%0 Journal Article
%T The resistance of Georgia coastal marshes to hurricanes
%D 2024
%V 15
%N 4
%B Ecosphere
%9 Article
%Z published
%M GCE.1347
%R 10.1002/ecs2.4821
%X Ecosystems vary broadly in their responses to disturbance, ranging from highly impacted to resilient or resistant. We conducted a large-scale analysis of hurricane disturbance effects on coastal marshes by examining 20 years of data from 10 sites covering 100,000 ha at the Georgia Coastal Ecosystems Long-Term Ecological Research site distributed across gradients of salinity and proximity to the ocean. We analyzed the impacts of Hurricanes Matthew (in 2016) and Irma (in 2017) on marsh biota (plants, crabs, and snails) and physical attributes (erosion, wrack deposition, and sedimentation). We compared these variables prior to the storms (2000–2015) to years with storms (2016, 2017) to those after the storms (2018–2020). Hurricanes generated storm surges that increased water depth and salinity of oligotrophic areas for up to 48 h. Biological variables in the marsh showed few effects of the hurricanes. The only physical variable affected was creek bank slumping; however, slumping had already increased a year before the hurricanes, suggesting that slumping could have a different cause. Thus, our study uncovered only minor, ephemeral impacts on Georgia coastal marshes, highlighting their resistance to hurricane disturbance of the lower magnitude that typically confronts this region of coastline.
%U https://doi.org/10.1002/ecs2.4821
%A Smith, Rachel S.
%A Pennings, Steven C.
%A Alber, Merryl
%A Craft, Christopher B.
%A Byers, James
%K climate change, coastal protection, disturbance ecology, GCE-LTER, resilience, salt marshes, storm surge, Signature Publication

%0 Journal Article
%T Variance reflects resilience to disturbance along a stress gradient: experimental evidence from coastal marshes
%D 2024
%V 2024
%P e4241
%B Ecology
%9 Article
%Z published
%M GCE.1317
%R 10.1002/ecy.4241
%X Quantifying ecosystem resilience to disturbance is important for understanding the effects of disturbances on ecosystems, especially in an era of rapid global change. However, there are few studies that have used standardized experimental disturbances to compare resilience patterns across abiotic gradients in real-world ecosystems. Theoretical studies have suggested that increased return times are associated with increasing variance during recovery from disturbance. However, this notion has rarely been explicitly tested in field, in part due to the challenges involved in obtaining long-term experimental data. In this study, we examined resilience to disturbance of 12 coastal marsh sites (five low-salinity and seven polyhaline (=salt) marshes) along a salinity gradient in Georgia, USA. We found that recovery times after experimental disturbance ranged from 7 to >127 months, and differed among response variables (vegetation height, cover and composition). Recovery rates decreased along the stress gradient of increasing salinity, presumably due to stress reducing plant vigor, but only when low-salinity and polyhaline sites were analyzed separately, indicating a strong role for traits of dominant plant species. The coefficient of variation of vegetation cover and height in control plots did not vary with salinity. In disturbed plots, however, the CV was consistently elevated during the recovery period and increased with salinity. Moreover, higher CV values during recovery were correlated with slower recovery rates. Our results deepen our understanding of resilience to disturbance in natural ecosystems, and point to novel ways that variance can be used either to infer recent disturbance, or, if measured in areas with a known disturbance history, to predict recovery patterns.
%U https://doi.org/10.1002/ecy.4241
%A Wang, J.
%A Guo, Hongyu
%A Alber, Merryl
%A Pennings, Steven C.
%K disturbance, salt marsh, Spartina, Juncus, Zizaniopsis, resistance, resilience, SINERR Publication, Signature Publication, UGAMI Publication

