Bare Mudflat Research Articles

The turbulent soundscape of intertidal oyster reefs.

Turbulence and sound are important cues for oyster reef larval recruitment. Numerous studies have found a relationship between turbulence intensity and swimming behaviors of marine larvae, while others have documented the importance of sounds in enhancing larval recruitment to oyster reefs. However, the relationship between turbulence and the reef soundscape is not well understood. In this study we made side-by-side acoustic Doppler velocimeter turbulence measurements and hydrophone soundscape recordings over 2 intertidal oyster reefs (1 natural and 1 restored) and 1 adjacent bare mudflat as a reference. Sound pressure levels (SPL) were similar across all three sites, although SPL > 2000 Hz was highest at the restored reef, likely due to its larger area that contained a greater number of sound-producing organisms. Flow noise (FN), defined as the mean of pressure fluctuations recorded by the hydrophone at f < 100 Hz, was significantly related to mean flow speed, turbulent kinetic energy, and turbulence dissipation rate (ε), agreeing with theoretical calculations for turbulence. Our results also show a similar relationship between ε and FN to what has been previously reported for ε vs. downward larval swimming velocity (w b ), with both FN and w b demonstrating rapid growth at ε > 0.1 cm2 s-3. These results suggest that reef turbulence and sounds may attract oyster larvae in complementary and synergistic ways.

Quantifying Wave-Induced Hydrodynamics Near A Saltmarsh Cliff: An Experimental Piv Study

Nature-based flood defences receive increasing interest as a viable option for improving flood safety worldwide. A contemporary case is using the ability of saltmarshes to attenuate waves during storm conditions for strengthening coastal flood defences. To ensure a long-term reinforcement of flood protection, it is important to understand the erosion mechanisms of saltmarshes during storms. One of the critical locations for erosion is at the transition between the saltmarsh and the bare mudflat, often characterized by a vertical step or cliff. These cliffs vary between 0.2 to 2.0 m in height, depending on soil characteristics and local hydrodynamics. However, wave-induced hydrodynamics that controls the (mass) erosion at the saltmarsh cliff are not fully understood. Also the role of saltmarsh vegetation on these near-cliff hydrodynamics are not clearly quantified. In this research, we present high-resolution measurements of wave-induced hydrodynamics at a saltmarsh cliff performed in a scaled wave flume experiment.

Effects of land-use on soil C, N, and P stocks and stoichiometry in coastal wetlands dependent on soil depth and latitude

Coastal land-use is increasingly affected by Spartina alterniflora invasion, coastal reclamation, and climate change, which have been suggested to exert vital controls on soil carbon (C), nitrogen (N), and phosphorus (P) cycles, however, the effects on the geographical distributions of these element stocks and stoichiometry remain unclear. We analyzed the depth (0–100 cm) and latitudinal (19–41°N) patterns of soil C, N, and P contents, stocks, and ratios in 120 Chinese coastal wetlands differing in land-use (reclaimed wetlands, natural wetlands, invasive wetlands, and bare mudflats) and climate (tropics, subtropics, and temperate). We observed stable depth patterns of soil contents, stocks, and ratios, owing to the stable depth patterns of soil conditions in each land-use. Top soils (0–30 cm) generally had higher C, N, and P contents and N:P ratio but lower C:N and C:P ratios than deep soils (30–100 cm). We found that soil C content and P stock remained constant, soil C stock, N and P contents and N:P ratio increased significantly, but soil N stock and C:N and C:P ratios decreased significantly with decreasing latitude; however, such correlations tended to be weaker in reclaimed wetlands and invasive wetlands. Land-use changes also significantly altered the magnitude of soil element stoichiometry. The effects of S. alterniflora invasion on soil C, N, and P storages can be shifted from negative in tropics to positive in temperate regions, whereas the negative effects of coastal reclamation in tropics disappeared in temperate regions. Overall, compared with natural wetlands, S. alterniflora invasion slightly decreased, whereas coastal reclamation largely decreased soil C, N, and P contents and stocks. Compared with bare mudflats, S. alterniflora invasion significantly increased C and N contents and N:P ratio but decreased C:N ratio, whereas coastal reclamation significantly decreased P content and stock and C:N ratio but increased N:P ratio, especially in top soils. Our findings will be helpful for understanding and assessing soil C sequestration and nutrient cycling in globally disturbed coastal wetlands.

