Estuarine Wetlands Research Articles

Salinity stress and atmospheric dryness co-limit evapotranspiration in a subtropical monsoonal estuarine mangrove wetland

Salinity stress and atmospheric dryness co-limit evapotranspiration in a subtropical monsoonal estuarine mangrove wetland

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

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

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.

Soil carbon pools and microbial network stability depletion associated with wetland conversion into aquaculture ponds in Southeast China

Wetlands, which are ecosystems with the highest soil surface carbon density, have been severely degraded and replaced by artificial reclamation for fish and shrimp ponds in recent years. This transformation is causing intricate shifts in soil carbon pools and microbial stability. In this study, we examined natural wetlands and reclaimed aquaculture ponds in Southeast China to analyze the structure and network stability of soil microbial communities following the reclamation of estuarine wetlands and to elucidate the microbial-mediated mechanisms for regulating soil organic carbon (SOC). The aquaculture ponds presented significantly less average SOC content than the natural wetlands (p < 0.05). ACE, Chao1, and Shannon's indices of bacteria and fungi were decreased in aquaculture ponds. Less numbers of nodes and edge links in the co-occurrence network of soil fungi and bacteria in aquaculture ponds. This suggests reduced correlation and stability within the microbial network of aquaculture ponds. Decomposers in soil fungi (e.g. Dung Saprotroph) reduced. Reduced proportions of key phyla Ascomycota, Basidiomycota and Rozellomycota in the soil fungal network. Reduced proportions of key phyla Proteobacteria, Chloroflexi and Desulfobacterota in the soil bacterial network. In conclusion, our results suggest that converting wetland paddocks to intensive aquaculture ponds results in carbon pool loss and reduces soil microbial network stability. The results highlight the importance of protecting or moderately restoring mangrove wetlands along the coast of southeastern China. It is also predicted that such measures may enhance the storage capacity of soil carbon pools and improve the stability of carbon sequestration by soil microorganisms, thus offering a potential solution for mitigating global climate change.

Fate of soil organic carbon in estuarine mangroves: Evidences from stable isotopes and lignin biomarkers

Coastal wetlands are increasingly recognized for their role in climate change mitigation, particularly through the sequestration of soil organic carbon (SOC). Despite widespread acknowledgement of their importance, the variation in organic carbon (OC) sources among different estuarine mangrove wetlands, and how these sources interact with environmental factors, is not fully elucidated. This research focuses on the role of estuarine mangrove wetlands in climate change mitigation through SOC sequestration. It explores the distribution, sources, and decomposition of SOC in a wetland with four mangrove communities along a tidal gradient. These include a tidal flat, a Sonneratia apetala forest, a mixed S. apetala and Kandelia obovata forest, and a K. obovata forest. The study employs biogenic element analysis (C, N, lignin phenols) and natural stable carbon isotope ratios (δ13C and δ15N) to assess SOC. Key findings show a decrease in SOC and total nitrogen (TN) from the upstream K. obovata forest to the downstream tidal flat. A stable isotope mixing model reveals a diminishing mangrove-derived OC contribution in topsoil (0–40 cm), estimated at 62 % in the K. obovata forest, 45 % in the central region, and 24 % in tidal flats. Soil profiles suggest microbial decomposition as the main isotope fractionation mechanism, with lignin analysis indicating woody angiosperms as the primary OC source. These findings enhance understanding of OC origins and decomposition in coastal wetlands and inform “blue carbon” management, highlighting the terrestrial-estuary continuum's significance.

