Mangrove Growth Research Articles

Survival of young planted mangroves in a calm bay environment during a tropical cyclone

The efforts of mangrove plantations are not always successful, and the reasons for their failure remain unclear. In this study, the growth of planted mangroves (Kandelia sp.) was monitored in a mangrove forest on Amami Island, Japan, to investigate their survival over the first three years. A strong typhoon passed near the island 16 months after planting. Although the mangroves were planted at the frontal edge of the intertidal zone, most of young mangroves survived without visible damage. The external forces acting on the plants, such as wave forces, storm surge forces, wind drag forces, and oscillatory acceleration, were estimated by applying an integrated analysis model for tropical cyclones, storm surges, wind waves, and plant kinematics. These analyses yielded three main results. First, although large waves over 10 m in height were generated offshore, the mangrove forest was located in the innermost part of the bay, resulting in considerable wave attenuation. Second, the wave period in the bay was much shorter than that in the open ocean, which may have promoted resonance between waves and mangrove plants. The oscillatory acceleration of the young mangroves was estimated to have approximately the same magnitude as that of the gravitational force. Third, the young mangroves could withstand a fairly strong typhoon, but this may have been fortuitous because the timing of the adverse wind wave conditions coincided with low tide. It is estimated that if the tides had been higher, the oscillatory acceleration would have been five times that of the gravitational acceleration. Although this study only presents examples of specific mangrove species in a particular location, the findings can be used to improve the attempts to restore mangrove forests and thereby protect coastal settlements from the adverse effects of tropical cyclones.

An integrated satellite characterization and hydrodynamic study in assessing coastal dynamics in Cirebon, West Java

Located on the northern coast of Java Island, the coastal area of Cirebon is an area with rapid population growth and extensively developed as settlement areas, industrial estates, fisheries, agriculture, and public service infrastructures. Coastal dynamics issues have been occurring in the coastal area of Cirebon, which is characterized by significant changes in shoreline position. Moreover, some critical infrastructures are not functioning properly and may cause high maintenance costs and economic loss to the related stakeholders. This study aims to provide a greater understanding of the coastal dynamics along the 73.16 km of Cirebon shoreline through remote sensing and GIS methods supported by hydrodynamic analysis. This study applied coastal characterization, coastal structure identifications, and coastal processes assessments, including erosion and accretion analysis, hydrodynamic and tidal analysis, and inundation projection. The study indicates that some areas have been subject to significant erosion and accretion during the last two decades, with the total lengths of the eroded and accreted shoreline being −21.9 km (35.6%) and ＋39.6 km (64.4%), respectively. Furthermore, the coastal structures significantly influence the coastline’s dynamic and mitigate the negative impacts of coastal floods. Jetty access channels in the west area have caused partial coastal erosion, while the breakwaters in the east area accelerated sedimentation processes and improved the growth of mangroves simultaneously. This study also simulated the potentially inundated areas by 2050 in four scenarios based on projected sea level rise, land subsidence, and extreme wave events. Policies to prevent such potential hazards are needed to avoid negative impacts on the living quality and vital economic sectors. This study provides insight into coastal characterization, potential coastal hazards, and their driving processes in time and space scale for coastal adaptation planning policies and sustainable coastal hazard management and mitigation.

High site elevation enhanced nitrogen fixation and the stability of diazotrophic community in planted Sonneratia apetala mangrove sediments

