Area 1: External Drivers of Change

External Drivers of Change

Our goal for this area is to characterize external drivers such as climate change, sea-level rise, and human alterations of the landscape in terms of long-term trends, spatio-temporal variability, and occurrence of extreme events (e.g., storms, droughts) so that we can investigate the links between external drivers and ecosystem response. This includes collecting ongoing information on climate and oceanographic conditions, sea level, and river discharge (Fig 1).

Research Objectives

A) Environmental Drivers

• 1A.1 - Collect ongoing information on climate and oceanographic conditions, sea level, and river discharge
• 1A.2 - Maintain eddy covariance tower in Duplin River
• 1A.3 - Monitor Altamaha River water entering the GCE domain
• 1A.4 - Conduct dendrochronology analysis

B) Human Drivers

• 1B.1 - Assess Native American oyster harvesting practices
• 1B.2 - Evaluate how human activity relates to marsh inundation patterns
• 1B.3 - Track shoreline armoring

Current Progress Report

Below is an update for each of the Area 1 objectives as reported in the most recent annual report. For a list of all reports click here (Annual Reports).

A) Environmental Drivers

• 1A.1 - Collect ongoing information on climate and oceanographic conditions, sea level, and river discharge

  Activities:  Several meteorological stations are used to characterize the GCE domain (Fig. 1), including long-term climate data collected at Marsh Landing and the GCE flux tower. We also track sea level (including a GCE tide gage), offshore wind forcing, and river discharge.

  Significant Results: We did a detailed analysis of both the mean and frequency of extremes of temperature, drought, and discharge in the GCE domain, which we built on for our renewal proposal (Fig. 2).

Fig1. Locations of observing stations used for boundary conditions (ML is Marsh Landing; UGAMI is UGA Marine Institute).

Fig. 2. Fig. 1. Left axes: Long-term patterns in mean annual (a) river discharge (USGS gage at Doctortown), (b) Palmer Drought Severity Index (NOAA), (c) air temperature (NWS UGAMI station),and (d) annual mean high water levels (Fort Pulaski, GA). Right axes: frequency of (a) months in a given year when minimum daily discharge < 60 m³s^-1, (b) months in a year of extreme drought (PDSI < -4), (c) days in a year with mean temperature > 31^oC, (d) number of hours tide levels exceeded the NOAA high-tide flooding threshold (> 0.59 m above MHHW) Period of the GCE project shaded in peach, with dashed lines showing projections through GCE-V.

• 1A.2 - Maintain eddy covariance tower in Duplin River

  Activities: The GCE flux tower on the Duplin River measures CO2/H2O, weather conditions, radiation, water levels, and soil temperature

  Significant Results: We used 10 years of flux tower data to develop response curves for NEE as a function of tidal flooding and season (Fig. 3), which we will build on in GCE-V.

Fig. 3. Daytime 30-min NEE grouped by month relative to mean high water (MHW) at the GCE flux tower (2014-2023) show the lowest NEE during the growing season (April through August) and a non-linear increase as the marsh surface becomes inundated during tidal flooding.

• 1A.3 - Monitor Altamaha River water entering the GCE domain

  Activities: We routinely collect monthly samples of water entering the GCE domain via the Altamaha River for analysis of dissolved inorganic and organic nutrients, DIC and particulates.

  Significant Results: GCE contributed to a global database of DOM concentrations for use by the scientific community (Lonsburg 2024).

• 1A.4 - Conduct dendrochronology analysis

  Activities: We have completed a high-resolution radiocarbon tree ring analysis of bald cypress on the Georgia Coast.

  Significant Results: The dendrology studies show evidence for variability in tree growth associated with sea level change, which impacted the productivity of oyster reefs and caused die-offs of bald cypress (Napora et al., subm.).

B) Human Drivers

• 1B.1 - Assess Native American oyster harvesting practices

  Activities:  We have compiled a high-resolution chronology of oysters and clams from the past 5000 years.

  Significant Results: Thompson et al. (2024) found that Native peoples lived within a fluctuating coastal environment, and that the growth and decline of Native American villages were associated with rising and lowering sea level.

