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 and Accomplishments:  The GCE field crew was able to continue servicing our hydrographic instruments and collecting nutrient samples throughout the COVID lockdown, and so our data streams were uninterrupted. We observed increased salinity in the tidal forest (GCE11) in conjunction with Hurricane Irma, and a more recent increase that corresponded to a combination of high sea surface heights and low river flow. In contrast, we observed low salinities throughout the GCE domain in 2020 in response to high river discharge, resulting from high rainfall in 2020.

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

  Activities and Accomplishments: We installed a horizontal looking acoustic Doppler current profiler (HADCP) to measure along-channel current flow at the mouth of the Duplin River. Data from 2019-2020 has been processed for quality control and used to estimate hourly averaged along-channel velocity (Fig. 2). The instrument has been removed due to dock renovations, and we are evaluating where and how it can be redeployed.

Fig. 2. a) Channel velocity measured by the horizontal looking acoustic Doppler current profiler 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) Sea surface height measured at Hudson Creek, Meridian shows that significant inundation of up to 0.5 m started in August 2019, resulting 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: D. Di Iorio

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

  Activities and Accomplishments:  We have taken samples of opportunity to evaluate DOM composition in association with hurricanes that affected the GA coast in recent years. Letourneau and Medeiros (2019) observed large increase in DOC concentration and in the terrigenous signature of the DOM (analyzed by FT-ICR MS) after Hurricane Matthew. One month after the passage of Hurricane Irma, Letourneau et al. (in press) observed a 27% increase in DOC content and enhanced rates of DOC biodegradation (Fig. 3), demonstrating that hurricanes can have a large impact on organic matter composition and cycling in coastal systems.

Fig. 3. Spatio-temporal pattern of DOC consumption across the GCE domain. Percent consumption was highest in October, one month after the passage of Hurricane Irma. Source: Letourneau et al., in press, Limn. & Oceanog

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

  Activities and Accomplishments:  Our annual fall monitoring is also on track and was not interrupted by COVID. We also measured winter soil temperatures (which may be important for S. alterniflora phenology) at each of our core monitoring sites in 2019-2020 to evaluate variation among sites and marsh zones (see key findings). We are also using biomimics to evaluate how the thermal regimes experienced by macrofauna varies as a function of marsh elevation and organism location (e.g., buried in the soil vs. on the soil surface vs. in the plant canopy) (Fig. 4). The long-term plant data were used for two recent analyses: Liu and Pennings (2019) evaluated whether the “self-thinning” law applies to S. alterniflora (see key findings), and Liu and Pennings (2020) evaluated synchrony in plant production across multiple sites and two elevation zones (Fig. 5). They found the highest degree of synchrony of production within a species and within a zone, and no asynchrony that might allow one species to compensate for another during “bad” years.

Fig. 4. Temperature logger records from biomimics of Littoraria deployed at different heights above the soil surface (left) and mussels of different sizes (right). Source: R. Atkins and C. Osenberg

Fig. 5. Correlations between annual (2000-2017) fall biomass of Spartina alterniflora (SA), Juncus roemerianus (JR) and Zizaniopsis miliacea (ZM) at GCE monitoring locations. (a) within individual species or between species pairs, (b) between the creekbank and mid-marsh habitats, (c) between creekbank sites and (d) between mid-marsh sites. Error bars indicate + 1standard error. Source: Liu and Pennings, in press, Ecology

• 2A.5 - Characterize groundwater flow

  Activities and Accomplishments: We monitor groundwater levels and salinities at a series of wells associated with the high marsh manipulation. In 2019 we installed additional wells across the upland marsh transition at Marsh Landing where we have long-term observations of vegetation shifts. We are currently using this data to calibrate a groundwater model to hindcast hydrologic conditions coincident with changes in plant zonation (Fig. 6).

