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Wetlands, which are ecosystems with the highest soil surface carbon density, have been severely degraded and replaced by artificial reclamation for fish and shrimp ponds in recent years. This transformation is causing intricate shifts in soil carbon pools and microbial stability. In this study, we examined natural wetlands and reclaimed aquaculture ponds in Southeast China to analyze the structure and network stability of soil microbial communities following the reclamation of estuarine wetlands and to elucidate the microbial-mediated mechanisms for regulating soil organic carbon (SOC). The aquaculture ponds presented significantly less average SOC content than the natural wetlands (p < 0.05). ACE, Chao1, and Shannon's indices of bacteria and fungi were decreased in aquaculture ponds. Less numbers of nodes and edge links in the co-occurrence network of soil fungi and bacteria in aquaculture ponds. This suggests reduced correlation and stability within the microbial network of aquaculture ponds. Decomposers in soil fungi (e.g. Dung Saprotroph) reduced. Reduced proportions of key phyla Ascomycota, Basidiomycota and Rozellomycota in the soil fungal network. Reduced proportions of key phyla Proteobacteria, Chloroflexi and Desulfobacterota in the soil bacterial network. In conclusion, our results suggest that converting wetland paddocks to intensive aquaculture ponds results in carbon pool loss and reduces soil microbial network stability. The results highlight the importance of protecting or moderately restoring mangrove wetlands along the coast of southeastern China. It is also predicted that such measures may enhance the storage capacity of soil carbon pools and improve the stability of carbon sequestration by soil microorganisms, thus offering a potential solution for mitigating global climate change., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

High rates of relative sea level rise can cause coastal wetland submergence, jeopardizing the stability of soil organic matter (SOM) sequestered within wetlands. Following submergence, SOM can be lost through mineralization, exported into the coastal ocean, or reburied within adjacent subtidal sediments. By combining measures of soil physicochemical properties, microbial community abundance, organic carbon fractionation, and stable isotope signatures, this study characterized subsurface SOM within a coastal wetland to inform its potential fate under altered environmental conditions. Nine soil cores were collected to a depth of 150 cm from a wetland currently experiencing rapid erosion and submergence within Barataria Bay, LA (USA), and were sectioned into 10 cm intervals. Each soil segment was analyzed to determine total carbon (C), nitrogen (N), phosphorus (P), and stable isotope (δ13C and δ15N) content, as well as extractable ammonium (NH 4 +), nitrate (NO 3 −), and soluble reactive phosphorus (SRP). Extractable NH 4 + and SRP concentrations increased 7× and 11×, respectively, between 0–10 cm and 130–140 cm. Through quantitative PCR, number of gene copies of bacteria and sulfate reduction genes were found to decrease with depth while there was no change in number of gene copies of archaea. This study also demonstrated only small decreases in labile: refractory C ratios with depth; by combining δ15N data with labile:refractory C ratios and no observed change in C:N ratios with depth, we inferred the presence of minimally processed organic material within deep soils and high nutrient availability, challenging the applicability of the traditional theory of selective preservation and decreased soil quality with depth. As wetland submergence progresses and soils are exposed to oxygenated seawater, this relatively labile SOM and bioavailable N and P stored at depth has the potential for rapid mineralization and/or export into the coastal zone. Unlabelled Image • Ratios of labile: refractory carbon decreased with soil depth. • Total soil carbon content increased with soil depth. • High concentrations of bioavailable nitrogen and phosphorus are present at depth. • Overall, high carbon quality down to 150 cm [ABSTRACT FROM AUTHOR]

Abstract China has a long history of building hard engineered coastal defences for storm protection, which enables us to examine the economic effects of the hard engineering to mitigate storm damage. Examining historical storm impacts between 1989 and 2016, a significant negative relationship exists between the relative economic damages (i.e., TD/GDP) by storm and the length of existing hard engineering within the storm swath. This indicates that hard engineered defences play a critical role in storm mitigation. We estimated that the storm protection value provided by hard engineered defences in China is CNY 3.18 million/km [US$0.50 million/km] on average, with a median of CNY 1.69 million/km [US $0.27 million]. They provide an annual economic value of CNY 6.04 billion on average. Despite their great contribution to reduce total economic damages from storms, hard engineered defences are not as efficient as coastal wetlands. Coastal wetlands are more cost effective based on comparison from China and USA. This study highlights the need for the Chinese government to transfer focus from prevailing hard engineered defences to ecosystem-based measure or the combination of both measures to prevent storm damage in the future. Graphical abstract Unlabelled Image Highlights • Coastal engineered structures play significant role to mitigate storms in China. • Engineered structures are cost-effective for storm protection in China. • Coastal wetlands rank over engineered structures economically to mitigate storms. [ABSTRACT FROM AUTHOR]

