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Estuarine wetlands are characterized by high biodiversity and active fluctuations in redox-sensitive metals (RSMs). In this study, sediment samples were collected from two sites, one with and one without vegetation, in the Yellow River Estuary Wetland (YREW). Active forms of Fe, Mn, and U were extracted using Tessier's sequential extraction method, the bacterial community was analyzed through high-throughput sequencing, and the impact of the community on the RSMs was evaluated. The results indicated that the high nutrient content generated by vegetation withering had a positive effect on bacterial biodiversity, which led to high biomass and a wide variety of species in the sediments. Redox conditions and nutrient levels were the main factors influencing bacterial community structure. Under reducing conditions, genera such as Desulfococcus and Desulfosarcina were the main bacteria mediating the reduction of active Fe and Mn. Bacteria in genera such as Desulfatiglans and Desulfotomaculum were the main bacteria mediating the reduction of active U. These bacteria may result in obvious changes in the release of Fe, Mn, and U from salt marshes to nearshore regions. Our results can help to elucidate the interactions of bacteria and RSMs. [ABSTRACT FROM AUTHOR]

Background and Aims: Estuarine wetlands are important carbon sinks, with plant photosynthesis being a vital component of this process. Changes in the inundation depth of wetlands could alter leaf photosynthesis and thus ecosystem carbon uptake capacity, ultimately determining the size of carbon sink. However, the relationship between inundation depth and photosynthetic capacity has yet to be determined, especially in estuarine wetlands with complex hydrological conditions. In addition, there is also conflicting evidence regarding the effect of inundation depth on photosynthetic capacity. Methods: To better understand the mechanisms of photosynthetic capacity responding to inundation depth, we performed a field experiment with a gradient of inundation depths (0, 5, 10, 20, 30 and 40 cm) in estuarine wetland dominated by Phragmites australis in the Yellow River Delta, China. Results: Our results showed that inundation depth significantly altered leaf morphological traits, elements and photosynthetic capacity. In particular, leaf photosynthetic capacity was obviously increased with increasing inundation depth. The increased leaf area enhanced light harvesting ability of leaves, and then increased Pn at different inundation depths. Besides, higher leaf N content promoted leaf photosynthetic capacity at different inundation depths. Conclusion: Overall, the findings demonstrated that inundation depth significantly enhanced the photosynthetic capacity of P. australis, which was correlated with altered leaf functional traits in wetlands. Our results hold important implications for more accurately predicting the relationship between photosynthetic capacity and inundation depth in wetland ecosystems under climate change and more accurately estimating of the carbon sink capacity of wetland ecosystems in the future. [ABSTRACT FROM AUTHOR]

The composition and functional traits of plant communities and their changes along an environmental gradient are important bases for maintaining the carbon sinks of estuarine wetlands. To clarify the succession pattern of plant community in an estuary along an environmental gradient, this study considered the Liaohe Estuary wetland as the research object and divided the dominant plant community into a Phragmites australis community and high-, medium-, and low-density Suaeda salsa communities. We employed redundancy analysis, variance decomposition, and multiple regression to examine the impact of an environmental gradient on the functional traits and spatial distributions of plant communities in the Liaohe Estuary wetland. The findings revealed that as the elevation decreased, the soil salinity increased and the water content decreased. The distribution of plant communities followed the order of P. australis, high-density S. salsa, medium-density S. salsa, low-density S. salsa, and bare flat areas. When the soil salinity exceeded 21 g/kg and the soil moisture content was below 17%, the conditions were no longer suitable for the growth of S. salsa or P. australis. Soil salinity, total nitrogen content, clay content, and elevation were the most critical environmental factors affecting the functional traits of the plant communities. Soil biochemical characteristics, soil texture, and the physical environment accounted for 28.9%, 23.12%, and 11.51%, respectively, of the variation in the spatial distribution of plant communities. The proportions of the suitable area for the high-, medium-, and low-density S. salsa were 13.1%, 53.78%, and 33.12%, respectively. The results provide a theoretical basis for further elucidating the degradation mechanisms of estuarine wetlands, developing an evaluation index system for estuarine wetland ecological restoration, and optimizing ecological protection and restoration strategies. [ABSTRACT FROM AUTHOR]

Estuarine wetland vegetation (EWV) serves as a critical indicator of ecosystem health but is increasingly threatened by human activities and climate change. Though remote sensing (RS) data provide a holistic view of vegetation change with sufficient spatial resolution, temporal changes in EWV are still ambiguous because of the twisted signals between phenological dynamics and multi-scale external disturbances. To address these knowledge gaps, a method integrated with multi-resolution analysis wavelet transform (MRA-WT) and time-series RS images were utilized in this study to uncover detailed multiple-scale EWV dynamics from the perspectives of vegetation phenology and evolution trends. Our results showed that: 1) The MRA-WT effectively decomposes NDVI at multiple scales, revealing intra- and inter-annual dynamics of EWV in complex environments. 2) In the Jiuduansha (JDS) wetland, the phenological characteristics and evolution processes of EWV are determined by vegetation type and geographical location. 3) The EWV in the JDS wetland remained stable with gradual growth from 2000 to 2021, despite the impacts of sediment reduction, estuarine projects, and invasive species. However, a declining trend post-2018 serves as a warning sign of potential ecosystem issues. Moreover, higher spatial and temporal resolutions enable more precise tracking of fine-scale details in the dynamics of EWV with the proposed method.

