Natural Mangrove Research Articles

Copper, zinc, manganese, cadmium and chromium in crabs from the mangrove wetlands in Qi'ao Island, South China: Levels, bioaccumulation and dietary exposure

Abstract Mangrove wetlands are under increasing pollution pressure from human activities due to rapid industrialization and urbanization of coastal regions. Many pollutants such as heavy metals may be accumulated via food chains to hazardous levels which will thus bring potential health issues to humans. In the present study, three species of crabs (Sesarma dehaani, Sesarma plicata, Macrophthalmus japonicus) and associated sediments from three mangrove habitats with different vegetation were collected from the mangrove wetlands in Qi'ao Island, South China to investigate the levels, bioaccumulation and dietary exposure of heavy metals including copper (Cu), zinc (Zn), manganese (Mn), cadmium (Cd) and chromium (Cr). Metal concentrations in sediment samples were 65–91, 212–247, 506–1256, 0.6–1.3, and 8.8–14 mg/kg dry weight for Cu, Zn, Mn, Cd and Cr, respectively. The spatial heterogeneity of these metals in mangrove sediments was observed with a descendant order of metal concentrations as Mn > Zn > Cu > Cr > Cd at each site. Species-specific and tissue-specific accumulation of metals was also found in mangrove crabs, both in the degree of accumulation of particulate metals and the tissues in which they were most abundant. All biota-sediment accumulation factors (BSAF) values >1 for Cd in each crab species suggested that the native mangrove crabs tended to be good tools for the monitoring of Cd pollution in mangrove forests. Results of the estimated daily intake (EDI) and target hazard quotient (THQ) suggested that consumption of the mangrove crabs in Qi'ao Island might subject local residents to potential health risks as far as the metals are concerned.

Soil Organic Fractions in Cultivated and Uncultivated Soils of Costal Area in Bangladesh

Assessment of soil organic matter fractions can be instrumental in understanding the causes of limited nitrogen supply, and thus soil fertility restoration. A study was conducted in cultivated and uncultivated saline soil, in order to assay soil organic carbon (SOC), its particle-size fractions and their influence on cultivation and soil fertility at Sundarbans costal area in Bangladesh. Soil samples were taken from the 0 - 15 and 15 - 30 cm depths from four cultivated fields and from four nearby sites in a native mangrove forest as references. Soil samples were physically fractionated into sand (2000-50 μm), silt (50-2 μm) and clay ( silt > sand. The SOC pool and N in the clay-sized fraction were correlated to soil fertility indicators. More N was stored in the silt + clay size fractions, a generally more stable pool, than in the more labile sand-sized pool. The SOC pool in sand size fractions was far below in cultivated soils than in a reference uncultivated soil. Thus, the sand-sized pool emerged as the most likely cause of limited N supply in cultivated soils.

Study on morphological characters of some mangrove plants in South-eastern Ayeyarwady Delta of Myanmar

A study on the mangrvoe plants in Pyapon Township, Ayeyarwady Region, South-eastern Ayeyarwady Delta (between Lat. 94˚30′ and 95˚45′ North and between Long. 15˚30′ and 16˚25′ East), Myanmar was conducted within the period of March 2016 to February 2017. A total of 18 species of mangroves plants were recorded in the natural mangrove areas. In the present study, the taxonomic descriptions of mangrove plants were presented.

The response of stocks of C, N, and P to plant invasion in the coastal wetlands of China.

The increasing success of invasive plant species in wetland areas can threaten their capacity to store carbon, nitrogen, and phosphorus (C, N, and P). Here, we have investigated the relationships between the different stocks of soil organic carbon (SOC), and total C, N, and P pools in the plant-soil system from eight different wetland areas across the South-East coast of China, where the invasive tallgrass Spartina alterniflora has replaced the native tall grasses Phragmites australis and the mangrove communities, originally dominated by the native species Kandelia obovata and Avicennia marina. The invasive success of Spartina alterniflora replacing Phragmites australis did not greatly influence soil traits, biomass accumulation or plant-soil C and N storing capacity. However, the resulting higher ability to store P in both soil and standing plant biomass (approximately more than 70 and 15kg P by ha, respectively) in the invasive than in the native tall grass communities suggesting the possibility of a decrease in the ecosystem N:P ratio with future consequences to below- and aboveground trophic chains. The results also showed that a future advance in the native mangrove replacement by Spartina alterniflora could constitute a serious environmental problem. This includes enrichment of sand in the soil, with the consequent loss of nutrient retention capacity, as well as a sharp decrease in the stocks of C (2.6 and 2.2 t C ha-1 in soil and stand biomass, respectively), N, and P in the plant-soil system. This should be associated with a worsening of the water quality by aggravating potential eutrophication processes. Moreover, the loss of carbon and nutrient decreases the potential overall fertility of the system, strongly hampering the reestablishment of woody mangrove communities in the future.

