Spatial distribution of soil organic carbon across diverse vegetation types in a tidal wetland.

Tidal wetlands are significant contributors to global "blue carbon" resources. The water and salt gradients in tidal wetlands shape vegetation distribution and store significant amounts of soil organic carbon (SOC). We selected four distinct regions within the intertidal zone comprising three distinct vegetation types: low-tide saltmarsh Suaeda salsa (LS), high-tide saltmarsh Suaeda salsa (HS), mid-high-tide Phragmites australis (P), and high-tide Tamarix chinensis (T). Through field sampling and indoor analysis, we found significant differences in SOC levels across various vegetation types along the land-sea gradient. Among these, LS exhibited the highest SOC levels, while P had the lowest. Additionally, there were vertical variations of SOC within a 1-m range among different vegetation types. Mantel analysis and SEM demonstrated that SWC influences SOC content by manipulating vegetation types, thereby regulating total soil carbon. Overall, our findings provide valuable insights for further investigating the effects of vegetation succession on soil carbon pool evolution.

SAR image integration for multi-temporal analysis of Lake Manchar Wetland dynamics using machine learning.

The Manchar Lake wetland complex, Pakistan's largest freshwater-lake, faces unprecedented ecological challenges amidst climate change and human pressures, necessitating urgent, data-driven conservation strategies. This study employs cutting-edge multi-sensor remote sensing techniques to quantify and analyze the dynamic changes in this critical ecosystem from 2015 to 2023, aiming to provide a comprehensive understanding of wetland dynamics for informed management decisions. Integrating Sentinel-1 Synthetic Aperture Radar (SAR) and Sentinel-2 multispectral imagery, we assessed changes in wetland extent, vegetation health, and land-use patterns using spectral indices and topographic data. Our methodology achieved classification accuracies exceeding 92% across all study years, revealing significant ecosystem fluctuations. Water body extent exhibited a non-linear trend, expanding from 318.5 km² (5%) in 2015 to 397.0 km² (7%) in 2019, before contracting to 369.9 km² (6%) in 2023. This pattern was corroborated by MNDWI values. Concurrently, vegetation covers dramatically increased from 405.5 km² (7%) in 2019 to 1081.6 km² (18%) in 2023. The Enhanced Vegetation Index (EVI) reflected this trend, decreasing from 0.61 in 2015 to 0.41 in 2019, before recovering to 0.53 in 2023. Land use changes were substantial, with agricultural areas increasing from 118.4 km² (2%) in 2015 to 498.0 km² (8%) in 2023. SAR data consistently supported these observations. Topographic analysis, including the Topographic Wetness Index (TWI), provided crucial insights into wetland distribution and resilience. This comprehensive analysis highlights the complex interplay between natural processes and human influences shaping the Manchar-Lake ecosystem, underscoring the urgent need for adaptive management strategies in the face of rapid environmental change.

Unravelling the processes involved in biodegradation of chlorinated organic pollutant: From microbial community to isolated organohalide degraders.