A hydrodynamic-water quality model was established using MIKE21 to analyze the distribution of total nitrogen (TN) and total phosphorus (TP) in the wetland sediments of Liaohe Estuary National Wetland Park. The purpose of this model is to investigate the spatial and temporal variation patterns in wetland sediments and the distribution of pollutant contents. The research determines the applicability of this model in accurately predicting these patterns. The simulated contour map of the water quality concentration displays significant variation characteristics and reflects the actual concentration of pollutants in the wetland sediment of the Liaohe Estuary, proving the coupled model to be reasonable and accurate. The water quality simulation results indicate that water flowing through the wetland aids in purifying pollutants in the sediment, and the purification effect is more significant during the flood season. The MIKE21 model's treatment reveals that the content of TN in wetland sediments decreases from southwest to northeast in the surface layer, following the flow direction of surface water. As the depth increases, the content of TN also decreases, with the bottom layer showing a decrease from southwest to northeast. The TP in wetland sediments receives surface water runoff and diffuses from upstream to downstream. The content of TP gradually decreases with increasing depth. [ABSTRACT FROM AUTHOR]

Plant‐mediated CH4 emission is an important part of the ecosystem CH4 emission from vegetated wetlands. Inundation depth may alter the potential magnitude of CH4 releases by changing CH4 production and plant transport, but the relationships between plant‐mediated CH4 emissions and inundation depth are still uncertain, especially for estuarine wetlands with changeable hydrological processes. Besides, there are conflicting results regarding the role of inundation depth in plant‐mediated CH4 emissions.Here we conducted a novel inundation depth experiment (0, 5, 10, 20, 30 and 40 cm inundation depth) dominated by Phragmites australis in the Yellow River estuary, China. Soil CH4 emissions, ecosystem CH4 emissions, net ecosystem CO2 exchange (NEE), soil organic carbon (SOC) and plant traits were measured during the growing seasons of 2018, 2019 and 2020. Plant‐mediated CH4 emissions were the difference between ecosystem CH4 emissions and soil CH4 emissions.The results showed that inundation depth decreased soil CH4 emissions but increased ecosystem CH4 emissions. Plant‐mediated CH4 transport from Phragmites australis accounted for 99% of total ecosystem CH4 emissions under different inundation depths. Inundation depth strongly stimulated plant‐mediated CH4 emission from 0 to 20 cm during the growing seasons. The increased NEE enhanced plant‐mediated CH4 emissions by altering production, suggesting that carbon components derived from photosynthetic carbon input may benefit CH4 production. Additionally, the increased plant height promoted CH4 emission by regulating plant transport, indicating that plant traits may play an important role in transport of CH4.Our findings indicated that NEE and plant height play an important role in plant‐mediated CH4 emissions under different inundation depths in estuarine wetland. This study also highlights that hydrological regimes and plant traits are essential for the estimation of CH4 emissions in future projections of global wetland changes. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Estuaries are complicated systems to manage effectively, requiring the monitoring of robust environmental indicators to assess health and detect changes. Routine estuarine monitoring programmes in New Zealand have only existed for 30 years at most, but estuaries have been significantly affected by anthropogenic pressures for at least 100 years. We reconstructed long term changes in indicators of estuarine health using historical information from sediment cores and aerial photographs, and combined this information with recent monitoring data. This study is focused on four estuaries in the Waikato region of New Zealand, but the findings are likely applicable elsewhere. Sediment accumulation rates increased by orders of magnitude c. 100 years ago, but mangrove forests only started to rapidly expand c. 50 years ago, which coincided with the intensification of agriculture and urban development, and resultant declines in freshwater quality. Over the past 20 years, state of the environment monitoring shows declines in benthic health at most monitoring sites, as well as continuing sediment accumulation and mangrove expansion in some places. This adds to the weight of evidence that environmental management has not been sufficient to safeguard estuarine health and demonstrates the magnitude of change in these systems over the past 100 years. [ABSTRACT FROM AUTHOR]

Mangrove wetland ecosystem is a coastal ecological key area that combines ecological characteristics of land and marine environments. This study examined soil carbon (C), nitrogen (N), and phosphorus (P) and their stoichiometry in three dominant mangrove species (Aegiceras corniculatum, Kandelia obovata, and Avicennia marina) distributed in the Guangxi Beilun Estuary Nature Reserve, China. Results showed that soil organic carbon (SOC) was highest in K. obovata, whereas soil total nitrogen (TN) and phosphorus (TP) were highest in A. corniculatum. The C:N, C:P, and N:P ratios in K. obovata were greater than those in the others. The microbial biomass C (MBC), N (MBN), and P (MBP) concentrations varied in ranges of 33.45-249.44 mg kg-1, 5.17-9.17 mg kg-1, and 0.17-0.43 mg kg-1, respectively. Similar to soil C, N, and P stoichiometry, K. obovata had the highest MBC, MBC:MBN, and MBC:MBP values, whereas the highest MBN and MBN:MBP were found in A. marina, and the highest MBP was found in mudflats. Overall, this study demonstrated that the soil stoichiometry and soil microbial biomass responded differently to different plant communities and these differences might be accounted for by variations in the environmental conditions of the three communities. [ABSTRACT FROM AUTHOR]

Abstract Background The lateral movements of mass and energy across the terrestrial-aquatic interface are being increasingly recognized for their importance in the carbon (C) balance of coastal/estuarine wetlands. We quantified the lateral flux of detrital C in the Yangtze estuary where invasive Spartina alterniflora has substantially and extensively altered the ecosystem structure and functions. Our overall objective was to close the C budget of estuarine wetlands through field sampling, tower-based measurements, and modeling. Methods A lateral detrital C exchange evaluation platform was established in a case study of the Yangtze River Estuary to investigate the effect of ecosystem structural changes on lateral detrital C transfer processes. This study estimated the lateral detrital C exchange based on the gross primary production (GPP) by performing coupled modeling and field sampling. Tower-based measurements and MODIS time series and CH4 outgassing and biomass simultaneously measured the lateral detrital C flux to characterize the relative contributions of lateral (i.e., detritus) C fluxes to the annual marsh C budget. Results The C pools in the plants and soil of Spartina marshes were significantly higher than those of the native community dominated by Phragmites australis. The GPP based on MODIS (GPPMODIS) was 472.6 g C m−2 year−1 and accounted for 73.0% of the GPP estimated from eddy covariance towers (GPPEC) (646.9 ± 70.7 g C m−2 year−1). We also detected a higher GPPMODIS during the pre-growing season, which exhibited a similar lateral detrital C flux magnitude. On average, 25.8% of the net primary production (NPP), which ranged from 0.21 to 0.30 kg C m−2 year−1, was exported during lateral exchange. The annual C loss as CH4 was estimated to be 17.9 ± 3.7 g C m−2 year−1, accounting for 2.8% of the GPPEC. The net positive detrital C flux (i.e., more detritus leaving the wetlands), which could exceed 0.16 kg C m−2 day−1, was related to daily tides. However, the observed lateral detrital C flux based on monthly sampling was 73.5% higher than that based on daily sampling (i.e., the sum of daily sampling), particularly in March and October. In addition, spatiotemporal granularities were responsible for most of the uncertainty in the lateral detrital C exchange. Conclusion This research demonstrated that an integrated framework incorporating modeling and field sampling can quantitatively assess lateral detrital C transport processes across the terrestrial-aquatic interface in estuarine wetlands. However, we note some limitations in the application of the light-use efficiency model to tidal wetlands. Spartina invasion can turn the lateral C balance from a C source (209.0 g C m−2 year−1) of Phragmites-dominated marshes into a small C sink (-31.0 g C m−2 year−1). Sampling over a more extended period and continuous measurements are essential for determining the contribution of different lateral detrital C flux processes to closing the ecosystem C budgets. The sampling spatiotemporal granularities can be key to assessing lateral detrital C transfer.

