Tidal Marsh Research Articles

Changes in Fish Communities Before and After Establishment of Northern Snakehead in an Estuarine Marsh of the Chesapeake Bay Watershed

Abstract Northern Snakehead Channa argus an invasive freshwater piscivore discovered in the Potomac River in 2004, has spread throughout the Chesapeake Bay (Maryland, USA). The first incidental reports of Northern Snakehead in Blackwater National Wildlife Refuge (Chesapeake Bay) occurred during 2012. Since that time, Northern Snakehead have become established and has formed the basis for a popular harvest fishery in the Blackwater River drainage. This increase in abundance has caused concern about competition and predation on other species. To determine whether the fish community has changed in composition or relative abundance in Blackwater River drainage (Blackwater River and Little Blackwater River) since the introduction of Northern Snakehead, we replicated fish community surveys from 2006 and 2007 (pre-snakehead) and compared those fish community composition with data collected from 2018 to 2019 (post-snakehead). Subsequent seasonal surveys of fishes between 2021 and 2023 helped to substantiate our findings. Including pre-snakehead and post-snakehead survey periods, we caught 35 species (32 fish species and 3 invertebrate species) totaling 51,781 individuals. With few exceptions, species richness was similar between periods, with 27 fishes caught pre-snakehead and 26 species caught post-snakehead. However, of 22 species that we captured during both pre-snakehead and post snakehead survey periods, 19 declined in relative abundance, which was supported during subsequent seasonal surveys. These changes led to four of six sites having significantly different fish communities between survey periods. Fish communities experienced declines in relative abundances of popular prey species for Northern Snakehead: White Perch Morone americana, sunfish Lepomis, and killifishes Fundulus. Our study is among the first to document long-term fish community changes following establishment of Northern Snakehead in its introduced range.

Controls on spatial variation in porewater methane concentrations across United States tidal wetlands

Tidal wetlands can be a substantial sink of greenhouse gases, which can be offset by variable methane (CH4) emissions under certain environmental conditions and anthropogenic interventions. Land managers and policymakers need maps of tidal wetland CH4 properties to make restoration decisions and inventory greenhouse gases. However, there is a mismatch in spatial scale between point-based sampling of porewater CH4 concentration and its predictors, and the coarser resolution mapping products used to upscale these data. We sampled porewater CH4 concentrations, salinity, sulfate (SO42−), ammonium (NH4+), and total Fe using a spatially stratified sampling at 27 tidal wetlands in the United States. We measured porewater CH4 concentrations across four orders of magnitude (0.05 to 852.9 μM). The relative contribution of spatial scale to variance in CH4 was highest between- and within-sites. Porewater CH4 concentration was best explained by SO42− concentration with segmented linear regression (p < 0.01, R2 = 0.54) indicating lesser sensitivity of CH4 to SO42− below 0.62 mM SO42−. Salinity was a significant proxy for CH4 concentration, because it was highly correlated with SO42− (p < 0.01, R2 = 0.909). However, salinity was less predictive of CH4 with segmented linear regression (p < 0.01, R2 = 0.319) relative to SO42−. Neither NH4+, total Fe, nor relative tidal elevation correlated significantly with porewater CH4; however, NH4+ was positively and significantly correlated with SO42− after detrending CH4 for its relationship with SO42− (p < 0.01, R2 = 0.194). Future sampling should focus on within- and between-site environmental gradients to accurately map CH4 variation. Mapping salinity at sub-watershed scales has some potential for mapping SO42−, and by proxy, constraining spatial variation in porewater CH4 concentrations. Additional work is needed to explain site-level deviations from the salinity-sulfate relationship and elucidate other predictors of methanogenesis. This work demonstrates a unique approach to remote team science and the potential to strengthen collaborative research networks.