Geomorphological changes and sediment carbon accumulation at the bare mudflat-saltmarsh interface: The role of typhoons

Blue carbon stored in coastal wetlands can be highly impacted by extreme events, such as typhoons. However, the sediment carbon accumulation capacity in this circumstance, remains unclear. In this study, a field site crossing the bare mudflat-saltmarsh interface was established in Southern Hangzhou Bay, to investigate the geomorphological and subsequent sediment carbon accumulation changes during the typhoon season (2 months) and the succeeding calm weather period (10 months). Surface Elevation Tables (SETs) were used, together with GPS-RTK and UAV-LiDAR surveys, to observe surface elevation changes at different spatial scales. The elevation and sediment organic carbon density data were used to estimate the gain/loss of sediment carbon pool under the impact of two successive typhoons, “In-Fa” and “Chanthu”. This revealed that during the typhoon season, 6.3 cm of surface erosion occurred on the bare mudflat whilst rapid depositions of 6.1 and 12.3 cm occurred in Scirpus mariqueter and Spartina alterniflora habitats, respectively. In the gap between the two typhoon events, the bare mudflat experienced deposition of 4.2 cm, signalling recovery from erosion, but deposition within the saltmarsh front slowed. During the calm weather period, sediment deposition increased landward, with magnitudes of 13.1 cm, 16.4 cm, and 18.2 cm. Sediment carbon budget estimates indicated that during the typhoon season, the bare mudflat lost ~3.4 Mg C ha−1 but saltmarshes gained ~4.9 Mg C ha−1 in their sediment organic carbon pools. These changes in sediment carbon accumulation rates over the typhoon season accounted for >30 % of annual change in the study area, and may be associated with tidal creek dynamics. This study suggests the important role of typhoons in mediating the sediment carbon pool across the mudflat-saltmarsh interface. With future climate change, increasingly frequent catastrophic events could cause considerable changes in coastal blue carbon sequestration capacity.

Role of n-DAMO in Mitigating Methane Emissions from Intertidal Wetlands Is Regulated by Saltmarsh Vegetations.

Coastal wetlands are hotspots for methane (CH4) production, reducing their potential for global warming mitigation. Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) plays a crucial role in bridging carbon and nitrogen cycles, contributing significantly to CH4 consumption. However, the role of n-DAMO in reducing CH4 emissions in coastal wetlands is poorly understood. Here, the ecological functions of the n-DAMO process in different saltmarsh vegetation habitats as well as bare mudflats were quantified, and the underlying microbial mechanisms were explored. Results showed that n-DAMO rates were significantly higher in vegetated habitats (Scirpus mariqueter and Spartina alterniflora) than those in bare mudflats (P < 0.05), leading to an enhanced contribution to CH4 consumption. Compared with other habitats, the contribution of n-DAMO to the total anaerobic CH4 oxidation was significantly lower in the Phragmites australis wetland (15.0%), where the anaerobic CH4 oxidation was primarily driven by ferric iron (Fe3+). Genetic and statistical analyses suggested that the different roles of n-DAMO in various saltmarsh wetlands may be related to divergent n-DAMO microbial communities as well as environmental parameters such as sediment pH and total organic carbon. This study provides an important scientific basis for a more accurate estimation of the role of coastal wetlands in mitigating climate change.