Site elevation was decisive in determining effective mangrove restoration, and nitrogen availability was a decisive factor for mangrove growth and development. The biological nitrogen fixation conducted by diazotrophs was responsible for 40–60 % of the nitrogen demand of mangrove ecosystems, and the nitrogen dynamics of mangrove forests were primarily correlated with stand age. Understanding how site elevation affects sediment diazotrophs and their variation across stand age was critical for site selection for mangrove restoration and evaluating the functional rehabilitation and primary productivity of mangrove wetlands. Diazotrophic community and nitrogen fixation rate (NFR) in mangrove sediments with depth were compared among 12-year and 18-year-old S. apetala mangrove forests planted under high (H18) and low site elevations (L18 and L12), respectively. The results indicated the sediment nutrient pools (e.g., TOC, TN, and TS) and NFR in mangrove sediments followed an increasing trend with increased site elevation over time (H18 > L18 > L12), and NFR weakly increased with sediment depth. Moreover, the diazotrophic community structure was both elevation- and age-dependent. The relative abundance of the dominant diazotrophic group Desulfuromonadales (belonged to sulfate-reducing bacteria, SRB) decreased with increasing site elevation, while another SRB group Syntrophobacterales showed an opposite trend. Moreover, network analyses revealed more stable and less complicated networks in sediments with higher site elevation, which followed a similar trend with NFR by H18 > L18 > L12. This study provided new perspectives on the microbe-based assessment of mangrove functional restoration from the viewpoint of both diazotrophic communities and NFR. From this perspective, high site elevation had a higher nutrient pool, NFR, and diazotrophic community stability, which should be recommended for mangrove restoration in the future, and long-term rehabilitation would benefit the ecological functional (nitrogen fixation) restoration.

Estimation of Species-Scale Canopy Chlorophyll Content in Mangroves from UAV and GF-6 Data

The growth of mangroves is inhibited due to environmental degradation, and changes in the growing health of mangrove forests cause changes in internal physicochemical parameters. The canopy chlorophyll content is an important indicator to monitor the health status of mangroves. We study the effective inversion data sources and methods of mangrove health indicator parameters to monitor the health of mangrove ecosystems in typical areas of Beibu Gulf, Guangxi. In this study, we evaluated the capability of UAV, GF-6 data, and machine learning regression algorithms in estimating mangrove species-scale canopy chlorophyll content (CCC). Effective measures for mangrove pest and disease pressure, Sporobolus alterniflorus invasion, and anthropogenic risk are also explored, which are important for mangrove conservation and restoration. (1) We obtained several feature variables by constructing a combined vegetation index, and the most sensitive band of mangrove CCC was selected by the characteristic variable evaluation, and the CCC model at the mangrove species-scale was evaluated and validated. Through variable preferences, the feature variables with the highest contribution of Avicennia marina, Aegiceras corniculatum, Kandelia candel, and a collection of three categories of species in the UAV data were indices of RI35, MDATT413, RI35, and NDI35. (2) Random Forest, Gradient Boosting Regression Tree, and Extreme Gradient Boosting were evaluated using the root-mean-square error and coefficient of determination accuracy metrics. Extreme Gradient Boosting regression algorithms were evaluated for accuracy. In both UAV data and GF-6, RF achieved optimal results in inverse mangrove Aegiceras corniculatum species CCC, with higher stability and robustness in machine learning regressors. (3) Due to the sparse distribution of Kandelia candel in the study area and the low spatial resolution of the images, there is an increased possibility that individual image elements contain environmental noise, such as soil. Therefore, the level of CCC can effectively reflect the health status of mangroves and further reflect the increased possibility of the study area being exposed to risks, such as degradation. The establishment of the current protected areas and restoration of degraded ecosystems are effective measures to cope with the risks of mangrove pest and disease stress, invasion of Sporobolus alterniflorus, and anthropogenic activities, which are important for the protection and restoration of mangroves. This study provides an important data reference and risk warning for mangrove restoration and conservation.

Impact and prediction of pollutant on mangrove and carbon stocks: A machine learning study based on urban remote sensing data

Mangrove ecosystems have important ecological and economic values, especially their ability to store carbon. However, in recent years, human disturbance has accelerated mangrove degradation. Among them, the emission of pollutants cannot be ignored. It is of great significance for carbon emission reduction and ecological protection to study the impacts of different pollutants on mangroves and their carbon stocks. Based on the remote sensing data of coastal areas south of the Yangtze River in mainland China, this paper builds the ensemble learning model Random Forest (RF) and Gradient Boosting Regression (GBR) to empirically analyse the relationship between industrial wastewater, industrial sulfur dioxide (SO2), PM2.5 and mangrove forests. The results show that the pollutant concentration of meteorological normalisation is more stable. The importance of pollutants presents regional heterogeneity. The area of mangroves in different cities and the corresponding total carbon stocks show different trends with the increase or decrease of pollutants, and there is a dynamic balance between urban pollutant discharge and mangrove growth in some cities. The research in this paper provides an analysis and explanation from the perspective of machine learning to explore the relationship between mangroves and pollutants and at the same time, provides scientific suggestions for the formulation of future pollutant emission policies in different cities.