Denitrification, anammox, and DNRA are three important nitrogen (N) reduction pathways in estuarine sediments. Although salinity is an important variables controlling microbial growth and activities, knowledge about the effects of changing salinity on those three processes in estuarine and coastal wetland sediments are not well understood. Herein, we performed a 60-d microcosms experiment with different salinities (0, 5, 15, 25 and 35 ‰) to explore the vital role of salinity in controlling N-loss and N retention in estuarine wetland sediments. The results showed that sediment organic matter, sulfide, and nitrate (NO 3 −) were profoundly decreased with increasing salinity, while sediment ammonium (NH 4 +) and ferrous (Fe2+) varied in reverse patterns. Meanwhile, N-loss and N retention rates and associated gene abundances were differentially inhibited with increasing salinity, while the contributions of denitrification, anammox, and DNRA to total nitrate reduction were apparently unaffected. Moreover, denitrification rate was the most sensitive to salinity, and then followed by DNRA, while anammox was the weakest among these three processes. In other words, anammox bacteria showed a wide range of salinity tolerance, while both denitrification and DNRA reflected a relatively limited dynamic range of it. Our findings could provide insights into temporal interactive effects of salinity on sediment physico-chemical properties, N reduction rates and associated gene abundances. Our findings can improve understanding of the effects of saltwater incursion on the N fate and N balance in estuarine and coastal sediments. • Salinity plays a key role in regulating the nitrate reduction processes. • N-loss rates and N retention were both inhibited with increasing salinity. • Denitrification bacteria activity was the most sensitive to salinity. • Anammox bacteria activity showed a wide range of salinity tolerance. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Iron is an important element and its biogeochemical processes are vital to the matter and energy cycles of wetland ecosystems. Hydrology greatly controls characteristics of soil property and plant community in wetlands, which can regulate the behavior of iron and its oxides. However, it remains unclear how the spatial distribution of iron and its forms in estuarine wetlands responses to hydrological conditions. Five typical plant communities along a naturally hydrological gradient in the Yellow River Estuary wetland, including Phragmites australis in freshwater marsh (FPA), Phragmites australis in salt marsh (SPA), Tamarix chinensis in salt marsh (TC), Suaeda salsa in salt marsh (SS) and Spartina alterniflora in salt marsh (SA), as sites to collect soil samples. The total iron (FeT) and three iron oxides (complexed iron, Fep; amorphous iron, Feo; free iron, Fed) in samples were determined to clarify the spatial distribution of iron and explore its impact factors. The mean contents of FeT, Fep, Feo and Fed were 28079.4, 152.0, 617.2 and 8285.3 mg⋅kg–1 of soil at 0–40 cm depth in the different sites, respectively. The means were significantly different across communities along the hydrological gradient, with the higher values for SA on the upper intertidal zone and for SPA on the lower intertidal zone, respectively. Iron and its forms were positively correlated with the total organic carbon (TOC), dissolved organic carbon (DOC), total nitrogen (TN) and clay, and negatively correlated with electrical conductivity (EC). The indexes of iron oxides (Fep/Fed, Feo/Fed and Fed/FeT) were also different across communities, with a higher value for SA, which were positively correlated with soil water content (WC) and TOC. The results indicate that a variety of plant community and soil property derived from the difference of hydrology might result in a spatial heterogeneity of iron in estuarine wetlands.

Metal pollution has become an major issue governing the wetland ecosystem health. The southern coastal wetland of the Qiangtang Estuary are facing unusual perturbation due to rapid development along the embayment in recent decades. This study evaluated the bioavailability of metals (Cu, Pb, Cd, Cr and Zn) in the sediment of the southern coastal wetland of the Qiangtang Estuary using diffusive gradients in thin films (DGT) techniques and compared with several methods based on total metal content. The results showed that the contents of Cr, Pb, Cd and Cu in sediment, as detected using DGT, were considerably correlated with the exchangeable fraction and the content in Phragmites australis roots, while a weak correlation was observed for Zn. Therefore, DGT analysis could be used to evaluate the bioavailability and potential risk of Cr, Cd, Pb and Cu for P. australis. Quantitative indices, such as DGT concentration, bioaccumulation in P. australis, geoaccumulation index (Igeo) and potential ecological risk index (RI), revealed that Cd was a major potential ecological risk factor along the southern coast wetland of the Qiantang Estuary, especially in the upstream region, which is potentially more vulnerable to the anthropogenic pollution. [ABSTRACT FROM AUTHOR]