Harvested Spartina area performs better than native Scirpus in sedimentation and carbon preservation under storm surge

Typhoons pose threats to coastal wetlands, but the impacts on carbon stocks remain unclear. This study investigated typhoon effects on salt marsh carbon pools with different vegetation covers (harvested Spartina alterniflora, native Scirpusmariqueter, bare mudflat) in the Yangtze River estuary.During Typhoon Muifa (September 2022), significant erosion occurred in the Scirpus area while the harvested Spartina area experienced sediment deposition, indicating its stronger coastal protection capacity. Grain size analysis validated the geomorphic changes. The harvested Spartina area also captured coarser sediments from the mudflat. Wave data showed the amplified hydrodynamics during typhoons can transport more sediment into marshes.In the Scirpus area, surface sediments (0–15 cm) lost 43% organic carbon and 73% belowground biomass due to erosion. The deposited sediments after typhoons lacked the original high carbon content. In contrast, harvested Spartina areas maintained carbon levels despite intense hydrodynamics. The bare mudflat lost 43% total carbon after experiencing substantial erosion.This study demonstrates harvested Spartina areas effectively mitigated carbon loss and even facilitated carbon sequestration through enhanced sediment trapping during typhoons. With intensifying storm surges, seasonal harvesting of Spartina could balance coastal protection and ecological functions better than complete removal. The carbon sink capacity of sediments with native vegetation is vulnerable to typhoons due to limited resilience. Harnessing bio-geomorphic feedbacks is crucial for preserving blue carbon storage facing climate change.

Sediment Carbon Stock in Natural and Transplanted Mangroves in Bahrain, Arabian Gulf

Mangroves in the Arabian Gulf provide several biological, ecological, and environmental services. They are also considered among the largest carbon sinks. However, mangroves along the coastlines of the Arabian Gulf have degraded in recent decades, mainly due to urbanization and coastal development. Therefore, restoration and afforestation programs have been initiated to enhance the services and functions of mangrove ecosystems and as part of national targets to mitigate climate change. Increasing carbon sinks by quadrupling the current areas covered by mangroves through afforestation programs by 2035 is one of the strategies to mitigate climate change in Bahrain. The aim of the present study was to estimate the organic carbon stocks in the sediments of natural and transplanted mangroves in Bahrain. Within the protected areas of Tubli and Arad Bays, sediment samples were taken down to a depth of 70 cm from natural and transplanted mangroves as well as a bare mudflat. The findings of the present study indicated that the total sediment organic carbon concentrations at three sampling sites of natural and transplanted mangroves and the mudflat were 200.54 ± 24.52, 112.36 ± 55.51, and 81.56 ± 8.92 Mg C/ha, respectively. The natural mangroves in Tubli Bay differed considerably from those in Arad Bay (p ≤ 0.001), based on the concentrations of organic carbon in sediments. However, there was a noticeable similarity seen in the organic carbon of the mangroves in Arad Bay that were transplanted 25 years prior and the natural mangroves in Tubli Bay, indicating the importance of a long-term mangrove afforestation strategy to mitigate climate change in the Arabian Gulf.

Change in the community structure and organic carbon content of meio- and macrobenthos between tidal flat and salt marsh areas colonized by Spartina alterniflora in the Bahía Blanca estuary (SW Atlantic)

Salt marshes are regarded as among the most productive coastal ecosystems, important “blue carbon” sinks and a support for benthic communities with large abundances, whose structure may be strongly influenced by salt marsh vegetation. During the last few decades, Spartina alterniflora has been colonizing bare mudflats in the Bahía Blanca estuary, and a large increase in the area covered by salt marshes has been reported. This colonization can strongly influence the structure of benthic fauna and its role in the carbon cycle. The hypothesis of this study was that the community structure and the organic carbon contained in the meio- and macrobenthos change between tidal flats and salt marshes recently colonized by S. alterniflora. Response variables studied to compare the tidal flat and salt marsh were density, biomass and production to biomass (P/B) ratio of macro- and meiobenthos. Density and biomass of Gastropoda and P/B ratio of Nematoda were higher on the salt marsh than on the tidal flat. By contrast, density and biomass of Polychaeta were higher on the tidal flat. These results suggest that the expansion of S. alterniflora marshes on tidal flats produces changes in the structure of the macro- and meiobenthos community (taxonomic composition and biomass) that have an influence on carbon cycling.