Impact of pollution on the feeding, bioturbation and biomass of Uca annulipes in Gazi and Mikindani mangroves, Kenya

Owuor MA, Aloo-Obudho P, Cannicci S, Gitundu JK. 2017. Impact of pollution on the feeding, bioturbation and biomass of Uca annulipes in Gazi and Mikindani mangroves, Kenya. Ocean Life 1: 61-68. Marine pollution is one of the main anthropogenic factors globally recognized that affect the estuarine and coastal ecosystems. Mangroves received the pollutant since they are intercepting between land and ocean. Despite the utilization of natural mangrove as pollution buffers, how these pollutants might impact the biodiversity of the ecosystems remains a great question. Here, we aimed at determining the impact of pollution on the feeding, bioturbation, and biomass of the fiddler crab Uca annulipes in two regions, Gazi and Mikindani, all along the Kenya Coast. The mangroves in Mikindani on Tudor creek represented peri-urban mangroves that are heavily impacted by municipal wastewater. Meanwhile, the mangroves in Gazi Bay in the South Coast of Kenya served mangroves not affected by direct sewage input. Furthermore, Crabs U. annulipes are one of the most important groups of mangrove epifauna. We adopted a stratified nested design to investigate the impacts of pollution on the feeding, bioturbation, and biomass of U. annulipes. We applied a layered random sampling approach at each site that spanned in 2 × 2 m2 quadrats in desert and Avicennia zones during July, August and October 2005. The data collection depended on each full moon springs and new moon springs. Different parameters were measured, chlorophyll a (Chl a) concentrations in the feeding pellets and unprocessed soils, amount of bioturbated clays (expressed as dry weight of excavated material and feeding pellets), and biomass (dry weight) of U. annulipes. Four-factor Analysis of Variance (ANOVA) tests were applied to determine whether there was a significant difference in feeding, bioturbation, and biomass of U. annulipes within the two sites. Our findings show substantial differences in chlorophyll a concentration in the feeding pellets in the Avicennia zone of the peri-urban mangroves. Moreover chlorophyll a level did not vary between the processed and unprocessed soils in the Avicennia zone. In Gazi, a significant difference in the bioturbated material was recorded compared to Mikindani. The results demonstrate a consistent increase in crab biomass at the peri-urban site, then the non-urban mangroves. The Avicennia zone of the suburban location had a higher U. annulipes biomass compared to the non-urban Gazi. There was no association between the mass of bioturbated material and Uca biomass. The results also show that the amount of excavated material did not relate to the Uca biomass.

Numerical modelling of hydraulics and sediment dynamics around mangrove seedlings: Implications for mangrove establishment and reforestation

Mangroves grow in the coastal and intertidal zones at tropical and subtropical latitudes. It is widely accepted that the establishment, growth and survival of mangrove seedling depend on the environmental conditions such as temperature, tidal regime and hydrodynamics. To date we know that, in cohesionless sediment, the higher the flow velocity the greater the eroded volume and, thus, the stronger the scour around the mangrove seedling which can lead to its uprooting or death. However, how a mangrove seedling (cm-scale) alters the flow pattern and the sediment transport is, to date, still poorly understood. Four suits of numerical experiments were setup with the same mangrove seedling and subjected to flow speeds of 5 cm·s−1, 10 cm·s−1 and 15 cm·s−1 as well as a rarely occurring extreme scenario 50 cm·s−1. The hydro- and sediment dynamics were simulated using a coupled sediment-hydrodynamic continuum approach: the Finite Volume Method utilizing the software package OpenFOAM. The two phases, silty sediment and water, constitute a mixture. The distribution of the sediment phase in the water phase was estimated with the drift-flux approximation. A natural mangrove seedling (Rhizophora mucronata) was digitized employing photogrammetry and discretized into the model domain. This numerical model was validated against experimental observations and is able to capture the main features of the flow and sediment transport around a mangrove seedling. The numerical simulations showed that a downward flow associated to a horseshoe vortex enhances scour in front of the mangrove seedling and a vortex shedding keeps the sediment in suspension or re-suspends the sediment in the rear of the mangrove seedling. Thus, a mangrove seedling has a significant influence on the flow pattern and sediment transport: the higher the flow speed, the less stable the sediment bed. Additionally, these findings could help to better understand how the settlement of mangrove seedlings and sediment dynamics affect mangrove establishment and why the colonization or restoration of tidal flats is successful or not. This paper is an initial study focusing on a single mangrove seedling on a cm-scale. It is anticipated to extend the interactions between several seedlings as well as mangrove roots. With this successfully utilized approach, it will be possible in the future to investigate the impact of several mangrove seedlings forming a matrix on a m-scale on sediment dynamics. So, this work creates the basis to study more complex sediment transport processes such as erosion and sediment trapping in mangrove forests.