• 1B.2 - Evaluate how human activity relates to marsh inundation patterns

  Activities: We continued monitoring flooding of upland, populated areas on Sapelo Island that occurs via legacy infrastructure (drainage canals), and are building a community advisory board to partner with us on upcoming projects.

  Significant Results: Data from monitoring wells in the Hogg Hummock community suggest that the ditch network is increasing community flood risk.

• 1B.3 - Track shoreline armoring

  Activities: We collected new aerial imagery in 2024 which will allow us to update our assessment of shoreline armoring.

  Significant Results: Coleman et al. (2024) found that the majority of new shoreline modifications occurred adjacent to existing structures, and used our data to predict future increases in these structures (Fig. 4).

Fig. 4. a) locations of shoreline modification in a given year) b) % length of the GA coast predicted to be composed of modified shoreline segments. Source: Coleman et al. 2024.

Area 1 Publications from GCE-IV

Robinson, M., Alexander, C.R. Jr. and Venherm, C. 2022. Shallow Water Estuarine Mapping in High-Tide-Range Environments: A Case Study from Georgia, USA. Special Issue: Shallow Water Mapping. Estuaries and Coasts. 45:980-999. (DOI: https://doi.org/10.1007/s12237-021-01032-y)

Hardy, D. and Heynen, N. 2021. "I am Sapelo": Racialized Uneven Development and Land Politics within the Gullah/Geechee Corridor. Environment and Planning E: Nature and Space. 5(1):401-425. (DOI: 10.1177/2514848620987366)

Ritchison, B.T., Thompson, V.D., Lulewicz, I.H., Tucker, B. and Turck, J.A. 2021. Climate Change, Resilience, and the Fisher-Hunter-Gatherers of Late Holocene Georgia Coast. Quaternary International. (DOI: 10.1016/j.quaint.2020.08.030)

Burns, C., Alber, M. and Alexander, C.R. Jr. 2020. Historical Changes in the Vegetated Area of Salt Marshes. Estuaries and Coasts. (DOI: https://doi.org/10.1007/s12237-020-00781-6)

Crotty, S.M., Ortals, C., Pettengill, T.M., Shi, L., Olabarrieta, M., Joyce, M.A., Altieri, A.H., Morrison, E., Bianchi, T.S., Craft, C.B., Bertness, M.D. and Angelini, C. 2020. Sea-level rise and the emergence of a keystone grazer alter the geomorphic evolution and ecology of southeast US salt marshes. PNAS. 117:17891-17902. (DOI: https://doi.org/10.1073/pnas.1917869117)

Heynen, N. 2020. A plantation can be a commons: Re-Earthing Sapelo Island through Abolition Ecology. Antipode. 0(0):20. (DOI: 10.1111/anti.12631)

Thompson, V.D., Rick, T., Garland, C.J., Thomas, D.H., Smith, K.Y., Bergh, S., Sanger, M., Tucker, B., Lulewicz, I.H., Semon, A.M., Schalles, J.F., Hladik, C.M., Alexander, C.R. Jr. and Ritchison, B.T. 2020. Ecosystem stability and Native American oyster harvesting along the Atlantic Coast of the United States. Science Advances. 6. (DOI: 10.1126/sciadv.aba9652)

Letourneau, M.L. and Medeiros, P.M. 2019. Dissolved organic matter composition in a marsh-dominated estuary: Response to seasonal forcing and to the passage of a hurricane. Journal of Geophysical Research: Biogeosciences. 124:1545-1559. (DOI: 10.1029/2018JG004982)

Napora, K., Cherkinsky, A., Speakman, R.J., Thompson, V.D., Horan, R. and Jacobs, C. 2019. Radiocarbon Pretreatment Comparisons of Bald Cypress (Taxodium distichum) Wood Samples from a Massive Buried Deposit on the Georgia Coast, USA. Radiocarbon. 61:1755-1763.

Turck, J.A. and Thompson, V.D. 2019. Human-Environmental Dynamics of the Georgia Coast. In: Reeder-Myers, L., Turck, J. and Rick, T. (editors). The Archaeology of Human-Environmental Dynamics on the North American Atlantic Coast. University Press of Florida, Gainesville, GL.