Background: The lateral movements of mass and energy across the terrestrial-aquatic interface are being increasingly recognized for their importance in the carbon (C) balance of coastal/estuarine wetlands. We quantified the lateral flux of detrital C in the Yangtze estuary where invasive Spartina alterniflora has substantially and extensively altered the ecosystem structure and functions. Our overall objective was to close the C budget of estuarine wetlands through field sampling, tower-based measurements, and modeling. Methods: A lateral detrital C exchange evaluation platform was established in a case study of the Yangtze River Estuary to investigate the effect of ecosystem structural changes on lateral detrital C transfer processes. This study estimated the lateral detrital C exchange based on the gross primary production (GPP) by performing coupled modeling and field sampling. Tower-based measurements and MODIS time series and CH4 outgassing and biomass simultaneously measured the lateral detrital C flux to characterize the relative contributions of lateral (i.e., detritus) C fluxes to the annual marsh C budget. Results: The C pools in the plants and soil of Spartina marshes were significantly higher than those of the native community dominated by Phragmites australis. The GPP based on MODIS (GPPMODIS) was 472.6 g C m−2 year−1 and accounted for 73.0% of the GPP estimated from eddy covariance towers (GPPEC) (646.9 ± 70.7 g C m−2 year−1). We also detected a higher GPPMODIS during the pre-growing season, which exhibited a similar lateral detrital C flux magnitude. On average, 25.8% of the net primary production (NPP), which ranged from 0.21 to 0.30 kg C m−2 year−1, was exported during lateral exchange. The annual C loss as CH4 was estimated to be 17.9 ± 3.7 g C m−2 year−1, accounting for 2.8% of the GPPEC. The net positive detrital C flux (i.e., more detritus leaving the wetlands), which could exceed 0.16 kg C m−2 day−1, was related to daily tides. However, the observed lateral detrital C flux based on monthly sampling was 73.5% higher than that based on daily sampling (i.e., the sum of daily sampling), particularly in March and October. In addition, spatiotemporal granularities were responsible for most of the uncertainty in the lateral detrital C exchange. Conclusion: This research demonstrated that an integrated framework incorporating modeling and field sampling can quantitatively assess lateral detrital C transport processes across the terrestrial-aquatic interface in estuarine wetlands. However, we note some limitations in the application of the light-use efficiency model to tidal wetlands. Spartina invasion can turn the lateral C balance from a C source (209.0 g C m−2 year−1) of Phragmites-dominated marshes into a small C sink (-31.0 g C m−2 year−1). Sampling over a more extended period and continuous measurements are essential for determining the contribution of different lateral detrital C flux processes to closing the ecosystem C budgets. The sampling spatiotemporal granularities can be key to assessing lateral detrital C transfer. [ABSTRACT FROM AUTHOR]

• Roots of P. australis enhance Fe-OC coupling, especially in low-tide areas. • Rhizosphere Fe-OC fluctuates seasonally, higher in low-tide flats in the growing season. • Plant growth stages significantly influence Fe-OC dynamics in tidal flat wetlands. • Significant rise in FeRB abundance in low-tide flat during non-growing season. • Seasonal shifts in microbial communities affect Fe-OC content in tidal sediments. As sea levels rise, coastal tidal wetlands are increasingly threatened by flooding and salt stress, highlighting the importance of iron (Fe) (hydr-) oxides in soil for stabilizing organic carbon (OC). This study focuses on Phragmites australis , common in the Yangtze River Estuary, exploring the interplay between OC and Fe (hydr-) oxides in the rhizosphere of P. australis across various seasons and elevations. It also examines microbial community shifts in the Fe oxidation–reduction cycle. Results show that in the non-growing season (January), Fe (hydr-) oxides and total organic carbon (TOC) levels in the rhizosphere soil of high-tide P. australis are significantly higher than during the growing season (August), with a notable increase in Fe oxide-bound OC (Fe-OC). The content of Fe-OC in tidal wetland soil fluctuates with plant growth stages and elevation. Notably, during the growing season, the Fe-OC content in the rhizosphere of low-tide P. australis is markedly higher than in high-tide areas, reversing in the non-growing season. The presence of P. australis roots is found to significantly enhance the accumulation and coupling of Fe (hydr-) oxides and OC, especially in low-tide areas compared to bare flats. This coupling is affected by the organic matter contributed by roots, microbial metabolism, and redox conditions of the soil. The study also highlights how plant and microbial metabolism regulate the response of rhizosphere Fe-OC across different tidal flat elevations. In low-tide environments during the non-growing season, the prevalence of Fe-reducing bacteria results in decreased Fe-OC content, while in high-tide areas, increased organic matter input boosts complexed Fe-OC formation. Overall, this study emphasizes the significance of plant metabolism in understanding the impact of sea level rise on Fe-OC stores in tidal wetlands, a vital factor for comprehending C cycling mechanisms and assessing C sequestration potential under future climate change scenarios. [ABSTRACT FROM AUTHOR]

Temperature sensitivity (Q10) is important to reveal carbon decomposition responding to climate change. It’s remains limited to understand how Q10 of anaerobic soil organic matter (SOM) decomposition is regulated by soil property in various wetlands with distinct hydrological characteristics. In the present study, samples of soil at the depths of 0–10 cm, 10–20 cm and 20–30 cm were collected in three typical Phragmites australis marshes, including a freshwater marsh (FPa), a no-tidal salt marsh (NTPa) and a tidal salt marsh (TPa), in the Yellow River estuary. The soil samples were incubated at 10 °C, 20 °C and 30 °C, respectively, to determine the rates of anaerobic CO2 production, Q10 values, and their relations to soil properties. Over 70-d incubation, temperature rise significantly increased the mean rates by 70%–136% (from 10 °C to 20 °C) and 64%–142% (from 20 °C to 30 °C) among the marshes, with the mean Q10 values ranging from 1.61 to 2.66. The rates of CO2 production and Q10 values were significantly affected by wetland type and soil depth. Among marshes, the Q10 of the FPa and NTPa soils was higher than that of the TPa soil (for 0–10 cm and 10–20 cm but for 20–30 cm); along soil depths, the Q10 of the top soil was higher than that of the subsoil (for FPa and NTPa but for TPa). Q10 was affected by total organic carbon (TOC), salinity and pH, and the effects were different with marshes. TOC was a main factor regulating Q10 for the freshwater and the no-tidal salt marshes, while salinity and pH were main factors for the tidal salt marsh. The findings highlight an interactive mechanism of soil property and tidal underlying the response of SOM decomposition to temperature change in estuarine wetlands.

