Bianchi, T. S., Allison, M. A., Zhao, J., Li, X., Comeaux, R. S., Feagin, R. A., et al. (2013). Historical reconstruction of mangrove expansion in the Gulf of Mexico: Linking climate change with carbon sequestration in coastal wetlands. Estuarine, Coastal and Shelf Science, 119, 7–16.
Abstract: There has been considerable interest in a recently recognized and important sink in the global carbon pool, commonly referred to as “blue carbon”. The major goal of this study was to determine the historical reconstruction of mangrove expansion (Avicennia germinans) into salt marshes (Spartina alterniflora) and its effects on carbon sequestration and soil chemistry in wetland soils of the northwestern Gulf of Mexico. We used bulk stable isotopic, chemical biomarker analyses, and aerial imagery analysis to identify changes in OC wetland sources, and radiotracers (137Cs and 210Pb) for chronology. Soil cores were collected at two sites at Port Aransas, Texas (USA), Harbor Island and Mud Island.
Stable isotopic values of δ13C and δ15N of all soil samples ranged from −26.8 to −15.6‰ and 1.8–10.4‰ and showed a significant trend of increasing depletion for each isotope from bottom to surface soils. The most depleted δ13C values were in surface soils at the Mud Island (Mangrove 2) location. Carbon sequestration rates were greater in mangroves and for the Mud Island Mangrove 1 and the Marsh 1 sites ranged from 253 to 270 and 101–125 g C m−2 yr−1, respectively. Lignin storage rates were also greater for mangrove sites and for the Mud Island Mangrove 1 and the Marsh 1 ranged from 19.5 to 20.1 and 16.5 to 12.8 g lignin m−2 yr−1, respectively. Τhe Λ8 and Λ6 values for all cores ranged from 0.5 to 21.5 and 0.4 to 16.5, respectively, and showed a significant increase from bottom to surface sediments. If regional changes in the Gulf of Mexico are to persist and much of the marsh vegetation was to be replaced by mangroves, there could be significant increases on the overall storage and sequestration of carbon in the coastal zone.
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Breithaupt, J. L., Smoak, J. M., Rivera-Monroy, V. H., Castañeda-Moya, E., Moyer, R. P., Simard, M., et al. (2017). Partitioning the relative contributions of organic matter and mineral sediment to accretion rates in carbonate platform mangrove soils. Marine Geology, 390, 170–180.
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Charles, S. P., Kominoski, J. S., Armitage, A. R., Guo, H., Weaver, C. A., & Pennings, S. C. (2020). Quantifying how changing mangrove cover affects ecosystem carbon storage in coastal wetlands. Ecology, 101(2), e02916.
Abstract: Despite overall global declines, mangroves are expanding into and within many subtropical wetlands, leading to heterogeneous cover of marsh-mangrove coastal vegetation communities near the poleward edge of mangroves' ranges. Coastal wetlands are globally important carbon sinks, yet the effects of shifts in mangrove cover on organic-carbon (OC) storage remains uncertain. We experimentally maintained black mangrove (Avicennia germinans) or marsh vegetation in patches (n = 1,120, 3 x 3 m) along a gradient in mangrove cover (0-100%) within coastal wetland plots (n = 10, 24 x 42 m) and measured changes in OC stocks and fluxes. Within patches, above and belowground biomass (OC) was 1,630% and 61% greater for mangroves than for recolonized marshes, and soil OC was 30% greater beneath mangrove than marsh vegetation. At the plot scale, above and belowground biomass increased linearly with mangrove cover but soil OC was highly variable and unrelated to mangrove cover. Root ingrowth was not different in mangrove or marsh patches, nor did it change with mangrove cover. After 11 months, surface OC accretion was negatively related to plot-scale mangrove cover following a high-wrack deposition period. However, after 22 months, accretion was 54% higher in mangrove patches, and there was no relationship to plot-scale mangrove cover. Marsh (Batis maritima) leaf and root litter had 1,000% and 35% faster breakdown rates (k) than mangrove (A. germinans) leaf and root litter. Soil temperatures beneath mangroves were 1.4 degrees C lower, decreasing aboveground k of fast- (cellulose) and slow-decomposing (wood) standard substrates. Wood k in shallow soil (0-15 cm) was higher in mangrove than marsh patches, but vegetation identity did not impact k in deeper soil (15-30 cm). We found that mangrove cover enhanced OC storage by increasing biomass, creating more recalcitrant organic matter and reducing k on the soil surface by altering microclimate, despite increasing wood k belowground and decreasing allochthonous OC subsidies. Our results illustrate the importance of mangroves in maintaining coastal OC storage, but also indicate that the impacts of vegetation change on OC storage may vary based on ecosystem conditions, organic-matter sources, and the relative spatiotemporal scales of mangrove vegetation change.
