Area 4: Integration and Scaling Up

Objectives Progress Report Publications Show All  

Integration and Scaling Up

We use a combination of remote sensing, field investigations, and modeling to document and evaluate the consequences of long-term change and disturbance at the landscape scale.

Research Objectives

A) Disturbance-Scape

  • 4A.1 - Assess the effects of wrack perturbations
  • 4A.2 - Assess the effects of creek perturbations
  • 4A.3 - Assess the effects of dieback and other perturbations
  • 4A.4 - Synthesize results into a scaled-up disturbance-scape

B) Landscape Change

  • 4B.1 - Track habitat shifts along the Altamaha River estuary salinity gradient
  • 4B.2 - Conduct synoptic assessments of productivity
  • 4B.3 - Evaluate long-term change in vegetated marsh areas

C) Modeling

  • 4C.1 - Upgrade hydrodynamic models
  • 4C.2 - Enhance soil model
  • 4C.3 - Model plant production
  • 4C.4 - Develop driver-response models

Current Progress Report

Below is an update for each of the Area 4 objectives as reported in the most recent annual report. For a list of all reports click here (Annual Reports).

A) Produce synoptic descriptions of ecosystem properties

  • 4A.1 - Assess the effects of wrack perturbations

      Activities and Accomplishments:  We have begun a large-scale effort to track wrack disturbance on the landscape via regular drone flights. During the first year, we identified a test site that we used to optimize flight conditions, develop a workflow for image processing and classification, and standardize protocols for ground-truthing. We also used the test site to obtain ground-truth data for field validation of NDVI. In Dec. 2019 we began regular monthly flights at a 23 ha site (Airport Marsh). For each flight we identify perturbations (wrack packets) using PCA and machine learning techniques and then compare them with previous imagery in order to quantify patch size, frequency, and longevity. Drone imagery is used to guide selection of patches for field monitoring of plants, invertebrates, porewater, decomposition, and wrack characteristics, and we have also set up motion-activated cameras in the field to capture visits from mammals and birds. New wrack patches are added to the monitoring effort each quarter. Initial sampling of areas affected by wrack show that plant densities decreased and stem height increased in wrack patches, and that densities of the herbivorous marsh crab Sesarma reticulatum increased significantly in wrack-covered areas relative to controls.

  • 4A.2 - Assess the effects of creek perturbations

      Activities and Accomplishments:  The headward erosion of tidal creeks has been linked to grazing by Sesarmid crabs (Vu et al. 2017; Vu and Pennings 2018). We have evidence that creeks affected by this phenomenon have become increasingly prevalent over the past few decades, which has implications for invertebrate communities and predator-prey interactions on the marsh platform (Crotty et al., 2020; key findings). We took advantage of a space-for-time substitution to evaluate marsh disturbance and recovery due to this phenomenon (Wu et al., in press). We found multiple patterns of disturbance magnitude and recovery trajectory for the various response variables that belied any simple univariate understanding of "disturbance and recovery." We are also calculating rates of creekbank slumping/accretion to assess the relative importance of different geomorphic features in controlling erosion.

Area 4 Figure 1

Fig. 1. Wrack packets identified from drone flights at airport marsh, July 2019 – May 2020. Source: T. Lynn, M. Alber, and D. Mishra

  • 4A.3 - Assess the effects of dieback and other perturbations

      Activities and Accomplishments:  Dieback is an important drought-associated disturbance in the GCE domain (Silliman et al. 2005, McFarlin et al. 2015, Angelini et al. 2016). If we experience a drought or see other signs of perturbation (i.e., plants thinning due to increased inundation), these should be captured by our drone flights. Our plan is to use a similar field protocol to that being used for the wrack assessment to follow these areas in the field. To date, however, no droughts or dieback have been observed during GCE-IV.