The main factors controlling plant litter decomposition rates are litter quality and environmental factors. We investigated how different salinity and inundation conditions influence the decomposition rate and how litter quality affects dynamic change during the decomposition process in the Yellow River Delta wetland in northeastern China. To do this, we designed a field experiment using the litter bag method to study two selected dominant halophyte species (Phragmites australis and Suaeda salsa). We found litter decomposed faster when inundated across a range of salinities. Both the water chemical oxygen demand and NH3-N concentration were inversely correlated with salinity. The ratio of nitrogen to phosphorous showed an upward trend during the process of decomposition. The decomposition rate increased during the later stage of the process. Under inundation conditions, the decomposition rate of only S. salsa showed a positive correlation with salinity. The study results suggest that moderately higher salinity would increase anaerobic decomposition owing to the combined effect of salinity and inundation. The implications of our findings may be used to further assess the impact of environmental parameters and litter quality on the decomposition rate in estuarine wetland and can help determine a strategy for wetland reparation and remediation.

• Deep Bay opens to Pearl River Estuary and receives discharge from Shenzhen River. • Pearl River had a strong role on the bay hydrodynamics especially in the wet season. • Land reclamation within the bay will enhance pollution intrusion from Pearl River. • Reclamation would benefit the removal of pollutants from Shenzhen River. • Simulation results confirm the complex interconnection of bay and estuary. Deep Bay (DB) is a semi-enclosed bay that opens to the middle part of the Pearl River Estuary (PRE), the largest estuarine wetland area in the world. Like many rivers around the world, the Pearl River has in recent years experienced more frequent and more severe flow variations. It was hypothesized that Pearl River flow variation would affect the environment of DB, where locates large area of Ramsar wetlands of international importance. The anthropogenic factor of land reclamation was also hypothesized to alter the Pearl River flow and thus affect DB and the PRE environment. Simulations were performed to model water and salt transport processes under different scenarios of Pearl River flow variation and land reclamation. It was found that the Pearl River had a strong governing role on the hydrodynamics of DB, especially in the wet season. The simulation results indicated that in the wet season, the waters at the mouth of DB and DB as a whole were respectively composed of 50–80% and 31–37% of water discharged from the Pearl River. Moreover, it was shown that a 20% increase in Pearl River flow in the wet season would result in 0.2% and 3.3% more Pearl River water flushing into the bay before and after reclamation, respectively. Therefore, reclamation is predicted to stress the coastal ecosystem in DB, as it will enhance the intrusion of pollutants from the Pearl River into the bay head. However, it would benefit the removal and dilution of pollutants directly discharged into the bay from the Shenzhen River. Our results confirm that the hydrodynamic interconnection of bay and estuary in an estuarine system is complex, and should be carefully examined when assessing the environmental impacts of climate change and anthropogenic engineering projects. [ABSTRACT FROM AUTHOR]

In estuarine wetland ecosystems, the heavy metal content and especially the metal fractionation are influenced by water and salinity conditions. We collected sediments from the intertidal zone of the Yellow River Delta, where the water and salinity conditions changed frequently. The incubation experiments at different water and salinity levels were carried out in the laboratory to investigate the migration of Cr, Cu, Zn, Cd and Pb in the intertidal sediments. The results showed that the proportions of the residual fractions of Cr, Cu, Zn and Pb in the intertidal sediments were high, and the exchangeable Cd fraction was the highest. The Cr and Pb fractionations were significantly associated with the water level conditions. Different water level conditions were significantly related to the contents of the oxidizable fractions of Cr, Zn, and Cd. Except for the oxidizable Cu fraction, all Cu fractions were significantly correlated with the water conditions. Increasing salinity enhanced the migration risk of Cd and Pb. High salinity reduced the migration risk of Cr, Cd and Cu. The results of this study demonstrated that tidal floods increased the migration risk of Cd and Pb, and high salinity reduced the migration of Cr, Cd and Cu. [ABSTRACT FROM AUTHOR]

The abundant estuarine wetlands supported by the complex river network in the Pearl River Delta are under intense anthropogenic influence, which threatens the local ecosystem. This paper examines the benthic macroinvertebrate diversity and abundance within the Pearl River Estuary through a field study. Fieldwork, based on the integral index of connectivity (IIC) of the wetland network, was carried out in the Pearl River Estuary. The responses of macroinvertebrate metrics to the integral connectivity gradient in the wetland network were examined. Statistical analyses (CCA) revealed that the benthic abundance in high-hydrological-connectivity riverine habitats was clearly distinct from that in low-connectivity habitats. Statistical analysis demonstrated that the diversity and abundance of the macrobenthos populations were determined by the integral connectivity of the wetland network. A non-linear model was developed to depict the relationship between macroinvertebrate diversity and network connectivity. Thus, conservation efforts in estuarine wetlands should focus on the macroinvertebrate diversity response in wetland patches with specific connectivity characteristics in the wetland network of the Pearl River Delta. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ecology & Rural Environment is the property of Journal of Ecology & Rural Environment Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Due to the intensified human activities in coastal areas in recent years, the estuary wetlands have been seriously degraded. The artificial restoration using mangrove plants is considered to be an effective restoration method. The research on soil nitrogen and phosphorus mainly focuses on the natural mangrove wetlands, but there is limited information about the effects of mangrove restoration on it. The combination of field sampling and laboratory experiment were used to analyze total nitrogen and total phosphorus contents under different planting patterns during wetland restoration in Jinjiang estuary, Fujian Province. The results revealed that the total nitrogen and total phosphorus contents were higher than control, and there were significant differences between different mixed-vegetation types and planting densities, which indicated that mangrove restoration promoted their accumulation and the planting patterns could affect their concentrations. Additionally, the complex hy-drological process may also be an important factor in the estuarine areas. [ABSTRACT FROM AUTHOR]

