Palynological and Carbon-Isotopic Techniques for Reconstruction of Paleomarsh Salinity Zones.

Palynological and carbon-13 analyses were studied to determine their practicality as tools for paleoecological reconstruction of marsh vegetation communities of the Mississippi delta plain. Both were calibrated on marsh surface sediment samples from four vegetation zones within Barataria Basin, Louisiana: fresh, intermediate, brackish and salt marsh. Samples were taken concurrent to vegetation sampling to allow comparison of sediment data to plant biomass and clip plot data from each of the four zones. The \partial\sp{13}C of sedimentary carbon reflects the proportion of C-3 and C-4 species at a site (which corresponds to a salinity gradient in the basin). The average from all sites within each wetland type is $-$27.8, $-$22.1, $-$16.9 and $-$16.2\perthous, for fresh, intermediate, brackish and salt marshes. This method can distinguish among the fresh, intermediate and brackish vegetation zones. A seasonal study of pollen carried by Mississippi River was conducted to determine the impact of river floodwaters on a marsh pollen assemblages. River water assemblages vary seasonally and reflect pollen sources from without the drainage basin. Types abundant during high river stage, indeterminate grains (assumed to present reworked material), Pinus, Quercus, Taxodium, TCT, Ambrosia and Chenopodiaceae-Amaranthaceae type, are assumed to be over-represented in marshes subject to river flooding. Each of the four vegetation zones has a characteristic pollen assemblage. Assemblages are not affected by over-representation of local sources, but appear to reflect the composition of the entire vegetation zone (extra-local sources). Classification of modern pollen assemblages by discriminant functions is highly successful (94% correct classification rate) even when common river-borne taxa are excluded from the analysis. When applied to buried marsh deposits (ca. 2,000 yr B.P.) classification results from both techniques generally agree indicating that \partial\sp{13}C values are not significantly shifted by diagenetic processes in the sediments. Comparison of information provided by both techniques, however, also demonstrates that important analogues (i.e., progradational marshes) are missing from the suite of modern samples

Invertebrate communities of Bay of Fundy salt marsh pools: comparison of a natural and recovering marsh

Disturbed salt marshes may recover with little additional management once tidal inundation is restored. We assessed the success of such recovery by comparing the invertebrate biota of Bay of Fundy salt marsh pools in a reference site at Dipper Harbour to that of Saints Rest marsh that had been drained for over a century and to which tidal flooding had been returned ~50 years prior to our study. The sediments and vegetation of salt marsh pools were sampled seasonally throughout one year. Average biomass of pool invertebrates ranged from 1.8 to 4.0 g dry wt m−2, depending on the amount of vegetation cover in the pools. The most abundant organisms of the pools were the gastropod Ecrobia truncata (=Hydrobia tottentei), Tubificidae (=Naididae) oligochaetes, and Chironomidae (=Chironomini). We compared overall abundance and biomass of the invertebrates in the pool communities, assessing the month of sampling, pool elevation, and source marsh as explanatory variables. Our analyses revealed that marsh origin of pools seldom explained a significant amount of variance, and when it did, the proportion of variance explained was usually lower than elevation of pools and month of sampling. Diversity of invertebrates found in all pools was higher at the recovering site with species richness >40% higher than in the reference site. We conclude that after an estimated 50 years since dyke failure and return of tidal flooding to Saints Rest marsh, that the ecosystem function represented by pools and their fauna has recovered

Dinoflagellate Cysts Track Eutrophication In The Northern Gulf Of Mexico

We examined organic-walled dinoflagellate cysts from one 210Pb-dated sediment core and 39 surface sediment samples from the northern Gulf of Mexico to determine the relationship between nutrient enrichment and cyst assemblages in this region characterized by oxygen deficiency. The core spans from 1962 to 1997 and its sampling location is directly influenced by the Mississippi River plume. Surface sediments were collected in 2006, 2007, 2008, and 2014 and represent approximately 1 to 4 years of accumulation. A total of 57 cyst taxa were recorded, and four heterotrophic taxa in particular were found to increase in the top section (1986–1997) of the core—Brigantedinium spp., cysts of Archaeperidinium minutum, cysts of Polykrikos kofoidii, and Quinquecuspis concreta. These taxa show a similar increasing trend with variations in US fertilizer consumption and Mississippi River nitrate concentrations, both of which increased substantially in the 1970s and 1980s. The same four heterotrophic taxa dominated dinoflagellate cyst assemblages collected near the Mississippi River Bird’s Foot Delta where nutrient concentrations were higher, especially in 2014. We propose that these cyst taxa can be used as indicators of eutrophication in the Gulf of Mexico. A canonical correspondence analysis (CCA) supports this proposition. The CCA identified sea-surface nutrient concentrations, sea-surface temperature, and sea-surface salinity as the most important factors influencing the cyst assemblages. In addition, cysts produced by the potentially toxic dinoflagellates Pyrodinium bahamense and Lingulodinium polyedrum were documented, but did not appear to have increased over the past 50 years