  • 4A.4 - Synthesize results into a scaled-up disturbance-scape

      Activities and Accomplishments:  Visualization of the cumulative distribution of wrack shows that it is concentrated at channel edges and is quite dynamic over time (Fig. 1). Our goal is to develop a cradle-to-grave view of wrack and other perturbations and to use them to produce scaled-up estimates of the system-wide importance of these events for ecosystem properties such as NPP.

B) Landscape Change

  • 4B.1 - Track habitat shifts along the Altamaha River estuary salinity gradient

      Activities and Accomplishments:  As sea-level rise causes salt water to intrude further upstream, there is the potential that there will be upstream shifts in intertidal vegetation (e.g., brackish marsh converting to salt marsh). In the GCE domain this would manifest most clearly along the salinity gradient of the Altamaha River estuary. We therefore have multiple efforts underway to detect these changes: We conduct an annual survey of the distribution of bankside Spartina cynosuroides (characteristic of brackish marshes) and sample permanent plots at four sites with mixed vegetation as part of our fall monitoring effort. In 2018 we added observations of vegetation on Broughton Island, which is located in the middle of the estuary and has a dynamic mix of oligohaline and mesohaline species and also established an annual photo survey of bankside trees in the tidal fresh forest. We developed a random forest classifier to generate maps delineating 11 tidal habitat types based on orthoimagery collected in 2017 and 2018, which we are using for change detection analysis associated with the passage of Hurricane Irma. This past year we acquired Sentinel-2 satellite imagery to map marsh and forest distributions along the corridor and we are also collecting ground-truth observations in the forest. We are particularly interested in evidence for tree mortality as the result of salt encroachment.

  • 4B.2 - Conduct synoptic assessments of productivity

      Activities and Accomplishments:  In GCE-III we used data from Landsat5 period of record (1984 to 2011) to evaluate changes in S. alterniflora biomass at a site on Sapelo Island. We have now extended these analyses both temporally (to include Landsat8) and spatially (to the entire Georgia coast). The spatial analysis was made possible by habitat maps developed for the GA coast as part of a leveraged project, following the approach we first took for the Duplin River (Hladik et al. 2013). Our expanded analysis showed long-term declines in S. alterniflora biomass along all of the GA coast except in the Altamaha River estuary (which has the most freshwater input). Over the coming years our goal is to derive similar algorithms to assess biomass patterns for brackish and fresh marsh species. We are also poised to get scaled-up GPP estimates of the domain from MODIS. We have parameterized a Light Use Efficiency (LUE) model for S. alterniflora within the flux tower site, which is an important step towards developing a model that we can use on a per-pixel basis for all of the marshes within the GCE domain. Eventually, we plan to use this framework to create a time-series of GPP estimates for the study area at 8-day intervals from 2000 to 2021.

  • 4B.3 - Evaluate long-term change in vegetated marsh area

      Activities and Accomplishments:  One of the most important questions we would like to address is whether the GCE marshes will be resilient to future changes such as sea-level rise. Burns et al. (2020 a, b) used historical aerial photos to evaluate changes in marsh features over approximately 70 years (see key findings). Although the marshes were dynamic, losses (primarily due to channel widening) were largely offset by gains in other areas (primarily channel contraction, with some migration into the upland). Langston et al. (2020) used a vertical accretion model to predict that the GCE marshes will be stable in the vertical direction through 2100 due to existing “elevation capital”, in contrast to marshes elsewhere that are perched lower in the tidal range (i.e., VCR). However, the long-term stability of salt marshes remains an area of active research as there are many unknowns regarding feedbacks between flooding depth, plant growth and sediment accretion.

C) Modeling

  • 4C.1 - Upgrade hydrodynamic models

      Activities and Accomplishments:  One of our major accomplishments in GCE-III was the implementation of a hydrodynamic model (FVCOM) in both the GCE domain and the Duplin River (McKnight 2016, Wang et al. 2017). We are now in the process of switching to the Delft3D modeling framework because of the added flexibility and additional functions available. Comparisons with observations from GCE hydrographic moorings indicate that the heat and salt balances are realistically represented. We are currently working on implementing a water quality model.

