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Abstract

The hotspots for mangrove diversity and plastic emissions from rivers overlap in Asia, however very few studies have investigated anthropogenic marine debris (AMD) pollution in these threatened coastal ecosystems. Despite Hong Kong's position at the mouth of the Pearl River, a major source of mismanaged waste in Asia, the mangroves in Hong Kong have never been extensively surveyed for AMD. Here we assessed the patterns of AMD abundance within 18 mangrove forests across Hong Kong surveying both their landward and seaward zones. We recorded and categorised, according to their material and potential uses, both the amount of debris items and area they covered, to better quantify its potential impact on the mangroves. Across Hong Kong mangroves, the average abundance of debris was 1.45 ± 0.38 (SE) items m⁻², with an average coverage of 6.05% ± 1.59%. Plastic formed a high proportion of AMD accounting for 70.31% by number of items and 49.71% by area covered, followed by glass/ceramics and wood/bamboo. Disposable food packaging, fishing gear and industrial and construction related waste were the major sources of AMD we documented. On average, we recorded about six times more debris items m⁻² at the landward sites than at the seaward one, but these abundances varied between the East and the West coastlines of Hong Kong. Our data confirms the hypothesis that landward areas of mangrove forests act as traps and retain marine borne debris, but they also suggest that direct dumping of waste from the land could represent a serious impact for these forests placed in between the land and the sea. More research is needed to ascertain the impact of land disposed debris on mangrove degradation, and this study strongly advocates for a cultural shift about the perception of these forests by the public.

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... However, our study revealed a significantly higher concentration of litter (15.94 ± 2.86 items/m 2 ) in mangroves of the Mumbai region, than in the previous report by Selvam et al. (2021a) in Mumbai (8.82 ± 3.47 items/m 2 ). Noted litter concentrations of the present study were also higher than those reported by Martin et al. (2019) in the mangrove of the Red Sea (0.66 ± 0.18 items/m 2 ), Arabian Gulf (1.21 ± 0.53 items/m 2 ), respectively, and 1.45 ± 0.38 items/m 2 in Hong Kong (Luo et al., 2022), 1.29 ± 0.67 items/m 2 in Cebu Island, Philippines (Paler et al., 2022). In contrast, overall litter abundance was found to be lower than 12.6 ̶ 73.1 items/m 2 in Penang Island, Malaysia (Yin et al., 2019), 92 ± 28 items/m 2 in Ambon and Baguala Bay, Indonesia (Suyadi and Manullang, 2020), and 27 items/m 2 in Central Java (van Bijsterveldt et al., 2021). ...
... The litter composition from our study well corroborated with the described composition of marine litter in other mangroves around the globe. For example, plastic forms a high proportion of marine debris, accounting for 70.31 % of Hong Kong's mangrove forests (Luo et al., 2022), 70.2 % in Cebu, Philippines (Paler et al., 2022), and 89 % in Indonesian mangrove forests (Winarni et al., 2022). In mangroves of Mahim creek, Mumbai, plastics were the major dominating debris, contributing to 55% ̶ 71 % of total solid waste, followed by synthetic rubber and glass items (Singare, 2012a). ...
... Our results support previous studies that noted mangroves trap floating litter, and complex aerial root systems act as a filter, preventing litter from being moved into the ocean by the flow of tides, currents, and waves (Luo et al., 2022;Luo et al., 2021;Martin et al., 2019;Selvam et al., 2021a). Systematic studies and standardized models on the environmental hazards caused by marine litter/plastics on coastal vegetation, like seagrass, macroalgae, and mangroves, are at a nascent stage. ...
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Mangrove forests occur along ocean coastlines throughout the tropics, and support numerous ecosystem services, including fisheries production and nutrient cycling. However, the areal extent of mangrove forests has declined by 30-50% over the past half century as a result of coastal development, aquaculture expansion and over-harvesting. Carbon emissions resulting from mangrove loss are uncertain, owing in part to a lack of broad-scale data on the amount of carbon stored in these ecosystems, particularly below ground. Here, we quantified whole-ecosystem carbon storage by measuring tree and dead wood biomass, soil carbon content, and soil depth in 25 mangrove forests across a broad area of the Indo-Pacific region--spanning 30° of latitude and 73° of longitude--where mangrove area and diversity are greatest. These data indicate that mangroves are among the most carbon-rich forests in the tropics, containing on average 1,023Mg carbon per hectare. Organic-rich soils ranged from 0.5m to more than 3m in depth and accounted for 49-98% of carbon storage in these systems. Combining our data with other published information, we estimate that mangrove deforestation generates emissions of 0.02-0.12Pg carbon per year--as much as around 10% of emissions from deforestation globally, despite accounting for just 0.7% of tropical forest area.