Abstract Land reclamation can impact a variety of ecosystem services provided by coastal wetlands. The dynamics of coastal blue carbon storage (CBCS) altered by land use/land cover (LULC) transformation and its linkage with natural and anthropogenic driving processes was analyzed in the Yellow River Delta (YRD), China. Using LULC data in the YRD during 1970–2010, the LULC transformation in four periods (i.e., 1970–1980, 1980–1990, 1990–2000 and 2000–2010) and their cumulative conversions within coastal wetlands were tracked to investigate the flow of LULC transformation. The spatiotemporal dynamics of the CBCS were then modeled and investigated by InVEST based on the LULC transformation in relation to their driving processes. The results indicated that the CBCS in the YRD has been substantially altered by continuous LULC transformation driven by the natural and anthropogenic processes, totally decreased by 10.2% (1.63 × 106 Mg) during 1970–2010 followed the loss of 2028 km2 natural wetlands converted to socioeconomic land use. The 78% of increased CBCS were contributed by single natural (e.g., succession) or anthropogenic (e.g., restoration) driving process at the seaward edge within tidal area, whereas 71% of decreased CBCS was linked with multiple driving processes in inland areas. In addition, the anthropogenic driving processes caused much greater loss (−5.97 × 105 Mg) than gain (6.81 × 104 Mg) in CBCS, compared with a net gain of CBCS (1.04 × 104 Mg) brought by the natural driving processes. The study can facilitate to develop coastal management strategy to balance and mitigate the conflicted LULC between socioeconomic development and maintenance of multiple ecosystem services incorporating CBCS. Graphical abstract Unlabelled Image Highlights • The linkage between carbon storage with LULC driving process was investigated. • Coastal wetlands in the Yellow River Delta exhibited net loss due to reclamation. • Carbon storage was impacted by natural and anthropogenic LULC driving process. • The carbon storage decreased by 10.2% in the Yellow River Delta during 1970–2010. [ABSTRACT FROM AUTHOR]

Abstract Coastal water quality assessment is challenging due to the complex hydrological environment in mangrove swamps. Such assessment requires a good understanding of swamp hydrology and potential solute reactions. In this study, we investigated the concentration variations of a suite of major elements (Na+, K+, Ca2+, Mg2+, SO 4 2−, HCO 3 – and Cl−), nutrients such as dissolved inorganic phosphorous (DIP) and silicate (DSi), and heavy metals (Cu, Zn, As, Hg, Cd, Pb and Cr) along a typical mangrove transect in Daya Bay, China. The transect comprises a tidal creek, a mudflat and two mangrove zones. The major elements exhibited various degrees of dilution and loss, such as losses of K+ due to uptake by mangrove trees and of SO 4 2− due to microbial sulfate reduction. Numerical simulations of groundwater flow showed that the inland fresh groundwater can continuously discharge through the landward mangrove zone, where high concentrations of DIP and DSi occurred. However, the middle mangrove zone served as a sink of DIP and DSi due to the weak hydrodynamic environment. The spatial distribution of heavy metal concentrations showed that only Cu pollution occurred in the creek zone. The Metal Pollution Index (MPI) was developed to compare the enrichment capability of heavy metals at the different sampling sites. Results showed that the intertidal groundwater has the strongest heavy metal enrichment capability, followed by sea water, inland groundwater and river water. Within the intertidal zone, the creek zone has the highest MPI, followed by the mangrove zone and the mudflat zone. The local water circulation occurred around the creek should contribute the high MPI in the creek zone. Graphical abstract Unlabelled Image Highlights • Sampling should be conducted in different sites in a mangrove swamp. • Local water circulation was intensified around the creek zone. • Water quality has a high spatial heterogeneity along the intertidal transect. • The intertidal groundwater can enrich more heavy metal than seawater. • The middle mangrove zone had a low permeability serving as a sink of DIP and DSi. [ABSTRACT FROM AUTHOR]

Coastal mangrove swamps play an important role in nutrient cycling at the land-ocean boundary. However, little is known about the role of periodic seawater-groundwater exchange in the nitrogen cycling processes. Seawater-groundwater exchange rates and inorganic nitrogen concentrations were investigated along a shore-perpendicular intertidal transect in Daya Bay, China. The intertidal transect comprises three hydrologic subzones (tidal creek, mangrove and bare mudflat zones), each with different physicochemical characteristics. Salinity and hydraulic head measurements taken along the transect were used to estimate the exchange rates between seawater and groundwater over a spring-neap tidal cycle. Results showed that the maximum seawater-groundwater exchange occurred within the tidal creek zone, which facilitated high-oxygen seawater infiltration and subsequent nitrification. In contrast, the lowest exchange rate found in the mangrove zone caused over-loading of organic matter and longer groundwater residence times. This created an anoxic environment conducive to nitrogen loss through the anammox and denitrification processes. Potential oxidation rates of ammonia and nitrite were measured by the rapid and high-throughput method and rates of denitrification and anammox were measured by the modified membrane inlet mass spectrometry (MIMS) with isotope pairing, respectively. In the whole transect, denitrification accounted for 90% of the total nitrogen loss, and anammox accounted for the remaining 10%. The average nitrogen removal rate was about 2.07 g per day per cubic meter of mangrove sediments. [ABSTRACT FROM AUTHOR]

The presence of pharmaceutical and personal care products and drugs of abuse (PPCPs) in wastewater treatment plants (WWTPs) indicates discharge of the effluent may not be suitable for the ecological balance of water ecosystems, such as wetlands. These PPCPs degrade water quality, considered as an ecosystem service (ES), provoking serious environmental impacts. Assessing the monetary value of PPCPs can be used as a proxy for environmental status of the ES of water quality (ESWQ). Considering PPCPs as non-desirable outputs of WWTPs, the shadow prices methodology has been implemented using directional distance function to measure the environmental avoided cost of removing salicylic acid (SA), methylparaben (MP), and THCOOH from WWTPs effluents discharged to Albufera Natural Park (Spain). The SA shows the highest shadow price (138.16 €/μg), followed by THCOOH (48.15 €/μg), and MP (30.66 €/μg). These values are interpreted as the environmental cost that would be avoided if SA, MP, and THCOOH were removed from WWTPs effluents. The non-parametric tests show that wastewater treatment technology, together with population equivalent (as a proxy of the size of urban areas) and seasonality are factors that influence shadow prices obtained. The approach used in this study highlights the use of PPCPs as status indicators of ESWQ quantified in monetary units. As a way to synthesize the essential concepts to implement the shadow prices approach, this study proposes a flow diagram to represent the relationship between all the factors involved in this work. The use of shadow prices methodology proves that removing SA, MP, and THCOOH is associated with a measurable improvement in the ESWQ of Albufera Natural Park. The findings of this study will be useful for plant managers in order to make decisions about the removal of PPCPs in WWTPs effluents. [ABSTRACT FROM AUTHOR]

