Area 2: Long-term Patterns of Estuary and Intertidal Variation

Long-term Patterns of Estuary and Intertidal Variation

We track the temporal and spatial variability of the habitats within the GCE study area through a combination of field monitoring and remote sensing in order to evaluate ecosystem responses to long-term change and domain perturbations. The field monitoring program includes regular sampling in both the water column and intertidal habitat at a series of 11 core long-term monitoring sites that range across the domain (Fig. 1).

Research Objectives

A) Field Monitoring

• 2A.1 - Continue the GCE core monitoring program in the water column
• 2A.2 - Measure water exchange between the Duplin River and Doboy Sound
• 2A.3 - Evaluate patterns of dissolved organic matter in the water column
• 2A.4 - Continue the core monitoring program in the marsh and tidal fresh forests
• 2A.5 - Characterize groundwater flow

B) Remote Sensing

• 2B.1 - Continue Phenocam observations
• 2B.2 - Continue regular aerial photographs of the GCE domain
• 2B.3 - Establish drone surveys of selected sites
• 2B.4 - Make use of satellite imagery to scale up observations

Current Progress Report

Below is an update for each of the Area 2 objectives as reported in the most recent annual report. For a list of all reports click here (Annual Reports).

A) Field Monitoring

• 2A.1 - Continue the GCE core monitoring program in the water column

  Activities:  We maintain sondes at 10 sites and collect CTD profiles and sample water quality at 12 sites. (Table 1, Fig. 1). We had two sondes offline due to lost pilings. GCE6 was replaced in Nov. and the coast guard anticipates installing a new piling at GCE9 in 2025.

  Significant Results:  We are preparing to transition our nutrient, DIC, and DOC sample analyses to the Spivak lab. Methods are largely in place and analyses will begin in early 2025.

Fig. 1. GCE domain showing core monitoring stations.

Table 1. Monitoring program for GCE-IV. LTER core areas are 1: primary production, 2: populations, 3: organic matter cycling, 4: inorganic nutrients, 5: disturbance.

• 2A.2 - Measure water exchange between the Duplin River and Doboy Sound

  Activities: This activity was paused in 2022 due to difficulty in maintaining the horizontal acoustic profiler in strong currents with heavy biofouling.

• 2A.3 - Evaluate patterns of dissolved organic matter in the water column

  Activities:  We used field data to develop an algorithm that can estimate dissolved organic carbon in the GCE domain from satellite (Landsat) imagery.

  Significant Results:  Castalao and Medeiros (2024) identified a large input of DOC in association with Hurricane Irma (Fig. 2)

Fig. 2. Long-term (2013-2023) a) average and b) standard deviation of DOC concentration (µmol L^-1) in the GCE domain estimated from Landsat observations. Source: Castelao and Medeiros 2024.

• 2A.4 - Continue the core monitoring program in the marsh and tidal fresh forests

  Activities:  We measure plants, invertebrates and soils in 2 zones at each of our 10 marsh sites, and also monitor SETs at each site (Table 1, Fig. 3). This past year we installed new rod SETs at 5 sites. In the tidal forest we measure plants, litterfall, and sediment elevation. We also monitor vegetation mixtures on Sapelo Island and along the salinity gradient of the Altamaha estuary (Obj 4B1).

  Significant Results:  Our long-term observations of plants and invertebrates indicate that at some sites Spartina plants are getting taller while at the same time snail densities are decreasing. We are following up on these observations, which may be a response to increased inundation due to sea level rise.

• 2A.5 - Characterize groundwater flow

  Activities: We maintain a series of groundwater wells in the high marsh at Marsh Landing as well as in association with the high marsh manipulation (Obj. 3A3). We also monitor pond water levels to evaluate groundwater patterns across Sapelo Island.

  Significant Results:  Our groundwater wells show evidence for winter expansion of the freshwater lens, which is disrupted during drought years. This may increase porewater salinity in the high marsh root zone during spring growth periods.

B) Remote Sensing

• 2B.1 - Continue Phenocam observations

  Activities:  We maintain the “GCESapelo” and “GCEJuncus" Phenocams (Fig. 3), both of which are part of the National Phenocam network, and continue collection of ancillary biophysical data including whole plant biomass.