How exotic Sonneratia species affect the spatiotemporal dynamics of mangroves in Shenzhen Bay, China: A remote sensing perspective

Mangroves are essential forest communities in tropical and subtropical coastal zones, providing unique ecological functions and significant social and economic value. Accurate and efficient monitoring of mangroves is crucial for their protection and management. The impact of exotic species on native species is still debated, especially for mangroves, the spatiotemporal dynamics of introduced species and native mangrove species need to be closely monitored. This study aimed to investigate how exotic mangrove species affects the spatial dynamics of mangroves in Shenzhen Bay, China. Yearly Landsat images from 2000 to 2011 and Chinese high spatial resolution images during 2012–2022 were obtained and the pixel-based and multiscale object-based methods were used to obtain mangrove distribution. The results showed that: (1) Overall, mangroves in the study area increased from 281.51 ha to 526.43 ha from 2000 to 2022, with different spatiotemporal patterns in Shenzhen (+5.14%) and Hong Kong (+2.38%); (2) rapid spread of Sonneratia species was one of the main contributions to the growth of mangrove hotspots, and growth hotspots were mainly concentrated in the estuary delta; and (3) Sonneratia mangrove species was dominant in interspecific competition, not only invading the habitat of local mangroves, but also preventing the expansion of native mangrove growth. The results provide a reference for fine-scale and accurate mangrove mapping with high spatial and temporal resolutions, and highlight the need to pay more attentions to the spread and invasive potential of exotic mangrove species in the study area, as well as cooperation in adjacent reserves.

Mangrove Land Suitability Assessment Using Weighted Linear Combination: A Case Study of La Union Province Coastline, Philippines

Land suitability assessments play a crucial role in determining optimal land use patterns to meet specific requirements, particularly in the context of forest restorations and plantations. However, there is a lack of studies reporting such assessments for mangrove rehabilitation and reforestation in the Philippines, leading to low survival rates (10-20%) due to improper site selection and site-species matching. This study aims to identify and narrow down suitable sites for mangrove growth in La Union Province, facilitating ground truthing for site selection and species matching. The Geographic Information System (GIS) method, specifically the Weighted Linear Combination (WLC) using ArcMap software, was employed. The study identified four suitable sites along the coastline of La Union within the jurisdictions of Aringay, Bangar, Sto. Tomas, and the City of San Fernando, all actively involved in mangrove conservation. However, mangrove planting efforts in other municipalities along the coastline of La Union, such as Agoo, Balaoan, and Bauang, were not reflected on the maps due to data resolution limitations. Nevertheless, the study's findings should be regarded as a supportive tool in the site determination process, with ground truthing and assessment remaining essential. Integrating the study's results with mangrove rehabilitation/reforestation efforts offers efficiency options that have the potential to enhance project success rates.

KARAKTER VEGETASI, KEANEKARAGAMAN MAKROZOOBENTOS DAN KARBON PADA SEDIMEN DI KAWASAN MANGROVE NUSA LEMBONGAN DAN ESTUARI PERANCAK

Natural mangroves can be found in Nusa Lembongan, which is bordered by coral reefs, while in the Perancak Estuary, some of the lands are former ponds. The aim of the study was to determine the density, canopy cover, and organic carbon content in mangrove sediments. Data were collected from 3 stations, using transects measuring 10 x 10 m to determine density, height, trunk circumference, and canopy cover, as well as macrozoobenthos sampling. The mangrove density in Lembongan is very high, the tree height reaches 8 – 10 meters, and the mangrove canopy cover is in a good category. The macrozoobenthos diversity index is in the medium category and the carbon content in the sediments is high. Mangroves in Perancak Estuary are densely dense, with an average tree height of 8 meters, and canopy cover in the good category. The index of macrozoobenthos diversity was moderate and the organic carbon in the sediments was lower than in the mangroves at Nusa Lembongan. The character of the mangrove vegetation is different in the two areas. The Nusa Lembongan mangrove growing area is directly opposite the sea, but in the Perancak Estuary, it tends to be closed and flows by a large river around it. The mangrove growth zone is still natural in the Nusa Lembongan area, in contrast to the Perancak Estuary mangrove area which has been rehabilitated at several points.
 Keywords: Mangrove vegetation; macrozoobenthos; carbon on sediment