The Influence of Accessibility And Facilities on Visitor Satisfaction in Mangrove Forests Pantai Indah Kapuk

Green nature in particular in Angke Kapuk Nature Park is a natural conservation area that is used for natural tourism activities and centered on the development of ecotourism. This mangrove forest nature park is a natural conservation area dominated by mangrove vegetation. Nature Park is very influenced by several things, especially accessibility and facilities provided. This research purposes to determine the effect of accessibility and existing facilities in Taman Wisata Alam to visitor satisfaction. The method of analysis used in this research is descriptive and quantitative method of regression. This method is do so that it can give conclusion and picture how accessibility and facility can influence visitor satisfaction. Based on the results of research on the Influence of Accessibility and Facilities to the Mangrove Forest Visitor Satisfaction in Pantai Indah Kapuk, it can be seen that the level of influence given variable X1 (Accessibility) to variable Y (Visitor Satisfaction) is 23.8% and the level of influence given variable X2 (Facility) to variable Y (Visitor Satisfaction) is equal to 76,3%. Therefore, managers should pay more attention to aspects that affect customer satisfaction

Study on the Status and Countermeasures of Mangrove Protection in Hainan Province—A Case Study of Qinglan Harbour Mangrove Nature Reserve

This research investigates the status of mangrove conservation in Qinglan Harbour Mangrove Nature Reserve in Hainan Province, then analyzes and proposes corresponding countermeasures. The Qinglan Harbour Mangrove Nature Reserve has problems such as the continuous reduction of mangrove area, the reduction of biodiversity, serious water pollution and serious soil pollution. The main causes are economic factors, policy factors, scientific and cultural factors. Finally, this paper uses the theory of ecological environment pluralistic governance model to propose solutions from the three main bodies of government, enterprises and residents.

Spartina alterniflora invasion alters soil bacterial communities and enhances soil N2O emissions by stimulating soil denitrification in mangrove wetland

Chinese mangrove, an important ecosystem in coastal wetlands, is sensitive to the invasive alien species Spartina alterniflora. However, the effects of the S. alterniflora invasion on mangrove soil N2O emissions and the underlying mechanisms by which emissions are affected have not been well studied. In this study, the N2O emitted from soils dominated by two typical native mangroves (i.e. Kandelia obovata: KO; Avicennia marina: AM), one invaded by S. alterniflora (SA), and one bare mudflat (Mud) were monitored at Zhangjiang Mangrove Estuary (where S. alterniflora is exotic). Together with soil biogeochemical properties, the potential denitrification rate and the composition of soil bacterial communities were determined simultaneously by 15NO3− tracer and high-throughput sequencing techniques, respectively. Our results showed that S. alterniflora invasion significantly (p < 0.05) increases soil N2O emissions by 15–28-fold. In addition, isotope results revealed that the soil potential denitrification rate was significantly (p < 0.05) enhanced after S. alterniflora invasion. Moreover, the S. alterniflora invasion significantly (p < 0.05) decreased soil bacterial α-diversity and strongly modified soil bacterial communities. Indicator groups strongly associated with S. alterniflora were Chloroflexia, Alphaproteobacteria, and Bacilli, each of which was abundant and acts as connector in the co-occurrence network. FAPROTAX analysis implied that the S. alterniflora invasion stimulated soil denitrification and nitrification while depressing anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA). Redundancy analysis (RDA) found that soil organic matter (SOM) and pH were the most important environmental factors in altering soil bacterial communities. Taken together, our results imply that the S. alterniflora invasion in mangrove wetlands significantly stimulates soil denitrification and N2O emissions, thereby contributing N2O to the atmosphere and contributing to global climate change.