Coastal wetlands are well known for their considerable capacity to store carbon (C). However, the spatial patterns and major controls of soil C concentration and C density in coastal wetlands remain poorly known. We measured soil total C concentration up to one meter depth and assessed environmental and biological factors influencing soil C input and decomposition processes across various geomorphologic settings and mangrove forest types at Dongzhai Bay, China. Structural equation modeling (SEM) was used to determine the causal pathways of influencing factors on soil C concentration. We found that the variation pattern of soil C concentration across geomorphologic settings and forest types was mirrored by soil properties. From 68 to 94% (varying with soil depth) variations of soil C concentration were explained by the inter-related influencing factors included in SEM. In the upper 60 cm soil layers, soil moisture was the most important factor affecting soil C concentration. In the 60–100 cm subsoil zone, the proportion of finer soil particles was the primary control of soil C concentration variation. In contrast, aboveground biomass and nearness of sampling site to the open water, which affect autochthonous and allochthonous C inputs, had relatively weak effects on soil C concentration compared to soil properties, which affect C decomposition. Soil C concentration was a good predictor of soil C density at all soil depths. The results suggest that top- and subsoil C concentrations in mangroves are subjected to different environmental controls, but taken together, mangrove soil C storage may be primarily controlled by soil property-mediated C decomposition rate. Subsoil C deserves more attention since it may respond differently to environmental changes than the better-known topsoil C. [ABSTRACT FROM AUTHOR]

The main pathways for phosphorus flux from land to sea are particle-associated (erosion) and dissolved runoff (rivers, groundwater, and agricultural drainage systems). These pathways can act as diffused sources for aquatic systems and support primary production, therefore, counteracting the efforts aimed at reducing phosphorus input from point sources such as sewage treatment plants. Phosphorus supports primary production in the water column and can elevate phytoplankton and macrophyte growth. Coastal wetlands with emerged ( Phragmites australis ) and submerged ( Stuckenia pectinata and Chara sp.) macrophytes can affect phosphorus fluxes in the land-water transitional zone. The macrophytes have the potential to act as a buffer for phosphorus run-off. The aim of this study was to determine the phosphorus stocks in the transitional land-sea zone of a cold temperate lagoon at the southern Baltic Sea. Phosphorus in macrophytes, water samples, and phytoplankton growth were analyzed along a gradient moving away from the wetland. The phosphorus stocks in the above ground biomass of the Phragmites plants were the highest at the end of August and with more than 8000 mg P m − 2 in the interior zone of the wetland, threefold the amount of P in Phragmites plant tissue at the wetland fringe. The submerged macrophytes stored only 300 mg P m − 2 , close to the wetland. Concentrations of soluble reactive phosphorus in the water column were higher in the zones of emerged macrophytes than in the zones of submerged macrophytes and decreased along the land-sea transect. Phytoplankton could grow proximal to the wetland during all seasons, but not further away. This study indicates that macrophytes can act as phosphorus sinks. However, short-term releases of phosphate within the Phragmites wetland have the potential to lead to phytoplankton growth. Phytoplankton can use these nutrient pulses either immediately or later, and support high biomass and turbidity within the system. [ABSTRACT FROM AUTHOR]

Atmospheric nitrogen deposition caused by human activities has been receiving much attention. Here, after long-term simulated ammonium and nitrate nitrogen deposition (NH 4 Cl, KNO 3 , and NH 4 NO 3 ) in the Yellow River Delta (YRD), a sensitive coastal wetland ecosystem typified by a distinct wet and dry season, methane fluxes were measured, by adopting a closed static chamber technique. The results showed that deposition of ammonium nitrogen accelerated methane emissions all year round. Ammonium nitrogen deposition transformed the YRD from a methane sink into a source during the dry season. Methanocellaceae is the only methanogen with increased abundance after the application of NH 4 Cl and NH 4 NO 3 , which promoted methane emissions, during the wet season. The findings suggested that Methanocellaceae may facilitate methane emissions in response to increased ammonium nitrogen deposition. Other methanogens might have profited from ammonium supplementation, such as Methanosarcinaceae. Deposition of nitrate nitrogen did not affect methane flux significantly. To the best of our knowledge, this study is the first to show that Methanocellaceae may be responsible for methane production in coastal wetland system. This study highlights the significant effect of ammonium nitrogen and slight effect of nitrate nitrogen on methane emission in the YRD and it will be helpful to understand the microbial mechanism responding to increased nitrogen deposition in the sensitive coastal wetland ecosystem. [ABSTRACT FROM AUTHOR]