Mangrove Biodiversity Assessment Using UAV Lidar and Hyperspectral Data in China’s Pinglu Canal Estuary

Mangrove forests are a valuable resource for biological and species diversity, and play a critical role in maintaining biodiversity. However, traditional plant biodiversity survey methods, which rely on labor-intensive field surveys, are not suitable for large-scale continuous spatial observations. To overcome this challenge, we propose an innovative framework for mangrove biodiversity assessment and zoning management based on drone low-altitude remote sensing, integrating data such as vertical structure features and spectral diversity features extracted from on-site measurements, airborne LiDAR, and hyperspectral data. This study focuses on the Maowei Sea mangrove community, located in the estuary of China’s first Pinglu Canal since the founding of the People’s Republic of China. Using the proposed framework, we construct an evaluation index for mangrove biodiversity at the levels of species diversity, ecosystem diversity, and landscape diversity, achieving a quantitative calculation of mangrove biodiversity and an evaluation of spatial distribution patterns. The results show that the biodiversity index of mangroves ranges from 0 to 0.63, with an average value of 0.29, and high-biodiversity areas are primarily concentrated in the southwest of the study area, while low-value areas are mainly located in the north. We also select the elevation and offshore distance of mangrove growth for the spatial zoning of biodiversity. The core area of biodiversity occupies the smallest area, at 2.32%, and is mainly distributed in areas with an elevation of 1.43–1.59 m and an offshore distance of 150.08–204.28 m. Buffer zones and experimental zones account for a significant proportion, with values of 35.99% and 61.69%, respectively. Compared to traditional methods for monitoring mangrove biodiversity, such as community field-sample surveys, the proposed method using unmanned-aerial-vehicle LiDAR and hyperspectral coupling technology to assess mangrove biodiversity and establish a zoning management framework is more conducive to formulating mangrove biodiversity conservation strategies. The study provides a feasible solution for the large-scale biodiversity mapping of mangroves in the Maowei Sea at the estuary of the Pinglu Canal.

Distribution of mangroves with different aerial root morphologies at accretion and erosion sites in Ca Mau Province, Vietnam

Aerial roots are a vital feature that allow mangroves to survive in anaerobic and unstable soil conditions. Mangrove species have different aerial root characteristics and show their own site-specific distribution. The distribution of three types of aerial roots with different morphological characteristics was investigated between accretion and erosion sites in Ca Mau, Vietnam. Stilt roots, pneumatophores and knee roots were the three main aerial root types in the study area. Stilt roots of Rhizophora apiculata BL. and pneumatophores of Avicennia species were the two most abundant root types at the study sites, dominating erosion and accretion sites, respectively. Stilt roots had a higher number of primary roots in seaward plots than in landward plots (p < 0.05), supporting the ability of R. apiculata to withstand erosion of the surface. Tidal erosion moved away sediment and exposed roots, which resulted in higher aboveground stilt root height in seaward plots than in landward plots at erosion sites (p < 0.05). The higher density and biomass of pneumatophores in seaward plots than those in landward plots at accretion sites (p < 0.05) confirmed the adaptation of Avicennia to newly accreted sites where tidal inundation and anaerobic conditions limited mangrove growth. The density of A. alba decreased with the distance from the sea at both erosion and accretion sites, implying that this species was a pioneer species adapted to newly accreted sites or disturbed sites among mangrove species. Bruguiera parviflora with knee roots was distributed in more stable conditions. Mangrove species with different root types displayed a zonal distribution with increasing distance from the shoreline. This distribution reflects mangrove species adaptabilities and species-specific roles in the context of coastal processes and site conditions, which should be considered in coastal mangrove restoration.