Flooding promotes the coalescence of microbial community in estuarine habitats

Microbial community coalescence describes the mixing of microbial communities and their integration with the surrounding environment, which is common in natural ecosystems and has potential impacts on ecological processes. However, few studies have focused on microbial community coalescence between different habitats in estuarine regions. In this study, we comprehensively investigated the environmental characteristics and bacterial community changes of different habitats (water body (Water), subtidal sediments (SS) and intertidal salt marsh sediments (SM)) in Luanhe estuary during flood and normal flow periods. The results showed that flood event significantly reduced the salinity of the estuarine habitats, changed the nutrient structure and intensified the eutrophication of estuarine water. By calculating the proportion of overlapping groups and applying the ‘FEAST’ algorithm, we revealed that flood event facilitated the migration of bacterial communities along alternative pathways across habitats, markedly enhanced the cross-habitat mobility of bacterial communities, which underscores the pivotal role of flood event in driving bacterial community coalescence. Flood-induced community coalescence not only increased the α-diversity of bacterial communities within habitats, but also increased the proportion of overlapped species between habitats, ultimately leading to homogenization between habitats. Canonical correlation analysis combined co-occurrence network analysis revealed that flood event attenuated the role of environmental filtration in microbial assembly, while increased the impact of dispersal processes and intensified interspecific competition among microorganisms, led to the change of keystone species and reduced the complexity and stability of bacterial communities. In conclusion, this study demonstrates the complex effects of flood events on estuarine microbial communities from the perspective of multi-habitat interactions in the estuary, and emphasizes the key role of river hydrodynamic conditions in facilitating the coalescence of estuarine microbial communities. We look forward to further attention and research on estuarine microbial coalescence, which will provide new insights into assessing the stability and resilience of estuarine ecosystems under flood challenges and the sustainable management of estuarine wetlands.

Living estuarine shorelines as nature-based green engineering for coastal stabilization: A scientometric analysis

Natural estuarine wetland shorelines play a crucial role in coastal stabilization and preserving ecological security patterns. The effectiveness of estuarine shoreline engineering in reducing coastal erosion and maintaining the stability of ecosystem structures and functions is tightly linked to their types and structures. Although the living estuarine shorelines have received increasing attention, there have been few systematic literature reviews on the development process, research hotspots and future trends in this field. Here we summarized the literatures, and analyzed them in terms of annual publications, subject categories, co-cited journals, countries, institutions, authors, references, and keywords based on OriginPro, VOSviewer, and CiteSpace softwares. Results showed that the studies on living estuarine shorelines have experienced a rapid development phase since 2004, which is mainly categorized into Environmental Sciences and Oceanography, and the research institutions and scholars are mainly from the USA and China. The effects of human activities and climate change on the structures and functions of estuarine ecosystems are the dominant topics. Furthermore, the nature-based management solutions have been proposed to improve the functions and services of estuarine ecosystems. Currently, the habitats of estuarine wetlands worldwide have undergone varying degrees of degradation, therefore, the ecological conservation and restoration of estuarine shorelines urgently require the active participation of the public. It is highly important to integrate multi-disciplinary and multi-technology approaches to construct nature-based, more resilient, multi-service synergistic, and composite living shorelines in coastal zones. The findings of this research can provide scientific guidelines for the adaptive management and conservation of estuarine wetlands.

Aboveground Carbon Stocks across a Hydrological Gradient: Ghost Forests to Non-Tidal Freshwater Forested Wetlands

Upper estuarine forested wetlands (UEFWs) play an important role in the sequestration of atmospheric carbon (C), which is facilitated by their position at the boundary of terrestrial and maritime environments but threatened by sea level rise. This study assessed the change in aboveground C stocks along the estuarine–riverine hydrogeomorphic gradient spanning salt-impacted freshwater tidal forested wetlands to freshwater forested wetlands in seasonally tidal and nontidal landscape positions. Standing stocks of C in forested wetlands were measured along two major coastal river systems, the Winyah Bay in South Carolina and the Savannah River in Georgia (USA), replicating and expanding a previous study to allow the assessment of change over time. Aboveground C stocks on these systems averaged 172.9 Mg C ha−1, comparable to those found in UEFWs across the globe and distinct from the terrestrial forested ecosystems they are often considered to be a part of during large-scale C inventory efforts. Groundwater salinity conditions as low as 1.3 ppt were observed in conjunction with losses of aboveground C. When viewed in context alongside expected sea level rise and corresponding saltwater intrusion estimates, these data suggest a marked decrease in aboveground C stocks in forested wetlands situated in and around tidal estuaries.