Effects of inorganic nitrogen enrichment on soil CH4 and CO2 production in freshwater and mesohaline marshes across six estuaries in China

Eutrophication is an important environmental stressor in coastal wetlands that alters ecosystem processes including primary production and the carbon cycle. However, how different nitrogen eutrophication scenarios may affect CH4 and CO2 production along a salinity gradient in coastal wetlands is poorly known. We collected the surface soil samples from both tidal freshwater and mesohaline Phragmites australis marshes in six main estuaries in China and conducted inorganic nitrogen enrichment anaerobic incubation experiments. Background soil CH4 and CO2 production rates were strongly correlated with total nitrogen but not salinity. On average, nitrate enrichment decreased soil CH4 and CO2 production rates by ca. 20 % in freshwater marsh and 16–43 % in mesohaline marshes, whereas ammonium enrichment decreased CO2 production by ca. 26–30 % but had no effect on CH4 production. Salinity was not an important mitigating factor in either eutrophication scenario. In most cases, nitrogen addition decreased the extracellular enzyme activities of β-1,4-glucosidase and cellobiohydrolase, but increased the activity of β-N-acetyl glucosaminidase, phenol oxidase and peroxidase. Nitrate addition decreased the mcrA gene abundance on average by 34–35 % but ammonium addition had insignificant effect. Total nitrogen availability was an important driver of CH4 and CO2 production rates in these tidally influenced coastal wetlands. Our results showed that tidal marshes with salinity < 15 ppt had similar soil CH4 production rates, and increasing inorganic nitrogen eutrophication might lower soil microbial carbon gas production in both tidal freshwater and mesohaline marshes.

Identifying and filling critical knowledge gaps can optimize financial viability of blue carbon projects in tidal wetlands

One of the world’s largest “blue carbon” ecosystems, Louisiana’s tidal wetlands on the US Gulf of Mexico coast, is rapidly being lost. Louisiana’s strong legal, regulatory, and monitoring framework, developed for one of the world’s largest tidal wetland systems, provides an opportunity for a programmatic approach to blue carbon accreditation to support restoration of these ecologically and economically important tidal wetlands. Louisiana’s coastal wetlands span ∼1.4 million ha and accumulate 5.5–7.3 Tg yr−1 of blue carbon (organic carbon), ∼6%–8% of tidal marsh blue carbon accumulation globally. Louisiana has a favorable governance framework to advance blue carbon accreditation, due to centralized restoration planning, long term coastal monitoring, and strong legal and regulatory frameworks around carbon. Additional restoration efforts, planned through Louisiana’s Coastal Master Plan, over 50 years are projected to create, or avoid loss of, up to 81,000 ha of wetland. Current restoration funding, primarily from Deepwater Horizon oil spill settlements, will be fully committed by the early 2030s and additional funding sources are required. Existing accreditation methodologies have not been successfully applied to coastal Louisiana’s ecosystem restoration approaches or herbaceous tidal wetland types. Achieving financial viability for accreditation of these restoration and wetland types will require expanded application of existing blue carbon crediting methodologies. It will also require expanded approaches for predicting the future landscape without restoration, such as numerical modeling, to be validated. Additional methodologies (and/or standards) would have many common elements with those currently available but may be beneficial, depending on the goals and needs of both the state of Louisiana and potential purchasers of Louisiana tidal wetland carbon credits. This study identified twenty targeted needs that will address data and knowledge gaps to maximize financial viability of blue carbon accreditation for Louisiana’s tidal wetlands. Knowledge needs were identified in five categories: legislative and policy, accreditation methodologies and standards, soil carbon flux, methane flux, and lateral carbon flux. Due to the large spatial scale and diversity of tidal wetlands, it is expected that progress in coastal Louisiana has high potential to be generalized to similar wetland ecosystems across the northern Gulf of Mexico and globally.

Structure and Function of Soil Bacterial Communities in the Different Wetland Types of the Liaohe Estuary Wetland.