Monitoring tidal hydrology in coastal wetlands with the Mini Buoy: applications for mangrove restoration

Acquiring in situ data of tidal flooding is key for the successful restoration planning of intertidal wetlands such as salt marshes and mangroves. However, monitoring spatially explicit inundation time series and tidal currents can be costly and technically challenging. With the increasing availability of low-cost sensors and data loggers, customized solutions can now be designed to monitor intertidal hydrodynamics with direct applications for restoration and management. In this study, we present the design, calibration, and application of the “Mini Buoy”, a low-cost underwater float containing an acceleration data logger for monitoring tidal inundation characteristics and current velocities derived from single-axis equilibrium acceleration (i.e. logger tilt). The acceleration output of the Mini Buoys was calibrated against water-level and current-velocity data in the hypertidal Bay of Fundy, Canada, and in a tidally reconnected former aquaculture pond complex in North Sumatra, Indonesia. Key parameters, such as submersion time and current velocities during submergence, can be determined over several months using the Mini Buoy. An open-source application was developed to generate ecologically meaningful hydrological information from the Mini Buoy data for mangrove restoration planning. We present this specific SE Asian mangrove restoration application alongside a flexible concept design for the Mini Buoy to be customized for research and management of intertidal wetlands worldwide

A blueprint for blue carbon: Toward an improved understanding of the role of vegetated coastal habitats in sequestering CO2

Recent research has highlighted the valuable role that coastal and marine ecosystems play in sequestering carbon dioxide (CO2). The carbon (C) sequestered in vegetated coastal ecosystems, specifically mangrove forests, seagrass beds, and salt marshes, has been termed "blue carbon". Although their global area is one to two orders of magnitude smaller than that of terrestrial forests, the contribution of vegetated coastal habitats per unit area to long-term C sequestration is much greater, in part because of their efficiency in trapping suspended matter and associated organic C during tidal inundation. Despite the value of mangrove forests, seagrass beds, and salt marshes in sequestering C, and the other goods and services they provide, these systems are being lost at critical rates and action is urgently needed to prevent further degradation and loss. Recognition of the C sequestration value of vegetated coastal ecosystems provides a strong argument for their protection and restoration; however, it is necessary to improve scientific understanding of the underlying mechanisms that control C sequestration in these ecosystems. Here, we identify key areas of uncertainty and specific actions needed to address them

Elevated temperature and nutrients lead to increased N2O emissions from salt marsh soils from cold and warm climates

Salt marshes can attenuate nutrient pollution and store large amounts of ‘blue carbon’ in their soils, however, the value of sequestered carbon may be partially offset by nitrous oxide (N2O) emissions. Global climate and land use changes result in higher temperatures and inputs of reactive nitrogen (Nr) into coastal zones. Here, we investigated the combined effects of elevated temperature (ambient + 5℃) and Nr (double ambient concentrations) on nitrogen processing in marsh soils from two climatic regions (Quebec, Canada and Louisiana, U.S.) with two vegetation types, Sporobolus alterniflorus (= Spartina alterniflora) and Sporobolus pumilus (= Spartina patens), using 24-h laboratory incubation experiments. Potential N2O fluxes increased from minor sinks to major sources following elevated treatments across all four marsh sites. One day of potential N2O emissions under elevated treatments (representing either long-term sea surface warming or short-term ocean heatwaves effects on coastal marsh soil temperatures alongside pulses of N loading) offset 15–60% of the potential annual ambient N2O sink, depending on marsh site and vegetation type. Rates of potential denitrification were generally higher in high latitude than in low latitude marsh soils under ambient treatments, with low ratios of N2O:N2 indicating complete denitrification in high latitude marsh soils. Under elevated temperature and Nr treatments, potential denitrification was lower in high latitude soil but higher in low latitude soil as compared to ambient conditions, with incomplete denitrification observed except in Louisiana S. pumilus. Overall, our findings suggest that a combined increase in temperature and Nr has the potential to reduce salt marsh greenhouse gas (GHG) sinks under future global change scenarios

The Future of Blue Carbon Science

The term Blue Carbon (BC) was first coined a decade ago to describe the disproportionately large contribution of coastal vegetated ecosystems to global carbon sequestration. The role of BC in climate change mitigation and adaptation has now reached international prominence. To help prioritise future research, we assembled leading experts in the field to agree upon the top-ten pending questions in BC science. Understanding how climate change affects carbon accumulation in mature BC ecosystems and during their restoration was a high priority. Controversial questions included the role of carbonate and macroalgae in BC cycling, and the degree to which greenhouse gases are released following disturbance of BC ecosystems. Scientists seek improved precision of the extent of BC ecosystems; techniques to determine BC provenance; understanding of the factors that influence sequestration in BC ecosystems, with the corresponding value of BC; and the management actions that are effective in enhancing this value. Overall this overview provides a comprehensive road map for the coming decades on future research in BC science