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Charles, S. P., Kominoski, J. S., Troxler, T. G., Gaiser, E. E., Servais, S., Wilson, B. J., et al. (2019). Experimental Saltwater Intrusion Drives Rapid Soil Elevation and Carbon Loss in Freshwater and Brackish Everglades Marshes. Estuaries and Coasts, 42(7), 1868–1881.
Abstract: Increasing rates of sea-level rise (SLR) threaten to submerge coastal wetlands unless they increase soil elevation at similar pace, often by storing soil organic carbon (OC). Coastal wetlands face increasing salinity, marine-derived nutrients, and inundation depths from increasing rates of SLR. To quantify the effects of SLR on soil OC stocks and fluxes and elevation change, we conducted two mesocosm experiments using the foundation species sawgrass (Cladium jamaicense) and organic soils from freshwater and brackish Florida Everglades marshes for 1 year. In freshwater mesocosms, we compared ambient and elevated salinity (fresh, 9 ppt) and phosphorus (ambient, + 1 g P m(-2) year(-1)) treatments with a 2 x 2 factorial design. Salinity addition reduced root biomass (48%), driving 2.8 +/- 0.3 cm year(-1) of elevation loss, while soil elevation was maintained in freshwater conditions. Added P increased root productivity (134%) but also increased breakdown rates (k) of roots (31%) and leaves (42%) with no effect on root biomass or soil elevation. In brackish mesocosms, we compared ambient and elevated salinity (10, 19 ppt) and inundated and exposed conditions (water level 5-cm below and 4-cm above soil). Elevated salinity decreased root productivity (70%) and root biomass (37%) and increased k in litter (33%) and surface roots (11%), whereas inundation decreased subsurface root k (10%). All brackish marshes lost elevation at similar rates (0.6 +/- 0.2 cm year(-1)). In conclusion, saltwater intrusion in freshwater and brackish wetlands may reduce net OC storage and increase vulnerability to SLR despite inundation or marine P supplies.
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Coldren, G. A., & Proffitt, C. E. (2017). Mangrove seedling freeze tolerance depends on salt marsh presence, species, salinity, and age. Hydrobiologia, 803(1), 159–171.
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Greenberg, C. H., Goodrick, S., Austin, J. D., & Parresol, B. R. (2015). Hydroregime Prediction Models for Ephemeral Groundwater-Driven Sinkhole Wetlands: a Planning Tool for Climate Change and Amphibian Conservation. Wetlands, 35(5), 899–911.
Abstract: Hydroregimes of ephemeral wetlands affect reproductive success of many amphibian species and are sensitive to altered weather patterns associated with climate change. We used 17 years of weekly temperature, precipitation, and water-depth measurements for eight small, ephemeral, groundwater-driven sinkhole wetlands in Florida sandhills to develop a hydroregime predictive model. To illustrate its utility for climate-change planning, we forecasted weekly wetland water-depths and hydroperiods (2012-2060) using our model and downscaled climate data from the CSIRO Mk3.5 Global Circulation Model under an A1B emissions scenario. We then examined how forecasted water depths and hydroperiods might alter reproductive success, and thereby populations, of five anuran species. Precipitation and water-depth from the prior week were significant predictors of water depth. Our model forecasted shallower depths and shortened hydroperiods for most wetlands when used with the CSIRO Mk3.5 A1B scenario. The forecasted hydroregimes would likely provide adequate reproductive opportunity for only one of the five species we examined. We demonstrate the utility of our model in examining how different climate-change scenarios might affect hydroregimes and, indirectly, biological diversity. Climate change uncertainty highlights the importance of retaining multiple, hydrologically diverse wetlands on landscapes to maximize the potential for successful reproduction by species having differing hydroregime requirements.