Pyrene biodegradation by bacterial consortia enriched from coastal and marine sediments: Insights into bacterial community structures and functions

As a representative polycyclic aromatic hydrocarbon (PAH), pyrene poses a significant threat to the environment and public health due to its persistence and potential toxicity. Extensive research has been conducted on biodegradation of pyrene, highlighting the crucial need to unravel its degradation mechanisms. Coastal and marine sediments are promising sources for discovering microbial candidates capable of degrading pyrene. In this study, three bacterial consortia, designated as BS, YS, and SS, were enriched from sediments collected from the Bohai Sea, Yellow Sea, and Liao River estuarine wetland, respectively. The bacterial consortia BS, YS, and SS demonstrated high pyrene degradation efficiencies, achieving 86.61 %, 80.39 %, and 75.70 % degradation at the concentration of 50 mg/L within 8 days, respectively. High-throughput sequencing of 16S rRNA gene amplicons revealed Pandoraea, Delftia, and Pseudomonas as the dominant populations in bacterial consortia BS, YS, and SS, respectively, with some species potentially being novel pyrene degraders. Further analysis included identifying pyrene degradation metabolites by LC-Q-TOF-MS (high-performance liquid chromatography tandem quadrupole time-of-flight mass spectrometry) and predicting functional genes through PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved Stats). Based on these results, the metabolic pathways for pyrene degradation by the bacterial consortia were proposed, which predominantly involved the dioxygenation pathway. Overall, these findings should offer valuable bacterial resources for facilitating the bioremediation of PAH-contaminated environments.

Effects of salinity on nitrogen reduction pathways in estuarine wetland sediments

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 (NO3−) were profoundly decreased with increasing salinity, while sediment ammonium (NH4+) 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.

Distribution, sources, impact factors and ecological risks of sediment heavy metals from typical estuarine wetlands in tropical islands

Heavy metal contamination in the estuarine wetlands of tropical islands is becoming increasingly severe. This study focused on four typical estuarine wetlands of Hainan Island, including the mangrove and seagrass areas in Lingshui County, the mangrove and seagrass areas in Xinying Port, the mangrove area in Sibi Wan, and the seagrass area in Huachang Wan. By analyzing the heavy metal content in the surface sediments of these wetlands, we investigated the distribution characteristics and levels, explored their influencing factors, and assessed ecological risk of heavy metals in these areas. It was found the accumulation of heavy metals was high from obvious sampling sites of human activities, the type of sediment could affect the adsorption of heavy metals, with silty mudflats accumulating more. TOC/TN indicated that the organic sources of mangroves were diverse, included environmental impacts and human interference. According to the soil accumulation index and potential ecological risk index in these areas, almost all heavy metals were unpolluted except for As, which showed moderate pollution levels. The overall ecological risk in these areas was relatively low. The results of principal component analysis and correlation analysis indicated that Pb, Cu, and As were primarily sourced from human activities, while Cr was mainly of natural origin. Moreover, the distribution of heavy metals in the study areas was principally affected by TOC and salinity.