Hundreds of studies have demonstrated the bioremediation of chlorinated organic pollutants (COPs) in flooded environments. However, the role of specific functional strains in degrading COPs under complex media such as wetlands is still unclear. Here, we focused on the microbial characteristics of COP-polluted sediments, identified the bacteria responsible for degradation and conducted a genomic analysis of these bacteria. Four strains were obtained and identified as Petrimonas sulfuriphila PET, Robertmurraya sp. CYTO, Hungatella sp. CloS1 and Enterococcus avium PseS3, respectively. They were capable of degrading a typical COP, γ-hexachlorocyclohexane (γ-HCH). The residual γ-HCH concentrations were 58.8 % (PET), 45.6 % (CYTO), 60.2 % (CloS1), and 69.3 % (PseS3) of its initial value, respectively. Strain PET, CYTO and CloS1 could degrade γ-HCH to its dehalogenation product chlorobenzene. Each strain harbors genes annotated to the pathway of halogenated organic matter degradation (e.g. 2-haloacid dehalogenase) and cobalamin biosynthesis, which are involved in the degradation of COPs. Comparative genomic analysis of the four strains and other classical organohalide-respiring bacteria (e.g. Dehalococcoides mccartyi and Sulfurospirillum multivorans DSM 12446) showed that they share orthologous clusters related to the cobalamin biosynthetic process (GO:0009236). VB12 was also detected in the culture systems of the four strains, further highlighting the importance of cobalamin in COPs degradation. In the genome of the four strains, some genes were annotated to the halogenated organic matter degradation and cobalamin biosynthesis pathway within horizontal gene transfer (HGT) regions. This further indicated that microorganisms carrying these genes can adapt faster to pollution stress through HGT. Together, these findings revealed the co-evolution mechanism of functional strains and may provide novel insights into improved bioremediation strategies for COP-polluted complex media based on generalist organochlorine-degrading bacteria.

Pretreated polystyrene is degraded by a microbial consortium enriched from wetland plastic waste.

The biodegradation of polystyrene (PS), a type of plastic with aromatic rings in its polymer chain, is a critical environmental goal worldwide. Microbial degradation of PS has been reported, but the underlying mechanisms are poorly understood. Here, we constructed a microcosm wetland containing PS plastic. We isolated six highly efficient PS plastic-degrading bacterial strains and created a microbial consortium (MCs) consisting of these strains. After a 30-day incubation period, MCs-treated PS exhibited hallmarks of degradation, including -CO- formation, reduced hydrophobicity, surface porosity, and 20 % weight loss. The efficiency of PS degradation was enhanced by using a combination of physical-chemical pretreatment and biological methods, increasing the microbial degradation rate by 20 %. Antioxidant 2246 (C23H32O2) was detected in the culture supernatant via GC-MS. Metatranscriptomic sequencing analysis provided insight into the possible metabolic pathway of PS degradation by the composite bacteria. We identified 31 highly expressed genes encoding proteins that function in carbon metabolism pathways and 34 unique proteases which catalyze the cleavage of long polymer chains. The resulting small molecules are absorbed and further degraded intracellularly by enzymes such as coenzyme synthase, hydratase, transferase, carboxylase, and dehydrogenase. These findings lay the foundation for the efficient and sustainable degradation of PS.

Assessing the health of wetland using the PSR approach with reference to the Renuka Ramsar Site, India.

Wetlands are important ecosystems, and few of them, owing to unique characteristics, have been designated the status of Ramsar sites under the convention of wetlands. Despite the status, few of these wetlands are under threat owing to their social importance. Renuka wetland is one such important Ramsar site in India, which is culturally an embodiment of the Goddess Renuka ji. An international fair is held every year at the lake which attracts thousands of pilgrims and tourists. This event is one of the major contributors to anthropogenic risk; other pressures are siltation, pollution, land use activities, and invasive species. Under such a scenario, it becomes important to assess the health of wetlands to take timely decisions about their management. This study evaluates the health of Renuka wetland, using the Pressure State and Response (PSR) model. Relevant data related to the wetland and its catchment from a wide spectrum of sources, namely, field, laboratory, and remote sensing were combined to assess the health of the wetland. Ten indicators were identified, and Analytic Hierarchy Process (AHP) was used to assign weights to the indicators. The wetland health index of Renuka wetland is 0.35, indicating that the lake is in poor condition exhibiting degraded functioning, high external pressure, low vigor, poor resilience, and stability. The study also revealed that the water quality deteriorates post-fair. Thus, the wetland needs attention in terms of management so that the health of the lake improves and is sustained in the future. The study contributes to Sustainable Development Goal 6.6 which focuses on protecting and restoring water-related ecosystems and aims at healthier ecosystems.