Organic carbon is a key component of soils and plays a fundamental role in soil fertility and climate change. Determining the importance of potential drivers of soil organic carbon (SOC) and thus predicting the distribution of SOC are important for measuring carbon sequestration or emissions. Coastal wetlands are precious land resources that are currently undergoing rapid reclamation in China. The alternations in soil physicochemical conditions caused by reclamation can strongly impact the cycle of organic carbon. However, identification of the important drivers of SOC dynamics and prediction of SOC using the potential drivers remain largely unclear. In this study, we used classification and regression tree (CART) to identify the importance of the potential drivers of SOC at 241 sites from an intensively managed reclamation zone of eastern China. Multiple linear regressions (MLR) and random forest (RF) models were applied to predict the distribution of SOC using continuous variables, such as the contents of Cl, CaO, Fe 2 O 3 , Al 2 O 3 , SiO 2 , clay, silt, and sand as well as the soil pH, along with categorical variables, such as land use and reclamation duration. The results indicate that the soil/sediment pH was the most important variable impacting SOC, followed by the Cl and silt contents. The RF and MLR involving all predictor variables produced much higher R 2 and lower error indices than the RF and MLR models involving independent variables (pH and CaO). RF performed much better than MLR as it revealed much lower error indices (ME, MSE, and RMSE) and a higher R 2 than MLR. The superiority of RF in predicting SOC is related to its capability to deal with non-linear and hierarchical relationships between SOC and predictors. Analyses of land use effects on SOC dynamics indicated that paddy soils were superior in sequestering SOC than other land use types, which is likely ascribed to the rapid desalination and dealkalization of paddy field management. Therefore, paddy field management is recommended as an environment-friendly approach for managing newly reclaimed lands. [ABSTRACT FROM AUTHOR]

Coastal wetlands are important CH 4 sources to the atmosphere. Coastal wetlands account for ~ 10% of the total area of natural wetlands in China, but the size of this potential CH 4 source remains highly uncertain. We introduced the influence of salinity on CH 4 production and CH 4 diffusion into a biogeophysical model named CH4MOD wetland so that it can be used in coastal wetlands. The improved model can generally simulate seasonal CH 4 variations from tidal marshes dominated by Phragmites and Scirpus . However, the model underestimated winter CH 4 fluxes from tidal marshes in the Yellow River Delta and YanCheng Estuary. It also failed to capture the accurate timing of the CH 4 peaks in YanCheng Estuary and ChongMing Island in 2012. The improved model could generally simulate the difference between the annual mean CH 4 fluxes from mangrove sites in GuangZhou and HaiKou city under different salinity and water table depth conditions, although fluxes were systematically underestimated in the mangrove site of HaiKou city. Using the improved model, the seasonal CH 4 emissions simulated across all of the coastal wetlands ranged from 0.1 to 44.90 g m − 2 , with an average value of 7.89 g m − 2 , which is in good agreement with the observed values. The improved model significantly decreased the RMSE and RMD from 424% to 14% and 314% to − 2%, respectively, and improved the EF from − 18.30 to 0.99. Model sensitivity analysis showed that CH 4 emissions were most sensitive to P ox in the tidal marshes and salinity in the mangroves. The results show that previous studies may have overestimated CH 4 emissions on a regional or global scale by neglecting the influence of salinity. In general, the CH4MOD wetland model can simulate seasonal CH 4 emissions from different types of coastal wetlands under various conditions. Further improvements of CH4MOD wetland should include the specific characteristics of CH 4 processes in mangroves to decrease the uncertainty in estimating regional or global CH 4 emissions from natural wetlands. [ABSTRACT FROM AUTHOR]

Sea-level rise associated with climate change presents a major challenge to plant diversity and ecosystem service provision in coastal wetlands. In this study, we investigate the effect of sea-level rise on benthos, vegetation, and ecosystem diversity in a tidal wetland in west Wales, the UK. Present relationships between plant communities and environmental variables were investigated through 50 plots at which vegetation (species and coverage), hydrological (surface or groundwater depth, conductivity) and soil (matrix chroma, presence or absence of mottles, organic content, particle size) data were collected. Benthic communities were sampled at intervals along a continuum from saline to freshwater. To ascertain future changes to the wetlands' hydrology, a GIS-based empirical model was developed. Using a LiDAR derived land surface, the relative effect of peat accumulation and rising sea levels were modelled over 200 years to determine how frequently portions of the wetland will be inundated by mean sea level, mean high water spring and mean high water neap conditions. The model takes into account changing extents of peat accumulation as hydrological conditions alter. Model results show that changes to the wetland hydrology will initially be slow. However, changes in frequency and extent of inundation reach a tipping point 125 to 175 years from 2010 due to the extremely low slope of the wetland. From then onwards, large portions of the wetland become flooded at every flood tide and saltwater intrusion becomes more common. This will result in a reduction in marsh biodiversity with plant communities switching toward less diverse and occasionally monospecific communities that are more salt tolerant. While the loss of tidal freshwater wetland is in line with global predictions, simulations suggest that in the Teifi marshes the loss will be slow at first, but then rapid. While there will be a decrease in biodiversity, the model indicated that at least for one ecosystem service, carbon storage, there is potential for an increase in the near future. [ABSTRACT FROM AUTHOR]