Soil bacterial communities play a crucial role in the functioning of estuarine wetlands. Investigating the structure and function of these communities across various wetland types, along with the key factors influencing them, is essential for understanding the relationship between bacteria and wetland ecosystems. The Liaohe Estuary Wetland formed this study's research area, and soil samples from four distinct wetland types were utilized: suaeda wetlands, reed wetlands, pond returning wetlands, and tidal flat wetlands. The structure and function of the soil bacterial communities were examined using Illumina MiSeq high-throughput sequencing technology in conjunction with the PICRUSt analysis method. The results indicate that different wetland types significantly affect the physical and chemical properties of soil, as well as the structure and function of bacterial communities. The abundance and diversity of soil bacterial communities were highest in the suaeda wetland and lowest in the tidal flat wetland. The dominant bacterial phyla identified were Proteobacteria and Bacteroidota. Furthermore, the dominant bacterial genera identified included RSA9, SZUA_442, and SP4260. The primary functional pathways associated with the bacterial communities involved the biosynthesis of valine, leucine, and isoleucine, as well as lipoic acid metabolism, which are crucial for the carbon and nitrogen cycles. This study enhances our understanding of the mutual feedback between river estuary wetland ecosystems and environmental changes, providing a theoretical foundation for the protection and management of wetlands.

Study on the structure and energy flow of the salt marsh wetland ecosystem in Liaohe Estuary based on the Ecopath model

Salt marshes are one of the three blue carbon ecosystems recognized by the Intergovernmental Panel on Climate Change (IPCC). However, coastal salt marshes in China are facing the risk of degradation. To reveal the status of the salt marsh wetland ecosystem in Liaohe Estuary, an Ecopath model composed of 14 functional groups was constructed based on the 2019 ecological survey data. A comprehensive analysis of the system’s food web structure, energy flow processes, and overall ecosystem characteristics was conducted. The results show that the energy flow in the Liaohe Estuary salt marsh wetland ecosystem is mainly distributed in three integrated trophic levels. The utilization rates of trophic levels II and III are low, easily causing blockages in the lower trophic levels of the ecosystem’s energy flow. The total system throughput of the Liaohe Estuary salt marsh wetland ecosystem is 49,099.039 t·km²·a−1;. The system connectivity index and the system omnivory index are 0.207 and 0.109, respectively. Compared with other wetland systems, the ecosystem has a larger scale, but the overall ecosystem characteristic index reveals lower stability and complexity of the Liaohe Estuary salt marsh wetland system.

Mangrove afforestation as an ecological control of invasive Spartina alterniflora affects rhizosphere soil physicochemical properties and bacterial community in a subtropical tidal estuarine wetland

Background The planting of mangroves is extensively used to control the invasive plant Spartina alterniflora in coastal wetlands. Different plant species release diverse sets of small organic compounds that affect rhizosphere conditions and support high levels of microbial activity. The root-associated microbial community is crucial for plant health and soil nutrient cycling, and for maintaining the stability of the wetland ecosystem. Methods High-throughput sequencing was used to assess the structure and function of the soil bacterial communities in mudflat soil and in the rhizosphere soils of S. alterniflora, mangroves, and native plants in the Oujiang estuarine wetland, China. A distance-based redundancy analysis (based on Bray–Curtis metrics) was used to identify key soil factors driving bacterial community structure. Results S. alterniflora invasion and subsequent mangrove afforestation led to the formation of distinct bacterial communities. The main soil factors driving the structure of bacterial communities were electrical conductivity (EC), available potassium (AK), available phosphorus (AP), and organic matter (OM). S. alterniflora obviously increased EC, OM, available nitrogen (AN), and NO3−-N contents, and consequently attracted copiotrophic Bacteroidates to conduct invasion in the coastal areas. Mangroves, especially Kandelia obovata, were suitable pioneer species for restoration and recruited beneficial Desulfobacterota and Bacilli to the rhizosphere. These conditions ultimately increased the contents of AP, available sulfur (AS), and AN in soil. The native plant species Carex scabrifolia and Suaeda glauca affected coastal saline soil primarily by decreasing the EC, rather than by increasing nutrient contents. The predicted functions of bacterial communities in rhizosphere soils were related to active catabolism, whereas those of the bacterial community in mudflat soil were related to synthesis and resistance to environmental factors. Conclusions Ecological restoration using K. obovata has effectively improved a degraded coastal wetland mainly through increasing phosphorus availability and promoting the succession of the microbial community.