  • 4C.2 - Enhance soil model

      Activities and Accomplishments:  Our soil model (Miklesh & Meile 2018) predicts porewater salinity based on hydrology and evapotranspiration. We are now developing a dynamic model of soil temperature based on a radiation balance coupled with a one-dimensional heat propagation model in the subsurface to study the effect of changes in external drivers, inundation patterns, and potential porewater mixing (Fig. 21).

Area 4 Figure 2

Fig. 2. Major drivers (left) and initial results (right) of soil temperature model. Source: J. Kolb and C. Meile

  • 4C.3 - Model plant production

      Activities and Accomplishments:  We are working on both empirical and mechanistic models of plant production. Our Belowground Ecosystem Resilience Model (BERM) uses extreme gradient boosting to predict below-ground biomass of S. alterniflora based on a suite of environmental (i.e., elevation, temperature) and biological (i.e., foliar N, plant phenology) variables (O’Connell et al., in review). One of the exciting things about this effort is that it is based on above-ground proxies and can be scaled with readily available remote sensing data to evaluate spatiotemporal patterns (Fig. 3). We are also developing a whole-plant balanced growth model that we can use to evaluate the time-course of recovery from disturbance.

  • 4C.4 - Develop driver-response models

      Activities and Accomplishments:  We are using a variety of approaches to link external drivers to response variables, particularly in the context of our disturbance framework. We have analyzed our long-term salinity data from the Altamaha River estuary and found that high salinity events could be explained by low river flow, strong up-estuary winds, or (to a lesser extent) unusually high tides (Sheldon & Alber 2019). We are currently using several agnostic statistical approaches (wavelet analysis, empirical mode decomposition) to evaluate hydrological drivers in comparison with satellite-derived biomass estimates (Objective C2), and we are also using data on both response and recovery from the SALTEx experiment to generate driver-response curves for multiple parameters (pore water nutrients, plant community composition, sediment elevation).

Fig. 3.Above (left) and belowground (right) biomass of Spartina at the GCE flux tower marsh on 6/15/16 (left) and 9/15/16 (right), estimated with our BERM model. Color ramps indicates biomass in g m-2. Source: O’Connell et al., in review., New Phytol.

Area 4 Publications from GCE-IV

Burns, C., Alexander, C.R. Jr. and Alber, M. 2021. Assessing long-term trends in lateral salt-marsh shoreline change along a U.S. East Coast latitudinal gradient. Journal of Coastal Research. 37.

O'Connell, J.L., Mishra, D., Alber, M. and Byrd, K.B. (accepted). BERM: A belowground ecosystem resilience model for estimating Spartina alterniflora belowground biomass. New Phytologist.

Wu, F., Ortals, C., Ruiz, J., Farrell, W.R., McNichol, S.M., Angelini, C., Spivak, A.C., Alber, M., Tong, C. and Pennings, S.C. (in press). Disturbance is complicated: headward-eroding saltmarsh creeks produce multiple responses and recovery trajectories. Limnology & Oceanography.

Zinnert, J.C., Nippert, J.B., Rudgers, J.A., Pennings, S.C., Gonzalez, G., Alber, M., Baer, S.G., Blair, J.M., Burd, A.B., Collins, S.L., Craft, C.B., Di Iorio, D., Dodds, W.K., Groffman, P.M., Herbert, E., Hladik, C.M., Li, F., Litvak, M., Newsome, S., O'Donnell, J., Pockman, W.T., Schalles, J.F. and Young, D.R. 2021. State Changes: Insights from the U.S. Long Term Ecological Research Network. Ecosphere.

