Area 3: Marsh Response to Disturbance

Objectives Progress Report Publications Show All  

Marsh Response to Disturbance

We work in each of our key marsh habitats to understand ecosystem response to major perturbations. A) In the Spartina marsh, we are assessing changes in inundation and top-down control. B) In the upstream areas of brackish/fresh marsh and tidal forest, we are evaluating the effect of increases in salinity that occur as the result of droughts, storm surge, or upstream sea level intrusion. C) In the high marsh, we are assessing changes in runoff at the upland/marsh border.

Research Objectives

A) In the Spartina marsh, we are assessing changes in inundation and top-down control.

  • 3A.1 - Evaluate drivers of Spartina alterniflora production
  • 3A.2 - Continue our predator removal manipulation
  • 3A.3 - Quantify ecosystem effects of marsh perturbations
  • 3A.4 - Conduct standardized disturbance manipulations
  • 3A.5 - Investigate marsh fauna interactions

B) In the upstream areas of brackish/fresh marsh and tidal forest, we are evaluating the effect of increases in salinity that occur as the result of droughts, storm surge, or upstream sea level intrusion.

  • 3B.1 - Assess upstream habitat transitions
  • 3B.2 - Track recovery from our salt water intrusion manipulation

C) In the high marsh, we are assessing changes in runoff at the upland/marsh border.

  • 3C.1 - Assess habitat dynamics at vegetation borders
  • 3C.2 - Continue our upland manipulation

Current Progress Report

2019 Area 3 Figure 1

Fig. 1. Annual cycle of Gross Primary Production, GPP (a) and Light Use Efficiency, LUE (b) calculated from the GCE flux tower. LUE is GPP/PAR. Source: Peter Hawman et al., in prep.

Below is an update for each of the Area 3 objectives as reported in the most recent annual report. For a list of all reports click here (Annual Reports).

A) 1. Evaluate drivers of Spartina alterniflora production

  • 3A.1 - Evaluate drivers of Spartina alterniflora production
    • Activities:  We deployed soil temperature sensors at the core marsh sites to evaluate its relationship to Spartina green-up. We are also planning to manipulate temperature in a greenhouse experiment.

      Results: Hawman et al. used general additive models to evaluate the annual cycle of GPP and light use efficiency measured at the flux tower (Fig. 1), and found that the cloudiness index and daily maximum tide height are the primary factors that explain deviation in Spartina light use efficiency. This work was presented at multiple conferences and is being written up for publication.

  • 3A.2 - Continue our predator removal manipulation

      Activities: We continue sampling the predator exclusion experiment initiated in summer 2016. In 2019 we began sampling pore water and decomposition, conducted tethering experiments with fiddler crabs and Littoraria, and completed a literature search to identify which species are likely being excluded by the treatment.

      Results:  The results from the PredEx manipulation indicate that nekton are exerting top-down control of marsh invertebrates, with evidence for a short-lived release that may be compensated for by mesopredators such as mud crabs (Fig. 2). Initial results suggest that pore water salinity and pH do not vary with treatment. However, decomposition in predator exclusion plots was significantly greater than controls, presumably due to greater oxygenation by crab burrows. Soil bulk density (0-5 cm) was also lower, although not significantly, while there was no difference in soil C and N.

2019 Area 3 Figure 2

Fig. 2. Densities of a) Littoraria b) fiddler crab burrows and c) mud crab burrows observed in the predator exclusion experiment. By year 3 both Littoraria and fiddler crabs exhibited an apparent release from predation when nekton was excluded, but this effect disappeared in year 4 when the abundance of mud snails (mesopredators) increased inside the treatments. Source: Joe Morton and Brian Silliman.

  • 3A.3 - Quantify ecosystem effects of marsh perturbations

      Activities:  We conducted a study of marsh perturbation and recovery at headward-eroding creeks that are subject to Sesarma herbivory (Fig. 3). We also developed a protocol for field monitoring the impacts of wrack and drought disturbance.

      Results:  We have evidence that grazed creeks have become increasingly prevalent over the past few decades and are causing a significant increase in drainage density by accelerating creek incision, which has implications for invertebrate communities and predator-prey interactions on the marsh platform (Crotty et al., in review).

2019 Area 3 Figure 3

Fig. 3. The mud crab, Sesarma reticulatum (a), can cause headward erosion of a tidal creeks (b) at a rate of 1-2 m/yr. We sampled quadrats along transects that went through areas of crab activity as a space-for-time substitution to evaluate the effects of this perturbation (c). Blue squares indicate quadrats. Source: Steve Pennings.

  • 3A.4 - Conduct standardized disturbance manipulations

      Activities:  We are participating in a distributed "DragNet" experiment aimed at understanding how grasslands recover from disturbances under different nutrient regimes. We also plan to initiate a standardized disturbance experiment across the GCE domain based on observations of natural marsh perturbations. We continue to monitor recovery from a wrack disturbance experiment conducted in 2011.

  • 3A.5 - Investigate marsh fauna interactions

      Activities:  We began field measurements to evaluate how interactions between cordgrass and ribbed mussels influence tide water chemistry and the net import/export of materials from marshes.