%0 Journal Article
%T Photosynthetic Performance of Tidally Flooded Spartina Alterniflora Salt Marshes
%D 2023
%V 128
%N 3
%B JGR Biogeosciences
%9 Article
%Z published
%M GCE.1303
%R 10.1029/2022JG007161
%X Spartina alterniflora has a distinct flood-adapted morphology, and its physiological responses are likely to vary with differences in tidal submergence. To understand these responses, we examined the impacts of tidal inundation on the efficiency of Photosystem II (φPSII) photochemistry and leaf-level photosynthesis at different canopy heights through a combination of in situ chlorophyll fluorescence (ChlF), incident photosynthetically active radiation, and tide levels. Our result showed small declines (7%–8.3%) in φPSII for air-exposed leaves when the bottom canopies were tidally submerged. Submerged leaves produced large reductions (30.3%–41%) in φPSII. Our results suggest that when submerged, PSII reaction centers in S. alterniflora leaves are still active and able to transfer electrons, but only at ∼20% of the typical daily rate. We attribute this reduction in φPSII to the decrease in the fraction of “open” PSII reaction centers (10% of the total) and the stomatal conductance rate caused by the tidal submergence. To our knowledge, this flooding induced leaf-level reduction of φPSII for S. alterniflora in field settings has not been reported before. Our findings suggest that canopy-level φPSII is dependent on the proportion of submerged versus emerged leaves and highlight the complexities involved in estimating the photosynthetic efficiency of tidal marshes.
%U https://doi.org/10.1029/2022JG007161
%A Mao, Lishen
%A Mishra, Deepak
%A Hawman, Peter
%A Narron, Caroline
%A O'Connell, Jessica L.
%A Cotten, David L.
%K Spartina alternifora, chlorophyll fluorescence, photosynthetically active radiation, PAR, Signature Publication, Student Publication

%0 Journal Article
%T Ephemeral microbial responses to pulses of bioavailable carbon in oxic and anoxic salt marsh soils
%D 2023
%V 185
%B Soil Biology and Biochemistry
%9 Article
%Z published
%M GCE.1307
%R 10.1016/j.soilbio.2023.109157
%X Roots of salt marsh grasses contribute to soil building but also affect decomposition by releasing bioavailable carbon exudates and oxygen. Disentangling exudate and oxygen effects on decomposition is difficult in the field but essential for marsh carbon models and predicting the impacts of global change disturbances. We tested how pulsed, simulated exudates affect soil metabolism under oxic and anoxic conditions, and whether carbon and oxygen availability facilitate mineralization of existing organic matter (i.e., priming). We conducted a laboratory experiment in flow-through reactors, adding carbon pulses weekly for 84 days and then following starvation under low carbon conditions. Oxygen consumption and sulfide production were inhibited under anoxic and oxic conditions and slowed by 21 ± 10% and 55 ± 8%, respectively, between 1- and 5- days following exudate pulses. Respiration rates immediately following and between pulses increased over time, suggesting that microbes capitalize on and may acclimate to patchy resources. Starvation caused oxygen consumption and sulfide production to fall 28% and 78% in oxic and anoxic treatments. Smaller decreases in oxygen consumption following pulses could suggest greater access to secondary carbon sources and that sulfate reducers were more reliant on exudates. Soil organic carbon was not the likely secondary source because porewater dissolved inorganic carbon δ13C values did not change during transit through the reactors, despite a ∼26‰ difference between the supplied seawater and marsh soil. Interpretation of oxygen consumption rates is complicated by non-respiratory oxidation of reduced inorganic compounds and possibly significant lithoautotrophy. Exudate pulses elicited rapid and ephemeral respiratory responses, particularly under anoxia, but non-respiratory oxidation of reduced compounds obscured the impact of oxygen availability in our experimental system. Despite this, greater aerobic respiration rates suggest that oxygen availability has more potential to regulate carbon mineralization in coastal wetlands than root exudates.
%U https://doi.org/10.1016/j.soilbio.2023.109157
%A Spivak, Amanda C.
%A Pinsonneault, Andrew J.
%A Hintz, Christopher
%A Brandes, J.
%A Megonigal, Patrick
%K Salt marsh, Rhizosphere, Organic carbon, Redox, Priming, Sulfur oxidation, Signature Publication