Diversity of benthic macrofauna and physical parameters of sediments in natural mangroves and in afforested mangroves three decades after compensatory planting

Mangroves in the Arabian Gulf are under pressure from land use change, leading to compensatory planting at sites without natural mangroves. In this study, we examine the potential long-term success of this form of afforestation of mangroves as a conservation measure supporting biodiversity. We compared the community of benthic macrofauna (in total 13,522 individuals from 75 species) and physical parameters at 15 sampling points in five afforested mangrove communities and 19 stations in four natural mangrove communities in Qatar. Three decades after afforestation, there were no significant differences between the benthic macrofauna in natural and afforested mangroves as regards total abundance, species richness, Shannon’s diversity, effective number of species, or evenness. Only species richness of Crustacea was significantly higher in natural mangroves. Total organic carbon (TOC), sand, and clay content did not differ. This contradicts findings at the same locations 10 years after afforestation, when benthic macrofauna diversity, TOC, and clay content were lower at afforested sites than at natural mangrove sites. Our results suggest that compensatory planting of mangroves in areas without previous natural occurrence can potentially compensate for loss of biodiversity due to coastal development and that physical parameters may become more similar in afforested mangroves and natural mangroves over time. Furthermore, the increase in TOC in sediments in afforested mangroves over time can help mitigation of climate change. Importantly, the results highlight the need for long-term studies and perspectives when evaluating conservation practices.

Bioaccumulation and cycling of polybrominated diphenyl ethers (PBDEs) and dechlorane plus (DP) in three natural mangrove ecosystems of South China

Polybrominated diphenyl ethers (PBDEs) and dechlorane plus (DP) in mangrove sediments and tissues of nine species from three Mangrove Reserves of Hainan Island were studied. The average concentrations of PBDEs and DP in mangrove leaves, branches, roots and fruits were 1048, 498, 546 and 364 pg g−1 dw, and 294, 181, 108 and 165 pg g−1 dw, respectively. The elevated PBDEs and DP concentrations in mangrove leaves may be caused by atmospheric sedimentation. The predominant PBDE congeners in sediments were BDE-209 and those in mangrove tissues were BDE-28. The average fanti (ratio of [anti-DP]/[DP]) of DP in sediments and tissues were 0.47 and 0.32, respectively. Sonneratia hainanensis, a fast growing mangrove plant, has a relatively high tolerance and absorptive capacity to PBDEs and DP in sediments, suggesting that it could be used as an effective plant for phytoremediation. The biota sediment accumulation factors (BSAFs) of PBDEs in mangrove branches were positively correlated with log KOW (R2 = 0.43, p < 0.05). The standing accumulation, annual absorption, annual net retention, annual return, and turnover period of PBDEs and DP in mangrove tissues of the ecosystems were estimated, and the results indicated that mangroves are playing an important role in retaining PBDEs and DP.

Mangrove Sediment Microbiome: Adaptive Microbial Assemblages and Their Routed Biogeochemical Processes in Yunxiao Mangrove National Nature Reserve, China.

Microorganisms play important roles in mangrove ecosystems. However, we know little about the ecological implications of mangrove microbiomes for high productivity and the efficient circulation of elements in mangrove ecosystems. Here, we focused on mangrove sediments located at the Yunxiao National Mangrove Reserve in southeast China, uncovering the mangrove microbiome using the 16S rRNA gene and shotgun metagenome sequencing approaches. Physicochemical assays characterized the Yunxiao mangrove sediments as carbon (C)-rich, sulfur (S)-rich, and nitrogen (N)-limited environment. Then phylogenetic analysis profiling a distinctive microbiome with an unexpected high frequency of Chloroflexi and Nitrospirae appeared to be an adaptive characteristic of microbial structure in S-rich habitat. Metagenome sequencing analysis revealed that the metabolic pathways of N and S cycling at the community-level were routed through ammonification and dissimilatory nitrate reduction to ammonium for N conservation in this N-limited habitat, and dissimilatory sulfate reduction along with polysulfide formation for generating bioavailable S resource avoiding the biotoxicity of sulfide in mangrove sediments. In addition, methane metabolism acted as a bridge to connect C cycling to N and S cycling. Further identification of possible biogeochemical linkers suggested Syntrophobacter, Sulfurovum, Nitrospira, and Anaerolinea potentially drive the coupling of C, N, and S cycling. These results highlighting the adaptive routed metabolism flow, a previously undescribed property of mangrove sediment microbiome, appears to be a defining characteristic of this habitat and may significantly contribute to the high productivity of mangrove ecosystems, which could be used as indicators for the health and biodiversity of mangrove ecosystems.