Abstract NaCl and Na 2 SO 4 salts often dominate in estuarine wetland soils. However, it is unclear how different salt types affect carbon mineralization as a response to salinity levels. In this study, soil samples (0–13 cm) collected in the Liaohe estuarine wetland were amended with NaCl and Na 2 SO 4 salts at five salt levels: 1 mS·cm−1 (EC1), 3 mS·cm−1 (EC3), 5 mS·cm−1 (EC5), 10 mS·cm−1 (EC10) and 18 mS·cm−1 (EC18). The amended soils were incubated for 193 d, and the carbon mineralization rates were periodically measured. NaCl has decreased carbon mineralization at all salinity levels, but the effect of Na 2 SO 4 was found only in the high salinity level (EC18). We found a significant ion-specific effect of salt types on carbon mineralization at the lower salinity levels (EC1, EC3 and EC5) but no significant ion-specific effect at the higher salinity levels (EC10 and EC18). The salt effects highly varied with incubation time and the time changes were depended on salt types. The results suggest that there may be a salinity threshold (5–10 mS·cm−1) that impacts the ion-specific effect (NaCl and Na 2 SO 4) on carbon mineralization, depending on the salinity level and the ionic physiochemical behaviors. Highlights • NaCl decreased carbon mineralization at all the salinity levels. • Effect of Na 2 SO 4 on carbon mineralization appeared only at the high salinity level. • There was an ion-specific effect of salts and it varied with incubation time. • A salinity threshold (5–10 mS·cm−1) may impact the ion-specific effect. [ABSTRACT FROM AUTHOR]

Abstract The decomposition of salt marsh plants is affected by the variation of physiochemical factors caused by the change of tide level. In the present study, plant tissues of Spartina alterniflora from controlled metal exposure experiments were subjected to a field decomposition trial at different tidal levels in a tidal flat of Chongming Island, Shanghai. The contents of the metals and Pb stable isotope ratios of the plant litter and the adjacent sediment were followed. The mass loss rate of the root and leaf litters of S. alterniflora decreased with the increase of burial time. Leaf had the highest decomposition rate (0.009 day−1 to 0.020 day−1) compared to that of the roots (0.004 day−1 to 0.005 day−1) and stems (0.002 day−1 to 0.006 day−1). Leaf had the highest decomposition rate possibly due to the significantly lower C/N ratio (16.0–44.6) compared to that of the roots (32.8–88.9) and stems (43.7–120.9). The mass loss rate of the roots and leaves of S. alterniflora was higher in the high tidal marsh than that in the low tidal marsh, especially at the late stages of decomposition. The concentrations of metals in leaf litter of S. alterniflora increased, whereas the pools of metals in most of the plant litters decreased significantly with the increasing of the decomposition time. The ratios of 207Pb/206Pb and 208Pb/206Pb in the root litters decreased significantly in the first 290 days of decomposition and then increased significantly at Day 350, while the Pb isotope ratios in adjacent sediment showed no significant changes. Fast mass loss of plant litters induced the significant decrease in metals' pools at early stages of decomposition, and release of the plant tissue Pb was greatly inhibited due to the slowed mass loss at the late stages of decomposition. Graphical abstract Unlabelled Image Highlights • The mass loss rate of the root and leaf decreased with the increase of burial time. • The mass loss rate of the leaf and root was high in the high tidal marsh. • Metals' concentration increased in leaf with the increasing of decomposition time. • Pb isotope ratio in root litters decreased till the day 290 of decomposition. • Pb isotope ratios in adjacent sediment had no significant changes. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Remote Sensing is the property of Editorial Office of Journal of Remote Sensing & Science Publishing Co. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil microbes play vital roles in estuarine wetlands. Understanding the soil bacterial community structure and function profiles is essential to reveal the ecological functions of microbes in estuarine wetlands. Herein, soil samples were collected from Liao River estuarine wetland, Northeast China, along the river to the estuarine mouth, and soil bacterial communities were explored. Results showed that soil physiochemical properties, bacterial community structure and functions exhibited distinct variations influenced by geographical location. Bacterial phyla in soils were dominated by Proteobacteria and Bacteroidetes, while Gillisia and Woeseia were the predominant genera. Soil pH, electrical conductivity and nitrogen-related nutrients were the important factors affecting bacterial community structure. Based on PICRUSt prediction, the genes related to metabolism of nitrogen, sulfur and methane showed spatial distribution patterns, and the abundances of most biomarker genes increased as the distance from estuarine mouth extended. These findings could enrich the understanding of soil microbiome in estuarine wetlands. • Soil physicochemical properties varied greatly with the geographical location. • Relative abundances of dominant phyla and genera differed with spatial distance. • Soil pH, EC and N-nutrients were the key factors affecting bacterial communities. • Genes related to N, S and methane metabolism exerted spatial distribution patterns. [ABSTRACT FROM AUTHOR]

An estuarine wetland is an area of high ecological productivity and biodiversity, and it is also an anthropic activity hotspot area, which is of concern. The wetlands in estuarine areas have suffered declines, which have had remarkable ecological impacts. The land use changes, especially wetland loss, were studied based on Keyhole and Landsat images in the Liao River delta from 1962 to 2016. The dynamics of the ecosystem service values (ESVs), suitable habitat for birds, and soil heavy metal potential ecological risk were chosen to estimate the ecological effects with the benefit transfer method, synthetic overlaying method, and potential ecological risk index (RI) method, respectively. The driving factors of land use change and ecological effects were analyzed with redundancy analysis (RDA). The results showed that the built-up area increased from 95.98 km2 in 1962 to 591.49 km2 in 2016, and this large change was followed by changes in paddy fields (1351.30 to 1522.39 km2) and dry farmland (189.5 to 294.14 km2). The area of wetlands declined from 1823.16 km2 in 1962 to 1153.52 km2 in 2016, and this change was followed by a decrease in the water area (546.2 to 428.96 km2). The land use change was characterized by increasing built-up (516.25%), paddy fields (12.66%) and dry farmland (55.22%) areas and a decline in the wetland (36.73%) and water areas (21.47%) from 1962–2016. Wetlands decreased by 669.64 km2. The ESV values declined from 6.24 billion US$ to 4.46 billion US$ from 1962 to 2016, which means the ESVs were reduced by 19.26% due to wetlands being cultivated and the urbanization process. The area of suitable habitat for birds decreased by 1449.49 km2, or 61.42% of the total area available in 1962. Cd was the primary soil heavy metal pollutant based on its concentration, accumulation, and potential ecological risk contribution. The RDA showed that the driving factors of comprehensive ecological effects include wetland area, Cd and Cr concentration, river and oil well distributions. This study provides a comprehensive approach for estuarine wetland cultivation and scientific support for wetland conservation.