Article
The mangroves are well known for their ecological services and livelihood support to humankind. The mangrove forest is experiencing extreme pressure due to anthropogenic activities, mainly the debris pollution posing great harm to the mangrove ecosystems. The abundance, sources, and composition of surficial and trapped debris items in the six contiguous mangrove regions of Mumbai were studied by the belt-transect and quadrats method. A total number of 3526 surficial debris items (368 kg) were collected from twenty belt transects. The estimated mean surficial debris was 8.8 ± 3.4 pieces/m2 with a weight of 920 ± 317 g/m2. The mean trapped debris was 35 ± 10 pieces/tree and 2514 ± 758 g/tree. Plastic (62.4%) includes carry bags and food wrappers mainly. Shoreline/recreational activity-based debris (38.9%) and other items (32.7%) contributed significantly to the total debris pollution. The study provides evidence that the mangrove ecosystem acts as a natural filter and trap for coastal water debris. The trapped debris is a potential risk to the mangroves due to the barrier created on the canopy surface for the incident solar radiation utilized for photosynthesis. By conducting the cleaning programs in the mangrove vegetation stretches, the ecological disturbances to the mangrove ecosystems can be minimized. Further, the regular removal of trapped debris will complement coastal pollution management. The data generated from this study will help the policymakers and resource managers about the effective control and management of debris pollution in the mangroves region.
Article
Marine litter in mangroves comes mainly from poor waste management practices and its abundance is increased by natural catastrophes occurrence that affects coastal settlements, as occurred in November-2020, when two hurricanes (ETA and IOTA) destroyed homes and deposited litters in mangroves of the Providencia and Santa Catalina islands, in the Colombian Caribbean. This study aims to assess the litter pollution in mangrove forests of these islands after Hurricane IOTA. Litter pollution was high in mangroves near urban areas and low in mangroves with little urban influence. In three mangrove sectors with high pollution, litter densities of 0.4-1.4 items/m2 and masses of 0.1-1.2 kg/m-2 were determined; the majority were megalitter (sizes >1m). Plastics were the most abundant (>60%). Local community is aware of the litter pollution problem and their participation in scientific research and mangroves recovery is key to understanding the impacts of natural and anthropogenic events and for ecosystem conservation.
Article
We evaluated the status of anthropogenic marine debris (AMD) in two natural mangrove forests on Mauritius, one of which in proximity to human settlement (Mahebourg) and the other more remote (Ferney). AMD was collected monthly from October to December 2018 in 1500 m² at both sites and classified into material composition and their potential sources. In all, 2127 items (150.07 kg) was sampled at Mahebourg and 1098 items (43.71 kg) at Ferney. In line with global studies, plastic made up most of the debris in terms of both count (42.92%, 43.66%) and total weight (40.65%, 32.08%) at Mahebourg and Ferney respectively. Most debris originated from shoreline and recreational activities. This work sets a baseline to assess impacts of AMD on mangroves, public awareness required and future strategies for waste monitoring and management in mangroves that may be applied both locally and on other small islands.
Article
Marine debris and plastic pollution affect all coastal habitats, however coastal debris studies are predominantly performed on sandy beaches. Other coastal habitats, such as mangroves, remain understudied. Eighteen of the top twenty rivers that contribute the most plastic to the ocean are associated with mangroves, but very few of those forests were investigated in terms of plastic debris pollution. Here we discuss the results of the few available studies on macrodebris conducted in mangroves, which show that mangrove debris research is still in its early stages, with many areas of study to be further investigated. Indeed, the distinct structural complexity of mangroves increases their ability to trap debris from both terrestrial, freshwater and marine sources, resulting in impacts unique to the mangrove ecosystem. Our review highlights a significant lack in standardisation across the performed surveys. Here we suggest standardised guidelines for future integrated macrodebris and microplastic studies in mangroves to facilitate comparisons between studies. Such standardisation should prioritize the use of stratified random sampling, the measurement of the area covered by the debris and the abundance and type of macrodebris and microplastics found, in order to assess the ecological impact of macrodebris and its role as source of microplastics for adjacent ecosystems. We also advocate the use of standard categories across studies, based on those identified for surveying other coastal habitats. This review highlights an alarming knowledge gap in extent, sources and overall impacts of marine macrodebris, mainly constituted by plastic, on mangrove forests, which hinders policy making to address this issue. Standardised, reliable and extended research on this aspect of mangrove pollution is needed to manage and protect these endangered vegetated coastal ecosystems.
