Mesoscale geomorphic change on barrier estuarine regime at the tropical coast of Chandipur, India: Evidence from assessment of grain-size distribution

It is crucial for policy makers and environmental managers to determine the future dynamics of coastal wetlands, especially the existence of their response, disruption, and recovery regimes. Reconstruction of meso-scale evolution in coastal ecosystems can help to adapt coastal resource management techniques to the natural scales of system activity, thereby encouraging true biodiversity. This research provides an overview of decadal (mesoscale) geomorphic transition by high-resolution grain size analysis of a sediment deposit from a barrier estuary regime on the Chandipur coast, India. Coastal marshland’s grain size distribution (GSD) has generally been analyzed using End Member Mixing Models (EMMA) and Probability Density Function (PDF) methods (e.g. log-normal, log skew-Laplace). Although these techniques do not consider the compositional nature of the records, which can undermine the outcomes of the interpretation of sedimentary deposits. The approach to reliable granulometric analysis of lithostratigraphic sequences aims at establishing direct links between fluid dynamics and subsequent shifts in the texture of sediments. In this study, GSD analysis of marsh sediment is represented by compositional data analysis (CoDa) and a multivariate statistical framework. Barrier estuary evolution, presented by time lapses of satellite maps coupled with grain size and carbon content of marsh sediment, primarily reflects the evolving hydrodynamics of the back barrier area. These findings will provide a statistically robust analysis of the depositional system in coastal marshland. Multiannual environmental variations in the back barrier configuration illustrate the importance of this applied approach with respect to bridging the basis of estuarine evolution and process information.

Refining Estimates of Greenhouse Gas Emissions From Salt Marsh “Blue Carbon” Erosion and Decomposition

Coastal wetlands have sediments that contain organic matter preserved against decomposition for timespans that can range up to millennia. This “blue carbon” in wetland sediments has been proposed as a sink for atmospheric carbon dioxide and a potential source of greenhouse gases if coastal habitats are lost. A missing gap in the role of coastal habitats in the global carbon cycle is elucidating the fate of wetland sediment carbon following disturbance events, such as erosion, that can liberate organic matter to an oxygenated environment where decomposition can more readily occur. Here, we track the fate of previously stored salt marsh sediment by measuring the production of carbon dioxide (CO2) and methane (CH4) during an oxygenated incubation. Sediments from two depth horizons (5–10 cm and 20–25 cm) were incubated at two temperatures (20 and 30°C) for 161 days. Q10 of the decomposition process over the entire course of the experiment was 2.0 ± 0.1 and 2.2 ± 0.2 for shallow and deep horizons, respectively. Activation energy for the decomposition reaction (49.7 kJ ⋅ mol–1 and 58.8 kJ ⋅ mol–1 for shallow and deep sediment horizons, respectively) was used to calculate temperature-specific decomposition rates that could be applied to environmental data. Using high-frequency water temperature data, this strategy was applied to coastal states in the conterminous United States (CONUS) where we estimated annual in situ decomposition of eroded salt marsh organic matter as 7–24% loss per year. We estimate 62.90 ± 2.81 Gg C ⋅ yr–1 is emitted from eroded salt marsh sediment decomposition in the CONUS.

Identification of the natural background of phosphorus in the Scheldt river using tidal marsh sediment cores

Elevated phosphate (PO4) concentrations can harm the ecological status in water by eutrophication. In the majority of surface waters in lowland regions such as Flanders (Belgium), the local PO4 levels exceed the limits defined by environmental policy and fail to decrease, despite decreasing total phosphorus (P) emissions. In order to underpin the definition of currents limits, this study was set up to identify the pre-industrial background PO4 concentration in surface water of the Scheldt river, a tidal river in Flanders. We used the sedimentary records preserved in tidal marsh sediment cores as an archive for reconstructing historical changes in surface water PO4. For sediment samples at different depths below the sediment surface, we dated the time of sediment deposition and analysed the extractable sediment-P. The resulting time series of sediment-P was linked to time series of measured surface water PO4 concentrations (data 1967–present). By combining the sediment-P and water-PO4 data, the sorption characteristics of the sediment could be described. Those sorption characteristics allowed us to estimate a pre-industrial background surface water PO4 levels, based on deeper sediment-P that stabilised at concentrations smaller than the modern. In three out of the four cores, the sediment-P peaked around 1980, coinciding with the peak in surface water PO4. The estimated pre-industrial (~1800) background PO4-concentration in the Scheldt river water was 62 [57; 66 (95 %CI)] µg PO4-P/L. That concentration exceeds the previously estimated natural background values for lakes in Flanders (15–35 µg TP/L) and is about half of the prevailing limit in the Scheldt river (120 µg PO4-P/L). In the 1930s, river water concentrations were estimated at 140 [128; 148] µg PO4-P/L, already exceeding the current limit. The method developed here proved useful for reconstructing historical, background PO4 concentrations of a lowland tidal river. A similar approach can apply to other lowland tidal rivers to provide a scientific basis for local, catchment specific PO4 backgrounds.

Halomonas rituensis sp. nov. and Halomonas zhuhanensis sp. nov., isolated from natural salt marsh sediment on the Tibetan Plateau

Two novel Gram-stain-negative, aerobic and non-motile rods bacteria, designated TQ8ST and ZH2ST, were isolated from salt marsh sediment collected from the Tibetan Plateau. Strain TQ8ST was found to grow at 10–40 °C (optimum, 30 °C), pH 6.0–11.0 (optimum, pH 8.0–9.0) and in the presence of 2–12 % (w/v) NaCl (optimum, 6–8 %). Strain ZH2ST was found to grow at 15–40 °C (optimum, 30 °C), pH 7.0–10.0 (optimum pH 9.0) and in the presence of 2–10 % (w/v) NaCl (optimum, 4–6 %). Phylogenetic analysis based on the 16S rRNA gene sequences showed that strains TQ8ST and ZH2ST shared 99.07 % sequence similarity between each other and were affiliated with the genus Halomonas , sharing 97.48 % and 97.41 % of sequence similarity to their closest neighbour Halomonas sulfidaeris Esulfide1T, respectively. DNA–DNA hybridization analyses showed 61.0 % relatedness between strains TQ8ST and ZH2ST. The average nucleotide identity and the average amino acid identity values between the two genomes were 92.33 and 92.84 %, respectively. The values between the two strains and their close phylogenetic relatives were all below 95 %. The major respiratory quinones of strain TQ8ST were Q-9 and Q-8, while that of ZH2ST was Q-9. The main fatty acids shared by the two strains were C18 : 1 ω6c and/or C18 : 1 ω7c, C16 : 1 ω6c and/or C16 : 1 ω7c, C16 : 0 and C12 : 0 3-OH. Strain ZH2ST can be distinguished from TQ8ST by a higher proportion of C19 : 0 cyclo ω8c. The G+C content of the genomic DNA of strains TQ8ST and ZH2ST were 57.20 and 57.14 mol%, respectively. On the basis of phenotypic distinctiveness and phylogenetic divergence, the two isolates are considered to represent two novel species of the genus Halomonas , for which the names Halomonas rituensis sp. nov (type strain TQ8ST=KCTC 62530T=CICC 24572T) and Halomonas zhuhanensis sp. nov (type strain ZH2ST=KCTC 62531T=CICC 24505T) are proposed.