%0 Journal Article
%T Variation in synchrony of production among species, sites and intertidal zones in coastal marshes
%D 2021
%B Ecology
%9 Article
%Z published
%M GCE.1184
%R 10.1002/ECY.3278
%X Spatially synchronous population dynamics are important to ecosystem functioning and have several potential causes. By looking at synchrony in plant productivity over 18 years across two elevations in three types of coastal marsh habitat dominated by different clonal plant species in Georgia, USA, we were able to explore the importance of plant species and different habitat conditions to synchrony. Synchrony was highest when comparing within a plant species and within a marsh zone, and decreased across species, with increasing distance, and with increasing elevational differences. Abiotic conditions that were measured at individual sites (water column temperature and salinity) also showed high synchrony among sites, and in one case (salinity) decreased with increasing distance among sites. The Moran Effect (synchronous abiotic conditions among sites) is the most plausible explanation for our findings. Decreased synchrony between creekbank and mid-marsh zones, and among habitat types (tidal fresh, brackish and salt marsh) was likely due in part to different exposure to abiotic conditions and in part to variation in sensitivity of dominant plant species to these abiotic conditions. We found no evidence for asynchrony among species, sites or zones, indicating that one habitat type or zone will not compensate for poor production in another during years with low productivity; however, tidal fresh, brackish and salt marsh sites were also not highly synchronous with each other, which will moderate productivity variation among years at the landscape level due to the portfolio effect. We identified the creekbank zone as more sensitive than the mid-marsh to abiotic variation and therefore as a priority for monitoring and management.
%U https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.3278
%A Liu, Wenwen
%A Pennings, Steven C.
%K climate change, salt marsh, Juncus, Spartina, Zizaniopsis, synchrony, Signature Publication, SINERR Publication, UGAMI Publication, Student Publication

%0 Journal Article
%T BERM: A belowground ecosystem resilience model for estimating Spartina alterniflora belowground biomass
%D 2021
%B New Phytologist
%9 Article
%Z published
%M GCE.1226
%R 10.1111/nph.17607
%X Spatiotemporal patterns of Spartina alterniflora belowground biomass (BGB) are importantfor evaluating salt marsh resiliency. To solve this, we created the BERM (Belowground EcosystemResiliency Model), which estimates monthly BGB (30-m spatial resolution) from freelyavailable data such as Landsat-8 and Daymet climate summaries.Our modeling framework relied on extreme gradient boosting, and used field observationsfrom four Georgia salt marshes as ground-truth data. Model predictors included estimatedtidal inundation, elevation, leaf area index, foliar nitrogen, chlorophyll, surface temperature,phenology, and climate data. The final model included 33 variables, and the most importantvariables were elevation, vapor pressure from the previous four months, Normalized DifferenceVegetation Index (NDVI) from the previous five months, and inundation.Root mean squared error for BGB from testing data was 313 g m−2 (11% of the field datarange), explained variance (R2) was 0.62–0.77. Testing data results were unbiased across BGBvalues and were positively correlated with ground-truth data across all sites and years (r =0.56–0.82 and 0.45–0.95, respectively).BERM can estimate BGB within Spartina alterniflora salt marshes where environmentalparameters are within the training data range, and can be readily extended through a reproducibleworkflow. This provides a powerful approach for evaluating spatiotemporal BGB andassociated ecosystem function.
%U https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/nph.17607
%A O'Connell, Jessica L.
%A Mishra, Deepak
%A Alber, Merryl
%A Byrd, K. B.
%K Spartina, belowground biomass, model, Signature Publication