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

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

Effects of Hydraulic Retention Time on Removal of Cr (VI) and p-Chlorophenol and Electricity Generation in L. hexandra-Planted Constructed Wetland-Microbial Fuel Cell.

Hexavalent chromium (Cr (VI)) and para-chlorophenol (4-CP) are prevalent industrial wastewater contaminants that are recalcitrant to natural degradation and prone to migration in aquatic systems, thereby harming biological health and destabilizing ecosystems. Consequently, their removal is imperative. Compared to conventional chemical treatment methods, CW-MFC technology offers broader application potential. Leersia hexandra Swartz can enhance Cr (VI) and 4-CP absorption, thereby improving wastewater purification and electricity generation in CW-MFC systems. In this study, three CW-MFC reactors were designed with L. hexandra Swartz in distinct configurations, namely, stacked, multistage, and modular, to optimize the removal of Cr (VI) and 4-CP. By evaluating wastewater purification, electrochemical performance, and plant growth, the optimal influent hydraulic retention time (HRT) was determined. The results indicated that the modular configuration at an HRT of 5 days achieved superior removal rates and power generation. The modular configuration also supported the best growth of L. hexandra, with optimal photosynthetic parameters, and physiological and biochemical responses. These results underscore the potential of modular CW-MFC technology for effective detoxification of complex wastewater mixtures while concurrently generating electricity. Further research could significantly advance wastewater treatment and sustainable energy production, addressing water pollution, restoring aquatic ecosystems, and mitigating the hazards posed by Cr (VI) and 4-CP to water and human health.

Composition and storage of soil inorganic carbon as well as the controlling factors in coastal area of the northern Jiangsu, China.

The sequestration of soil inorganic carbon (SIC) especially pedogenic carbonate (PC) is one of the important pathways reducing the concentration of atmospheric carbon dioxide and thus mitigating climate change in coastal areas. Using the technology of 13C stable isotope, we analyzed the differences in the composition and storage of SIC, and explored the key physicochemical properties influencing soil PC storage in different horizons (0-10, 11-20, 21-40, 41-60, 61-80 and 81-100 cm) from Suaeda salsa wetland (SS), Spartina alterniflora wetland (SA), young poplar plantation (YP), and mature poplar plantation (MP) in coastal area of the northern Jiangsu Province. The results showed that except for the surface (0-10 cm) soil in MP, the SIC content was higher than SOC in all soil horizons. Overall, neither the soil PC to SIC ratio nor the SIC storage were significantly different in SA and SS soils. Compared to wetland soils (0-40 cm), the soil PC to SIC ratio was reduced by 32.7% and 54.1% and the PC storage was reduced by 40.5% and 59.2%, the lithogenic carbonate (LC) storage changed little, while the SIC storage was reduced by 21.0% and 17.9%, respectively in the YP and MP soils. Compared to the YP soils (0-100 cm), both the soil PC to SIC ratio and the PC storage were significantly reduced while the LC storage was significantly increased, especially at the 41-100 cm soil horizons, meanwhile, the SIC storage was not significantly changed in the MP soils. Results of the structural equation modeling (SEM) indicated that key factors influencing soil PC storage were the ratio of PC to SIC, followed by the SOC content and bulk density. SOC could inhibit the formation of soil PC. Generally, the coastal wetlands have greater SIC storage and sequestration potential than poplar plantations, and the PC sequestration can be regulated by modulating the ratio of PC to SIC and SOC content.

Ecohydrological changes recorded by sedimentary diatoms in the Dajiuhu Wetland in Shennongjia over the past 40 years.