Fig. 6. Groundwater wells were installed in Feb. 2019 in an area of vegetation transition at Marsh Landing. (a) stratigraphy, (b) simulated groundwater flow patterns at high tide, showing lateral flow from the upland toward the marsh in the sand layers and upward flow through the mud. Source: A. Wilson and S. Sanders

B) Remote Sensing

• 2B.1 - Continue Phenocam observations

  Activities and Accomplishments:  The GCESapelo Phenocam, which is focused on a Spartina marsh, contributes data (a 4-band digital image) to the National Phenocam Network every 30 min. We are now in the process of setting up a second Phenocam with both S. alterniflora and Juncus roemerianus in its field of view. O’Connell et al. (2020) used the first 4 years of Phenocam imagery to develop a spring warm-up model for S. alterniflora. The model was then used to hindcast an almost 11-day advance in green-up onset since 1958 (Fig. 7).

Fig. 7. Long-term record of change in (top) mean winter soil temperatures and (bottom) green-up day of year (doy) predicted from the climate record in panel A through the use of the spring warming model. Modern green-up dates from the PhenoCam (mean of all zones) also are superimposed and RMSE is provided for the difference between modern and long-term estimates for overlapping years. Solid lines show best fit (P < 0.001); dashed lines represent the 95% CI. Source: O’Connell et al. 2020, Ecosystems

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

  Activities and Accomplishments:  We collect periodic high-resolution aerial photographs (georeferenced, 15 cm resolution, in 4-band color/NIR) of the Altamaha Sound and Duplin River that we use to evaluate shifts in creek morphology, marsh area, shoreline armoring, and marsh habitats over time. Aerial photography was taken in 2017 and 2018 with funds from a RAPID grant related to Hurricane Irma, and we are planning another flyover this coming year.

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

  Activities and Accomplishments:  We acquired a Matrice 200 drone with a Micasense RedEdge Altum camera and obtained appropriate permits and FAA licenses. We are using the drone to conduct monthly flyovers of selected marshes to track disturbances over time (see Area 4). We have also begun annual drone flights of three areas to evaluate transitional areas associated with vegetation shifts in the high marsh and are in the process of selecting areas where we will use regular drone flights to evaluate creek disturbance.

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

  Activities and Accomplishments:  We are explicitly using satellite imagery to evaluate habitat transitions and disturbance in Area 4. However, we also make use of satellite-based remote sensing to scale up our observations for many aspects of the project. O’Connell et al. (2020) used Phenocam imagery to groundtruth a model for MODIS that detects marsh flooding and developed an algorithm to filter these observations when assessing plant dynamics. Narron et al. (in prep) have developed a similar model for Landsat8, which shows how flooding patterns vary over both space and time at a much higher resolution than MODIS (Fig. 8). O’Donnell and Schalles used Landsat5 data to evaluate productivity trends over 28 years (ground-truthed with GCE core monitoring data), and this work is now being extended to Landsat8 and Sentinel 2. We are also investigating whether we can scale up our estimates of S. alterniflora biomass from drone imagery to MODIS observations, which have a coarser pixel size but much more extensive temporal and spatial coverage (Fig. 9).

Fig. 8. Spatial (left) and temporal (right) variation in salt marsh flooding frequency at the GCE flux tower based on Landsat 8 satellite imagery. Image on the left shows % time each pixel was flooded over period 2013-2020 (see scale bar); inset shows image from GCE Phenocam, with field of view shown in purple. Panels on right show annual patterns of % flooding. Source: Narron et al., in prep

Fig. 9. Comparison of biomass estimates from drone (left) and Sentinel 2 satellite (right) imagery, both scaled to 10 m. Source: J. Schalles

Area 2 Publications from GCE-IV

Letourneau, M.L., Schaefer, S.C., Chen, H., McKenna, A., Alber, M. and Medeiros, P.M. (in press). Spatio-temporal changes in dissolved organic matter composition along the salinity gradient of an estuarine complex in the southeastern U.S. Limnology and Oceanography.

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)

Area 2 Publications from GCE-III

Journal Articles

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)

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.

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.