Collaborative multiple change detection methods for monitoring the spatio-temporal dynamics of mangroves in Beibu Gulf, China

ABSTRACT Mangrove ecosystems are one of the most diverse and productive marine ecosystems around the world, although losses of global mangrove area have been occurring over the past decades. Therefore, tracking spatio-temporal changes and assessing the current state are essential for mangroves conservation. To solve the issues of inaccurate detection results of single algorithms and those limited to historical change detection, this study proposes the detect–monitor–predict (DMP) framework of mangroves for detecting time-series historical changes, monitoring abrupt near-real-time events, and predicting future trends in Beibu Gulf, China, through the synergetic use of multiple detection change algorithms. This study further developed a method for extracting mangroves using multi-source inter-annual time-series spectral indices images, and evaluated the performance of twenty-one spectral indices for capturing expansion events of mangroves. Finally, this study reveals the spatio-temporal dynamics of mangroves in Beibu Gulf from 1986 to 2021. In this study, we found that our method could extract mangrove growth regions from 1986 to 2021, and achieved 0.887 overall accuracy, which proved that this method is able to rapidly extract large-scale mangroves without field-based samples. We confirmed that the normalized difference vegetation index and tasseled cap angle outperform other spectral indexes in capturing mangrove expansion changes, while enhanced vegetation index and soil-adjusted vegetation index capture the change events with a time delay. This study revealed that mangrove changes displayed historical changes in the hierarchical gradient from land to sea with an average annual expansion of 239.822 ha in the Beibu Gulf during 1986–2021, detected slight improvements and deteriorations of some contemporary mangroves, and predicted 72.778% of mangroves with good growth conditions in the future.

Tidal creeks mediate micro-climate within artificial mangroves at their northmost boundary in China

One of the primary constraints for mangrove restoration is the low temperature in relatively high latitude regions. Yueqing Bay, at a latitude of 28.20°N, is the northmost region for the artificial mangrove forests in China. It is hypothesized that in this region, the micro-climate nearby tidal creeks can benefit the growth of mangroves, as the inundation process can mediate air temperature and soil temperature. To test this hypothesis, field observation was conducted to measure mangrove characteristics, hydrology and air/soil temperature within a channelised mangrove forest and compare variations between a tidal creek and its adjacent platform. LiDAR data and field measurement both indicated a height decrease of mangrove trees (Kandelia obovata) from the tidal creek edge to the platform. This pattern suggested that the presence of tidal creeks was able to promote the growth of mangrove in their northmost boundary and the mediation of microclimatic condition should be further investigated. The temperature profile data revealed that the key zone of temperature affected by tidal inundation was within a range of 5 cm and -15 cm referring to bed levels. Temperature monitoring in the winter revealed that compared with the platform, a mean increase of 0.6 °C in both air temperature and soil temperature were found in the tidal creek. However, spring tides and neap tides showed different effects on temperature mediation by the presence of tidal creeks. The greatest temperature increase was observed to occur in neap tides, reaching maximum of 9 °C in air and 3 °C in soil. Thus, the warming effects of tidal creeks in this region was most important in neap tides. In the northmost boundary of mangrove distribution in China, winter low temperature was considered to be the key restraint for mangrove restoration. Field survey found the growth of mangroves reached a maximal along the tidal creek edge in this region. This pattern was explained by the fact that the presence of tidal creeks increased winter temperature of mangroves and channelisation was found to be a potential technique to promote the growth of artificial mangroves in the relatively high latitude regions.