Anthropogenic hydrological regulation is profoundly altering the structure and function of wetland ecosystems. Due to the scarcity of long-term monitoring records, the responses of wetland ecosystems to anthropogenic hydrological regulation remain unclear. We reconstructed past ecohydrological changes in Dajiuhu Wetland during the last 40 years and explored the driving forces, based on multiproxy records of a 44-cm-length sediment core collected from Wuhaohu Lake of Dajiuhu Wetland in Shennongjia, Hubei. The results showed that the diatom community in Wuhaohu Lake had experienced three major stages, including the dominance of benthic diatoms between 1980 and 2008, the rapid increase in planktonic diatoms between 2008 and 2016, and the dominance of small-sized fragilarioid species after 2016. Results of redundancy analysis showed that change in diatom assemblage was significantly correlated with total organic carbon, total nitrogen and the ratios of Mn to Fe. Diatom floral changes after 2008 indicated the shift of Wuhaohu Lake from an early organic-rich peatland to a shallow lake, mainly in response to an increase in water table driven by damming. From 2016, the increases in benthic and epiphytic diatoms responded to the expansion of aquatic plants and improved light penetration after the relocation of local population. Sedimentary diatom records revealed the process of environmental changes, and hence would provide a scientific basis for the environmental protection of wetlands.

Nature based solutions for removal of steroid estrogens in wastewater.

Estrogens are a growing problem in wastewater discharges because they are continuously entering the environment and are biologically active at extremely low concentrations. Their effects on wildlife were first identified several decades before, but the environmental limits and the remedial measures are still not completely elucidated. Most conventional treatment processes were not designed with sufficiently long retention times to effectively remove estrogens. Nature-based wastewater treatment technologies such as treatment wetlands (TW) and high-rate algal ponds (HRAP) are economically feasible alternatives for decentralized wastewater treatment and have promise for removing steroid hormones including estrogens. For small communities with populations below 50,000, the overall cost of TWs and HRAPs is considerably lower than that of advanced decentralized treatment technologies such as activated sludge systems (AS) and sequencing batch reactors (SBR). This results from the simplicity of design, use of less materials in construction, lower energy use, operation and maintenance costs, and operation by non-skilled personnel. The nature-based technologies show high removal (>80%) for both natural and synthetic estrogens. Estrogen removal in TWs can be enhanced using alternative media such as palm mulch, biochar, and construction wastes such as bricks, instead of traditional substrates such as sand and gravel. While TWs are effective in estrogen removal, they have the disadvantage of requiring a relatively large footprint, but this can be reduced by using intensified multilayer wetland filters (IMWF). Using filamentous algae in HRAP (high-rate filamentous algal pond; HRFAP) is an emerging technology for wastewater treatment. The algae supply oxygen via photosynthesis and assimilate nutrients into readily harvestable filamentous algal biomass. Diurnal fluctuations in oxygen supply and pH in these systems provide conditions conducive to the breakdown of estrogens and a wide range of other emerging contaminants. The performance of these nature-based systems varies with seasonal changes in environmental conditions (particularly temperature and solar irradiation), however a greater understanding of operating conditions such as loading rate, hydraulic retention time (HRT), pond/bed depth, dissolved oxygen (DO) concentration and pH, which influence the removal mechanisms (biodegradation, sorption and photodegradation) enable TWs and HRAPs to be successfully used for removing estrogens.

Passive dispersal potential of medaka eggs by attaching to waterbirds.

Colonization of new habitats is a key event in forming current distributions in organisms. It has been speculated that freshwater fish eggs can be dispersed passively by attaching to or egestion from waterbirds that arrive in wetland habitats. Recent research showed that some freshwater fish eggs could be excreted alive from birds and then successfully hatch, but scientific evidence of bird-mediated fish dispersal is still limited to endozoochory (internal transport through a bird's digestive tract). Here, we experimentally suggest the dispersal potential in another way or epizoochory (external dispersal by attaching to waterbirds), using medaka Oryzias latipes, which spawns on aquatic plants. Our field experiment showed that waterbirds could carry artificial aquatic plants among waterbodies. Medaka eggs attached to aquatic plants could survive in the air for up to 18 h with a median lethal period of 16.3 h. Those two findings raise the possibility of the epizoochory of medaka in nature.