      Results:  Tethering experiments with Littoraria show that the probability of survival increases with body size: for every millimeter increase in shell height, the log odds of survival increases by 0.16048.

B) In the upstream areas of brackish/fresh marsh and tidal forest, we are evaluating the effect of increases in salinity that occur as the result of droughts, storm surge, or upstream sea level intrusion.

  • 3B.1 - Assess upstream habitat transitions

      Activities:  We conduct an annual survey of bankside vegetation and sample plots with mixed vegetation to document transitions along the Altamaha River salinity gradient. In 2018 we added an annual photo survey of trees in the tidal fresh forest and observations on Broughton Island, which has a dynamic mix of oligohaline and mesohaline species. We have also sampled bald cypress deposits for a longer dendrochronology analysis (Fig. 4, Napora et al. 2019).

      Results:  Herbert et al. (in press) found that long-term addition of N and P to a tidal freshwater marsh in the Altamaha increased above-ground biomass, microbial biomass and N cycling, and N, P, and C assimilation and burial more than either nutrient alone (Fig. 5), and suggest that the ability of these habitats to mitigate eutrophication will depend on the quantity and relative proportion of N versus P entering the system.

2019 Area 3 Figure 4

Fig. 4. Dendrochronology from bald cypress tree cookies collected on the Georgia coast showing changes in annual tree rings from 393 1642. Periods of fluctuations are indicated in orange. Source: Kat Napora and Victor Thompson.

2019 Area 3 Figure 5

Fig. 5. Total (a) C (%), (b) N (%), and (c) P (g P dry g-1) in the top 20 cm of soils in a tidal freshwater marsh in the Altamaha River that was fertilized for a period of 10 years with N and P, alone or in combination, as indicated. Source: Herbert et al. in press.

  • 3B.2 - Track recovery from our salt water intrusion manipulation

      Activities:  We sampled porewater, greenhouse gases, vegetation, invertebrates, and soil biomarkers in the SALTEx experiment to track recovery following cessation of dosing in December 2017.

      Results:  Widney et al. (2019) published a synthesis of the biochemical effects of the SALTEx experiment showing that three years of saltwater intrusion increased porewater Cl-, SO4, HS and inorganic N (NH4 and NO3) and decreased plant N storage (see Key Findings). Manuscripts regarding the changes in soil elevation and the vegetation response are both in review.

C) In the high marsh, we are assessing changes in runoff at the upland/marsh border

  • 3C.1 - Assess habitat dynamics at vegetation borders

      Activities:  We monitor vegetation dynamics in 9 high marsh mixtures and have begun annual drone flights to scale up to the surrounding landscape. We also operate two web applications where citizen scientists align and extract data from photographs taken along transects that begin in the high marsh.

  • 3C.2 - Continue our upland manipulation

      Activities:  The high marsh experiment has had little effect on water flow, and hence there have been no effects on plants or invertebrates. However, data from the wells are being analyzed to calculate hydraulic gradients for groundwater flow models (Fig. 6).

2019 Area 3 Figure 5

Fig. 6. Groundwater wells were installed in Feb. 2019 in an area of vegetation transition at Marsh Landing. (a) stratigraphy and overall flow patterns, (b) the difference in hydraulic head (top) between well R4 and R3B, which is net positive (landward) and (bottom) between well R3B and R2B, which is net negative (creekward).

Area 3 Publications from GCE-IV

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

Widney, S., Smith, D., Herbert, E., Schubauer-Berigan, J.P., Li, F., Pennings, S.C. and Craft, C.B. 2019. Chronic but not acute saltwater intrusion leads to large release of inorganic N in a tidal freshwater marsh. Science of the Total Environment. 695. (DOI: https://doi.org/10.1016/j.scitotenv.2019.133779)

Area 3 Publications from GCE-III

Journal Articles

Li, F. and Pennings, S.C. 2019. Response and Recovery of Low-Salinity Marsh Plant Communities to Presses and Pulses of Elevated Salinity. Estuaries and Coasts. 42:708-718. (DOI: 10.1007/s12237-018-00490-1)

Herbert, E., Schubauer-Berigan, J.P. and Craft, C.B. 2018. Differential effects of chronic and acute simulated seawater intrusion on tidal freshwater marsh carbon cycling. Biogeochemistry. 138:137154. (DOI: 10.1007/s10533-018-0436-z)

Li, F. and Pennings, S.C. 2018. Responses of tidal freshwater and brackish marsh macrophytes to pulses of saline water simulating sea level rise and reduced discharge. Wetlands. 38:885-891. (DOI: 10.1007/s13157-018-1037-2)

Alexander, C.R. Jr., Hodgson, J. and Brandes, J. 2017. Sedimentary processes and products in a mesotidal salt marsh environment: insights from Groves Creek, Georgia. Geo-Marine Letters. 37:345-359. (DOI: 10.1007/s00367-017-0499-1)

Jung, Y. and Burd, A.B. 2017. Seasonal changes in above- and below-ground non-structural carbohydrates (NSC) in Spartina alterniflora in a marsh in Georgia, USA. Aquatic Botany. 140:13-22. (DOI: https://doi.org/10.1016/j.aquabot.2017.04.003)

Craft, C.B., Herbert, E., Li, F., Smith, D., Schubauer-Berigan, J.P., Widney, S., Angelini, C., Pennings, S.C., Medeiros, P.M., Byers, J. and Alber, M. 2016. Climate change and the fate of coastal wetlands. Wetland Science and Practice. 33(3):70-73.