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Griscom, B. W., Adams, J., Ellis, P. W., Houghton, R. A., Lomax, G., Miteva, D. A., et al. (2017). Natural climate solutions. Proc Natl Acad Sci USA, 114(44), 11645–11650.
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Hahus, I., Migliaccio, K., Douglas-Mankin, K., Klarenberg, G., & Munoz-Carpena, R. (2018). Using Cluster Analysis to Compartmentalize a Large Managed Wetland Based on Physical, Biological, and Climatic Geospatial Attributes. Environ Manage, 62(3), 571–583.
Abstract: Hierarchical and partitional cluster analyses were used to compartmentalize Water Conservation Area 1, a managed wetland within the Arthur R. Marshall Loxahatchee National Wildlife Refuge in southeast Florida, USA, based on physical, biological, and climatic geospatial attributes. Single, complete, average, and Ward's linkages were tested during the hierarchical cluster analyses, with average linkage providing the best results. In general, the partitional method, partitioning around medoids, found clusters that were more evenly sized and more spatially aggregated than those resulting from the hierarchical analyses. However, hierarchical analysis appeared to be better suited to identify outlier regions that were significantly different from other areas. The clusters identified by geospatial attributes were similar to clusters developed for the interior marsh in a separate study using water quality attributes, suggesting that similar factors have influenced variations in both the set of physical, biological, and climatic attributes selected in this study and water quality parameters. However, geospatial data allowed further subdivision of several interior marsh clusters identified from the water quality data, potentially indicating zones with important differences in function. Identification of these zones can be useful to managers and modelers by informing the distribution of monitoring equipment and personnel as well as delineating regions that may respond similarly to future changes in management or climate.
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Hinson, A. L., Feagin, R. A., Eriksson, M., Najjar, R. G., Herrmann, M., Bianchi, T. S., et al. (2017). The spatial distribution of soil organic carbon in tidal wetland soils of the continental United States. Glob Change Biol, 23(12), 5468–5480.
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Kidwell, D. M., Dietrich, J. C., Hagen, S. C., & Medeiros, S. C. (2017). An Earth's Future Special Collection: Impacts of the coastal dynamics of sea level rise on low-gradient coastal landscapes. Earth's Future, 5(1), 2–9.
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Marazzi, L., Gaiser, E. E., Jones, V. J., Tobias, F. A. C., & Mackay, A. W. (2017). Algal richness and life-history strategies are influenced by hydrology and phosphorus in two major subtropical wetlands. Freshw Biol, 62(2), 274–290.
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Mazzei, V., Wilson, B. J., Servais, S., Charles, S. P., Kominoski, J. S., & Gaiser, E. E. (2019). Periphyton as an indicator of saltwater intrusion into freshwater wetlands: insights from experimental manipulations. Ecol Appl, 30(3), e02067.