Extreme rainstorm reshuffles the spatial distribution of heavy metals and pollution risk in sediments along the mangrove tidal flat

Mangroves as typical blue carbon ecosystems exhibit a high level of heavy metal accumulation capability. In this study, we investigated how extreme rainstorm effects the spatial variability and pollution risk of sediment heavy metals (i.e., Fe, Mn, Cr, Cu, Zn, Cd, Pb, As and Hg) at different compartments of a typical tidal flat, including the bare mudflat, mangrove zone, and tidal creek in Shenzhen Bay, China. The results showed that the extreme rainstorm can change the sediment particle size, which further regulated the spatial distribution, and source-sink pattern of heavy metals. Due to the strong rainstorm flushing, the concentrations of most heavy metals increased toward the sea and the comprehensive pollution level increased by 8.3 % after the extreme rainstorm. This study contributes to better understanding of how extreme rainstorm regulates heavy metal behavior in mangrove sediments to achieve sustainable development of mangroves under the pressures of extreme weather events.

Climatic effect from oyster reef restoration in Spartina alterniflora invaded intertidal mudflat: From the perspective of CH4 and N2O production

Spartina alterniflora is a dominant invasive species along the coast of China. A surprising phenomenon that the oyster reef formation is substituting the S. alterniflora invasion, was recently observed in the west coast of Bohai Bay, North China. As the intertidal mudflat ecosystem is critical for coastal blue carbon, this paper aims to evaluate the climatic effect of the alternation from the perspective of potential CH4 and N2O production. The sediment geochemical properties and potential CH4 and N2O productions were therefore measured in sediments dominated by Spartina alterniflora (SA), oyster reef (OR), mixture of S. alterniflora and oyster reef (SA-OR) and bare mudflat (BM) at an intertidal mudflat. Meanwhile, sediment microbial community structure and function genes were also determined utilizing metagenome high-throughput sequencing technology. Our results indicated that the formation of oyster reef in S. alterniflora invaded intertidal mudflat might slightly reduce the sediment potential CH4 production and enhance the sediment potential N2O production. The oyster reef formation could alter the community composition of methanogens and the abundance of functional genes in methanogenesis, and transform the main pathway from methylotrophic to hydrogenotrophic methanogenesis in surface sediments. Metagenome sequencing revealed that the oyster reef formation may promote nitrification, inhibit dissimilatory nitrate reduction (DNRA) and nitrate assimilation functions, and reduce the abundance of nosZ genes. Mantel analysis showed that pH, soluble salt and dissolved carbon (DC) were the most important factors influencing the composition of microbial community. In general, our results imply that the growth of oyster reef in the S. alterniflora invaded area has opposing effects from the prospective of the potential CH4 and N2O production.

Effects of microtopographic patterns on plant growth and soil improvement in coastal wetlands of the Yellow River Delta.

