Area 1: External Drivers of Change

Objectives Progress Report Publications Show All  

External Drivers of Change

We track long-term changes in external drivers such as climate change, sea level rise, and human alterations of the landscape and to statistically characterize these external drivers 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, domain perturbations, and ecosystem responses.

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 - Measure exchange between the Duplin R and Doboy Sound

B) Human Activities

  • 1B.1 - Evaluate how human activity relates to impervious surface and shoreline structures
  • 1B.2 - Assess human modifications of oyster reefs

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

2019 Activities Figure 1

Fig. 1. Locations of observing stations used for boundary conditions (ML is Marsh Landing; UGAMI is UGA Marine Institute).

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

      Activities:  A series of meteorological stations are used to characterize the GCE domain (Fig. 1). The station at Marsh Landing serves as our primary station for ClimDB. We now also generate 15-minute summaries from our eddy covariance flux tower. Referenced sea level data, offshore wind forcing, and river discharge are also tracked.

      Results:  An analysis of sea level rise rates at NOAA buoys near GCE shows that rates were 2x higher from 1999-2019 than from 1940-1999. A manuscript with these observations is currently under review at PNAS (Crotty et al. subm.).

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

      Activities:  The GCE eddy covariance flux tower on the Duplin River measures CO2, H2O, weather conditions, radiation, water levels, and soil temperature. This past year we registered the tower with the Ameriflux network, installed additional radiation sensors and a second soil temperature gauge, standardized the processing of raw eddy covariance fluxes, and developed methodologies for integrating fluxes and exploring uncertainty in the data.

      Results:  Eddy covariance data collected in 2019 have been processed to the levels of 30-minute net ecosystem exchange (NEE), gap-filled, and partitioned into gross primary production and ecosystem respiration. Feagin et al. (in press) included GCE data in a larger effort that used eddy covariance data to create a MODIS-based blue carbon model to estimate GPP of tidal wetlands.

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

      Activities:  We collect monthly samples of river water entering via the Altamaha River for analysis of dissolved inorganic nutrients, DIC, alkalinity, and pH. We also completed a directed study to evaluate the DOM signatures of water entering the system.

      Results:  Letourneau and Medeiros (2019) found increased biodegradation of DOC when the discharge of the Altamaha River was high, and the DOM composition was more terrigenous in character. This paper, in JGR Biogeosciences, was featured as an EOS research spotlight.

  • 1A.4 - Measure exchange between the Duplin R and Doboy Sound

      Activities:  We run a horizontal looking acoustic Doppler current profiler (HADCP) to measure along-channel current flow at the mouth of the Duplin River.

      Results:  Tidally averaged currents measured by the HADCP show a residual along-channel flow that is predominately outwards (Fig.2). This may correspond to connectivity with surrounding waters of Sapelo Sound to the north and Teakettle Creek to the west during periods of high inundation (spring high tides, sea surface heights > 0).

2019 Activities Figure 2

Fig. 2. a) Channel velocity measured by the horizontal looking acoustic Doppler current profiler (HADCP) moored at Marsh Landing showing tidal variations with strong spring/neap modulations. b) Tidally averaged currents show a residual along channel flow that is predominately outwards with an average flow of -2 cm/s. c) The sea surface height measured at Hudson Creek, Meridian shows that significant inundation of up to 0.5 m occurred starting in August 2019 and resulted in greater outflow speeds. d) Winds at the Gray’s Reef Buoy NDBC41008. Hurricane Dorian passed Georgia Sept 4, 2019 (blue arrow) with strong southerly winds, which caused the mean SSH to go above 0.6 m. Source: Daniela Di Iorio.

B) Human Activities

  • 1B.1 - Evaluate how human activity relates to impervious surface and shoreline structures

      Activities:  We are developing a detailed land use history of the Hog Hammock Community on Sapelo Island. We have also deployed data loggers in drainage ditches to evaluate salt water incursion into populated areas.

      Results:  Turck et. al. (in review) and Thompson (2019) have documented resilience and possible sustainable management practices among Native American communities.

  • 1B.2 - Assess human modifications of oyster reefs

      Activities:  We measured 37,805 oysters from Late Archaic and Mississippian period sites and are currently compiling radiocarbon dates and climate data for these samples. We have also mapped all oyster reefs in the GCE domain.

      Results:  Thompson et al. (in review) demonstrated significant spatio-temporal variability in oyster size, with larger oysters in the lowest, and hence earliest, deposits at some sites and a non-random pattern that often clustered by island, which they ascribe to processes related to territoriality, fishing rights, and coastal environmental variability.

Area 1 Publications from GCE-IV

Ritchison, B.T., Thompson, V.D., Lulewicz, I.H., Tucker, B. and Turck, J.A. (in review). Climate Change, Resilience, and the Fisher-Hunter-Gatherers of Late Holocene Georgia Coast. Quaternary International.

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)

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.

Area 1 Publications from GCE-III

Journal Articles

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.

 
LTER
NSF

This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959 and OCE-1237140. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.