Assessing the nutrient removal performance from rice-crayfish paddy fields by an ecological ditch-wetland system.

Agricultural drainage from catchments significantly impacts aquatic ecosystems due to high nitrogen and phosphorus concentrations in runoff. While original ecological ditches and wetlands have demonstrated effectiveness in nutrient load removal, the overall impact of an ecological ditch-wetland system (EDWS) on agricultural nutrient removal has received limited attention. This study conducted a field experiment to investigate the physicochemical conditions and nutrient removal efficiency of an EDWS for purifying nutrient discharge from rice-crayfish paddy fields. Variations in water temperature (WT), dissolved oxygen (DO), pH, and total suspended solids (TSS) within the EDWS were assessed. Nutrient concentrations-including total nitrogen (TN), ammonium nitrogen (NH4-N), nitrate nitrogen (NO3-N), total phosphorus (TP), and soluble reactive phosphorus (SRP)-were monitored from the tillering to the ripening stage of the rice growth cycle. The evaluation of nutrient removal efficiencies in the EDWS revealed that ecological ditches exhibited higher removal efficiencies compared to wetlands. The average total removal efficiencies for TN, NH4-N, NO3-N, TP, and SRP were 37.50 %, 39.38 %, 38.62 %, 37.94 %, and 39.51 %, respectively, with peak removal efficiencies observed at specific growth stages of the rice crop. Furthermore, the study explored the influence of hydraulic retention time on nutrient removal efficiency in the EDWS, indicating higher nutrient discharge removal efficiencies under low water discharge rates. Linear regression analysis identified water discharge, influent nutrient loads, and TSS as significant factors affecting nutrient removal efficiency in the EDWS. This study provides valuable insights into the effectiveness of EDWS in purifying nutrient discharge from rice-crayfish paddy fields, highlighting their potential as sustainable solutions for nutrient management in agricultural landscapes.

Are pools created when restoring extracted peatlands biogeochemically similar to natural peatland pools?

In the last 25 years, several degraded peatlands in eastern Canada have been restored toward their natural structure. Pools are common in natural peatlands and are important habitats for unique flora and fauna. Because of their ecological value, pools have been created in some restored peatland sites. Nevertheless, the biogeochemistry of created pools in a restoration context has seldom been studied. The objective of our study is to characterize the biogeochemistry of created pools from restored peatlands and compare them with natural pools along a chronosequence since their creation. We measured different biogeochemical variables (pH, concentrations of nitrogen (N), phosphorus (P), dissolved organic carbon (DOC), dissolved organic matter (DOM), base cations-calcium (Ca), sodium (Na), magnesium (Mg), and potassium (K)-and dissolved gases-methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O)-) in 61 pools distributed over seven peatlands in eastern Canada. The sites represent a range of conditions, from natural to restored peatlands with pools ranging from 3 to 22 years old. Created and natural pools had distinctive biogeochemistry, with created pools being generally less acidic (pH >5) and 2.5 times more concentrated in nutrients (N and P) than in natural pools. DOC, N, P, dissolved gases, and base cations concentrations were lower in natural pools than in created pools, and varied between created sites. The oldest created pools (age >17 years) tend to approach the biogeochemical characteristics of natural pools, indicating that created pools may, over time, provide habitats with similar conditions to natural pools. A return of created pools to a natural pool-like biogeochemistry could thus inform on the success of peatland restoration.

Effects of river infrastructure, dredged material placement, and altered hydrogeomorphic processes: The stress ecology of floodplain wetlands and associated fish communities.