Coastal wetlands link terrestrial with marine ecosystems and are influenced from both land and sea. Therefore, they are ecotones with strong biogeochemical gradients. We analyzed sediment characteristics including macronutrients (C, N, P, K, Mg, Ca, S) and heavy metals (Mn, Fe, Cu, Zn, Al, Co, Cr, Ni) of two coastal wetlands dominated by Phragmites australis at the Darss-Zingst Bodden Chain, a lagoon system at the Southern Baltic Sea, to identify the impact of adjacent land use and to distinguish between influences from land or sea. In the wetland directly adjacent to cropland (study site Dabitz) heavy metal concentrations were significantly elevated. Fertilizer application led to heavy metal accumulation in the sediments of the adjacent wetland zones. In contrast, at the other study site (Michaelsdorf), where the hinterland has been used as pasture, heavy metal concentrations were low. While the amount of macronutrients was also influenced by vegetation characteristics (e.g. carbon) or water chemistry (e.g. sulfate), the accumulation of heavy metals is regarded as purely anthropogenic influence. A principal component analysis (PCA) based on the sediment data showed that the wetland fringes of the two study sites are not distinguishable, neither in their macronutrient status nor in their concentrations of heavy metals, whereas the interior zones exhibit large differences in terms of heavy metal concentrations. This suggests that seaside influences are minor compared to influences from land. Altogether, heavy metal concentrations were still below national precautionary and action values. However, if we regard the macronutrient and heavy metal concentrations in the wetland fringes as the natural background values, an accumulation of trace elements from agricultural production in the hinterland is apparent. Thus, coastal wetlands bordering croplands may function as effective pollutant buffers today, but the future development has to be monitored closely to avoid breakthroughs due to exceeded carrying capacities. [ABSTRACT FROM AUTHOR]

The occurrence of 17 relevant pharmaceuticals and 7 heavy metals in the waters of the Pego–Oliva Marsh Natural Park (Valencia Community, Spain) were monitored. Thirty four zones (including the lagoon and the most important irrigation channels), covering the main land uses and water sources, were selected for sampling. Thirty three of them were contaminated with at least one pharmaceutical. Ibuprofen and codeine were the pharmaceuticals more frequently detected, in concentrations between 4.8 and 1.2 ng/L and a maximum of 59 ng/L and 63 ng/L, respectively. Regarding metals, Zn showed values under the detection limit in all the samples, while Cd, Co, Cr, Cu, Ni and Pb were detected at concentrations lower than the WHO and EU maximum levels for drinking waters. Ni showed significant direct correlations with diazepam, norfloxacin, ofloxacin and fenofibrate, and inverse relationships with ibuprofen, at 99 and 95% of significance. Cu, Co and Cr also showed significant correlations with some of the pharmaceuticals. These interactions could favor the synergistic/antagonistic interactions among pharmaceuticals and metals in the marsh, which can affect its aquatic fauna and flora or even human health. The influences of the water sources, land uses and spatial distribution of both types of contaminants were also studied. [ABSTRACT FROM AUTHOR]

Coastal wetlands are complex hydrogeological systems, in which saline groundwater usually occurs. Salinity can be attributed to many origins, such as dissolution of minerals in the sediments, marine contribution and evapotranspiration, among others. The aim of this paper is to evaluate the processes that condition the hydrochemistry of an arid marsh, Playa Fracasso, located in Patagonia, Argentina. A study of the dynamics and geochemistry of the groundwater was carried out in each hydrogeomorphological unit, using major ion and isotope ( 18 O and 2 H) data, soil profiles descriptions and measurements, and recording of water tables in relation to the tidal flow. Water balances and analytical models based on isotope data were used to quantify the evaporation processes and to define the role of evaporation in the chemical composition of water. The results obtained show that the groundwater salinity of the marsh comes mainly from the tidal inflow, to which the halite and gypsum dissolution is added. These mineral facies are the result of the total evaporation of the marine water flooding that occurs mostly at the spring high tides. The isotope relationships in the fan and bajada samples show the occurrence of evaporation processes. Such processes, however, are not mainly responsible for the saline content of groundwater, which is actually generated by the dissolution of the typical evaporite facies of the arid environment sediments. It is concluded that the evapotranspiration processes condition groundwater quality. This is not only due to the saline enrichment caused by the evapotranspiration of shallow water, but also because such processes are the main drivers of the formation of soluble salts, which are then incorporated into the water by groundwater or tidal flow. [ABSTRACT FROM AUTHOR]

Coastal wetlands are areas that suffer from great pressure. Much of it is due to the rapid development of the surrounding artificial landscapes, where socio-economic factors lead to alterations in the nearby environment, affecting the quality of natural and agricultural systems. This work analyses interconnections among landscapes under the hypothesis that urban-artificial impacts could be detected on soils and waters of an agro-ecological protected area, L’Albufera de Valencia Natural Park, located in the vicinity of the City of Valencia, Spain. The methodological framework developed addresses two types of anthropogenic pressure: (1) direct, due to artificialisation of soil covers that cause soil sealing, and (2) indirect, which are related to water flows coming from urban populations through sewage and irrigation systems and which, ultimately, will be identified by the presence of emerging pharmaceutical contaminants in waters of the protected area. For soil sealing, a methodology based on temporal comparison of two digital layers for the years 1991 and 2011, applying Geographical Information Systems and landscapes metrics, was applied. To determine presence of emerging contaminants, 21 water samples within the Natural Park were analysed applying liquid chromatography tandem mass spectrometry for the detection of 17 pharmaceutical compounds. Results showed that both processes are present in the Natural Park, with a clear geographical pattern. Soil sealing and presence of pharmaceuticals are more intensive in the northern part of the study area. This is related to population density (detection of pharmaceuticals) and land cover conversion from agricultural and natural surfaces to artificial ones (soil sealing). [ABSTRACT FROM AUTHOR]