Conversion of coastal marsh to aquaculture ponds decreased the potential of methane production by altering soil chemical properties and methanogenic archaea community structure

Coastal wetlands are among the most productive and dynamic ecosystems globally, contributing significantly to atmospheric methane (CH4) emissions. The widespread conversion of these wetlands into aquaculture ponds degrades these ecosystems, yet its effects on CH4 production and associated microbial mechanisms are not well understood. This study aimed to assess the impact of land conversion on CH4 production potential, total and active soil organic C (SOC) content, and microbial communities. We conducted a comparative study on three brackish marshes and adjacent aquaculture ponds in southeastern China. Compared to costal marshes, aquaculture ponds exhibited significantly (P < 0.05) lower CH4 production potential (0.05 vs. 0.02 μg kg−1 h−1), SOC (17.64 vs. 6.97 g kg−1), total nitrogen (TN) content (1.62 vs. 1.24 g kg−1) and carbon/nitrogen (C/N) ratio (10.85 vs. 5.66). CH4 production potential in aquaculture ponds was influenced by both microbial and abiotic factors. Specifically, the relative abundance of Methanosarcina slightly decreased in aquaculture ponds, while the potential for CH4 production declined with lower SOC contents and C/N ratio. Overall, our findings demonstrate that converting natural coastal marshes into aquaculture ponds reduces CH4 production by altering key soil properties and the structure and diversity of methanogenic archaea communities. These results provide empirical evidence to enhance global carbon models, improving predictions of carbon feedback from wetland land conversion in the context of climate change.

Can We Protect China's Northern Coast Wetlands From Tidal Dynamics by Restoring Native Species After Spartina alterniflora Is Eradicated? A Model‐Based Analysis

ABSTRACTIn recent years, the Chinese government has implemented a series of initiatives with the objective of eradicating the invasive Spartina alterniflora along the entire coastline. This has given rise to concerns about the potential for subsequent coastal erosion and salt marsh shrinkage. This study introduces a novel contribution in the form of a model‐based analysis, grounded in fieldwork from the Yellow River Delta, which assesses the potential of native Suaeda salsa as an alternative for coastal protection. Our approach is distinctive in that it not only compares the flow velocity reduction effects of S. alterniflora and S. salsa, but also evaluates the efficacy of three distinct planting patterns in managing tidal dynamics. In this study, we present a significant finding: while both species can mitigate tidal flow velocity, S. alterniflora shows superior performance, which represents a novel point of discussion in the field of coastal wetland management. Furthermore, our research indicates that dense aggregated planting patterns are particularly effective during storm surges, offering a strategic insight for future ecological engineering. However, we recognize the potential limitations of our approach, including the need for continuous management to control the spread of S. alterniflora and the necessity for further research to optimize the restoration potential of S. salsa under varying tidal conditions. Our findings highlight the importance of a balanced approach, suggesting the retention of a portion of S. alterniflora while also emphasizing the strategic planting of S. salsa in high‐density configurations to enhance coastal resilience.

Response of a patchy intertidal mudflat‐marsh transition zone to a typhoon

AbstractWhile tidal marshes are valued for their ability to reduce the impact of storm waves on shores, there is still more limited understanding of how storm waves impact the integrity of tidal marshes, particularly in mudflat‐marsh transition zones with patchy vegetation cover. This study aims to investigate changes in hydrodynamics, sediment bed elevation, and patchy vegetation cover along the sea‐to‐land elevation gradient in response to super typhoon IN‐FA, making landfall in 2021 in a mudflat‐marsh transition zone of the Yangtze Estuary (China). Utilizing in‐situ measurements and drone surveys, our results show: (1) A landward decrease in storm‐induced wave energy, flow velocities, turbulence, and erosion across a 200‐m mudflat‐marsh transition zone; (2) Elevation‐dependent spatial reconfiguration of marsh vegetation patches in response to the storm; (3) Different marsh response below and above an elevation threshold where a shift between marsh gain and marsh loss occurred. The observed landward decrease in storm‐induced marsh loss is attributed to a trade‐off between reduced disturbances due to landward increasing friction from the sediment bed and vegetation, and the landward increasing capacity of the vegetation to cope with disturbances. Our findings provide new insights relevant to the response of marsh systems to storms, and highlight the importance of the gradual and adequately wide sea‐to‐land gradient in delivering marsh resistance to extreme events.