To clarify the effects of microtopography on plant growth and soil water, salt and nutrient characteristics of saline soils in mudflats within muddy coastal zones and explore suitable microtopographic modifications. Six microtopographic modification patterns, namely, S-shaped, stripe-shaped, pin-shaped, stepshaped, dense stripe-shaped and crescent-shaped patterns, were established in the coastal mudflats of the Yellow River Delta. The soil water, salt, ion, total carbon, total nitrogen, and total phosphorus contents and their ecological stoichiometric characteristics were measured and analyzed after theimplementation of different microtopographic modification patterns, with bare mudflats as the control. The results showed that microtopographic modification significantly changed the soil water and salt contents and the soil total carbon, total nitrogen and total phosphorus contents. Compared with the bare ground, microtopographic transformation significantly promoted the growth of the pioneer plant Suaeda salsa, significantly increased the soil water and nutrient contents, and significantly decreased the soil salinity. The soil salinity was mainly reduced by Na+ and Cl- ions. The soil salinity and nutrient contents gradually decreased with increasing soil depth, indicating the occurrence of surface aggregation. Compared to that of the bare ground, the soil C/N was significantly lower and the N/P was significantly higher in the microtopographic treatments, and the overall performance suggested soil N limitation. The ions contained in the saline soil were dominated by Na+ and Cl-, followed by Mg2+ and SO4 2-, with lower contents of K+, Ca2+ and HCO3 -. Among the six microtopography modification patterns, the crescent-shaped pattern best promoted vegetation restoration. This pattern was the most effective in reducing soil salinity, with a 98.53% reduction in soil salinity compared with that of bare ground, followed by the pin-shaped pattern. Compared with that in the bare ground samples, the nutrient content in the samples from the step-shaped modification increased by 23.27%; finally, the S-shaped, step-shaped and dense stripe-shaped patterns performed poorly in terms of plant restoration and soil improvement. It is suggested that a crescent-shaped pattern should be considered first when carrying out microtopographic transformation on the beaches of the Yellow River Delta, followed by stripe-shaped and pin-shaped patterns. The dense strip-shaped should not be adopted.

Integrated assessment of the impact of land use changes on groundwater recharge and groundwater level in the Drava floodplain, Hungary

Land-use/land-cover (LULC) change is considered a key human factor influencing groundwater recharge in floodplains. Without accurate estimations, the impact of LULC change on water balance components may be either significantly understated or exaggerated. This paper assesses the impacts of LULC changes from 1990 to 2018 on water balance components and groundwater levels of the Drava floodplain, Hungary, where human interference has led to a critical environmental situation. In this study, a spatially-distributed water balance model (WetSpass-M), and a groundwater flow model (MODFLOW-NWT) were integrated to assess the impacts of LULC changes. The moderate expansion of built-up areas increased surface runoff, while the afforestation of arable land and meadows and the overgrowth of bare mudflats with willow shrubs increased evapotranspiration. As a consequence, total annual groundwater recharge decreased by 5.3 × 107 m3 in the floodplain with an average of 335 mm year−1 and 317 mm year−1 in 2012 and 2018, respectively. Moreover, an average groundwater level decline by 0.1 m is observed in the same period. Declined groundwater recharge, increased runoff, and evapotranspiration exerted a negative effect on water resources in the Drava basin. The approach tested in this paper allows temporal and spatial estimation of hydrological components under the changes of LULC, providing quantitative information for decision-makers and stakeholders to implement efficient and sustainable management of water resources in the Drava floodplain. The provided integrated model is also applicable to regionally.

Cordgrass Spartina alterniflora acts as a key carbon source to support macrozoobenthos in the salt marsh and nearby mudflat communities

Exotic cordgrass Spartina can influence the trophic interaction and functioning of coastal ecosystems by altering the availability or palatability of carbon sources utilized by macrozoobenthos. Previous studies focused mainly on the trophic dynamics in Spartina-invaded mangroves or marshes, but the effect of Spartina on the diet of macrozoobenthos inhabiting the nearby unvegetated mudflat remains largely unexplored. By analyzing carbon and nitrogen stable isotopes, we compare the trophic contribution of an exotic cordgrass Spartina alterniflora to the macrozoobenthos between the dense S. alterniflora area (DSA) and adjacent tidal bare mudflat (TBM) in the Hepu coast, Guangxi province. Macrozoobenthic species were more abundant in TBM than in DSA, but the difference in carbon and nitrogen stable isotopes was insignificant for the seven conspecifics between two sampling areas, where similar organic carbon sources and trophic levels for macrozoobenthos were found. The MixSIAR mixing model revealed that S. alterniflora acted as the most important carbon source for many macrozoobenthic species and all guilds in DSA and TBM. This study showed that S. alterniflora can benefit the adjacent bare mudflat by supplying detritus as the carbon source for macrozoobenthos, which is favorable for maintaining the biodiversity and trophic dynamics of macrozoobenthic communities in coastal ecosystems.

Does experimental seaweed cultivation affect benthic communities and shorebirds? Applications for extensive aquaculture.