Tropical coastal wetlands provide a range of ecosystem services that are closely associated with microbially-driven biogeochemical processes. Knowledge of the main players and their drivers in those processes can have huge implications on the carbon and nutrient fluxes in wetland soils, and thus on the ecosystems services we derive from them. Here, we collected surface (0–5 cm) and subsurface (20–25 cm) soil samples along a transect from forested freshwater wetlands, to saltmarsh, and mangroves. For each sample, we measured a range of abiotic properties and characterised the diversity of bacterial communities using 16S rRNA gene amplicon sequencing. The alpha diversity of bacterial communities in mangroves exceeded that of freshwater wetlands, which were dominated by members of the Acidobacteria, Alphaproteobacteria and Verrucomicrobia, and associated with high soil pore-water concentrations of soluble reactive phosphorous, and nitrogen as nitrate and nitrite (N-NO X −). Bacterial communities in the saltmarsh were strongly stratified by depth and included members of the Actinobacteria, Chloroflexi, and Deltaproteobacteria. Finally, the mangroves were dominated by representatives of Deltaproteobacteria , mainly Desulfobacteraceae and Synthrophobacteraceae , and were associated with high salinity and soil pore-water concentrations of ammonium (N-NH 4 +). These communities suggest methane consumption in freshwater wetlands, and sulfate reduction in deep soils of marshes and in mangroves. Our work contributes to the important goal of describing reference conditions for specific wetlands in terms of both bacterial communities and their drivers. This information may be used to monitor change and assess wetland health and function. Unlabelled Image • Reference conditions for selected coastal wetlands were established. • Soil bacterial diversity, abiotic properties and their interactions were considered. • Alpha diversity followed the order mangroves > saltmarsh > freshwater. • Community composition differed with abiotic conditions between wetlands. • Communities in the saltmarsh were significantly stratified by depth. [ABSTRACT FROM AUTHOR]

Massive die-off in salt marshes is one of the most common examples of widespread degradation in marine and coastal ecosystems. In salt marshes, tidal channel networks facilitate the exchange of water, nutrients, sediments and biota with the open marine environments. However, quantitative analyses of the role of channel networks in alleviating vegetation die-off in salt marshes are scarce. Here we quantified the spatial-temporal development of marsh vegetation die-off in the northern Liaodong Bay by analyzing aerial images before, during, and after a drought (from 2014 to 2018). We found that Suaeda salsa marshes have recently experienced large-scale die-off. The extent of vegetation die-off increases with increasing distance from the channel network. Moreover, our results suggested that efficient tidal channel networks (high drainage density, low mean unchanneled path length) can mitigate die-off at the watershed scale. We presented possible abiotic & biotic processes in channel networks that explain this spatial dynamic. Our study highlights the importance of efficient tidal channel networks in mitigating die-off and enhancing the resistance of marshes to droughts, and call for incorporating theses dynamics in coastal restoration and management. Unlabelled Image • Suaeda salsa marshes in the northern Liaodong Bay have experienced large-scale die-off. • Vegetation along channel networks was less degraded than that in the interior of the marsh. • Salt marshes with efficient tidal channel networks can mitigate vegetation degradation by droughts. [ABSTRACT FROM AUTHOR]

Tidal channel networks are ubiquitous features of coastal landforms that control the input and output of intertidal water, sediment and nutrients. Nevertheless, those intertidal platforms have undergone extensive losses due to human activities such as land reclamation. Identifying how tidal channel networks respond to land reclamation is critical to our prediction of the fate of residual tidal landforms. However, the morphological changes in the channel networks in the Yellow River Delta (YRD) impacted by severe reclamation remain unclear. Here, we analyzed the spatiotemporal dynamics of channel networks on two scales (the delta scale and the zone scale) under the double stress of land reclamation and natural pressure by comparing a comprehensive suite of morphological channel characteristics, including channel segment count, channel order, length, fractal dimension, drainage density and drainage efficiency. The results show that the interannual dynamics of tidal channel networks in the delta over the last three decades have experienced two periods: a favorable period during 1984–2000 and an adverse period during 2001–2018. The spatiotemporal patterns of channel networks varied with zones. Land reclamation exerted a dominant influence on shifting the evolutionary trend of channel networks on both the delta scale and the zone scale when reclamation proportion exceeded a certain threshold. Sediment siltation could to a certain degree mitigate the impact of reclamation on tidal channel networks development. Our study highlighted the effect of reclamation on the geomorphological evolution of tidal channel networks and identified its impact threshold which could further be used to guide coastal zone restoration and management. Unlabelled Image • The Yellow River Delta has experienced a large scale of reclamation in the past three decades. • Tidal channel networks in different areas of YRD had different evolutional patterns. • Reclamation exerted a dominant effect on development of tidal channel networks. • The influence of reclamation on tidal channel networks exist threshold effect. [ABSTRACT FROM AUTHOR]