Seasonal groundwater salinity dynamics in the mangrove supratidal zones based on shallow groundwater salinity and electrical resistivity imaging data

Soil salinity plays an essential role in the growth of mangroves. Mangroves usually grow in intertidal zones. However, in Karimunjawa National Park (KNP), Indonesia, mangroves are also found in supratidal zones. Thus, this study aims to determine why mangroves can grow in this supratidal zone, even during the dry season. We analyze seasonal changes in groundwater flow and salinity dynamics using the hydraulic head, shallow groundwater salinity, and electrical resistivity imaging (ERI) data. The result shows that variation in groundwater salinity is caused by seawater intrusion, which is generated by a hydraulic gradient due to the sea level being higher than the water table in KNP. Rainfall and evapotranspiration, which change seasonally, likely affect the water table fluctuation and salt concentration. ERI images indicate this seawater intrusion in the top sediment up to the bedrock boundary. However, the resistivity difference in the wet and dry seasons shows that remarkable resistivity change occurs at the deeper layer (50–60 m below ground level (BGL)), likely due to freshwater recharge from rainwater on the land side. Groundwater in the KNP is shallow and saline; thus, mangroves in this zone, e.g., Ceriops tagal and Lumnitzera racemosa, can grow because their roots can reach this groundwater. These mangrove species can still grow in this zone even though the shallow groundwater is very saline (46–50 ppt). However, this condition might cause these mangroves to grow stunted. Thus, freshwater availability is crucial for mangrove growth in this supratidal zone to dilute this high groundwater salinity.

Relationship between sediment type, total organic matter, and water quality on mangrove density on Tunda Island, Serang Banten

Environmental conditions that are quite important in the growth of mangroves are the type of sediment, organic matter, and water quality because the organic matter produced can be useful for mangrove fertility. This study aims to determine the type of sediment, the percentage of total organic matter, water quality, mangrove density, and determine the relationship between sediment types, total organic matter, and water quality on mangrove density on Tunda Island, Serang, Banten. This study used a survey method while collecting data using a purposive sampling method. Mangrove density was obtained through the line transect plot method. The sediment type test used the dry sieving method, the total organic matter (BOT) test used the loss on ignition (LOI) method, the statistical test used the multiple correlation method. All data was then analyzed in a quantitative descriptive manner. The results of the study are that the type of sediment in Tunda Island mangroves is dominated by silty sand and sand. The total organic matter contained in mangrove sediments ranges from 2.40% - 3.62% which is included in the moderate to high category. Salinity values ranged from 31 - 34.33 ppt included in the high category. The pH value ranges from 7.33 - 7.70 which is included in the good category for mangrove growth. Temperature values ranging from 27.37oC - 31.63oC are included in the good category for mangrove growth because they can still grow and develop normally. The mangrove density level is dominated by the dense category, which is 2,400 ind/Ha at station 1 and 1,700 ind/Ha at station 2, and the rare category is 1,000 ind/Ha at station 3 and 900 ind/Ha at station 4. There is a significant relationship between sediment type, total organic matter, water quality with mangrove density.Keywords: BOT; Mangroves; Sediment; Water Quality

Response Mechanism of Leaf Area Index and Main Nutrient Content in Mangrove Supported by Hyperspectral Data

Mangrove is the key vegetation in the transitional zone between land and sea, and its health assessment can indicate the deep-level ecological information. The LAI and six key nutrients of mangrove were selected as quantitative evaluation indicators, and the decisive evaluation method of mangrove growth was expected. The mangrove reserve of Dongzhai Port National Nature Reserve in Hainan Province, China, was selected as the study area, with an area of 17.71 km2. The study area was divided into adjacent urban areas, aquaculture areas, and agricultural production areas, and key indicators are extracted from satellite hyperspectral data. The extraction process includes spectral data preprocessing, spectral transformation, spectral combination, spectral modeling, and precision inspection. The spatial distribution of LAI and six key nutrient components of mangrove in the study area were obtained. LAI and Chla need to calculate the index after high-order differentiation of the spectrum; MSTR and Chlb need to calculate the envelope after the second-order differential of the spectrum; TN and TP are directly changed by original or exponential spectrum; the spectral transformation method adopted by TK was homogenization after first-order differential. The results of the strength of nutrient content along the three regions show that there was no significant difference in the retrieval index of mangroves in the three regions, and the overall health level of mangroves was consistent. Chla was the key identification component of mangrove growth and health. The contents of nutrient elements with correlation coefficient exceeding 0.80 include MSTR and TK (0.98), Chla and TP (0.96), Chla and TK (0.87), MSTR and Chla (0.86), MSTR and TK (0.83), and MSTR and TP (0.81). The study quantifies the relationship between different LAI and nutrient content of mangrove leaves from the perspectives of water, leaf biology, and chemical elements, which improved our understanding of the relationship between key components during mangrove growth for the first time.