Fig. 3. Field of view of the GCEJuncus PhenoCam on 8/18/2024, showing the marsh exposed @17:39h (top) and flooded @19:09h (bottom).

• 2B.2 - Continue regular aerial photographs of the GCE domain

  Activities:  Updated high-resolution (0.15 cm) imagery of the Georgia coast was collected in February 2024.

  Significant Results:  Currin (2023) developed a 1-m classified raster image of wetland plant communities from the 2018 orthoimagery and we are now using the same approach to classify previous imagery (2013) to assess changes in habitat distribution over time.

• 2B.3 - Establish drone surveys of selected sites

  Activities:  We use our UAV to conduct monthly flyovers of selected marshes to track disturbance (Obj 4A), as well as an annual survey of high marsh plant communities. We purchased a new UAV this past year (TerraView RangePro X8) as the previous one had failed.

  Significant Results:  We are producing estimates of Spartina biomass based on an algorithm developed for the high-resolution drone imagery (See Key Accomplishments).

• 2B.4 - Make use of satellite imagery to scale up observations

  Activities:  We continue to use multiple satellite platforms to evaluate various aspects of coastal ecosystems in the GCE domain and beyond, including estimation of DOC concentration (Obj 2A3), suspended sediment (4B3), tidal flooding (2B1), and marsh productivity (Obj 4B2).

  Significant Results: Our flood detection algorithm, which leveraged the GCESapelo Phenocam data (Obj. 2B1), has been cross-calibrated with Landsat 5, 7, 8, and 9, providing 40 years of data for use in long-term marsh inundation analysis (Fig. 4; Julien et al., subm.).

Fig. 4. Change in flooding probability on Sapelo Island from 1984-2023. Green indicates salt marsh areas experiencing an increase in flooding, while brown indicates a decrease. Source: Julien, subm.

Area 2 Publications from GCE-IV

Costomiris, G., Hladik, C.M. and Craft, C.B. 2024. Multivariate Analysis of the Community Composition of Tidal Freshwater Forests on the Altamaha River, Georgia. Special Issue: Coastal Forest Dynamics and Coastline Erosion—Series II. Forests. 15(1). (DOI: 10.3390/f15010200)

Yang, Z., Alexander, C.R. Jr. and Alber, M. 2024. The dynamics of marsh-channel slump blocks: an observational study using repeated drone imagery. Biogeosciences. 21:1757-1772. (DOI: 10.5194/bg-21-1757-2024)

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)

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)

O'Connell, J.L., Alber, M. and Pennings, S.C. 2020. Microspatial differences in soil temperature cause phenology change on par with long-term climate warming in salt marshes. Ecosystems. 23:498–510. (DOI: https://doi.org/10.1007/s10021-019-00418-1)

Alber, M. and O'Connell, J.L. 2019. Elevation drives gradients in surface soil temperature within salt marshes. Geophysical Research Letters. 46:5313-5322. (DOI: https://doi.org/10.1029/2019GL082374)

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)

Liu, W. and Pennings, S.C. 2019. Self-thinning and size-dependent flowering of the grass Spartina alterniflora across space and time. Functional Ecology. 33:1830-1841. (DOI: 10.1111/1365-2435.13384)

Miklesh, D.M. and Meile, C. 2018. Controls on porewater salinity in a Southeastern salt marsh. PeerJ. 6:e5911. (DOI: 10.7717/peerj.5911)

Meile, C. 2023. Presentation: Carbon fluxes and environmental drivers in an intertidal marsh. , April 27, Chungham National University, Dajeon, South Korea.

Schalles, J.F., Hladik, C.M., O'Donnell, J., Miklesh, D.M., Pudil, T. and Nealy, N. 2021. Presentation: Satellite and drone remote sensing to study decadal scale and high resolution spatial-temporal patterns and declines of Spartina alterniflora above-ground biomass in Georgia, USA salt marshes. Session 2. 1st International Symposium on Coastal Ecosystems and Global Change (CoEco1), April 18, 2021, Xiamen University, Xiamen, China.