The integration and application of genomic information in mangrove conservation.

Article impact statement: Genomic information can help prevent species loss, facilitate reserve design and maximize adaptive potential of natural mangrove populations.

Appearance can be deceptive: shrubby native mangrove species contributes more to soil carbon sequestration than fast-growing exotic species

Increased recognition of mangrove high carbon storage potential has prompted carbon sequestration as one of the main goals in mangrove afforestation. In southern China, the introduced fast-growing Sonneratia apetala and native Kandelia obovata have been widely afforested since the mid-1980s. While S. apetala has spread extensively, the implications and ecosystem services are yet to be ascertained. Soil/root coring was conducted in two 12-year-old S. apetala and K. obovata plantations, respectively. Fine-root mass and soil physicochemical properties were obtained and compared. Fine-root mass and soil organic carbon stock ranged between 129 and 394 g m−2 and 7.9 and 15.8 Mg C ha−1, respectively. Soil organic carbon stock and fine-root mass were both significantly different between the forests. Organic carbon in soil is significantly correlated to fine-root mass and organic carbon in fine roots. The contribution to soil organic carbon by fine-root mass may be different between the two species. Growth and physiological traits not only may influence stand characteristics but also soil properties that drive overall carbon accumulation. Contrary to the original expectation driving the introduction, the shrubby native K. obovata may have higher potential as a carbon sink than the introduced S. apetala.

Soil-microbial communities indexing from mangroves rhizosphere and barren sandy habitats

This work assessed the role of mangrove vegetation on soil characteristics of mangrove sediment and barren sandy soil in order to assess the impact of mangrove vegetation on the coastal soil. The soil samples were obtained from three sites (natural mangroves, planted mangroves, and non-mangrove sandy shore) located in the Vellar-coleroon estuarine complex for four seasons at three different soil depths (0–10, 10–50 and 50–100 cm). The samples were analyzed for microbial counts, nutrients and trace elements. The total fungal count was 42.5-fold higher in natural mangrove sediment than sandy soil as against the total heterotrophic bacterial count which was only 1.9-fold higher. Notably, planted mangrove sediment had higher total organic carbon, microbial carbon, N, P and K than the sandy soil. There was a significant correlation between soil temperature and microbial counts revealing that the temperature rise may be favorable for soil biospheres such as heterotrophs, saprophytes, and parasites. Remarkably, boron, cadmium, and cobalt were many folds greater in the natural mangrove sediments than that in planted mangrove sediment. This work has suggested that an amendment of sandy soil with nutrients nitrogen and microbial biomass is likely to transform the barren soil into carbon-rich mangroves.

Carbon dynamics and land use carbon footprints in mangrove-converted aquaculture: The case of the Mahakam Delta, Indonesia

Mangroves provide a number of important ecosystem services to humanity but their persistence is threatened from deforestation, conversion, and climate change. The Mahakam Delta was once among the largest mangrove forests in Southeast Asia comprising 2% of Indonesia’s total mangroves. Currently, about 62% of this extensive mangrove in the Mahakam Delta has been lost mainly due to conversion into aquaculture. To understand the impacts of mangrove conversion on carbon losses and therefore their values in climate change mitigation, we sampled 10 intact mangroves and 10 abandoned shrimp ponds to quantify: (1) the total ecosystem carbon stocks; (2) potential CO2 emissions arising from mangrove conversion to shrimp ponds; and (3) the land use carbon footprints of shrimp production. The mean ecosystem carbon stocks in shrimp ponds (499 ± 56 Mg C ha−1) was less than half of the relatively intact mangroves (1023 ± 87 Mg C ha−1). This equates to a potential annual emission factor over 16 years following mangrove conversion of 120 Mg CO2e ha−1 yr−1, which is similar with the total carbon loss from land conversion in freshwater tropical peat swamp forests. Inclusion of C losses from land use/cover change in a life cycle analysis (i.e., the land use carbon footprint) resulted in an estimated 2250 kg CO2-e emitted for every kg of shrimp produced in mangrove-converted ponds. Conversion of mangroves to shrimp ponds in the Mahakam Delta resulted in a carbon loss equivalent to 226 years of soil carbon accumulation in natural mangroves. Conservation of mangroves are of great value for inclusion in climate change mitigation strategies because of their large carbon stocks, the large carbon emissions generated from land use, and the potentially long period of time required to recover carbon stocks following abandonment.