Increasing nitrogen deposition has become one of major environmental concerns in coastal wetlands. However, little is known about the response of soil nitrous oxide (N 2 O) emissions, a powerful greenhouse gas, to the different levels and forms of nitrogen addition, in salt-affected coastal soils. To close the knowledge gap, a laboratory factorial incubation experiment with four nitrogen addition levels (0, no N addition; low-N, 45; medium-N, 90; high-N, 270 mg N kg−1), three forms (NO 3 − (KN); NH 4 + (NH); DN, NH 4 NO 3 (DN)), and three levels of salt addition (0, no salt addition; 12 ppt, low-salt; 35 ppt, high-salt) was carried out in two coastal soils with different initial salinity levels (LW: lower salinity wetlands; HW: higher salinity wetlands) in the Yellow River Delta, China. Results showed that, in no salt addition treatments, the cumulative N 2 O emissions were linearly related to nitrogen addition, and high nitrogen addition significantly promoted N 2 O emissions by 213% in LW soils and 848% in HW soils (p < 0.05), indicating that the mitigate effects of nitrogen addition to the deleterious salt stress were stronger in HW soils. Meanwhile, the promoting effects of DN and KN treatments were more obvious than NH treatments, suggesting that denitrification was responsible for the N 2 O emission. However, with salt addition, the nonlinear response pattern and reduced response sizes were observed for KN and DN treatments (p < 0.05), suggesting the alteration in responses of N 2 O emission to nitrogen addition by salt stress. In addition, the reduction and modification of response pattern was more obvious in soil with lower initial salinity. The findings of this work suggest the uniqueness and complexity of N 2 O emission responses to nitrogen inputs related to the salinity levels in coastal wetlands. Unlabelled Image • Nitrogen addition could linearly promoted N 2 O emission without salt stress. • Promoting effects with NO 3 − and NH 4 NO 3 form addition were more obvious than NH 4 +. • N 2 O emission was nonlinearly related to nitrogen addition under salt stress. • Salt stress decreased response size of N 2 O emission to nitrogen addition. • Soil with lower initial salinity experienced more obvious decline in response size. [ABSTRACT FROM AUTHOR]

River deltas contain complex self-organizing channel networks that continuously exchange fluxes of water, matter, energy, and information with their surroundings. The connectivity of these exchange processes plays a crucial role in controlling the evolution and dynamic stability of river deltas. However, connectivity patterns related to tidal channel networks have rarely been studied, especially in the Yellow River Delta (YRD), which is impacted by severe reclamation. Here, we evaluated the potential hydrological connectivity dynamics between the tidal channel network and its surroundings using an index of connectivity (IC) in the whole YRD and its three sub-regions: erosion zone, oil field zone and deposition zone. The results suggested that different areas had different spatial connectivity potential. The mean value of the IC related to the channel networks showed little difference for any zones. However, the total connectivity response area (CRA; set of connectivity response units) varied with the study scale. A decreasing trend was found on the delta scale and a relatively stable trend was found in the deposition zone. In terms of dynamic connectivity, the tidal flat system did not show a continuous trend over time. Our results indicated that the YRD is such a dynamic complex that a relatively stable connectivity pattern is unlikely to be achieved over time. Therefore, future ecological restoration based on hydrological connectivity needs to consider more related influencing factors and their temporal and spatial dynamics. Unlabelled Image • Spatio-temporal connectivity in Yellow River Delta (YRD) was investigated. • Different areas had different connectivity potential. • Connectivity response area (CRA) decreased over time in the erosion zone, whereas it maintained stable in the deposition zone. • YRD did not show a continuous connectivity pattern over time. [ABSTRACT FROM AUTHOR]

Coastal reclamation is a global threat to natural ecosystems, disturbing biological community structure, diversity and ecological function through habitat conversion. We have limited insights into the changes brought about by coastal reclamation for different land-use types. We used the Yellow River Delta (YRD) as a model because it is a region with intensive land reclamation, and we investigated the structural and functional variations of bacterial communities and their relations to edaphic properties under different land-use types. Our results showed that the high soil organic carbon (SOC), nitrate concentrations and salinity were found in oil field, aquaculture pond and salt pan, respectively, and low values in natural wetland. Land use was found to have significant influence on bacterial community diversity. To investigate the phylogenetic conservation of specific traits, we analyzed the relationship between soil bacterial assembly processes and edaphic properties. Bacterial traits phylogenetically conserved, and differs in depth. Our findings suggest that SOC served as a deep trait due to it negative correlation with deeper branches of phylogenetic clustering, while nitrate functioned as a shallow trait due to its positive correlation with phylogenetic clustering at finer branches. Soil salinity acted as a complex trait effected on both finer and deeper branches. Further potential functional gene co-occurrence network analysis revealed that land reclamation induced shifts of metabolic function by altering the functional gene connectivity. We found that the photosynthesis pathway was enriched in hub modules related to oil field (OF), while methane metabolism was enriched in hub modules linked to sea cucumber pond (CP1). In addition, two-component systems (TCS) were enriched with nitrate, ammonia, SOC and salinity-related modules. Therefore, our study highlights the importance of integrating multi-function and multi-process identification and prediction of coastal diverse reclamation impacts on coastal ecosystems. Unlabelled Image • Bacterial taxonomic and phylogenetic diversity vary with land-use types. • Soil factors as habitat filter alter the assembly process and metabolic function. • Enrichment and depleting effects differ among different land use types. • Highlight multi-function and -processes response of bacterial community [ABSTRACT FROM AUTHOR]