Napora, K. 2021. Refining cultural and environmental temporalities at the late Archaic-early woodland transition along the Georgia coast, UGA. Ph.D. Dissertation. University of Georgia, Athens, GA. 211 pages.

Bailey, M. and Heynen, N. 2020. Sweet (and sticky) redemption. In: Scalawag Magazine.

Area 1 Publications from GCE-III

Journal Articles

Narron, C., O'Connell, J.L., Mishra, D., Cotten, D.L., Hawman, P. and Mao, L. 2022. Flooding in Landsat across tidal systems (FLATS): An index for intermittent tidal filtering and frequency detection in salt marsh environments. Ecological Indicators. 141:109045. (DOI: 10.1016/j.ecolind.2022.109045)

Nahrawi, H.B., Leclerc, M.Y., Pennings, S.C., Zhang, G., Singh, N. and Pahari, R. 2020. Impact of tidal inundation on the net ecosystem exchange in daytime conditions in a salt marsh. Agricultural and Forest Meteorology. 294:108133. (DOI: https://doi.org/10.1016/j.agrformet.2020.108133)

Dugan, J., Emery, K., Alber, M., Alexander, C.R. Jr., Byers, J., Gehman, A., McLenaghan, N.A. and Sojka, S. 2018. Generalizing Ecological Effects of Shoreline Armoring Across Soft Sediment Environments. Estuaries and Coasts. 41(1):180-196. (DOI: 10.1007/s12237-017-0254-x)

Gehman, A., McLenaghan, N.A., Byers, J., Alexander, C.R. Jr., Pennings, S.C. and Alber, M. 2018. Effects of small-scale armoring and residential development on the salt marsh-upland ecotone. Estuaries and Coasts. 41(1):54-67. (DOI: 10.1007/s12237-017-0300-8)

O'Connell, J. and Alber, M. 2016. A smart classifier for extracting environmental data from digital image time-series: Applications for PhenoCam data in a tidal salt marsh. Environmental Modelling & Software. 84:134-139. (DOI: 10.1016/j.envsoft.2016.06.025)

Sheldon, J.E. and Alber, M. 2006. The calculation of estuarine turnover times using freshwater fraction and tidal prism models: a critical evaluation. Estuaries and Coasts. 29(1):133-146.

Sheldon, J.E. and Alber, M. 2002. A comparison of residence time calculations using simple compartment models of the Altamaha River estuary, Georgia. Estuaries. 25(6B):1304-1317.

Conference Papers (Peer Reviewed)

Sheldon, J.E. and Alber, M. 2005. Comparing Transport Times Through Salinity Zones in the Ogeechee and Altamaha River Estuaries Using SqueezeBox. In: Hatcher, K.J. (editor). Proceedings of the 2005 Georgia Water Resources Conference. Institute of Ecology, University of Georgia, Athens, Georgia.

Sheldon, J.E. and Alber, M. 2003. Simulating material movement through the lower Altamaha River Estuary using a 1-D box model. Hatcher, K.J. (editor). Proceedings of the 2003 Georgia Water Resources Conference. Institute of Ecology, University of Georgia, Athens, Georgia.

Blanton, J.O., Alber, M. and Sheldon, J.E. 2001. Salinity response of the Satilla River Estuary to seasonal changes in freshwater discharge. Pages 619-622 in: Hatcher, K.J. (editor). Proceedings of the 2001 Georgia Water Resources Conference. Institute of Ecology, University of Georgia, Athens, Georgia.

Conference Posters and Presentations

Dugan, J., Alber, M., Alexander, C.R. Jr., Byers, J., Emery, K., Gehman, A., Lawson, S. and McLenaghan, N.A. 2015. Poster: A conceptual model for predicting the ecological effects of coastal armoring in soft-sediment environments. Coastal and Estuarine Research Federation Biennial Meeting, August 30 - September 2, 2015, Estes Park, CO.

Dugan, J., Alber, M., Alexander, C.R. Jr., Byers, J., Emery, K., Gehman, A., Lawson, S. and McLenaghan, N.A. 2015. Poster: A conceptual model for predicting the ecological effects of coastal armoring in soft-sediment environments. Coastal and Estuarine Research Federation Biennial Meeting, November 8-12, 2015, Portland, OR.