Monitoring loss and recovery of mangrove forests during 42 years: The achievements of mangrove conservation in China

Mangroves are valuable ecosystems that have been protected and restored for decades in China. However, little is known about achievements of China’s mangrove conservation efforts. This study aims to analyze the effectiveness of these efforts by presenting long-term dynamics of mangrove forests areal extent at the national scale. To achieve this goal, 123 Landsat images, covering all the mangrove forests in China from 1973 to 2015, were interpreted. For the first time, we built a new dataset of China’s mangrove forest changes during past 42 years called Chinese Academy of Sciences Mangroves (CAS_Mangroves). Based on this dataset, we conducted case studies in seven mangrove national nature reserves to show dramatic changes of mangrove forests before and after the establishment of the reserves. Results showed that: 1) on the national scale, mangrove forests declined from 48,801 ha to 18,702 ha between 1973 and 2000, then partially recovered to 22,419 ha in 2015; 2) in each reserve, the areal extent of mangrove forests increased immediately after the reserve was established. Depending on our analysis, in the early time, agricultural reclamation caused the loss of mangrove forests; in contrast, recently, protection and reforestation actions prompt to mangrove forest restoration greatly. Because of China’s conservation efforts, since 2000, direct destruction by human beings has rarely happened, and natural disasters and the existing artificial seawalls have become major threats to mangrove forest in China. This study is an application of remote sensing technologies in evaluating effectiveness of conserving natural resources. And the experiences and achievements of China’s mangrove conservation efforts presented in this study will facilitate the development of applicable coastal management strategies globally, especially in developing countries.

Zhengella mangrovi gen. nov., sp. nov., a novel member of family Phyllobacteriaceae isolated from mangrove sediment

A Gram-negative strain, designed X9-2-2T, was isolated from mangrove sediment in Yunxiao Mangrove National Nature Reserve, China. Strain X9-2-2T showed less than 96.2 % 16S rRNA gene sequence similarity to type strains of species with validly published names. Phylogenetic analysis based on 16S rRNA gene sequences and rpoB protein sequences revealed that strain X9-2-2T formed a distinct monophyletic clade within the family Phyllobacteriaceae and clustered distantly with the genera Aliihoeflea, Phyllobacterium and Hoeflea. Cells of X9-2-2T were rod-shaped, motile with subpolar or lateral flagella and facultative anaerobic. Optimal growth occurred at 30-37 °C, at pH 7 and in the presence of 2 % NaCl. The DNA G+C content of strain X9-2-2T was 64.9 mol%. The major fatty acids were summed feature 8 (comprising C18 : 1ω7c and/or C18 : 1ω6c 56.0 %), iso -C17 : 0 (9.1 %) and C12 : 0 (6.6 %). The predominant respiratory quinone was ubiquinone-10 and the major polar lipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylmonomethylethanolamine, an unidentified aminolipid and two unidentified polar lipids. According to its morphology, physiology, fatty acid composition and 16S rRNA gene signature nucleotide patterns, strain X9-2-2T represents a novel species of a novel genus in the family Phyllobacteriaceae, for which the name Zhengella mangrovi gen. nov., sp. nov. is proposed. The type strain is X9-2-2T (=MCCC 1K03307T=JCM 32107T).

Species Diversity of Migratory Birds Along the Mangrove Nature Trails in Samut Songkhram Province, Thailand

Species Diversity of Migratory Birds Along the Mangrove Nature Trails in Samut Songkhram Province, Thailand

Effects of conversion of mangroves into gei wai ponds on accumulation, speciation and risk of heavy metals in intertidal sediments

Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] - [AVS])/foc, and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.