Recognition of the habitat values of coastal and floodplain wetlands has inspired research and engineering to restore biological functions after widespread species declines. However, the restoration and management of tidal river floodplains requires a more complete understanding of anthropogenic stressors on hydrogeomorphology and ecological processes. River floodplains near the ocean are affected by localized diking and dredging as well as basin-wide stressors such as dams. We evaluated the effects of stressors versus spatial position, both longitudinal and lateral to the mainstem, using physical and biological response variables in river floodplain wetlands. We categorized historical and modern stressors on the hydrogeomorphic regime of the lower Columbia River and estuary, northeast Pacific coast, including basin-scale management and local impacts. Using this categorization, we analyzed 44 attributes using field-collected data from 50 floodplain wetlands. Attributes represent channels, floods, plant communities, and fish communities. Here we show that plant and fish communities are stratified by position along the estuarine-riverine gradient, in contrast to physical habitat characteristics, which are stratified by stressors on hydrogeomorphic regimes and in some cases the lateral distance from the mainstem river on tributaries. Spatial position relative to water-level dynamics and salinity more strongly affect the biota than does stressor history. Stressor effects were greatest on the geomorphology observed in formerly diked, now reconnected wetlands and in wetlands with a history of dredged material placement; historically diked sites had anomalously deep channels with larger cross-sectional areas while sites with dredged material had shallow channels and lower levels of organic carbon in sediment. In wetlands subject only to landscape-scale stressors such as flow alterations by dams, organic carbon levels were higher. These findings provide natural resource managers with opportunities to enhance similarity to natural conditions and better understand future wetland evolution from different baselines of stressor history and river position.

Meta-analysis: Global patterns and drivers of denitrification, anammox and DNRA rates in wetland and marine ecosystems.

Nitrogen cycling is one of the most important biogeochemical processes on Earth, and denitrification, anammox and DNRA processes are important nitrogen cycling processes in estuarine ecosystems. However, due to the large input of anthropogenic nitrogen sources, a large number of environmental problems have now occurred in the estuary. But the global patterns and controlling factors of denitrification, anammox and DNRA rates in wetland marine ecosystems are not yet known. We reached our conclusions through a global synthesis of 546 observation sites from 78 peer-reviewed papers: The three rates were generally higher in areas near wetlands than in coastal areas. The rate of denitrification was highest in the subtropical region the seasonal variability was not significant; and TOC was the main factor controlling denitrification. The rate of anammox was significantly higher in the subtropical region than in the tropical and boreal zones, and the seasonal variability was significant; and at the same time, TN was the main driver of the anammox rate of the wetland ocean. DNRA rates were significantly higher in the tropics than in the subtropics and temperate zones; and the main driver of DNRA rates was temperature. Nitrogen cycle functional genes also had an indirect effect on their rates. With NH4 + -N significantly affecting nirK abundance and TN significantly affecting the gene abundance of nirS; TOC and TN had a greater effect on hzo abundance, which indirectly affected anammox rates; for DNRA, C/N significantly affects the gene abundance of nrfA, which indirectly affects the DNRA rate. Therefore, the findings of this study indicate that physicochemical indicators about N and climatic characteristics have a profound effect on the nitrogen cycling process, which provides a good feedback for studying the role of denitrification and provides a positive impact on global climate and environmental governance.

Land use dynamics and ecosystem service valuation in the Sanmenxia Reservoir wetland of the Yellow River.

The Sanmenxia Reservoir wetland (SRW) serves as a critical ecological buffer in the middle reaches of the Yellow River. Ongoing population growth and changes in land use have placed significant pressure on the wetland's ecosystems. However, existing research has yet to establish a spatiotemporal analysis method to assess the impact of land use change on the ecosystem service value (ESV). This gap hinders the precise regulation and sustainable development of land resources. To gain a comprehensive understanding of the land use dynamics and ecological functions of the SRW, this study introduced a refined ESV evaluation method. This method revised the equivalent factors from spatial, temporal, and hydrological perspectives, with an emphasis on the impact of sediment discharge. Furthermore, the Patch-level Land Use Simulation (PLUS) model was employed to project the land use structure in 2030, and the corresponding ESV was analyzed. The study revealed the following: (1) Cropland constituted the primary land type in the SRW. Over the last two decades, the build-up area exhibited the most significant single land use dynamics, with the transformation of bare land to cropland spanning the widest range and largest area. (2) From 2000 to 2020, the ESV increased by 0.64 billion CNY, with the water body contributing almost all the increase. (3) The projected ESV for 2030 is 2.94 billion CNY, indicating an increase in ecological functions in the near future. Policy makers should recognizethe impact of land use change on ESV and implement measures to rebalance land use structure. While ensuring the preservation of cropland and the protection of lives and property, it is advisable to consider expanding the water body area to facilitate comprehensive sustainable development within SRW.