Increasing salinity has important impacts on biogeochemical processes in estuary wetlands, with the potential to influence the soil respiration, dissolved organic carbon (DOC) and microbial population. However, it is unclear how soil respiration is related to changes in the DOC and microbial community composition with increasing salinity. In this study, soil cores were sampled from a brackish wetland in the Liaohe River estuary and treated by salinity solutions at four levels (fresh water, 3‰, 5‰, and 10‰). Samples of gas, water and soil were collected to determine the respiration rates and microbial community structure of the soil and the DOC leaching from the soil. Compared to the low-salinity treatments (fresh water and 3‰), the high-salinity treatments (5‰ and 10‰) decreased the soil respiration rates by 45–57% and decreased the DOC concentrations by 47–55%. However, no significant differences were observed within the low-salinity treatments nor the high-salinity treatments. There is a positive correlation between the soil respiration rates and DOC concentrations in all treatments, but it does not indicate a genetic cause-effect relationship between them. The microbial community structure varied with the salinity level, with higher β- and δ-Proteobacteria abundance, as well as higher Anaerolineae, and lower Clostridia abundance in the high-salinity treatments. The respiration rates were slightly negatively related to the richness of Proteobacteria and positively related to the richness of Clostridia. This study suggests that there may be a salinity threshold (3–10‰) impacting the organic carbon loss from estuarine brackish wetlands. In addition, the response of soil respiration to increasing salinity may be mainly linked to changes in the microbial community composition rather than changes in the DOC quantity. [ABSTRACT FROM AUTHOR]

Bacterial and archaeal communities play important roles in wetland ecosystems. Although the microbial communities in the soils and sediments of wetlands have been studied extensively, the comprehensive distributions of planktonic bacterial and archaeal communities and their responses to environmental variables in wetlands remain poorly understood. The present study investigated the spatiotemporal characteristics of the bacterial and archaeal communities in the water of an artificially irrigated estuarine wetland of the Liaohe River, China, explored whether the wetland effluent changed the bacterial and archaeal communities in the Liaohe River, and evaluated the driving environmental factors. Within the study, 16S rRNA quantitative PCR methods and MiSeq high-throughput sequencing were used. The bacterial and archaeal 16S rRNA gene abundances showed significant temporal variation. Meanwhile, the bacterial and archaeal structures showed temporal but not spatial variation in the wetland and did not change in the Liaohe River after wetland drainage. Moreover, the bacterial communities tended to have higher diversity in the wetland water in summer and in the scarce zone, while a relatively higher diversity of archaeal communities was found in autumn and in the intensive zone. DO, pH and PO4-P were proven to be the essential environmental parameters shaping the planktonic bacterial and archaeal community structures in the Liaohe River estuarine wetland (LEW). The LEW had a high potential for methanogenesis, which could be reflected by the composition of the microbial communities.

Researches on the functional diversity of benthic ecosystems have mainly focused on macrofauna, and studies on functional structure of ciliate communities have been based only on trophic- or size-groups. Current research was carried out on the changing patterns of classical and functional diversity of benthic ciliates in response to environmental gradients at three sites in a wetland in Yangtze Estuary. The results showed that changes of environmental factors (e.g. salinity, sediment grain size and hydrodynamic conditions) in the Yangtze Estuary induce variability in species composition and functional trait distribution. Furthermore, increased species richness and diversity did not lead to significant changes in functional diversity due to functional redundancy. However, salt water intrusion of Yangtze Estuary during the dry season could cause reduced functional diversity of ciliate communities. Current study provides the first insight into the functional diversity of ciliate communities in response to environmental gradients. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Plant species diversity monitoring in estuarine wetland using remote sensing has important significance for ecological environment protection. It is very difficult to accurately retrieve the plant species diversity of wetland by remote sensing. The in situ data in Hangzhou Bay wetland were measured in this study. The plant species diversity indexes, including the species richness index and Simpson index were used to analyze the wetland plant species diversity. The GF-1 (High Resolution) satellite image, combined with variation function was used to analyze the spatial heterogeneity of plant species diversity in the region, and to explore the optimal scale of remote sensing plant species diversity monitoring. The correlation of the standard deviation of normalized difference vegetation index (NDVI) of GF-1 image and the plant diversity index was analyzed and the remote sensing model of plant species diversity in estuarine wetland of Hangzhou Bay was constructed. The current findings showed that the optimal scale of monitoring wetland plant species diversity at Hangzhou Bay was 19×19 pixel of GF-1 image. The retrieved wetland plant species diversity level of Hangzhou Bay using the remote sensing model with the optimal scale was consistent with the actual situation. Studies have shown that GF-1 satellite can be used to monitor the plant species diversity at Hangzhou Bay estuarine wetland quickly and effectively. [ABSTRACT FROM AUTHOR]

This study aims to investigate the effects of region and three regional dominated mangrove species ( Avicennia marina, Aegiceras corniculatum and Kandelia candel) on the distribution of inorganic nitrogen and phosphorus. Measurement of the inorganic nitrogen and phosphorus and enzymatic activities was carried out in soils covered by three mangrove species in the Quanzhou Bay estuarine wetlands, a typical coastal wetland in China. Species with a higher biomass in upstream and midstream absorb more nitrogen from soils, and the retention of the available phosphorus in the soils of different regions causes the regional variation of phosphorus. In areas dominated by A. marina, nitrate nitrogen is lower while available phosphorus is higher. Meanwhile, nitrate nitrogen and available phosphorus are higher in the soils covered by K. candel. Moreover, all three species affect the elemental and enzymic stoichiometry. The mangrove species influences the diversity of the elemental and enzymic stoichiometric relationship through differential microenvironments, which induce the biodiversity of wetland ecosystems. Thus, this study may facilitate a better understanding of the transformation ability of mangroves to nitrogen and phosphorus and will therefore be beneficial for providing a basis for the ecological restoration of estuarine wetlands. [ABSTRACT FROM AUTHOR]