Extensive seaweed aquaculture is a growing industry expected to expand globally due to its relatively low impact and benefits in the form of ecosystem services. However, seaweeds are ecosystem engineers that may alter coastal environments by creating complex habitats on previously bare mudflats. These changes may scale up to top-consumers, particularly migratory shorebirds, species of conservation concern that regulate trophic webs at these habitats. Understanding how habitats are transformed and how this affects different species is critical to direct ecological applications for commercial seaweed management. We experimentally assessed through a Before-After Control-Impact design the potential changes exerted by Gracilaria chilensis farming on bare mudflats on the abundance, biomass, and assemblage structure of benthic macroinvertebrates, and their scaled-up effects on shorebirds' habitat use and prey consumption. As predicted, experimental cultivation of G. chilensis significantly affects different components of biodiversity that scale-up from lower to upper trophic levels. The total biomass of benthic macroinvertebrates increased with seaweed cultivation and remained high for at least 2 months after harvest, boosted by an increase in the median size of polychaetes, particularly Nereids. Tactile-foraging shorebirds tracked these changes at the patch level increasing their abundance and spending more time foraging at seaweed cultivated plots. These results suggest that seaweed farming has the potential to impact shorebird populations by favoring tactile-foraging species which could lead to a competitive disadvantage to species that rely on visual cues. Therefore, the establishment of new seaweed farms in bare mudflats at key sites for shorebirds must be planned warranting habitat heterogeneity (i.e., cultivated and non-cultivated areas) at the landscape level and based on a previous experimental approach to account for local characteristics. Fostering properly designed extensive seaweed farming over other aquaculture industries with greater negative environmental impacts would provide benefits for human well-being and for ecosystem functions.

Saltmarsh Carbon Stock Changes under Combined Effects of Vegetation Succession and Reclamation

Blue carbon ecosystems have been widely recognized for their carbon sequestration function to mitigate climate changes. However, both natural processes (e.g., interspecific competition) and human activities could alter the ability of blue carbon storage. To clarify the impacts of vegetation succession and reclamation on carbon stock changes, field investigation and laboratory analysis were conducted in a saltmarsh within Hangzhou Bay. Remote sensing data indicated a zonation pattern: the exotic speciesSpartina alternifloraencroached into the native speciesScirpus mariqueterat a rate of 3.51 km2a−1, butS. mariqueterexpanded to the front bare mudflat at a rate of 2.51 km2a−1. The carbon stock (1 m in depth) was found to be 85.37 Mg C ha−1for the exotic species, 56.52 Mg C ha−1for the native species, and 39.78 Mg C ha−1for the bare mudflat. The carbon burial rate varied among 3 habitats, from 0.63 Mg C ha−1a−1in the bare mudflat to 1.39 to 1.59 Mg C ha−1a−1in the vegetation sites. Within the study area, vegetation succession contributed an additional 4,858 Mg of organic carbon between 2017 and 2020 to the carbon pool. The organic carbon content of the reclamation site showed a considerable reduction, from 8.51 g kg−1to 3.34 g kg−1after 2 years of reclamation, resulting in an emission of 21.61 Mg C ha−1. Overall, the vegetation succession increased the carbon stock of the region while reclamation caused a net carbon loss in the saltmarshes. These findings can enrich the cognition to promote blue carbon management in coastal zones.

Blue carbon effects of mangrove restoration in subtropics where Spartina alterniflora invaded