%0 Journal Article
%T Disturbance is complicated: headward-eroding saltmarsh creeks produce multiple responses and recovery trajectories
%D 2021
%V 67
%P S86-S100
%B Limnology & Oceanography
%9 Article
%Z published
%M GCE.1185
%R 10.1002/lno.11867
%X Disturbances are one of the most important processes affecting natural systems, but there is a gap between the simplicity of conceptual models of disturbance and the rich complexity of empirical studies. We studied the perturbation caused by the movement of headward-eroding creeks onto the marsh platform in southeastern USA salt marshes. We measured the disturbance responses of 19 variables in terms of both magnitude (the difference between perturbed areas and control areas located on the marsh platform) and recovery trajectory (evaluated using a space for time substitution design along a marsh transect that ran the length of the newly-formed creek). Some variables (shoot density, root biomass, herbivorous snail density, soil pH, soil strength, soil temperature and elevation) declined sharply, while other variables (crab burrow density, soil organic matter and soil redox) increased sharply, in response to the heavily burrowed and grazed conditions at the creek head; these then recovered over subsequent years or decades. Other variables (shoot height, aboveground biomass, rhizome biomass, and light interception) declined sharply in the creek head, then overshot control values before recovering. Some variables (benthic algae, soil salinity) did not appear to be disturbed by the creek head. As hypothesized, plants recovered before soils and before snails. Disturbance magnitude and time to recovery were often greater directly adjacent to the new creekbank than for the same variables in a parallel transect further away from the creekbank that experienced an initial perturbation at the creek head but was not subject to the ongoing influence of the newly-formed creek, and in some cases variables never recovered, indicating a state change. Reducing the dimensionality of the data set into one or two principal component axes obscured the diverse ways in which different aspects of the system responded to and recovered from the perturbation. Our study illustrates the challenges in moving from simple conceptual models of disturbance to empirical studies in which multiple variables are likely to be affected differently and follow different recovery trajectories.
%U https://aslopubs.onlinelibrary.wiley.com/doi/full/10.1002/lno.11867
%A Wu, Fengrun
%A Pennings, Steven C.
%A Ortals, Collin
%A Ruiz, Jennifer
%A Farrell, William Reilly
%A McNichol, Samuel M
%A Angelini, Christine
%A Spivak, Amanda C.
%A Alber, Merryl
%A Tong, Chunfu
%K crabs, creek, disturbance, salt marsh, secondary succession, Student Publication, UGAMI Publication, SINERR Publication, Signature Publication

%0 Journal Article
%T Historical Changes in the Vegetated Area of Salt Marshes
%D 2020
%B Estuaries and Coasts
%9 Article
%Z published
%M GCE.1180
%R 10.1007/s12237-020-00781-6
%X Salt marshes are valuable ecosystems, and there is concern that increases in the rate of sea level rise along with anthropogenic activities are leading to the loss of vegetated habitat. The area of vegetated marsh can change not only through advance and retreat of the open fetch edge, but also due to channel widening and contracting, formation and drainage of interior ponds, formation and revegetation of interior mud flats, and marsh migration onto upland areas, each of which is influenced by different processes. This study used historical aerial photographs to measure changes in the extent of vegetated marsh over approximately 70 years at study marshes located in three long-term ecological research (LTER) sites along the US East coast: Georgia Coastal Ecosystems (GCE), Virginia Coast Reserve (VCR), and Plum Island Ecosystems (PIE). Marsh features were categorized into vegetated marsh, ponds, interior mud flats, and channels for three time periods at each site. The three sites showed different patterns of change in vegetated marsh extent over time. At the GCE study site, losses in vegetated marsh, which were primarily due to channel widening, were largely offset by channel contraction in other areas, such that there was little to no net change over the study period. The study marsh at VCR experienced extensive vegetated marsh loss to interior mud flat expansion, which occurred largely in low-lying areas. However, this loss was counterbalanced by marsh gain due to migration onto the upland, resulting in a net increase in vegetated marsh area over time. Vegetated marsh at PIE decreased over time due to losses from ponding, channel widening, and erosion at the open fetch marsh edge. Digital elevation models revealed that the vegetated areas of the three marshes were positioned at differing elevations relative to the tidal frame, with PIE at the highest and VCR at the lowest elevation. Understanding the patterns of vegetation loss and gain at a given site provides insight into what factors are important in controlling marsh dynamics and serves as a guide to potential management actions for marsh protection.
%U https://link.springer.com/article/10.1007/s12237-020-00781-6?wt_mc=Internal.Event.1.SEM.ArticleAuthorOnlineFirst
%A Burns, Christine
%A Alber, Merryl
%A Alexander, Clark R., Jr.
%K Salt marsh, LTER, Image analysis, Ponding, Marsh Migration, Signature Publication, Student Publication, UGAMI Publication