Article
Crab burrowing activity impacts several important biogeochemical processes within mangrove forests. Burrow morphology has been shown to be variable between brachyuran families, hence the community structure and composition of burrowing crabs may have the potential to impact ecosystems differently. By increasing belowground surface area, volume and bacterial microhabitats, large and complex burrows may differ from smaller and simpler burrows in their impact to nutrient and organic matter distribution. The central aim of this work was to provide a detailed quantification of the scale to which different mangrove crab families impact Hong Kong mangrove ecosystem through their burrowing activities. To achieve this goal, we recorded burrow densities and described specie-specific burrow morphology, through casts and 3D scans, of eight crab species belonging to four families, across three mangrove forests. Where present, the large and complex burrows of Parasesarma bidens (Sesarmidae) increased the total below ground air-sediment surface area per m² by ~190% and accounted for ~1.9% of excavated volume per m³ of mangrove sediment. On average, the burrows of Metaplax spp. (Varunidae) increased the surface area by ~55%, while the ocypodid and dotillid species accounted for a 10–25% increase across sites. Due to its densities and the complexity of its burrows, P. bidens showed to exert a wide impact on Hong Kong mangrove ecosystems unrivalled by other species. By incorporating species-specific burrow characteristics and actual burrow densities, we were able to accurately estimate the differential bioengineering role of the dominant mangrove crab species. Due to the functional role of crab bioengineering, our estimates are critical to assess Hong Kong mangrove ecosystem functioning and health.
Article
Plastic pollution in mangroves located in small islands was not well documented. This study found that mangrove ecosystem in small island was polluted by plastic debris (mainly film: 63% and fiber: 31%). Density of plastic debris in mangrove area was ranging from 10 ± 4 items m-2 to 230 ± 75 items m-2, mean density was 92 ± 28 items m-2. Landward was the most polluted zone mangrove (mean density: 155 ± 58 items m-2) or about 61% of plastic debris was distributed in this zone. This is corresponds to the sources of plastic waste was from land such as households and markets. Mean density of plastic debris was significantly correlated with mangrove health (r2 = 0.59, p = 0.00). This indicated that plastic debris negatively affected mangrove ecosystem directly and indirectly. Effective land-based plastic waste management and actions such as regular beach cleanup are essential to reduce plastic pollution and to ensure mangrove conservation.
Article
Mismanaged plastic waste is transported via rivers or city drains into the ocean where it accumulates in coastal sediments, ocean gyres and the deep ocean. Plastic harms marine biota and may ultimately return to humans via the food chain. Private initiatives proposing to collect plastic from the sea and rivers have gained widespread attention, especially in the media. However, few of these methods are proven concepts and it remains unclear how effective they are. Here we estimate the amount of plastic in the global surface ocean to assess the long-term legacy of plastic mass production, calculate the time required to clean up the oceans with river barriers and clean up devices, and explore the fate of collected plastic waste. We find that the projected impact of both single and multiple clean up devices is very modest. A significant reduction of plastic debris in the ocean can be only achieved with collection at rivers or with a combination of river barriers and clean up devices. We also show that the incineration and production of plastic has a significant long-term effect on the global atmospheric carbon budget. We conclude that a combination of reduced plastic emissions and reinforced collection is the only way to rid the ocean of plastic waste.
Article
Wetlands provide a wide range of ecosystem services, and so their conservation and wise use are receiving increasingly greater attention globally. China has a wealth of wetland ecosystems that are well known as hot spots of biological diversity. China has experienced a serious loss of wetlands owing to rapid urbanisation, population growth and industrialisation. Some of the major threats and challenges to wetlands are related to habitat degradation, loss of biodiversity and weaknesses in their protection and management. In this paper we review the distribution of wetlands in China and discuss the key factors that degrade these wetlands. We further discuss management strategies and make recommendations to strengthen the network of wetlands in China.