Impacts of different salinity levels on seedling growth and survival of black mangrove (Avicennia germinans)

Abstract. Matto AA, Jaikishun S, Ram M. 2023. Impacts of different salinity levels on seedling growth and survival of black mangrove (Avicennia germinans). Asian J For 7: 67-73. Mangroves are important for coastal protection and provide numerous ecosystem services such as breeding, feeding, and nursery grounds for commercial fishes. This research examined the survivability of black mangrove (Avicennia germinans (L.) L.) seedlings in seven salinity concentrations. Growth parameters were collected every ten days, and a post-harvest analysis was done at the end of the data collection period. The results indicated that as the salinity level increased, the growth of the seedlings was reduced. Salinity can affect the different parameters collected in the growth of young seedlings. In the control, which was given zero salinity (0 ppt), it was noted that the growth parameters were not significantly affected. The lower treatments, such as T2 (15 ppt), 3 (30 ppt), and 4 (45 ppt), indicated that the seedlings strive better in these conditions. In treatment 7, which was the highest salinity level (90 ppt), the growth parameters of the seedlings were reduced. The findings of this research indicated that black mangrove seedlings need a low salinity level to have a good growth establishment. Given the adaptability of A. germinans, these mangrove species are anticipated to be flexible to cope with a wide range of future climatic circumstances.

Groundwater discharge and saltwater-freshwater mixing in a mangrove wetland over tidal cycles: A field and modeling study

Material transport and transformations in mangrove wetlands are closely related to seawater-groundwater mixing processes, which can influence mangrove growth and development. Therefore, a clearer understanding of groundwater and salt transport dynamics in aquifers beneath mangrove wetlands is needed to accurately estimate chemical fluxes to mangrove ecosystems. We established a multi-level groundwater monitoring profile in a mangrove wetland and constructed a numerical model of tidally-driven groundwater flow and salt transport that was calibrated to salinity and pore water pressure. Model results indicated that 99% of groundwater discharge to the mangrove wetland was saltwater and that this discharge accounted for 33% of total discharge over a spring-neap tidal cycle. Tidal creeks that cross-cut the wetland received the remaining 67% of total discharge. Seawater infiltration from tidal action across the wetland formed a subsurface saltwater-freshwater mixing zone with a geometry that followed the undulation of a high permeably layer at depth. Model sensitivity tests showed that salinity distributions and groundwater discharge patterns were controlled strongly by wetland topography and anisotropy. Model cases with a gently sloping and flat mangrove platform led to substantially less salt mass in the subsurface compared to the base case with mangrove topographic relief. Models with lower anisotropy allowed salt to penetrate through the high-permeability layer to the base of the aquifer. The spatial patterns of fresh and saline groundwater discharge and mixing processes within mangrove wetlands as shown in this study may have implications for mangrove tree nutrient availability and for the prevalence and spatial distribution of mangroves along coastlines.

Spatio-Temporal Changes of Mangrove-Covered Tidal Flats over 35 Years Using Satellite Remote Sensing Imageries: A Case Study of Beibu Gulf, China