%0 Journal Article
%T Declines in plant productivity drive loss of soil elevation in a tidal freshwater marsh exposed to saltwater intrusion
%D 2020
%V 101
%N 12
%P 13
%B Ecology
%9 Article
%Z published
%M GCE.1200
%R 10.1002/ecy.3148
%X We experimentally increased salinities in a tidal freshwater marsh on the Altamaha River (Georgia, USA) by exposing the organic rich soils to 3.5 yr of continuous (press) and episodic (pulse) treatments with dilute seawater to simulate the effects of climate change such as sea level rise (press) and drought (pulse). We quantified changes in root production and decomposition, soil elevation, and soil C stocks in replicated (n = 6) 2.5 × 2.5 m field plots. Elevated salinity had no effect on root decomposition, but it caused a significant reduction in root production and belowground biomass that is needed to build and maintain soil elevation capital. The lack of carbon inputs from root production resulted in reduced belowground biomass of 1631 ± 308 vs. 2964 ± 204 g/m2 in control plots and an overall 2.8 ± 0.9 cm decline in soil surface elevation in the press plots in the first 3.5 yr, whereas the control (no brackish water additions) and the fresh (river water only) treatments gained 1.2 ± 0.4 and 1.7 ± 0.3 cm, respectively, in a 3.5‐yr period. There was no change in elevation of pulse plots after 3.5 yr. Based on measurements of bulk density and soil C, the decline of 2.8 cm of surface elevation resulted in a loss of 1.4 ± 0.08 kg C/m2 in press plots. In contrast, the control and the fresh treatment plots gained 0.7 ± 0.05 and 0.8 ± 0.05 kg C/m2, respectively, which represents a net change in C storage of more than 2 kg C/m2. We conclude that, when continuously exposed to saltwater intrusion, the tidal freshwater marsh’s net primary productivity, especially root production, and not decomposition, are the main drivers of soil organic matter (SOM) accumulation. Reduced productivity leads to loss of soil elevation and soil C, which has important implications for tidal freshwater marsh persistence in the face of rising sea level.
%U https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.3148
%A Solohin, Elena
%A Widney, Sarah
%A Craft, Christopher B.
%K decomposition, root production, saltwater intrusion, sea level rise, soil elevation, tidal wetlands, Signature Publication

%0 Journal Article
%T Ecosystem stability and Native American oyster harvesting along the Atlantic Coast of the United States
%D 2020
%V 6
%B Science Advances
%9 Article
%Z published
%M GCE.1181
%R 10.1126/sciadv.aba9652
%X The eastern oyster (Crassostrea virginica) is an important proxy for examining historical trajectories of coastal ecosystems. Measurement of ~40,000 oyster shells from archaeological sites along the Atlantic Coast of the United States provides a long-term record of oyster abundance and size. The data demonstrate increases in oyster size across time and a nonrandom pattern in their distributions across sites. We attribute this variation to processes related to Native American fishing rights and environmental variability. Mean oyster length is correlated with total oyster bed length within foraging radii (5 and 10 km) as mapped in 1889 and 1890. These data demonstrate the stability of oyster reefs despite different population densities and environmental shifts and have implications for oyster reef restoration in an age of global climate change.
%U https://advances.sciencemag.org/content/6/28/eaba9652/tab-pdf
%A Thompson, Victor D.
%A Rick, Torben
%A Garland, Carey J.
%A Thomas, David Hurst
%A Smith, Karen Y
%A Bergh, Sarah
%A Sanger, Matt
%A Tucker, Bryan
%A Lulewicz, Isabelle H.
%A Semon, Anna M
%A Schalles, John F.
%A Hladik, Christine M.
%A Alexander, Clark R., Jr.
%A Ritchison, Brandon Tyler
%K Ecosystem stability, Oysters, UGAMI Publication, Signature Publication