Decadal Changes (1980–2021) of Shoreline and Mangrove Cover in Sundarban Delta, India, Using Remote Sensing and GIS

Abstract Being situated in the estuary of the flood-dominated Hooghly River system, the macrotidal Indian Sundarban Delta (ISD) has become one of the most complex, dynamic, and rapidly changing landforms on Earth’s surface. To study the horizontal areal shifting of shoreline and its impact on mangrove cover in the region, the U.S. Geological Survey (USGS) satellite data of 1980, 1990, 2000, 2010, and 2021 were used. Remote sensing and geographic information system (GIS) techniques were employed in the investigation. Simultaneous prograding and retrograding shoreline shifting was distinguished almost in all the parts, although sediment-starved eastern and macrotidally more active southern lobes experienced dominantly retreating shift, and the sediment-engorged western lobe was demonstrated to be more dynamic. Net areal change over north–south tracks followed the trend of decreasing accretion to increasing erosion while going from west to east, whereas that over west–east tracks followed the trend of exponentially increasing erosion while going from north to south. Overall accretion of ∼91 km2 in the ISD accounted for the augmentation of sparse vegetation of ∼13 km2, whereas ∼243 km2 erosion called for the depletion of sparse and moderate vegetation of ∼18 and ∼174 km2, respectively, over the 41-yr period. Various oceanographic and riparian forces and actions, episodic natural events, etc., vis-a-vis several anthropogenic interventions—all together contributed to such changes. The findings may help the coastal environmentalists, professionals, planners, decision-makers, and implementers in formulating and taking up of suitable strategic measures for integrated and effective coastal zone management in this estuarine wetland forest.

Co-pollution risk of petroleum hydrocarbons and heavy metals in typically polluted estuarine wetlands: Insights from the Xiaoqing River

Excessive accumulation of total petroleum hydrocarbons (TPH) and heavy metals (HMs) in sediments poses a significant threat to the estuarine ecosystem. In this study, the spatial and temporal distribution, ecological risks, sources, and their impacts on the microbial communities of TPH and nine HMs in the estuarine sediments of the Xiaoqing River were determined. Results showed that the spatial distribution of TPH and HMs were similar but opposite in temporal. Ni, Cr, Pb, and Co concentrations were similar to the reference values (RVs). However, the other five HMs (Cu, Zn, Cd, As, and Hg) and TPH concentrations were 2.00–763.44 times higher than RVs; hence, this deserves attention, particularly for Hg. Owing to the water content of the sediments, Hg was mainly concentrated on the surface during the wet season and on the bottom during the dry season. Moreover, because of weak hydrodynamics and upstream pollutant sinks, TPH–HMs in the river were higher than those in the estuary. TPH and HM concentrations were negatively correlated with microbial diversity. Structural equation modeling showed that HMs (path coefficient = −0.50, p < 0.001) had a negative direct effect on microbial community structure and a positive indirect effect on TPH. The microbial community (path coefficient = 0.31, 0.01 < p < 0.05) was significantly correlated with TPH. In summary, this study explores both the chemical analysis of pollutants and their interaction with microbial communities, providing a better understanding of the co-pollution of TPH and HMs in estuarine sediments.

Distribution Status of Invasive Alien Species in the Estuarine Wetlands in East and South Coast, Korea

Based on the results of survey on estuarine ecosystem conducted from 2021 to 2023, this study analyzed the distribution pattern of invasive alien species. A total of six invasive alien species (&lt;i&gt;Micropterus salmoides&lt;/i&gt; [&lt;i&gt;M. salmoides&lt;/i&gt;], &lt;i&gt;Lepomis macrochirus&lt;/i&gt; [&lt;i&gt;L. macrochirus&lt;/i&gt;], &lt;i&gt;Lithobates catesbeianus&lt;/i&gt; [&lt;i&gt;L. catesbeianus&lt;/i&gt;], &lt;i&gt;Trachemys scripta&lt;/i&gt; [&lt;i&gt;T. scripta&lt;/i&gt;], &lt;i&gt;Pseudemys concinna&lt;/i&gt; [&lt;i&gt;P. concinna&lt;/i&gt;], and &lt;i&gt;Pseudemys nelsoni&lt;/i&gt; [&lt;i&gt;P. nelsoni&lt;/i&gt;]) were identified across 118 estuarine wetlands. The survey revealed 960 individuals of &lt;i&gt;M. salmoides&lt;/i&gt;, 2,596 individuals of &lt;i&gt;L. macrochirus&lt;/i&gt;, 1,088 individuals of &lt;i&gt;L. catesbeianus&lt;/i&gt;, and 44 individuals of &lt;i&gt;T. scripta&lt;/i&gt;, while 1 individual of &lt;i&gt;P. concinna&lt;/i&gt; and &lt;i&gt;P. nelsoni&lt;/i&gt; were found. These invasive species were found to be densely distributed in estuarine wetlands in the Haenam and Goheung regions of the southern coast. Furthermore, the distribution density varied depending on the characteristics and locations of the estuarine wetlands. It was observed that the distribution density was higher in closed type than in open type, in riverine than in lacustrine, and in the south coast than in the east coast. Once the basic survey of estuarine wetlands located on the west coast is completed, a clearer understanding of the nationwide distribution characteristics of invasive alien species in estuarine wetlands can be achieved. This information will be crucial for formulating appropriate management strategies tailored to the characteristics of wetlands or coastal areas in the future.