The estuarine wetlands in the Yangtze Estuary face increasing threats due to large-scale engineering projects and huge land requirements. As a Wetland National Nature Reserve and important stopover site for migratory shorebirds of the East Asian–Australasian Flyway, the Jiuduansha wetland, one of four main islands in the estuary, is of both national and international importance. Since 1998 the previously undisturbed wetland has been considerably modified by the adjacent Deep-water Navigation Channel project (DNC). In order to understand the role of the DNC for the evolution of the Jiuduansha wetland, we performed a diagnostic study from multiple perspectives, including deposition rate, area change, evolution track, geometric characteristics, and geomorphological change. By coupling GIS, geostatistics, and remote sensing techniques, this study demonstrates the impact of the DNC on the Jiuduansha wetland in a spatially explicit way. Multi-temporal bathymetric maps and Landsat images from before and after the DNC was constructed were adopted to conduct our study. We find that deposition has occurred in most parts of the wetland over the past almost 30 years, accounting for 67.3% of the total area. However, over 40% of the study area shows a decreasing trend in deposition rate. The spatial distribution of deposition–erosion patterns is closely linked to the DNC. We also find that the DNC has substantial effects on the evolution of the Jiuduansha wetland. The 0, 2, and 5 m isobaths in the Jiuduansha Shoal (JDS), as well as in the Jiangya Shoal (JYS), the Upper Shoal (US) and the Middle-Lower Shoal (MLS), show different response patterns to the DNC. Specifically, the south training jetty of the DNC has an “adsorption effect” on the JDS above the 2 m isobaths intersecting with it. As a result, the evolution track, geometric and geomorphological characteristics of the JDS were markedly altered in the short term. Our comprehensive analysis suggests that in the future, the JDS will become more elongated in both the upstream and downstream direction along the south training jetty, and that the south side of the JDS will be eroded. [ABSTRACT FROM AUTHOR]

Salinity distributions and gradients within an estuary are of great socioeconomic and ecological importance. In this study, a well-validated and process-based hydrodynamic model (Delft3D) was applied to investigate the salinity distributions and variations in the Yangtze Estuary subject to river discharge regulation by the Three Gorges Reservoir and morphological evolution of the estuary. The results indicate that the regulation of river discharge is the controlling factor for salinity variations in the estuary. Following construction of the Three Gorges Reservoir, the salinity significantly decreased during the dry season and slightly increased during the flood season. The morphological evolution of the estuary induced spatial salinity variations and affected the salinity in the estuarine wetlands (the Jiuduansha Shoal and East Chongming Mudflat). The salinity in the Jiuduansha Shoal increased from 1998 to 2010, whereas it decreased from 2010 to 2018. During the period 1998 to 2018, the salinity in the East Chongming Mudflat exhibited an increasing trend. These findings provide implications for management of water resources and wetlands in the Yangtze and other similar estuaries. • Regulation by Three Gorges Reservoir decreased salinity in Yangtze Estuary during dry season. • Morphological evolution of Yangtze Estuary induced spatial salinity variations. • Impact of Three Gorges Reservoir dominated that of morphological evolution. [ABSTRACT FROM AUTHOR]

The wetland in the Yangtze Delta plays an important role in coastal protection against erosion, water purification, and habitat maintenance of migratory birds. The Yangtze Delta is one of the largest economic zones (e.g., Shanghai) in China. Human activities severely affect wetland evolution. Wetland mapping was performed from multi-temporal remote sensing data of Landsat during the period 2000-2010 at intervals of about 5 years, and spatiotemporal changes in wetland characteristics as well as driving forces for such changes were analyzed. Results indicated the Yangtze River estuarine wetland area experienced a net increase of 63 % during the period of 2000-2010; from 2005 onwards, however, the rate of increase has decreased. Human activities, including upstream dam construction, estuarine engineering, land reclamation, and ecological engineering, played an important role in wetland evolution during this short period. Reduction of riverine sediment loads led to decreases in the increase rate of estuary wetland; 95 % of the estuarine shoreline is embanked by seawalls, which exerts negative effects because closure promotes substantial degradation of wetland areas. Urbanization and expansion of Shanghai facilitated regular land reclamation of wetland and led to 35 % wetland loss. Intentional artificial planting of aquatic plants and groyne construction accelerated sediment deposition and wetland formation to compensate for coastal wetland loss. [ABSTRACT FROM AUTHOR]

Many efforts have been made to control invasive Spartina alterniflora and to restore coastal wetlands along the Pacific Rim . This study is the first to report the effects of a Spartina -eradication program on soil greenhouse gas (GHG) emissions. In this study S. alterniflora was eradicated in a pilot program covering an area of 0.63 km 2 in a Yangtze River estuarine wetland. In the following year after the eradication program was complete, plant growth, soil microbial activities, as well as CO 2 , CH 4 and N 2 O emissions were investigated. S. alterniflora ramets did not re-grow after the eradication program, while a native plant, Phragmites australis , thrived and produced taller but rather thinner ramets. CO 2 , CH 4 and N 2 O emissions in areas previously covered by S. alterniflora declined based on measurements made a year after eradication. This may have been caused by the removal of this plant as well as by flooding and/or by the reduced soil microbial biomass and dehydrogenase and β-glucosidase activities. CH 4 fluxes significantly increased in the program sites where the native species P. australis was retained, while CO 2 and N 2 O fluxes showed no significant changes. Our study revealed that GHG emissions can be greatly altered by an invasive plant eradication program and analysis of such emissions should be included in comprehensive assessments designed to guide successful restoration practices. Based on scenario analysis, we suggest that from the view of GHG emission equivalency, planting P. australis in approximately 50% of the area where S. alterniflora was eradicated would be appropriate in future management. [ABSTRACT FROM AUTHOR]