Schalles, J.F., Hladik, C.M., O'Donnell, J., Miklesh, D.M., Pudil, T., Nealy, N. and Currin, H. 2021. Presentation: Serious multidecadal declines in aboveground biomass of the keystone salt marsh species, Spartina alterniflora, are related to climate change in coastal Georgia, USA. Wetlandscapes: Understanding the Large-scale Wetland Functions in the Landscape Symposium. 11th INTECOL International Wetlands Conference, October 14, 2021, Christchurch, New Zealand (virtual, prerecorded).

O'Connell, J.L., Alber, M., Mishra, D. and Byrd, K. 2020. Presentation: Structural heterogeneity in above vs belowground biomass pools differ for Spartina alterniflora monocultures, with consequences for forecasting ecosystem resiliency. Ecological Society of America.

Area 2 Publications from GCE-III

Journal Articles

Lehmann, M.K., Gurlin, D., Pahlevan, N., Binding, C., Fichot, C., Gitelson, A., Mishra, D., Schalles, J.F., Simis, S., Smith, B. and Spyrakos, E. 2023. GLORIA - A globally representative hyperspectral in situ dataset for optical sensing of water quality. Nature - Scientific Data. 10:1130958, 6 April 2023(100 (2023)):13 p. (DOI: doi.org/10.1038/s41597-023-01973-y)

Liu, W. and Pennings, S.C. 2021. Variation in synchrony of production among species, sites and intertidal zones in coastal marshes. Ecology. (DOI: 10.1002/ECY.3278)

Schaeffer, B., Neely, M., Spinosa, A., Serafy, E., Odermatt, D., Weathers, K., Barracchini, T., Bouffard, D., Carvalho, L., Comny, R., De Keukelaere, P., Hunter, P., Jamet, C., Joehnk, K., Johnston, J., Knudby, A., Minaudo, C., Pahlevan, N., Rose, K., Schalles, J.F. and Tzortziou, M. 2021. Integrating inland and coastal water quality data for actionable knowledge. Special Issue: Big Earth Data and Remote Sensing in Coastal Environments. Remote Sensing. 13; 23 July 2021(15):24 p. (DOI: doi.org/10

Schaeffer, B., Neely, M., Spinosa, A., Serafy, E., Odermatt, D., Weathers, K., Barracchini, T., Bouffard, D., Carvalho, L., Comny, R., De Keukelaere, P., Hunter, P., Jamet, C., Joehnk, K., Johnston, J., Knudby, A., Minaudo, C., Pahlevan, N., Rose, K., Schalles, J.F. and Tzortziou, M. 2021. Integrating inland and coastal water quality data for actionable knowledge. Special Issue: Big Earth Data and Remote Sensing in Coastal Environments. Remote Sensing. 13; 23 July 2021(15):24 p. (DOI: doi.org/10

Liu, W. and Pennings, S.C. 2019. Self-thinning and size-dependent flowering of the grass Spartina alterniflora across space and time. Functional Ecology. 33:1830-1841. (DOI: 10.1111/1365-2435.13384)

Peterson, R.N., Meile, C., Peterson, L., Carter, M. and Miklesh, D.M. 2019. Groundwater discharge dynamics into a salt marsh tidal river. Estuarine, Coastal and Shelf Science. 218:324-333. (DOI: 10.1016/j.ecss.2019.01.007)

Damashek, J., Tolar, B., Liu, Q., Okotie-Oyekan, A., Wallsgrove, N.J., Popp, B.N. and Hollibaugh, J.T. 2018. Microbial oxidation of nitrogen supplied as selected organic nitrogen compounds in the South Atlantic Bight. Limnology and Oceanography. 64:982-995. (DOI: 10.1002/lno.11089)

Li, S., Hopkinson, C.S., Schubauer-Berigan, J.P. and Pennings, S.C. 2018. Climate drivers of Zizaniopsis miliacea biomass in a Georgia, U.S.A. tidal fresh marsh. Limnology and Oceanography. 63:2266-2276. (DOI: 10.1002/lno.10937)