Organic matter composition and stability in estuarine wetlands depending on soil salinity

Coastal wetlands are key players in mitigating global climate change by sequestering soil organic matter. Soil organic matter consists of less stable particulate organic matter (POM) and more stable mineral-associated organic matter (MAOM). The distribution and drivers of MAOM and POM in coastal wetlands have received little attention, despite the processes and mechanisms differ from that in the upland soils. We explored the distribution of POM and MAOM, their contributions to SOM, and the controlling factors along a salinity gradient in an estuarine wetland. In the estuarine wetland, POM C and N were influenced by soil depth and vegetation type, whereas MAOM C and N were influenced only by vegetation type. In the estuarine wetland, SOM was predominantly in the form of MAOM (> 70 %) and increased with salinity (70 %–76 %), leading to long-term C sequestration. Both POM and MAOM increased with SOM, and the increase rate of POM was higher than that of MAOM. Aboveground plant biomass decreased with increasing salinity, resulted in a decrease in POM C (46 %–81 %) and N (52 %–82 %) pools. As the mineral amount and activity, and microbial biomass decreased, the MAOM C (2.5 %–64 %) and N pool (8.6 %–59 %) decreased with salinity. When evaluating POM, the most influential factors were microbial biomass carbon (MBC) and dissolved organic carbon (DOC). Key parameters, including MBC, DOC, soil salinity, soil water content, aboveground plant biomass, mineral content and activity, and bulk density, were identified as influencing factors for both MAOM abundance. Soil water content not only directly controlled MAOM, but together with salinity also indirectly regulated POM and MAOM by controlling microbial biomass and aboveground plant biomass. Our findings have important implications for improving the accumulation and increased stability of soil organic matter in coastal wetlands, considering the global sea level rise and increased frequency of inundation.

Effects of sulfamethazine on microbially-mediated denitrifying anaerobic methane oxidation in estuarine wetlands

Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) is an important methane (CH4) consumption and nitrogen (N) removal pathway in estuarine and coastal wetlands. Antibiotic contamination is known to affect microbially mediated processes; however, its influences on n-DAMO and the underlying molecular mechanisms remain poorly understood. In the present study, using 13CH4 tracer method combined with molecular techniques, we investigated the responses of n-DAMO microbial abundance, activity, and the associated microbial community composition to sulfamethazine (SMT, a sulfonamide antibiotic, with exposure concentrations of 0.05, 0.5, 5, 20, 50, and 100 µg L−1). Results showed that the effect of SMT exposure on n-DAMO activity was dose-dependent. Exposure to SMT at concentrations of up to 5 µg L−1 inhibited the potential n-DAMO rates (the average rates of nitrite- and nitrate-DAMO decreased by 92.9 % and 79.2 % relative to the control, respectively). In contrast, n-DAMO rates tended to be promoted by SMT when its concentration increased to 20–100 µg L−1 (the average rates of nitrite- and nitrate-DAMO increased by 724.1 % and 630.1 % relative to the low-doses, respectively). Notably, low-doses of SMT suppressed nitrite-DAMO to a greater extent than nitrate-DAMO, indicating that nitrite-DAMO was more sensitive to SMT than nitrate-DAMO. Molecular analyses suggest that the increased n-DAMO activity under high-doses SMT exposure may be driven by changes in microbial communities, especially because of the promotion of methanogens that provide more CH4 to n-DAMO microbes. Moreover, the abundances of n-DAMO microbes at high SMT exposure (20 and 50 µg L−1) were significantly higher than that at low SMT exposure (0.05–5 µg L−1). These results advance our understanding of the ecological effects of SMT on carbon (C) and N interactions in estuarine and coastal wetlands.