Synergetic effect of pyrrhotite and zero-valent iron on Hg(â ¡) removal in constructed wetland: Mechanisms of electron transfer and microbial reaction.

Effective removal of mercury (Hg) from wastewater is significant due to its high toxicity, especially methylmercury (MeHg). Reducing of Hg(II) to Hg(0) in constructed wetlands (CWs) using iron-based materials is an effective strategy for preventing the formation of MeHg. However, the surface passivation of zero-valent iron (ZVI) limits its application. Herein, synergetic ZVI and pyrrhotite were utilized to enhance Hg removal in CWs. Results indicated that the removal of total Hg, dissolved Hg, and particulate Hg in CWs with ZVI and pyrrhotite were improved by 21.68 ± 0.76 %, 13.02 ± 0.88 %, and 22.27 ± 0.76 % compared to that with single ZVI or pyrrhotite. Pyrrhotite increased the surface corrosion of ZVI, thereby facilitating the process of iron reduction. The redox of iron promoted the generation of EPS, which could provide electrons for Hg(II) reduction. The sulfur also participates in electron transfer by driving the methylation of Hg and provides sulfides to form FeS-Hg complexes and HgS precipitation. The abundance of key enzymes that involved in iron reduction and Hg transformation was enhanced with the addition of ZVI and pyrrhotite. The synergetic of pyrrhotite and ZVI enhances the removal of Hg in CW, offering a promising technology for high-efficiency treatment of Hg.

Identifying toxic elements in water, sediments, and roots of mangrove forest (Avicennia marina) in Chabahar Bay, Sea of Oman.

Mangroves play a crucial role in filtering pollutants from water and sediments. However, excessive accumulation of potentially toxic elements (PTEs) has harmful effects on marine organisms. This article investigates the concentration and distribution of PTEs in water, sediment, and the roots of endangered mangrove species in Chabahar Bay, a subtropical coastal wetland. The relationship between PTE absorption and accumulation rates with flow rate, mangrove extent, and sedimentation was also explored. Water, sediments, and aerial roots samples were taken at four stations along the wetland from upstream fresh water toward outfall. According to the results, Cd had more distribution in sediment and water samples and plants did not play as adsorbent in the study area. The lowest and highest PTEs concentrations were detected in water and sediment media, respectively. The average concentrations of PTEs in the sediments in the Chabahar Bay were Fe > Cr > Zn > Ni > Cu > Pb > Co > As > Cd while in aerial roots of the mangroves were Fe > Zn > Ni > Cr > Cu > Co > As > Pb > Cd. Except Zn, As, and Cd, there was a good correlation between increasing PTEs content in the sediments with decreasing flow velocity and increasing vegetation density along stations 3 to 4. In addition, the amount of PTEs uptake by the mangroves was less than that of global wetlands. The results also demonstrated a greater uptake in aerial roots in saline water for Cr, Ni and Co. Since the absorption rate of PTEs by the aerial roots of pneumatophores is slower than that in sediments, elevated concentrations of PTEs in the sediment can disrupt the entire ecosystem, leading to a potential decline in biodiversity. These toxins can enter the food chain, affecting not only organisms directly interacting with the sediment but also higher trophic levels, such as fish and birds.

Hydrogeochemical dynamics under saltwater-freshwater mixing in a mangrove wetland over tidal cycles.

