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). The GCE9 sonde remains offline pending replacement of a Coast Guard piling.

  Significant Results:  We are using the relationships between average and variance of salinity measured by the sondes to guide site selection for the GCE renewal proposal (Fig. 2).

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.

Fig. 2. Analysis of long-term salinity data from GCE sondes. Points represent the annual average (x-axis) and variance (y-axis) of daily maximum salinities measured by sondes for each year at a given site. Source: M. Alber.

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

  Activities: This activity was paused due to difficulty in maintaining the HADCP in strong currents with heavy biofouling.

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

  Activities:  We use Landsat data to characterized DOC variability in the estuary (Fig. 3).

  Significant Results:  Reimer et al. (2023) found a strong relationship between terrestrially derived carbon and acidification in marshes, but little evidence that it influences acidification offshore (Fig. 4).

Fig. 3. Average DOC concentration (uM) in the GCE domain from 2013-2023, estimated based on Landsat imagery. Source: P. Medeiros and R. Castelao.

Fig. 4. Terrestrial index versus (A) DIC, (B) TA, and (C) pH in surface samples in the coastal zone. Higher terrestrial index indicates greater contribution from terrestrially derived organic compounds. Symbols represent different months. Source: Reimer et al. 2023.

• 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 monitor SETs at each site (Table 1, Fig. 1). This year we installed new rod SETs at 5 sites. In the tidal forest we measure plants, litterfall, and sediment elevation. We monitor vegetation mixtures on Sapelo Island and along the salinity gradient of the Altamaha estuary (Obj 4B1).

  Significant Results:  Smith et al. (subm.) synthesized 22 years of annual monitoring data and found that both drought and snails suppressed Spartina biomass, although snails only had an effect when they were present at high densities (Fig. 5). We also used monitoring data to assess marsh response to hurricanes (see Key Accomplishments).

Fig. 5. Model predictions for the effects of snail density and average PDSI on aboveground S. alterniflora biomass for: the complete 22-year dataset (a), only plots that had = 80 snails m-2 (b), and only plots that had > 80 snails m-2 (c). Drought effects are identified in all three analyses, but snail effects are only identified in the third analysis because plant biomass is positively correlated with snail density when snails are rare. Source: Smith et al., sub

• 2A.5 - Characterize groundwater flow

  Activities: We maintain a series of groundwater wells in the high marsh at Marsh Landing (Fig. 6) and installed an inland well this year to capture upland conditions. We monitor pond water levels to evaluate groundwater patterns across Sapelo Island.

  Significant Results:  Groundwater simulations revealed seasonal declines in salinity in the high marsh, which was disrupted during drought and coincided with a shift in the plant community.

Fig. 6. Locations of groundwater wells and soil cores along the high marsh transect at the Marsh Landing site. Source: A. Wilson.

B) Remote Sensing

• 2B.1 - Continue Phenocam observations

  Activities:  We maintain the “GCESapelo” and “GCEJuncus" Phenocams, both of which are in the National Phenocam network, and installed a temperature and water level logger at the GCEJuncus site.

  Significant Results:  Our flood detection algorithm, which leveraged the GCESapelo Phenocam data, can now be used with Landsat 5, 7, 8 and 9, allowing us to assess flooding over 40 years. We have also reparametrized the model to use Sentinel-2 satellite imagery and to detect flooding in Juncus marshes.

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

  Activities:  High-resolution (0.15 cm) imagery of the Georgia coast was used with field data collected in 2022 to create a random forest classification of tidal marsh vegetation.

  Significant Results:  Currin (2023) classified orthoimagery of the Georgia coast into 12 different vegetation classes with an overall accuracy of 86.3% at a 1-m spatial resolution (Fig. 7).

Fig. 7. Random forest classification of the GCE domain into 12 vegetation classes using 1-m aerial orthoimagery (overall accuracy: 86.3%). Source: Currin 2023.

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

  Activities:  We use our UAV to conduct monthly flyovers of selected marshes to track disturbances over time. We conduct an annual survey of high marsh plant communities. This year we used a lidar drone to collect high resolution elevation data of Dean Creek and collected clip-plot data to develop an algorithm to relate Juncus biomass to drone imagery.

  Significant Results:  Lynn et al. (2023) and Yang et al. (subm.) used repeat drone imagery to characterize wrack and slump block disturbances (Obj 4A).

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

  Activities:  We are using Landsat, Sentinel-2, and PlanetScope satellite platforms to evaluate classification of marsh vegetation (Obj 2B2), tidal fresh forest (Obj 4B1), estimation of Spartina biomass (Obj 4B2 & 4BC), tidal flooding (Obj 2B2), DOC (Obj 2A3), and soil temperature (Obj 4C2). We also acquired >100 new CNES VENus cloud-free satellite images of the GCE domain.

  Significant Results:  Currin (2023) successfully used PlanetScope imagery to classify marsh vegetation.

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.