Risk Assessment and Sources Apportionment of Toxic Metals in Two Commonly Consumed Fishes from a Subtropical Estuarine Wetland System.

The widespread occurrence of heavy metals in aquatic environments, resulting in their bioaccumulation within aquatic organisms like fish, presents potential hazards to human health. This study investigates the concentrations of five toxic heavy metals (Pb, Hg, Zn, Cu, and Cr) and their potential health implications in two economically important fish species (Otolithoides pama and Labeo bata) from a subtropical estuarine wetland system (Feni estuary, Bangladesh). Muscle and gill samples from 36 individual fish were analyzed using energy dispersive X-ray fluorescence (EDXRF). The results revealed that the average quantities of heavy metals in both fishes' muscle followed the declining order of Zn (109.41-119.93 mg/kg) > Cu (45.52-65.43 mg/kg) > Hg (1.25-1.39 mg/kg) > Pb (0.68-1.12 mg/kg) > Cr (0.31-5.82 mg/kg). Furthermore, Zn was found to be present in the highest concentration within the gills of both species. While the levels of Cu, Zn, and Cr in the fish muscle were deemed acceptable for human consumption, the concentrations of Pb and Hg exceeded the permissible limits (>0.5 mg/kg) for human consumption. Different risk indices, including estimated daily intake (EDI), target hazard quotient (THQ), hazard index (HI), and carcinogenic or target risk (TR), revealed mixed and varying degrees of potential threat to human health. According to the EDI values, individuals consuming these fish may face health risks as the levels of Zn, Cu, and Cr in the muscle are either very close to or exceed the maximum tolerable daily intake (MTDI) threshold. Nevertheless, the THQ and HI values suggested that both species remained suitable for human consumption, as indicated by THQ (<1) and HI (<1) values. Carcinogenic risk values for Pb, Cr, and Zn all remained within permissible limits, with TR values falling below the range of (10-6 to 10-4), except for Zn, which exceeded it (>10-4). The correlation matrix and multivariate principal component analysis (PCA) findings revealed that Pb and Cr primarily stemmed from natural geological backgrounds, whereas Zn, Cu, and Hg were attributed to human-induced sources such as agricultural chemicals, silver nanoparticles, antimicrobial substances, and metallic plating. Given the significance of fish as a crucial and nutritious element of a balanced diet, it is essential to maintain consistent monitoring and regulation of the levels and origins of heavy metals found within it.

Management implications of habitat selection by whooping cranes (Grus americana) on the Texas coast