Hawkes, A., Kemp, A., Donnelly, J., Horton, B., Peltier, W., Cahill, N., Hill, D., Ashe, E. and Alexander, C. 2016. Relative Sea-Level Change in Northeastern Florida (USA) During the Last ~8.0 KA. Quaternary Science Reviews. (DOI: 10.1016/j.quascirev.2016.04.016)

Herbert, E., Boon, P., Burgin, A.J., Neubauer, S.C., Franklin, R.B., Ardon, M., Hopfensperger, K.N., Lamers, L. and Gell, P. 2015. A global perspective on wetland salinization: Ecological consequences of a growing threat to freshwater wetlands. Ecosphere. 6(10)(206):1-43. (DOI: 10.1890/ES14-00534.1)

Wieski, K. and Pennings, S.C. 2014. Latitudinal variation in resistance and tolerance to herbivory of a salt marsh shrub. Ecography. 37:763-769. (DOI: 10.1111/ecog.00498)

Porubsky, W.P., Joye, S.B., Moore, W.S., Tuncay, K. and Meile, C. 2011. Field measurements and modeling of groundwater flow and biogeochemistry at Moses Hammock, a backbarrier island on the Georgia coast. Biogeochemistry. 104:69-90. (DOI: 10.1007/s10533-010-9484-8)

Meile, C., Porubsky, W.P., Walker, R.L. and Payne, K. 2009. Natural Attenuation Of Nitrogen Loading From Septic Effluents: Spatial And Environmental Controls. Water Research. 44(5):1399-1408. (DOI: 10.1016/j.watres.2009.11.019)

Theses and Dissertations

Jung, Y. 2018. Modeling Growth and Production Dynamics of Spartina Alterniflora. Ph.D. Dissertation. University of Georgia, Athens, GA. 148 pages.

Ledoux, J.G. 2015. Drivers of groundwater flow at a back barrier island - marsh transect in coastal Georgia. M.S. Thesis. The University of Georgia, Athens. 104 pages.

Conference Papers (Peer Reviewed)

Porubsky, W.P. and Meile, C. 2009. Controls on groundwater nutrient mitigation: Natural attenuation of nitrogen loading from septic effluents. In: Hatcher, K.J. (editor). Proceedings of the Georgia Water Resources Conference. Athens, Georgia.

Conference Posters and Presentations

Widney, S., Smith, D., Schubauer-Berigan, J.P., Herbert, E., Desha, J. and Craft, C.B. 2017. Poster: Changes in sediment porewater chemistry in response to simulated seawater intrusion in tidal freshwater marshes, Altamaha River, GA. Society of Wetland Scientists Annual Meeting, June 5-8, San Juan, Puerto Rico.

Smith, D., Herbert, E., Li, F., Widney, S., Desha, J., Schubauer-Berigan, J.P., Pennings, S.C., Angelini, C., Medeiros, P.M., Byers, J., Alber, M. and Craft, C.B. 2016. Poster: Seawater Addition Long Term Experiment (SALTEx). Georgia Department of Natural Resources Coastal Resources Division 2016 Climate Conference, November 2-3, 2016, Jekyll Island, GA.

Ledoux, J.G., Alexander, C.R. Jr. and Meile, C. 2015. Poster: Groundwater flow at the Georgia coast: Magnitude and drivers across a back barrier island marsh transect. LTER All Scientists Meeting, Aug 30-Sept 2, Estes Park, CO.

Miklesh, D.M., McKnight, C.J., Di Iorio, D. and Meile, C. 2015. Poster: Controls on porewater salinity distributions in a southeastern salt marsh. LTER All Scientists Meeting, Aug 30-Sept 2, Estes Park, CO.

Ledoux, J.G., Alexander, C.R. Jr. and Meile, C. 2014. Poster: Delineating groundwater flow along a marsh transect at a back barrier island on the coast of Georgia. Southeastern Estuarine Research Society Fall meeting, November 6-8, Carolina Beach, NC.

Alexander, C.R. Jr., Alber, M., Hladik, C.M. and Pennings, S.C. 2010. Presentation: Physical-Biological Interactions in Coastal Settings: The Georgia Coastal Ecosystem LTER Example. American Geophysical Union - Meeting of the Americas, 9-13 August 2010, Foz do Iguacu, Brazil.

Alexander, C.R. Jr. 2008. Presentation: Stratigraphic Development of Holocene and Pleistocene Marsh Islands. Tidalites 2008 - Seventh International Conference on Tidal Environments, 25th-27th September, 2008, Qingdao, China.

 
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.