Liu, Q., Tolar, B., Ross, M., Cheek, J., Sweeney, C., Wallsgrove, N.J., Popp, B.N. and Hollibaugh, J.T. 2018. Light and temperature control the seasonal distribution of Thaumarchaeota in the South Atlantic Bight. ISME Journal. 12:1473-1485. (DOI: 10.1038/s41396-018-0066-4)

Takagi, K., Hunter, K.S., Cai, W.-J. and Joye, S.B. 2017. Agents of change and temporal nutrient dynamics in the Altamaha River Watershed. Ecosphere. 8(1):33. (DOI: 10.1002/ecs2.1519)

Wang, Y., Castelao, R. and Di Iorio, D. 2017. Salinity Variability and Water Exchange in Interconnected Estuaries. Estuaries and Coasts. (DOI: 10.1007/s12237-016-0195-9)

Whitby, H., Hollibaugh, J.T. and van den Berg, C.M. 2017. Chemical speciation of copper in a salt marsh estuary and bioavailability to Thaumarchaeota. Special Issue: Organic ligands - A key control on trace metal biogeochemistry in the ocean. Frontiers in Marine Sciences. 4. (DOI: 10.3389/fmars.2017.00178)

Caffrey, J.M., Hollibaugh, J.T. and Mortazavi, B. 2016. Living oysters and their shells as sites of nitrification and denitrification. Marine Pollution Bulletin. (DOI: 10.1016/j.marpolbul.2016.08.038.)

Li, S. and Pennings, S.C. 2016. Disturbance in Georgia salt marshes: variation across space and time. Ecosphere. 7(10):e01487. (DOI: 10.1002/ecs2.1487)

Tolar, B., Wallsgrove, N.J., Popp, B.N. and Hollibaugh, J.T. 2016. Oxidation of urea nitrogen in marine nitrifying communities dominated by Thaumarchaeota. Environmental Microbiology. (DOI: 10.1111/1462-2920.13457)

Conference Papers (Peer Reviewed)

Weston, N.B., Hollibaugh, J.T., Sandow, J.T. Jr. and Joye, S.B. 2003. Nutrients and dissolved organic matter in the Altamaha river and loading to the coastal zone. In: Hatcher, K.J. (editor). Proceedings of the 2003 Georgia Water Resources Conference. Institute of Ecology, University of Georgia, Athens, Georgia.

Conference Posters and Presentations

Craft, C.B., Stahl, M. and Widney, S. 2017. Presentation: Tidal freshwater forests: sentinels for climate change. 10th International Workshop on Nutrient Cycling and Retention in Natural and Constructed Wetlands, September 21-24, Trebon, Czech Republic.

Hollibaugh, J.T., Bratcher, A., Cheek, J., Liu, Q., Malagon, E., Popp, B.N., Ross, M., Schaefer, S.C., Sweeney, C., Tolar, B., van den Berg, C.M., Wallsgrove, N.J. and Whitby, H. 2017. Poster: LIGHT AND TEMPERATURE CONTROL THE SEASONAL DISTRIBUTION OF THAUMARCHAEOTA IN THE SOUTH ATLANTIC BIGHT. Fifth International Conference on Nitrification and Related Processes (ICoN5)23-27 July, 2017, 23-27 July, 2017, Vienna, Austria.

Peterson, R.N., Meile, C., Carter, M., Peterson, L., Waldorf, A. and Miklesh, D.M. 2017. Poster: Groundwater inputs to a back-barrier salt marsh tidal river. 2017 Chemical Oceanography Gordon Research Conference, July 2017, Holderness, NH.

Stahl, M., Widney, S. and Craft, C.B. 2017. Presentation: Tidal freshwater forests: a sentinel for climate change. SPEA Ph.D. Students' 17th Annual Conference, February 24, 2017, Bloomington, IN.

Widney, S., Stahl, M. and Craft, C.B. 2017. Presentation: Tidal forests: sentinels for climate change. Society of Wetland Scientists Annual Meeting, June 8, 2017, San Juan, Puerto Rico.