AbstractEffective habitat management for rare and endangered species requires a thorough understanding of their specific habitat requirements. Although machine learning models have been increasingly used in the analyses of habitat use by wildlife, the primary focus of these models has been on generating spatial predictions. In this study, we used machine learning models in combination with simulated management actions to guide planning and inform managers. We used data from 61 whooping cranes (Grus americana) tagged with GPS telemetry collars between 2009 and 2018 near Aransas National Wildlife Refuge in coastal Texas. We included variables based on topography, land use classification, vegetation height, plant phenology, drought, storm surge events, and both wild and prescribed fires. We then built models at multiple scales: population level, home range level, and roosting and daytime within home range level. We simulated responses to the two primary management actions used to enhance whooping crane habitat on Aransas National Wildlife Refuge: prescribed fire and removal of woody vegetation. At the population and home range scales, land use classification variables had the highest importance values, whereas the combined elevation and bathymetry layer was the most important predictor at both roosting and daytime within home range scales. Our findings revealed that the effects of fire, although generally modest, varied spatially. Areas dominated by estuarine wetlands exhibited higher predicted use within the first months after a fire, whereas those dominated by palustrine wetlands were more likely to be avoided in the immediate postfire years. Our simulation of vegetation removal identified the areas on Aransas National Wildlife Refuge where whooping cranes were predicted to benefit the most if vegetation were removed. These techniques can be used by other researchers wanting to examine and predict the effects of potential management actions on target species habitat.

Rapid mangrove expansion triggered by low river discharge episode in Nanliu river estuary, Beibu Gulf of China

Mangrove forest is a critical primary producer, biological habitat, and carbon sink in the subtropical-tropical coast zone, and the natural variation of mangrove coverage deserves study for a better understanding of the dynamics of mangrove coastal evolution. In this study, multispectral Landsat images from 1985 to 2018 are used to reconstruct the change in the coverage of mangrove (dominant species is Aegiceras corniculatum) and salt marsh (dominant species is Cyperus malaccensis) in the Nanliu River estuary. Tidal flat elevation measuring and 210Pb dating is used to study the substrate elevation when mangroves first colonize salt marsh. Historical temperature records, river discharge records, and the time series N/P concentration in sediment are analyzed. It is found that the mangrove forests have expanded rapidly in salt marsh since the mid-1980s. The change in factors such as accommodation space, cold event frequency, and nutrient supply cannot explain the origin of mangrove expansion. A low river discharge episode lasting for 8 years since 1986 is considered to have triggered the mangrove expansion in this area, as previously established salt marsh plants died due to germination restriction caused by high salinity and mangroves colonized the salt marsh habitat during this period. This case proves again that estuarine wetlands are very sensitive to salinity variation.

Effects of fresh-salt water interaction on spatial variations of soil organic carbon in reed wetland of Yellow River Estuary.

Estuarine wetlands exhibit significant interaction between fresh and salt water, with long-term carbon sequestration capability. We set up 60 sampling sites in the reed wetlands of the fresh-salt water interaction zone of the Yellow River Estuary, covering four different zones of the weak-intensity fresh-salt water interaction zone (WIZ), medium-intensity fresh-salt water interaction zone (MIZ), high-intensity interaction fresh-salt water zone (HIZ) and strong-intensity fresh-salt water interaction zone (SIZ). We investigated how fresh-salt water interaction affected the spatial variation of soil organic carbon (SOC) storage. The results showed that the area of reed wetland accounted for 17.8% of the total area of the fresh-salt water interaction zone the Yellow River Estuary, which mainly distributed in the WIZ and MIZ. The SOC content of reed wetland in the fresh-salt water interaction zone ranged from 1.09 to 3.65 g·kg-1, the SOC density was between 1.85-5.84 kg·m-2, and the SOC storage was (17.32±3.64)×104 t. The SOC content and SOC density decreased with increasing fresh-salt water interaction. There were significant differences in surface SOC content between different subzones of the fresh-salt water interaction zone. The surface SOC content decreased significantly with the increases of fresh-salt water interaction intensity. SOC density was positively correlated with SOC, TN, NH4+-N, and biomass, but negatively correlated with salt ions, soil bulk density, pH, and EC. SOC storage in the 0-30 cm soil layer accounted for 50.9%-64.2% of that in the 0-60 cm soil layer, while SOC storage in the 0-60 cm soil layer occupied 19.1%-37.7% of that in the 0-400 cm soil layer. The results could provide a scientific basis for accurately evaluating SOC storage of estuarine wetlands, improving carbon sink function and wetland management.