Growth of sulfate-reducing Desulfobacterota and Bacillota at periodic oxygen stress of 50% air-O2 saturation

BackgroundSulfate-reducing bacteria (SRB) are frequently encountered in anoxic-to-oxic transition zones, where they are transiently exposed to microoxic or even oxic conditions on a regular basis. This can be marine tidal sediments, microbial mats, and freshwater wetlands like peatlands. In the latter, a cryptic but highly active sulfur cycle supports their anaerobic activity. Here, we aimed for a better understanding of how SRB responds to periodically fluctuating redox regimes.ResultsTo mimic these fluctuating redox conditions, a bioreactor was inoculated with peat soil supporting cryptic sulfur cycling and consecutively exposed to oxic (one week) and anoxic (four weeks) phases over a period of > 200 days. SRB affiliated to the genus Desulfosporosinus (Bacillota) and the families Syntrophobacteraceae, Desulfomonilaceae, Desulfocapsaceae, and Desulfovibrionaceae (Desulfobacterota) successively established growing populations (up to 2.9% relative abundance) despite weekly periods of oxygen exposures at 133 µM (50% air saturation). Adaptation mechanisms were analyzed by genome-centric metatranscriptomics. Despite a global drop in gene expression during oxic phases, the perpetuation of gene expression for energy metabolism was observed for all SRBs. The transcriptional response pattern for oxygen resistance was differentiated across individual SRBs, indicating different adaptation strategies. Most SRB transcribed differing sets of genes for oxygen consumption, reactive oxygen species detoxification, and repair of oxidized proteins as a response to the periodical redox switch from anoxic to oxic conditions. Noteworthy, a Desulfosporosinus, a Desulfovibrionaceaea, and a Desulfocapsaceaea representative maintained high transcript levels of genes encoding oxygen defense proteins even under anoxic conditions, while representing dominant SRB populations after half a year of bioreactor operation.ConclusionsIn situ-relevant peatland SRB established large populations despite periodic one-week oxygen levels that are one order of magnitude higher than known to be tolerated by pure cultures of SRB. The observed decrease in gene expression regulation may be key to withstand periodically occurring changes in redox regimes in these otherwise strictly anaerobic microorganisms. Our study provides important insights into the stress response of SRB that drives sulfur cycling at oxic-anoxic interphases.1UtHR5dBbf2f8WaGLBYUtHVideo

Salinity increases under sea level rise strengthens the chemical protection of SOC in subtropical tidal marshes

The rise in sea levels due to global warming could significantly impact the soil organic carbon (SOC) pool in coastal tidal marshes by altering soil salinity and flooding conditions. However, the effects of these factors on SOC protection in coastal tidal marshes are not fully understood. In this study, we employed a space-for-time approach to investigate the variations in soil active carbon components and mineral-associated organic carbon under different salinity gradients (freshwater and brackish) and flooding frequencies (high and low tidal flats).The soil organic carbon (SOC) and easily oxidizable organic carbon (EOC) contents at the low-flooding frequency sites were higher than those at the high-flooding frequency sites. The dissolved organic carbon (DOC) content was higher at the high-salinity sites compared to the low-salinity sites, while the soil microbial biomass carbon (MBC) content was higher at the low-salinity sites than at the high-salinity sites. The EOC/SOC and DOC/SOC ratios were greater at the high-salinity sites than at the low-salinity sites, whereas the MBC/SOC ratios were higher at the low-salinity sites than at the high-salinity sites. Iron (Fe) and aluminum (Al) mineral-associated organic carbon [Fe(Al)-OC] and calcium-associated organic carbon (Ca-OC) contents were higher at the high-salinity sites compared to the low-salinity sites, and at the low-flooding frequency sites compared to the high-flooding frequency sites.Meanwhile, Fe(Al)-OC was the dominant fraction among mineral-associated organic carbon at all sites. The dominant phyla of bacterial community included Proteobacteria (49.31 %–66.36 %), Firmicutes (2.67 %–28.44 %), Chloroflexi (3.81 %–9.54 %), and Acidobacteria (4.28 %–7.02 %). In addition, Desulfobacca, a sulfate-reducing bacterium, promoted the formation of mineral-associated organic carbon.Random forest analysis showed that SOC and DOC were key factors in promoting mineral-associated organic carbon formation. Partial least squares path modeling (PLS-PM) indicated that sea level rise affects DOC content by altering soil physicochemical properties, promoting the formation of mineral-associated organic carbon.In summary, while soil organic carbon activity increases, the chemical association of minerals with organic carbon is becoming increasingly crucial for the protection of organic carbon under rising salinity conditions driven by sea level rise.