Hollibaugh, J.T., Liu, Q., Ross, M., Cheek, J., Sweeney, C., Tolar, B., Hagan, P., Whitby, H., Bratcher, A., Malagon, E., Lynn-Bell, N., Shalack, J., Reddy, C.M. and Walker, J.T. 2016. Poster: Coupling between Sediment and Water Column Populations of Ammonia Oxidizing Thaumarchaeota in a Salt Marsh Estuary.

Alber, M., Schaefer, S.C., Pomeroy, L.R., Sheldon, J.E. and Joye, S.B. 2008. Presentation: Nitrogen inputs to the Altamaha River estuary (Georgia, USA): a historic analysis. American Society of Limnology and Oceanography, 3/08, Orlando, FL.

Alber, M., Schaefer, S.C., Pomeroy, L.R., Sheldon, J.E. and Joye, S.B. 2008. Presentation: Nitrogen inputs to the Altamaha River estuary (Georgia, USA): a historic analysis. American Society of Limnology and Oceanography, 3/08, Orlando, FL.

Seay, J.E., Bishop, T.D. and Tilburg, C.E. 2006. Poster: Spatial and temporal variations of Porcelain Crab larval abundance in a Georgia Estuary. Southeastern Estuarine Research Society Fall 2006 Meeting, 19 October - 21 October 2006, Savannah, Georgia.

Pennings, S.C. 2005. Presentation: Physical forcing and variation in salt marsh plant productivity at multiple time scales. Ecological Society of America 2005 Meeting - Ecology at multiple scales, August 7-12, 2005, Montreal, Canada.

Shalack, J. and Bishop, T.D. 2004. Poster: Spatial and temporal variability in recruitment of decapod megalopae in the Duplin River, Georgia. Semiannual Meeting of the Southeastern Estuarine Research Society. Invertebrates - Poster Session. Southeastern Estuarine Research Society, 15-17 April 2004, Ft. Pierce, FL.

Bishop, T.D. 2003. Presentation: Invasive biology and status of the green porcelain crab (Petrolisthes armatus) in Georgia waters. South Georgia Invasive Species Workshop, sponsored by The Nature Conservancy and Sapelo Island National Estuarine Research Reserve. October 2003, Brunswick, GA.

Bishop, T.D. and Hurley, D. 2003. Poster: The non-indigenous porcelain crab, Petrolisthes armatus: population trends in the Sapelo Island National Estuarine Research Reserve. 2003 Estuarine Research Federation meeting. September 2003, Seattle, WA.

Bishop, T.D. and Hurley, D. 2003. Poster: The non-indigenous porcelain crab, Petrolisthes armatus: population trends in the Sapelo Island National Estuarine Research Reserve. National Estuarine Research Reserve System / National Estuarine Research Reserve Association Annual Meeting. October 2003, Charleston, S.C.

Bishop, T.D., Hurley, D. and Alber, M. 2003. Presentation: An inventory of the macroinvertebrate fauna of oyster reefs in the Duplin River, Georgia, with emphasis on non-indigenous species occurrence. 2003 Estuarine Research Federation meeting. Sept. 14-18, 2003, Seattle, WA.

Ogburn, M.B., Bishop, T.D. and Alber, M. 2003. Poster: Population dynamics of two salt marsh snails in three Georgia estuaries. Southeastern Estuarine Research Society meeting. March 2003, Atlantic Beach, NC.

Bishop, T.D., Alber, M. and Wiegert, R.G. 2001. Poster: Macrofaunal population shifts and changing coastal salinity regimes. ERF 2001: An Estuarine Odyssey. Estuarine Research Federation, Nov. 4-8, 2001, St. Pete Beach, Florida.

Goodbody, G., Bishop, T.D. and Alber, M. 2001. Presentation: Distribution of snails in the Satilla and Altamaha River Estuaries. Southeastern Estuarine Research Society Meeting. Southeastern Estuarine Research Society, Mar 01, 2001, Charleston, South Carolina.

Pennings, S.C., Bertness, M.D., Donnelly, J.P., Ewanchuk, P.J., Silliman, B.R. and Callaway, R.M. 2001. Presentation: Impacts of global change on coastal salt marshes. Keynote address to the German Limnological Association, September 17-21, 2001, Kiel, Germany.