Mangrove swamps and salt marshes are noted for their large carbon sequestration and storage capacity. In southeastern China, mangrove transplantation is conducted as ecological restoration where exotic Spartina alterniflora (hereafter Spartina) is removed. This study aimed to evaluate the effectiveness of mangrove transplantation on carbon sink potential. We analyzed chronological sediment accretion, soil carbon sequestration, and carbon storage of mangroves and Spartina on Maoyan and Ximen islands. Results showed that on both islands mangroves and invasive Spartina stored 12.7%–31.4% more carbon than bare mudflats over top meter soils, with Spartina outperforming restored mangroves. Both restored mangroves and invasive Spartina enhanced sediment accretion, but this enhancement was minimal in high sediment supply areas like Maoyan. Spartina invasion improved carbon sequestration capacity compared to bare mudflats in Maoyan, but mangrove restoration failed. In low sediment supply areas like Ximen, restored mangroves have outperformed Spartina invasion on carbon sequestration enhancement since >5 years of planting. Thus, carbon sink potential of mangrove restoration depended on sediment supply and time, with sediment supply being more important. We suggested that it was preferable to conduct mangrove restoration with Spartina eradication in low sediment supply areas in subtropics.

Soil Bacterial Community Structure in Different Micro-Habitats on the Tidal Creek Section in the Yellow River Estuary

Tidal creeks have attracted considerable attention in estuary wetland conservation and restoration with diverse micro-habitats and high hydrological connectivity. Bacterial communities act effectively as invisible engines to regulate nutrient element biogeochemical processes. However, few studies have unveiled the bacterial community structures and diversities of micro-habitats soils on the tidal creek section. Our study selected three sections cross a tidal creek with obviously belt-like habitats “pluff mudflat – bare mudflat – Tamarix chinensis community – T. chinensis-Suaeda salsa community– S. salsa community” in the Yellow River estuarine wetland. Based on soil samples, we dissected and untangled the bacterial community structures and special bacterial taxa of different habitats on the tidal creek section. The results showed that bacterial community structures and dominant bacterial taxa were significantly different in the five habitats. The bacterial community diversities significantly decreased with distance away from tidal creeks, as well as the dominant bacteria Flavobacteriia and δ-Proteobacteria, but in reverse to Bacteroidetes and Gemmatimonadetes. Moreover, the important biomarkers sulfate-reducing bacteria and photosynthetic bacteria were different distributions within the five habitats, which were closely associated with the sulfur and carbon cycles. We found that the bacterial communities were heterogeneous in different micro-habitats on the tidal creek section, which was related to soil salinity, moisture, and nutrients as well as tidal action. The study would provide fundamental insights into understanding the ecological functions of bacterial diversities and biogeochemical processes influenced by tidal creeks.

Early invasion of common cordgrass (Spartina anglica) increases belowground biomass and decreases macrofaunal density and diversity in a tidal flat marsh

Spartina anglica (hereafter Spartina) is an invasive perennial marsh grass shifting hydrodynamic regime and sediment characteristics in invaded area, thereby reducing macrobenthic diversity. There have been only a few studies focusing on the patch structure of Spartina according to size and its effects on macrofauna. A field experiment was conducted to identify effects of Spartina patches where they have been introduced no later than 5 years after invasion occurred on macrofauna assemblages in Ganghwa Island, South Korea. The survey area was divided into two sections according to vegetation: (1) Suaeda japonica vegetation from 0 to 60 m away from the levee, and (2) bare mudflat from 60 to 90 m away from the levee. The patch sizes of Spartina were categorized into small (1–4 m2), medium (5–11 m2), and large (13–40 m2) in area with four replicates for each section. The biomass ratio of the belowground and aboveground in the small size patch of Spartina was significantly higher than those in the medium and large size patch of Spartina. It indicated that more resource was allocated to rhizomes in small size patch with short invasion history (1 ~ 2 years). After Spartina invaded, macrofauna richness (70%), Shannon–Wiener diversity (80%), and density (67%) were decreased. However, infaunal deposit-feeding polychaete Perinereis linea and epifaunal gastropods Batillaria cumingi and Lactiforis takii increased by Spartina. Ordination of macroinvertebrate assemblages separated the habitat with Spartina invasion from the adjacent uninvaded tidal flat and Suaeda japonica habitats. This study offers a significant insight into early invasion strategies of an aggressive plant invader, Spartina for management of coastal wetlands and its impacts on macrofaunal assemblages.

