.