Seawater and groundwater interactions shape the hydrogeochemical profile of mangrove aquifers, revealing how biogeochemical processes adapt to saline-freshwater mixing via the fluctuating patterns of key hydrochemical indicators and primary biogenic elements. This study, utilizing a multi-level monitoring profile spanning the entire submerged aquifer within a mangrove wetland, analyzed the spatiotemporal dynamics of DO, ORP, pH, alkalinity and biogenic elements (C, N, S). The results revealed that among the basic hydrochemical parameters, total alkalinity showed the most stable spatiotemporal distribution and was positively correlated with salinity. pH demonstrated a significant negative correlation with salinity, whereas the correlations of ORP and DO with salinity were not substantial. The discharge of terrestrial freshwater into the mangrove wetland is marked by hydrogeochemical reactions favoring the input of Mg2+ and DIC, with potential iron mineral precipitation within the aquifer. Spatial distribution of biogenic elements in the groundwater showed no apparent pattern across sampling periods. DOC concentrations ranged from 0.3 to 1.3 mmol/L. Three components of dissolved organic matter were identified using three-dimensional fluorescence spectroscopy, with high molecular weight components (C1 + C2) accounting for an average of 47 to 73 %. Both elevated DOC concentrations and high molecular weight component ratios were primarily found in shallow layers of dense mangrove areas, decreasing with depth. Concentrations of ammonia, nitrite, and nitrate varied dynamically, reflecting active biochemical processes in the shallow to mid-layers of the aquifer. Furthermore, sulfate and sulfide concentrations, ranging from 0 to 26 mmol/L and 0.4 to 576.8 µmol/L, respectively, underscore the interplay of biogeochemical reactions, especially sulfate reduction. These findings highlight valuable insights into the complex biogeochemical processes within mangrove aquifers and provide theoretical guidance for protecting the ecological health of mangrove wetlands.

Enhanced remediation of real agricultural runoff in surface-flow constructed wetlands by coupling composite substrate-packed bio-balls, submerged plants and functional bacteria: Performance and mechanisms.

Import of agricultural runoff containing nutrients considerably contributes to eutrophication of receiving water bodies. Surface-flow constructed wetlands (SFCWs) are commonly applied for agricultural runoff purification, but the performance is usually unsatisfactory. In this study, suspended bio-balls filled with zeolite and iron-carbon (Fe-C) composite substrates, submerged macrophyte (Ceratophyllum demersum) and functional denitrifying bacteria were collectively added into SFCW microcosms to enhance the remediation efficiency for real agricultural runoff with high nutrient concentrations and low content of bioavailable organic matter. The bio-ball added SFCWs achieved notably higher pollutant removal efficiencies (21.1%, 80.2% and 47.5% for chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP), respectively) than the control (COD: 6.9%, TN: 64.4%, TP: 27.9%), because of the versatile functions of filling materials for pollutant removal. C. demersum plantation (COD: 44.2%, TN: 82.8% and TP: 53.7%) and functional bacteria inoculation (COD: 51.8%, TN: 85.8% and TP: 55.1%) further enhanced the efficiency of the SFCWs for agricultural runoff remediation. Bio-ball addition and C. demersum plantation significantly increased the humification degree and reduced the molecular weight of dissolved organic matter (DOM) in the agricultural runoff. Moreover, the two intensification measures also notably reduced organic and nitrogen contents in the wetland sediment. Remarkable distinction in bacterial community distribution patterns was observed in the SFCW sediment and filling substrates in bio-balls. Keystone genera including Clostridium_sensu_stricto_1 and Bacillus in the zeolite, Sphingomonas and Exiguobacterium in the Fe-C substrates and Sediminibacterium in the sediment might be critical for agricultural runoff remediation in the SFCW microcosms. The study highlights a high potential of the intensified SFCWs by these coupling measures for agricultural runoff remediation.