Abstract: Saltwater intrusion has particularly large impacts on karstic wetlands of the Caribbean Basin due to their porous, carbonate bedrock and low elevation. Increases in salinity and phosphorus (P) accompanying saltwater intrusion into these freshwater, P-limited wetlands are expected to alter biogeochemical cycles along with the structure and function of plant and algal communities. Calcareous periphyton is a characteristic feature of karstic wetlands and plays a central role in trophic dynamics, carbon storage, and nutrient cycling. Periphyton is extremely sensitive to water quality and quantity, but the effects of saltwater intrusion on these microbial mats remain to be understood. We conducted an ex situ mesocosm experiment to test the independent and combined effects of elevated salinity and P on the productivity, nutrient content, and diatom composition of calcareous periphyton from the Florida Everglades. We measured periphyton total carbon, nitrogen, and P concentrations and used settlement plates to measure periphyton accumulation rates and diatom species composition. The light and dark bottle method was used to measure periphyton productivity and respiration. We found that exposure to ~1 g P.m(-2) .yr(-1) significantly increased periphyton mat total P concentrations, but had no effect on any other response variable. Mats exposed to elevated salinity (~22 kg salt.m(-2) .yr(-1) ) had significantly lower total carbon and tended to have lower biomass and reduced productivity and respiration rates; however, mats exposed to salinity and P simultaneously had greater gross and net productivity. We found strong diatom species dissimilarity between fresh- and saltwater-treated periphyton, while P additions only elicited compositional changes in periphyton also treated with saltwater. This study contributes to our understanding of how the ecologically important calcareous periphyton mats unique to karstic, freshwater wetlands respond to increased salinity and P caused saltwater intrusion and provides a guide to diatom indicator taxa for these two important environmental drivers.
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McCarthy, M. J., Colna, K. E., El-Mezayen, M. M., Laureano-Rosario, A. E., Méndez-Lázaro, P., Otis, D. B., et al. (2017). Satellite Remote Sensing for Coastal Management: A Review of Successful Applications. Environmental Management, 60(2), 323–339.
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Oliver-Cabrera, T., & Wdowinski, S. (2016). InSAR-Based Mapping of Tidal Inundation Extent and Amplitude in Louisiana Coastal Wetlands. Remote Sensing, 8(5), 393.
Abstract: The Louisiana coast is among the most productive coastal areas in the US and home to the largest coastal wetland area in the nation. However, Louisiana coastal wetlands have been disappearing at an alarming rate due to natural and anthropogenic processes, including sea level rise, land subsidence and infrastructure development. Wetland loss occurs mainly along the tidal zone, which varies in width and morphology along the Louisiana shoreline. In this study, we use Interferometric Synthetic Aperture Radar (InSAR) observations to detect the extent of the tidal inundation zone and evaluate the interaction between tidal currents and coastal wetlands. Our data consist of ALOS and Radarsat-1 observations acquired between 2006-2011 and 2003-2008, respectively. Interferometric processing of the data provides detailed maps of water level changes in the tidal zone, which are validated using sea level data from a tide gauge station. Our results indicate vertical tidal changes up to 30 cm and horizontal tidal flow limited to 5-15 km from open waters. The results also show that the tidal inundation is disrupted by various man-made structures, such as canals and roads, which change the natural tidal flow interaction with the coast.
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Steinmuller, H. E., Foster, T. E., Boudreau, P., Hinkle C.R., & Chambers, L. G. (2020). Tipping Points in the Mangrove March: Characterization of Biogeochemical Cycling Along the MangroveSalt Marsh Ecotone. Ecosystems, 23, 417–434.
Abstract: Coastal wetland vegetation communities can respond to sea level rise via the encroachment of more salt- and inundation-tolerant species into existing vegetation communities. Black mangroves (Avicennia germinans L.) are encroaching on saltgrass (Distichlis spicata L.) within the Merritt Island National Wildlife Refuge in east central Florida (USA). Nine soil cores collected along three transects captured the transitions of both perceived abiotic drivers (salinity and inundation) and vegetation communities during both high- and low-water seasons to investigate patterns in soil biogeochemical cycling of carbon (C), nitrogen (N), and phosphorus (P). Results showed no change in soil carbon dioxide production along the ecotone during either season, though changes in enzyme activity and mineralization rates of N and P could indicate changes in C quality and nutrient availability affecting C degradation along the ecotone. All parameters, excluding microbial biomass carbon, showed higher rates of activity or availability during the low-water season. Long-term soil nutrient stores (total C, N, P) were greatest in the saltgrass soils and similar between the mangrove and transition zone soils, indicating a �tipping point� in biogeochemical function where the transition zone is functionally equivalent to the encroaching mangrove zone. Indicators of current biogeochemical cycling (that is, enzyme activity, potentially mineralizable N rates, and extractable ammonium concentrations) showed alterations in activity across the ecotone, with the transition zone often functioning with lower activity than within end members. These indicators of current biogeochemical cycling change in advance of full vegetation shifts. Increases in salinity and inundation were linked to mangrove encroachment.