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)

Feagin, R.A., Forbrich, I., Huff, T.P., Barr, J.G., Ruiz-Plancarte, J., Fuentes, J.D., Najjar, R., Vargas, R., Vazquez-Lule, A.L., Windham-Myers, L., Kroeger, K.D., Ward, E.J., Moore, G.W., Leclerc, M.Y., Krauss, K.W., Stagg, C.L., Alber, M., Knox, S.H., Schafer, K.V.R., Bianchi, T.S., Hutchings, J.A., Nahrawi, H.B., Noormets, A., Mitra, B., Jaimes, A., Hinson, A.L., Bergamaschi, B. and King, J.S. 2020. Tidal wetland Gross Primary Production across the continental United States, 2000-2019. Globa

Langston, A., Alexander, C.R. Jr., Alber, M. and Kirwan, M. 2020. Beyond 2100: Elevation capital disguises salt marsh vulnerability to sea-level rise in Georgia, USA. Estuarine, Coastal and Shelf Science.

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)

Spivak, A.C., Sanderman, J., Bowen, J.L., Canuel, E.A. and Hopkinson, C.S. 2019. Global-change controls on soil-carbon accumulation and loss in coastal vegetated ecosystems. Nature Geoscience. 12:685–692. (DOI: https://doi.org/10.1038/s41561-019-0435-2)

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

Vu, H. and Pennings, S.C. 2018. Predators mediate above- vs belowground herbivory in a salt marsh crab. Ecosphere. 9(2):e02107. (DOI: 10.1002/ecs2.2107)

Vu, H., Wieski, K. and Pennings, S.C. 2017. Ecosystem engineers drive creek formation in salt marshes. Ecology. 98(1):162-174.

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)

Angelini, C., Griffin, J., van de Koppel, J., Derksen-Hooijberg, M., Lamers, L., Smolders, A.J.P., van der Heide, T. and Silliman, B.R. 2016. A keystone mutualism underpins resilience of a coastal ecosystem to drought. Nature Communications. 7:12473. (DOI: 10.1038/ncomms12473)

O'Donnell, J. and Schalles, J.F. 2016. Examination of Abiotic Drivers and Their Influence on Spartina alterniflora Biomass over a Twenty-Eight Year Period Using Landsat 5 TM Satellite Imagery of the Central Georgia Coast. Special Issue: Remote Sensing in Coastal Environments. Remote Sensing. 8(6):22. (DOI: 10.3390/rs8060477)

McFarlin, C.R., Bishop, T.D., Hester, M. and Alber, M. 2015. Context-dependent effects of the loss of Spartina alterniflora on salt marsh invertebrate communities. Estuarine, Coastal and Shelf Science. 163:218-230. (DOI: 10.1016/j.ecss.2015.05.045)

Hladik, C.M., Schalles, J.F. and Alber, M. 2013. Salt marsh elevation and habitat mapping using hyperspectral and LIDAR data. Remote Sensing of the Environment. 139:318 - 330. (DOI: 10.1016/j.rse.2013.08.003)

Pennings, S.C. and Silliman, B.R. 2005. Linking biogeography and community ecology: latitudinal variation in plant-herbivore interaction strength. Ecology. 86:2310-2319.

McKnight, C.J. 2016. A modelling study of horizontal transport and residence time in the Duplin River estuary, Sapelo Island GA. M.S. Thesis. University of Georgia, Athens, GA.

Schalles, J.F. and Peffer, C. Presentation: Regulatory, Legal, and Ethical Considerations for Drone Operations - The view from coastal Georgia . Regulatory Legal and Ethical Considerations for Drone Operations. Drones in the Coastal Zone - U.S. Southeast and Caribbean Regional Workshop, October 22, 2020, Virtual (web-based).

Schalles, J.F. Presentation: High resolution salt marsh vegetation biomass mapping with an Altum 6 band camera and Matrice 210 drone. Introduction to Using Drones in the Coastal Zone. Drones in the Coastal Zone - U.S. Southeast and Caribbean Regional Workshop, October 14, 2020, Virtual (web-based).

Sheldon, J.E. and Alber, M. 2019. An Examination of High Salinity Events in the Altamaha River Estuary. In: Review prepared for GA DNR-CRD.

 
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This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959, OCE-1237140 and OCE-1832178. 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.