Water and nitrogen coupling regulates the present and future restoration trends under Spartina alterniflora invasion in a coastal salt marsh

Global change can easily cause the wetland ecosystem structure and function to be damaged by alien species. Former studies on Spartina alterniflora invasion only focused on the effect of aboveground communities, ignoring the potential regeneration of soil seed banks. Therefore, the study aimed to find the key resources that limit the S. alterniflora invasion and the regulation mechanism for S. alterniflora regeneration. Through investigating the S. alterniflora communities with different invasion stages, we studied the structure and composition of the aboveground communities and the soil seed banks, in response to the soil properties and water and nitrogen addition. The dominant competitive advantage of S. alterniflora was mainly affected by the aboveground biomass, which was regulated by soil NH4+-N and moisture content. Although the richness was same in the soil seed banks under the S. alterniflora communities with different coverage, S. alterniflora seeds maintained its specific competitive dominance. The niche breadth of S. alterniflora and the niche overlap between S. alterniflora and Tripolium pannonicum was the highest under low aboveground coverage. The soil seed bank germination experiments showed that the S. alterniflora density decreased when the soil nitrogen concentration exceeded 1 g/kg, while the density of native species E. crusgalli and T. pannonicum decreased when the water depth above the soil surface exceeded 2 cm. The successful naturalization of S. alterniflora invasion regulated by nitrogen-water coupling is a bet-hedging of the niche and fitness differences between invasive and native species in the coastal salt marsh of eastern China.

A New Coupled Biogeochemical Modeling Approach Provides Accurate Predictions of Methane and Carbon Dioxide Fluxes Across Diverse Tidal Wetlands

AbstractTidal wetlands provide valuable ecosystem services, including storing large amounts of carbon. However, the net exchanges of carbon dioxide (CO2) and methane (CH4) in tidal wetlands are highly uncertain. While several biogeochemical models can operate in tidal wetlands, they have yet to be parameterized and validated against high‐frequency, ecosystem‐scale CO2 and CH4 flux measurements across diverse sites. We paired the Cohort Marsh Equilibrium Model (CMEM) with a version of the PEPRMT model called PEPRMT‐Tidal, which considers the effects of water table height, sulfate, and nitrate availability on CO2 and CH4 emissions. Using a model‐data fusion approach, we parameterized the model with three sites and validated it with two independent sites, with representation from the three marine coasts of North America. Gross primary productivity (GPP) and ecosystem respiration (Reco) modules explained, on average, 73% of the variation in CO2 exchange with low model error (normalized root mean square error (nRMSE) &lt;1). The CH4 module also explained the majority of variance in CH4 emissions in validation sites (R2 = 0.54; nRMSE = 1.15). The PEPRMT‐Tidal‐CMEM model coupling is a key advance toward constraining estimates of greenhouse gas emissions across diverse North American tidal wetlands. Further analyses of model error and case studies during changing salinity conditions guide future modeling efforts regarding four main processes: (a) the influence of salinity and nitrate on GPP, (b) the influence of laterally transported dissolved inorganic C on Reco, (c) heterogeneous sulfate availability and methylotrophic methanogenesis impacts on surface CH4 emissions, and (d) CH4 responses to non‐periodic changes in salinity.

Prescribed fire regimes influence responses of fungal and bacterial communities on new litter substrates in a brackish tidal marsh.