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Taillie, P. J., Roman-Cuesta, R., Lagomasino, D., Cifuentes-Jara, M., Fatoyinbo, T., Ott, L. E., et al. (2020). Widespread mangrove damage resulting from the 2017 Atlantic mega hurricane season. Environ. Res. Lett., 15(6), 064010.
Abstract: Comprised of 17 named tropical storms, 6 of which were major hurricanes, the 2017 Atlantic hurricane season ranked as one of the most damaging and costly hurricane seasons on record. In addition to socio-economic impacts, many previous studies have shown that important coastal ecosystems like mangroves are shaped by severe storms. However, little is known about how the cumulative effects of storms over entire hurricane seasons affect mangroves across large regions. We used satellite imagery from the entire Caribbean and Gulf of Mexico region to show that 2017 resulted in disproportionate mangrove damage compared to baseline responses over the previous 8 years. Specifically, we observed 30 times more mangrove damage, via a reduction in the normalized difference vegetation index (NDVI), during 2017 compared to any of the eight previous hurricane seasons, and most (72%) of this damage persisted throughout the 7 month post-hurricane season period as indicated by no NDVI recovery. Furthermore, wind speed, rainfall, and canopy height data showed that mangrove damage primarily resulted from high maximum wind speeds, but flooding (cumulative rainfall), previous storm history, and mangrove structure (canopy height) were also important predictors of damage. While mangroves are known to be resilient to hurricane impacts, our results suggest that increasingly frequent mega-hurricane seasons in the Caribbean region will dramatically alter mangrove disturbance dynamics.
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Wilson, B. J., Wilson BJ, Servais, S., Servais S, Mazzei, V., Mazzei V, et al. (2018). Salinity pulses interact with seasonal dry-down to increase ecosystem carbon loss in marshes of the Florida Everglades. Ecol Appl, 28(8), 2092–2108.
Abstract: Coastal wetlands are globally important sinks of organic carbon (C). However, to what extent wetland C cycling will be affected by accelerated sea-level rise (SLR) and saltwater intrusion is unknown, especially in coastal peat marshes where water flow is highly managed. Our objective was to determine how the ecosystem C balance in coastal peat marshes is influenced by elevated salinity. For two years, we made monthly in situ manipulations of elevated salinity in freshwater (FW) and brackish water (BW) sites within Everglades National Park, Florida, USA. Salinity pulses interacted with marsh-specific variability in seasonal hydroperiods whereby effects of elevated pulsed salinity on gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem productivity (NEP) were dependent on marsh inundation level. We found little effect of elevated salinity on C cycling when both marsh sites were inundated, but when water levels receded below the soil surface, the BW marsh shifted from a C sink to a C source. During these exposed periods, we observed an approximately threefold increase in CO2 efflux from the marsh as a result of elevated salinity. Initially, elevated salinity pulses did not affect Cladium jamaicense biomass, but aboveground biomass began to be significantly decreased in the saltwater amended plots after two years of exposure at the BW site. We found a 65% (FW) and 72% (BW) reduction in live root biomass in the soil after two years of exposure to elevated salinity pulses. Regardless of salinity treatment, the FW site was C neutral while the BW site was a strong C source (-334 to -454 g C.m(-2) .yr(-1) ), particularly during dry-down events. A loss of live roots coupled with annual net CO2 losses as marshes transition from FW to BW likely contributes to the collapse of peat soils observed in the coastal Everglades. As SLR increases the rate of saltwater intrusion into coastal wetlands globally, understanding how water management influences C gains and losses from these systems is crucial. Under current Everglades' water management, drought lengthens marsh dry-down periods, which, coupled with saltwater intrusion, accelerates CO2 loss from the marsh.