Tidal flats provide ecosystem services to billions of people worldwide; however, their changing status is largely unknown. Several challenges in the fine extraction of tidal flats using remote sensing techniques, including tide-level and water-edge line changes, exist at present, especially regarding the spatial and temporal distribution of mangroves. This study proposed a tidal flats extraction method using a combination of threshold segmentation and tidal-level correction, considering the influence of mangrove changes. We extracted the spatial distribution of tidal flats in Beibu Gulf, Southwest China, from 1987 to 2021 using time-series Landsat and Sentinel-2 images, and further analyzed the dynamic variation characteristics of the total tidal flats, each coastal segment, and the range of erosion and silting. To quantitatively investigate the interaction between tidal flats and mangroves, this study established a regression model based on multi-temporal tidal flats and mangrove data. The results indicated that the overall accuracy of the tidal flat extraction results was 93.9%, and the kappa coefficient was 0.82. The total area of tidal flats in Beibu Gulf decreased by 130 km2 from 1987 to 2021, with an average annual change of −3.7 km2/a. In addition, a negative correlation between the tidal flat change area and mangrove change area in Shankou, Maowei Sea, and Pearl Bay was observed, with correlation coefficients of −0.28, −0.30 and −0.64, respectively. These results demonstrate that the distribution of tidal flats provides a good environment and expansion space for the rapid growth of mangroves. These results can provide references for tidal flats’ resource conservation, ecological health assessment, and vegetation changes in coastal wetlands in China and other countries in Southeast Asia.

Relationship between sediment type, total organic matter, and water quality on mangrove density on Tunda Island, Serang Banten

Environmental conditions that are quite important in the growth of mangroves are the type of sediment, organic matter, and water quality because the organic matter produced can be useful for mangrove fertility. This study aims to determine the type of sediment, the percentage of total organic matter, water quality, mangrove density, and determine the relationship between sediment types, total organic matter, and water quality on mangrove density on Tunda Island, Serang, Banten. This study used a survey method while collecting data using a purposive sampling method. Mangrove density was obtained through the line transect plot method. The sediment type test used the dry sieving method, the total organic matter (BOT) test used the loss on ignition (LOI) method, the statistical test used the multiple correlation method. All data was then analyzed in a quantitative descriptive manner. The results of the study are that the type of sediment in Tunda Island mangroves is dominated by silty sand and sand. The total organic matter contained in mangrove sediments ranges from 2.40% - 3.62% which is included in the moderate to high category. Salinity values ranged from 31 - 34.33 ppt included in the high category. The pH value ranges from 7.33 - 7.70 which is included in the good category for mangrove growth. Temperature values ranging from 27.37oC - 31.63oC are included in the good category for mangrove growth because they can still grow and develop normally. The mangrove density level is dominated by the dense category, which is 2,400 ind/Ha at station 1 and 1,700 ind/Ha at station 2, and the rare category is 1,000 ind/Ha at station 3 and 900 ind/Ha at station 4. There is a significant relationship between sediment type, total organic matter, water quality with mangrove density.Keywords: BOT; Mangroves; Sediment; Water Quality

Flexitraits, Natural Chemical Tracers of Plant Competition and Productivity in Pacific Mangroves

Metabolomic and genomic markers in plants have helped diagnose evolutionary pressures and resulting modern-day floristic diversification. Here we use a different set of metrics, 17 biochemical measures made at the whole tissue or bulk tissue level, to study diversification in resource use and productivity among Pacific mangroves. Three mangrove species Bruguiera gynmorhiza (BRGY), Rhizphora apiculata (RHAP), and Sonneratia alba (SOAL) were studied across 5 sites on the island of Kosrae, Federated States of Micronesia with measurements of the following chemical metrics: C, N, P, K, Na, Mg, Ca, B, S, Mn, Fe, Cu, Zn elements and isotope values δ2H, δ13C, δ15N, and δ34S. Species were remarkably distinct in chemical profiles, showing significant differences across all metrics. This indicated long-term resource use partitioning and optimization, with metrics showing physiology and patch-related differences. The patch-related differences meant that metrics were not really fixed in species, but represented flexible traits (“flexitraits”) in fingerprinting mangrove ecology. Effects of tree harvesting could be fingerprinted with the metrics at one of the Kosrae sites. Modeling showed two results. (1) Conservation efforts to preserve low-nutrient specialists like BRGY probably should involve removal of competing SOAL and RHAP rather than nutrient reductions. (2) Although mangrove growth rates were most limited by P, water was a strongly co-limiting factor. This study introduces a new physiological parameter to plant ecology, a water-to-phosphorus ratio, “normalized δ13C/P” or “f13C/P”, that should generally help diagnose how plant N and P nutrient use can be co-limited by water.