Processes modifying newly deposited litter substrates should affect fine fuels in fire-managed tidal marsh ecosystems. Differences in chemical composition and dynamics of litter should arise from fire histories that generate pyrodiverse plant communities, tropical cyclones that deposit wrack as litter, tidal inundation that introduces and alters sediments and microbes, and interactions among these different processes. The resulting diversity and dynamics of available litter compounds should affect microbial (fungal and bacterial) communities and their roles in litter substrate dynamics and ecosystem responses over time. We experimentally examined effects of differences in litter types produced by different fire regimes and litter loads (simulating wrack deposition) on microbial community composition and changes over time. We established replicated plots at similar elevations within frequent tidal-inundation zones of a coastal brackish Louisiana marsh. Plots were located within blocks with different prescribed fire regimes. We deployed different measured loads of new sterilized litter collected from zones in which plots were established, then re-measured litter masses at subsequent collection times. We used DNA sequencing to characterize microbial communities, indicator families, and inferred ecosystem functions in litter subsamples. Differences in fire regimes had large, similar effects on fungal and bacterial indicator families and community compositions and were associated with alternate trajectories of community development over time. Both microbial and plant community compositional patterns were associated with fire regimes, but in dissimilar ways. Differences in litter loads introduced differences in sediment accumulation associated with tidal inundation that may have affected microbial communities. Our study further suggests that fire regimes and tropical cyclones, in the context of frequent tidal inundation, may interactively generate substrate heterogeneities and alter microbial community composition, potentially modifying fine fuels and hence subsequent fires. Understanding microbial community compositional and functional responses to fire regimes and tropical cyclones should be useful in management of coastal marsh ecosystems.

Effect of biochar on soil chemical properties of tidal wetland in Jambi, Indonesia, and growth and yield of various rice varieties

The study aimed to determine the effect of biochar on the growth and yield of several rice varieties in a tidal wetland agroecosystem. This research used a split-plot design with the main plot was biochar application, consisting of three levels (no biochar, rice husk biochar, and coconut shell biochar), and the subplot was rice variety consisting of ten varieties (Inpara, Inpari 30, Kuning, Karya Rendah, Bujang Pelawah, Pandan Wangi, Bujang Berinai, Kwatek Tinggi, Candu, and Serai). Plant parameters observed were plant height, number of tillers, productive tillers, panicle length, number of grains per panicle, number of empty grains per panicle, milled rice weight, and weight of 1,000 grains. Results of this study showed that the application of biochar improved soil fertility by increasing organic carbon, available phosphorus and potassium, cation exchange capacity, and reducing the soluble iron in the soil. However, the application of biochar did not significantly affect the height of rice plants. The application of coconut shell biochar yielded the best results in increasing the number of productive tillers, the number of grains per panicle, grain dry weight, and reducing the number of empty grains per panicle.

Leveraging a decade of Landsat-8 spectral records for mapping blue carbon storage in tidal salt marshes

Tidal salt marsh ecosystems are known to accumulate and store large amounts of “blue” carbon, making them an important component of regional carbon cycle processes and a potential target for ecosystem-based carbon crediting efforts. However, blue carbon content in salt marshes can vary substantially at relatively small spatial scales. Understanding spatial variations of blue carbon storage at the landscape or local scale is important for developing carbon inventories, guiding ecological restorations, and informing habitat management strategies. We investigated the potential of spectral index records from the Landsat-8 Operational Land Imager spanning from 2014 to 2023 for mapping blue carbon storage in the soils of two tidal salt marsh systems in the Mid-Atlantic United States. The decadal mean of a non-photosynthetic vegetation index and standard deviations of a normalized difference vegetation index and a modified normalized difference water index were identified as predictors of blue carbon. These predictors were used to train a gradient boosted trees model for predicting soil organic matter content that achieved a testing set r-squared value of 0.67. We estimated that the two study marshes stored a combined 133-208 gigagrams of organic carbon in the top 30 cm of soil. We emphasize the need for better quantification of deep soil carbon in tidal salt marsh systems, which is likely quite high, and demonstrate the potential for satellite-based mapping of blue carbon within individual tidal wetland systems.