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Xiao, H., Wang, D., Medeiros, S. C., Hagen, S. C., & Hall, C. R. (2018). Assessing sea-level rise impact on saltwater intrusion into the root zone of a geo-typical area in coastal east-central Florida. Sci Total Environ, 630, 211–221.
Abstract: Saltwater intrusion (SWI) into root zone in low-lying coastal areas can affect the survival and spatial distribution of various vegetation species by altering plant communities and the wildlife habitats they support. In this study, a baseline model was developed based on FEMWATER to simulate the monthly variation of root zone salinity of a geo-typical area located at the Cape Canaveral Barrier Island Complex (CCBIC) of coastal east-central Florida (USA) in 2010. Based on the developed and calibrated baseline model, three diagnostic FEMWATER models were developed to predict the extent of SWI into root zone by modifying the boundary values representing the rising sea level based on various sea-level rise (SLR) scenarios projected for 2080. The simulation results indicated that the extent of SWI would be insignificant if SLR is either low (23.4cm) or intermediate (59.0cm), but would be significant if SLR is high (119.5cm) in that infiltration/diffusion of overtopping seawater in coastal low-lying areas can greatly increase root zone salinity level, since the sand dunes may fail to prevent the landward migration of seawater because the waves of the rising sea level can reach and pass over the crest under high (119.5cm) SLR scenario.
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Xu, T., Valocchi, A. J., Ye, M., Liang, F., & Lin, Y. - F. (2017). Bayesian calibration of groundwater models with input data uncertainty. Water Resour. Res., 53(4), 3224–3245.
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Zalman,, Keller,, Tfaily,, Kolton,, Pfeifer-Meister,, Wilson,, et al. (2018). Small differences in ombrotrophy control regional-scale variation in methane cycling among Sphagnum-dominated peatlands. Biogeochemistry, 139(2), 155–177.
Abstract: Although methane (CH4) dynamics are known to differ at broad scales among peatland types and with climate, there is limited understanding of the variability associated with anaerobic carbon (C) cycling, and, the mechanisms that control that variability, among low pH, Sphagnum moss-dominated peatlands within a geographical region with similar climate. This is important because upscaling of CH4 emissions to regional and global scales often considers peatlands as a single, or at most two, ecosystem type(s). Here, we report the results from two studies exploring the controls of CH4 cycling in peatlands from the Upper Midwest (USA). Potential CH4 production and resultant CO2:CH4 ratios varied by several orders-of-magnitude among these soils. These differences were only partially explained by pH and fiber content (a measure of degree of decomposition in peat), suggesting other, more complicated controls may drive CH4 cycling in ombrotrophic peat soils. Based in part on the results from this survey, we more intensively examined CH4 dynamics in three bog-like, acidic, Sphagnum-dominated peatlands in northern Minnesota that differed in their degree of ombrotrophy. Net CH4 flux was lowest in the peatland with well-developed hummocks, and the isotopic composition of the CH4 along with methanotroph gene expression indicated a strong role for CH4 oxidation in controlling net CH4 flux. There were limited differences in porewater chemistry (CH4 and dissolved inorganic C concentrations) or microbial community composition among sites, and potential CH4 production was also similar among the sites. Taken together, these experiments demonstrate that high variation in CH4 cycling in seemingly similar peatlands within a single geographical region is common. We suggest a one peatland represents all approach is inappropriate—even among Sphagnum-dominated peatlands—and caution must be used when extrapolating data from a single site to the landscape scale, even for outwardly very similar peatlands. Instead, the macroscale development of peatlands, and concomitantly their microtopography as expressed in the proportion of hummocks, hollows, lawns and pools, need to be considered as central controls over CH4 emissions.
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