Gehman, A., McLenaghan, N.A., Byers, J., Alexander, C.R. Jr., Pennings, S.C. and Alber, M. 2015. Poster: Effects of development and shoreline armoring on the high marsh ecosystem. Benthic Society Ecology Meeting 2015, March 4-7, 2015, Quebec City, CN.

Sheldon, J.E. and Burd, A.B. 2009. Presentation: An In-depth Look at Alternating Effects of Climate Signals on Freshwater Delivery to Coastal Georgia, U.S.A. Hydrologic Prediction in Estuaries and Coastal Ecosystems. CERF 2009: Estuaries and Coasts in a Changing World, November 1-5, 2009, Portland, OR.

Sheldon, J.E. and Burd, A.B. 2007. Poster: Detecting climate signals in river discharge and precipitation data for the central Georgia coast. 2007 AERS/SEERS Meeting, March 15-17, 2007, Pine Knoll Shores, NC.

Alber, M. and Sheldon, J.E. 2006. Calculating estuary turnover times during non-steady-state conditions using freshwater fraction techniques. Southeastern Estuarine Research Society meeting, Ponte Vedra Beach, Florida.

Alber, M. and Sheldon, J.E. 2006. Presentation: Simple tools for assessing coastal systems: can we get there from here? Coastal Observing Systems Workshop, LTER All Scientists Meeting, September 20-24, 2006, Estes Park Colorado.

Sheldon, J.E. and Alber, M. 2005. Poster: New and improved: Modeling mixing time scales in the Altamaha River estuary. GCE-LTER 2005 Annual Meeting. GCE-LTER, Feb. 11-12, 2005, Athens, Georgia.

Sheldon, J.E. and Alber, M. 2005. Presentation: Beyond whole-estuary flushing times: Using transport times through salinity zones to explain chlorophyll patterns in the Altamaha River estuary (Georgia, USA). Estuarine Interactions: biological-physical feedbacks and adaptations. 2005 Estuarine Research Federation Meeting. October 16-20, 2005, Norfolk, Virginia.

Sheldon, J.E. and Alber, M. 2004. Presentation: SqueezeBox: Flow-scaled 1-D box models for estuary residence time estimates. NOS Workshop on Residence/Flushing Times in Bays and Estuaries. National Oceanic and Atmospheric Administration, June 8-9, 2004, Silver Spring, Maryland.

Sheldon, J.E. and Alber, M. 2004. Presentation: SqueezeBox: Flow-scaled 1-D box models for estuary residence time estimates. Spring 2004 meeting. Southeastern Estuarine Research Society (SEERS), October 14-16, 2004, Wilmington, North Carolina.

Sheldon, J.E. and Alber, M. 2003. Poster: Modeling mixing time scales and transport of dissolved substances in the Altamaha River estuary. 2003 LTER All Scientist's Meeting, "Embarking on a Decade of Synthesis". LTER, Sept. 18-21, 2003, Seattle, Washington.

Sheldon, J.E. and Alber, M. 2003. Presentation: The equivalence of estuarine turnover times calculated using fraction of freshwater and tidal prism models. 2003 Estuarine Research Federation meeting, Sept. 14-18, 2003, Seattle, WA.

Sheldon, J.E. and Alber, M. 2001. Poster: Any way you slice it: A comparison of residence time calculations using simple compartment models of the Altamaha River estuary. ERF 2001: An Estuarine Odyssey (16th Biennial Conference of the Estuarine Research Federation). Freshwater Inflow: Science, Policy and Management. Estuarine Research Federation, Nov. 4-8, 2001, St. Pete Beach, Florida.

Alber, M. and Sheldon, J.E. 2000. Presentation: Residence times in the Altamaha River Estuary: a progress report. Southeastern Estuarine Research Society Meeting. Southeastern Estuarine Research Society, Oct 01, 2000, Tampa, Florida.

Newsletter and Newspaper Articles

Sheldon, W.M. Jr. 2006. Mining and Integrating Data from ClimDB and USGS using the GCE Data Toolbox. In: DataBits: An electronic newsletter for Information Managers: Spring 2006. Long Term Ecological Research Network, Albuquerque, NM.