Sediment dynamic responses of coastal salt marsh to wind waves and swells in a semi-open tidal flat

Coastal salt marshes provide effective protection to the coastal environments they front against coastal erosion by reducing the incoming wave energy. Understanding sediment dynamic processes in coastal salt marshes environments is of crucial importance for coastal defense. The objective of this study is to assess the impact of Spartina alterniflora (S. alterniflora) marshes on wave attenuation, sediment transport, and morphodynamics through extensive field records on the Cixi tidal flat in Hangzhou Bay. Results demonstrate that wave attenuation by S. alterniflora marshes increases proportionally with the intensification of wind waves at a consistent water depth or significant wave height. Moreover, wave attenuation in the context of wind waves surpasses that of swells. On average, the wave attenuation provided by S. alterniflora marshes during both wind waves and swells is more than six times greater than that offered by the adjacent mudflat. Additionally, net sediment fluxes within S. alterniflora marshes decrease by 37 % in the presence of swells and 84 % with wind waves, in comparison to the mudflat. The influence of S. alterniflora marshes on tidal flat accretion is more pronounced with wind waves than swells. Notably, observed from summer to winter, the surface accretion of tidal flats is highest (∼26 cm) at the edge of S. alterniflora marshes. This study contributes valuable insights into the complex interactions between salt marshes and hydrodynamic forces, essential for informing coastal management strategies.

Stimulation of methane production potential and alteration in community composition of methanogens following conversion of China’s coastal marshes to paddy fields

Conversion of coastal marshes to paddy fields can significantly affect methane (CH4) emissions. However, how such land conversion impacts methanogenesis, a key microbial process regulating CH4 emissions, is poorly known. This investigation adopted a space-for-time substitution method to compare soil methane production potential (MPP), abundance and community composition of methanogenic archaea between marsh land (covered by Kandelia candek, Phragmites australis, or Bruguiera sexangula) and nearby paddy fields in six different regions along the coast of China. Linear mixed-effects models showed that the conversion of salt marshes to paddy fields resulted in significant increases in overall MPP and abundance of methanogenic archaea by 343 % and 346 % in average, respectively. A significant variation in the community composition of methanogenic archaea was observed between marsh land and paddy fields, with the dominant genera shifting from Methanolobus (32.1 %) and Methanosarcina (27.3 %) to Methanobacterium (49.0 %). Partial least squares path model showed that the change of MPP was primarily driven by abundance of methanogenic archaea, and the abundance was affected by alterations in soil physicochemical properties (e.g., organic carbon content, NH4+ content, and salinity) and community composition of methanogenic archaea caused by land conversion. Moreover, both MPP and abundance of methanogenic archaea were significantly correlated with the conversion years. Collectively, this study was the first to show the dynamic response of MPP and community of methanogenic archaea to the conversion of coastal marshes to paddy fields, thereby enhancing our understanding of land conversion’s impact on CH4 cycling and the underlying mechanism.

Influence of Rivers, Tides, and Tidal Wetlands on Estuarine Carbonate System Dynamics

Variations in estuarine carbonate chemistry can have critical impacts on marine calcifying organisms, yet the drivers of this variability are difficult to quantify from observations alone, due to the strong spatiotemporal variability of these systems. Terrestrial runoff and wetland processes vary year to year based on local precipitation, and estuarine processes are often strongly modulated by tides. In this study, a 3D-coupled hydrodynamic-biogeochemical model is used to quantify the controls on the carbonate system of a coastal plain estuary, specifically the York River estuary. Experiments were conducted both with and without tidal wetlands. Results show that on average, wetlands account for 20–30% of total alkalinity (TA) and dissolved inorganic carbon (DIC) fluxes into the estuary, and double-estuarine CO2 outgassing. Strong quasi-monthly variability is driven by the tides and causes fluctuations between net heterotrophy and net autotrophy. On longer time scales, model results show that in wetter years, lower light availability decreases primary production relative to biological respiration (i.e., greater net heterotrophy) resulting in substantial increases in CO2 outgassing. Additionally, in wetter years, advective exports of DIC and TA to the Chesapeake Bay increase by a factor of three to four, resulting in lower concentrations of DIC and TA within the estuary. Quantifying the impacts of these complex drivers is not only essential for a better understanding of coastal carbon and alkalinity cycling, but also leads to an improved assessment of the health and functioning of coastal ecosystems both in the present day and under future climate change.