Wave attenuation potential, sediment properties and mangrove growth dynamics data over Guyana's intertidal mudflats: assessing the potential of mangrove restoration works

Abstract. Coastal mangroves, thriving at the interface between land and sea, provide robust flood risk reduction. Projected increases in the frequency and magnitude of climate impact drivers such as sea level rise and wind and wave climatology reinforce the need to optimize the design and functionality of coastal protection works to increase resilience. Doing so effectively requires a sound understanding of the local coastal system. However, data availability particularly at muddy coasts remains a pronounced problem. As such, this paper captures a unique dataset for the Guyana coastline and focuses on relations between vegetation (mangrove) density, wave attenuation rates and sediment characteristics. These processes were studied along a cross-shore transect with mangroves fringing the coastline of Guyana. The data are publicly available at the 4TU Centre for Research Data (4TU.ResearchData) via https://doi.org/10.4121/c.5715269 (Best et al., 2022) where the collection Advancing Resilience Measures for Vegetated Coastline (ARM4VEG), Guyana, comprises of six key datasets. Suspended sediment concentrations typically exceeded 1 g L−1 with a maximum of 60 g L−1, implying that we measured merely fluid-mud conditions across a 1 m depth. Time series of wind waves and fluid-mud density variations, recorded simultaneously with tide elevation and suspended sediment data, indicate that wave–fluid-mud interactions in the nearshore may be largely responsible for the accumulation of fine, muddy sediment along the coast. Sediment properties reveal a consolidated underlying bed layer. Vegetation coverage densities in the Avicennia-dominated forest were determined across the vertical with maximum values over the first 20 cm from the bed due to the roots and pneumatophores. Generalized total wave attenuation rates in the forest and along the mudflat were between 0.002–0.0032 m−1 and 0.0003–0.0004 m−1 respectively. Both the mangroves and the mudflats have a high wave-damping capacity. The wave attenuation in the mangroves is presumably dominated by energy losses due to vegetation drag, since wave attenuation due to bottom friction and viscous dissipation on the bare mudflats is significantly lower than wave dissipation inside the mangrove vegetation. Data collected corroborate the coastal defence function of mangroves by quantifying their contribution to wave attenuation and sediment trapping. The explicit linking of these properties to vegetation structure facilitates modelling studies investigating the mechanisms determining the coastal defence capacities of mangroves.

Spartina alterniflora Invasion Enhances Dissimilatory Nitrate Reduction to Ammonium (DNRA) Rates in the Yangtze River Estuary, China

Dissimilatory nitrate reduction to ammonium (DNRA) can save N by converting nitrate into ammonium and avoiding nitrate leaching and runoff in saltmarshes. However, little is known about the effects of invasive plants on DNRA in the upper and deeper soil layers in salt marshes. Here, we investigated DNRA rates in the soils of six different depth layers (0–5, 5–10, 10–20, 20–30, 30–50, and 50–100 cm) from the invasive Spartina alterniflora marshland, two native plants Scirpus mariqueter and Phragmites australis marshlands, and bare mudflat on Chongming Island, located in the Yangtze River Estuary, China. Our results show that S. alterniflora significantly increased DNRA rates in both the upper 50 cm soil and deeper 50–100 cm soil layers. With respect to the entire soil profile, the NO3− reduction content calculated from DNRA in S. alterniflora marshland was 502.84 g N m−2 yr−1, increased by 47.10%, 49.42%, and 38.57% compared to bare mudflat, S. mariquete, and P. australis, respectively. Moreover, NO3− reduction content from the 50–100 cm soil layers was almost identical to that in the upper 50 cm of the soil. In the month of May, DNRA is primarily regulated by SO42− and pH in the upper and deeper soil layers, respectively, whereas, in the month of October, soil pH accounted for the most variables of DNRA in both the upper and deeper soil layers. Altogether, these results from a new perspective confirm that S. alterniflora invasion increases soil N pool and may further push its invasion in salt marshes, and the importance of deeper soil in nitrogen cycling cannot be ignored.