Through binding of mineral particles and elements, glomalin-related soil protein (GRSP) plays a critical role in sustaining terrestrial soil quality and contributes to the fate of elements from terrestrial to aquatic ecosystems. There is little knowledge, however, of the metal sequestration patterns of GRSP in both terrestrial and aquatic soils, and this limits progress in understanding how environmental conditions influence GRSP characteristics. Here, we employed microcosm experiments to determine the molecular composition of original GRSP derived from three arbuscular mycorrhizal fungi, Glomus intraradices , Glomus versiforme and Acaulospora laevis. To gain insight into the metal sequestration patterns of environmental GRSP, we investigated major subtropical and tropical mangrove wetlands in southern China. GRSP-bound metals were significantly and positively correlated with total metals, and the metal binding contributed to the metal sequestration of mangrove soils. Fourier-transform infrared spectroscopy results showed that original- and environmental GRSP fractions contained hydroxyl, carboxyl, amide and carbonyl functional groups, which enhanced metal binding. Environmental process had no effect on the type of functional groups of the GRSP, while it significantly changed the relative content of the functional groups. The infrared fingerprint analyses of original- and environmental GRSP revealed field-specific, however, no taxon-specific characteristics of GRSP. Biostatistical analysis of the GRSP molecular composition further revealed that the soil pollution sources regulated the ratios of functional group contents associated with hydrocarbons, proteins, polysaccharides and nucleic acids. By GRSP infrared fingerprints coupled with multivariate analyses, we developed a technique for source identification of heavy metal pollution, giving more reliable evidence about contributing sources. Unlabelled Image • Revealing soil pollution by combining GRSP traits with multivariate analysis. • Soil environment process had no effect on the type of functional groups of GRSP. • Molecular composition ratios of GRSP were field-specific in mangrove soils. • GRSP-bound metals were linked with metal pollution sources in coastal wetlands. • GRSP, a novel bioindicator, provided new perspective for coastal management. [ABSTRACT FROM AUTHOR]

• The carbon market is growing. • Four carbon offset methodologies have been approved for wetland restoration. • Very few wetland restoration carbon offsets transected to date. • Simplification of existing methodologies may facilitate adoption of blue C offsets. Coastal wetlands have been valued for a variety of ecosystem services including carbon sequestration and long term storage. The carbon sequestered and stored in coastal habitat including mangroves, salt marshes, and seagrass beds is termed as blue carbon. However, these systems are threatened mainly due to sea level rise, limited sediment supply, edge erosion, and anthropogenic influences. These habitats require restoration and conservation to continue providing ecosystem services. The incentive for emission reductions, referred to as carbon offsets, is well established for other ecosystems like forestry and agriculture. Some blue carbon offset methodologies or protocols have been certified by various voluntary carbon markets; however to date, a few wetland restoration carbon offset in the US has been transacted. Thus, the goal of this paper is to discuss the existing carbon market and carbon market methodologies applicable to coastal wetland restoration and conservation in the US. Currently, four wetland carbon offset methodologies have been approved in the carbon market. These methodologies are site and/or project-specific depending on the type of the wetlands, vulnerability to loss, and restoration need. The appropriate carbon stock and Green House Gas (GHG) emission assessment is the basis of determining carbon offsets. Simplification of the existing methodologies and development of new site and project-specific methodologies could potentially help to realize blue carbon offsets in practice. The slowly growing demand for carbon offsets in the carbon market could potentially be fulfilled from the blue carbon pool. While this carbon offset is in the early stages, this review may help the inclusion of carbon offset component in the coastal restoration and conservation projects in United States and potentially across the globe. [ABSTRACT FROM AUTHOR]

Coastal wetlands accumulate enormous quantities of nitrogen due to their position at the interface between land and sea and high trapping capacity. Fortunately, they have high nitrogen (N) purifying (removal) capacity, which means that they likely play an important role in mitigating against coastal eutrophication. However studies that empirically measure the degree to which wetlands purify nitrogen and their removal pathways (e.g. denitrification, anammox, plant uptake, microbial immobilization, etc.) are rare. In this study, the N purification potential (denitrification and anammox) and enzyme activities related to denitrification in different subtropical wetlands types were conducted in nitrogen-enriched wetlands of Daya Bay, Southern China. We found the average N purification rate was 11.4 μmol N·kg−1·h−1, with denitrification accounting for 84.2%–100% of the total N 2 production in the wetlands of Daya Bay. The N purification potential in the wet season, subtidal areas and mangrove forests were generally observed to be higher than that in the dry season, high and low tidal areas, barren and estuary habitats, respectively. Correspondingly, these differences were mainly driven by the temperature, Eh and NH 4 -N, respectively. Additionally, the nitrate reductase (Nar) and nitrite reductase (Nir) activities tended to be similar among different seasons and tidal areas, however, Nir activity in mangrove forest was 1.5-fold and 2-fold of the estuarine and barren areas, respectively. Meanwhile, Nir showed a positive correlation with denitrification rate. These results indicate that NO 2 -N reduction, the key control mechanism for N purification, should be the rate-limiting step of the denitrification process in Daya Bay wetlands. Notably, mangroves could improve N removal rates by 48.0% compared to other wetlands. Therefore, protecting and restoring mangrove ecosystems could be an effective way to reduce the risk of coastal eutrophication. Unlabelled Image • The distribution of N purification potential and enzyme activity in eutrophic wetland were studied. • Denitrification (94.5%) is the chief N removal process in eutrophic coastal wetland. • The temperature, Eh and NH 4 -N are mainly control factors to N removal in Daya Bay. • NO 2 -N reduction reaction is the key rate-limiting of the denitrification process. • The mangrove could improve N removal rates by 48.0% compared to other wetland. [ABSTRACT FROM AUTHOR]