Article
Along the Upper Gulf of Thailand, coastal fences and breakwaters have been constructed using bamboo since 2005. Despite their potential benefits, bamboo structures disintegrate within seven years releasing floating debris which severely damages mangrove tree stems. The aim of the study was to investigate whether such stem damage resulted in the decline of Avicennia spp. stands along the Upper Gulf of Thailand. Tree health assessments were conducted to assess the probability of crown dieback in damaged and undamaged trees. Satellite-derived time-series of vegetation indices were used to detect long-term forest decline. In contrast to the unaffected landward mangroves, seaward mangroves were unable to recover from insect-induced defoliation events after the collapse of a nearby fence. Furthermore, there was a significantly higher probability that damaged trees showed signs of moderate-to-severe crown dieback. It is recommended that bamboo fences be secured by replacing individual stems before they become detached.
Article
Plastic pollution in the marine environment is a pervasive and increasing threat to global biodiversity. Prioritising management actions that target marine plastic pollution require spatial information on the dispersal and settlement of plastics from both local and external sources. However, there is a mismatch between the scale of most plastic dispersal studies (regional, national and global) and the scale relevant to management action (local). We use a fine-resolution hydrodynamic model to predict the potential exposure of coastal habitats and species (mangroves, coral reefs and marine turtles) to plastic pollution at the local scale of a management region (the 1,700 km2 Whitsunday Islands, Queensland, Australia). We assessed the potential exposure of mangroves, coral reefs and marine turtles to plastics during the two dominant wind conditions of the region; the trade wind and monsoon wind seasons. We found that in the trade wind season (April to September) all habitats and species had lower exposure than during the monsoon wind season (October to March). In both wind seasons we found a small proportion of coral reef habitat and large area of turtle habitat were in high potential exposure categories. Unlike coral reefs or marine turtles, mangroves had consistent hotspots of high exposure across wind seasons. Local scale management requires data at fine resolution to capture the variability that occurs at this scale. The outputs of our study can inform the development of conservation resources and local scale management action.
Article
Marine plastic waste has become an ever-increasing environmental threat in the world's ocean largely due to their unique properties and ubiquitous occurrence. They include diverse forms of land- and ocean-based sources of plastics and are estimated to account for up to 85% of marine debris worldwide. As secondary pollutants, marine microplastic particles (<5mm) are derived from pellet loss and degradation of macroplastics. Up to now, several reports have proposed negative impacts of both macro-sized and micro-sized plastics on marine biota. As one of the rapidly growing economies, China is the topmost contributor of plastic waste in the world. China's massive impact on the plastic levels of the ocean are a definite cause of concern and is developing multiple economic, environmental and biological complications. The research of plastics impact on coastal environments in China is only incipient. Here we review the available information on plastic waste, their impacts on marine biota and human health, and Chinese government policies and management initiatives. Although Chinese coastal environments (surface water, coastal sediments, water column) are affected by microplastics pollution, both from land-based and sea-based activities, their impacts on marine biota remain to be elucidated. Though national-level policies are modern and well suited for minimizing the impacts of plastic pollution, there is hardly any legislation for containment of microplastic pollution. Our objective is to review and summarize the information about the occurrence, impacts, and management of plastic pollution in the Chinese coastal environments in order to comprehend their widespread repercussions.
Article
Illegal dumping, referring to the intentional and criminal abandonment of waste in unauthorized areas, has long plagued governments and environmental agencies worldwide. Despite the tremendous resources spent to combat it, the surreptitious nature of illegal dumping indicates the extreme difficulty in its identification. In 2006, the Construction Waste Disposal Charging Scheme (CWDCS) was implemented, regulating that all construction waste must be disposed of at government waste facilities if not otherwise properly reused or recycled. While the CWDCS has significantly improved construction waste management in Hong Kong, it has also triggered illegal dumping problems. Inspired by the success of big data in combating urban crime, this paper aims to identify illegal dumping cases by mining a publicly available data set containing more than 9 million waste disposal records from 2011 to 2017. Using behavioral indicators and up-to-date big data analytics, possible drivers for illegal dumping (e.g., long queuing times) were identified. The analytical results also produced a list of 546 waste hauling trucks suspected of involvement in illegal dumping. This paper contributes to the understanding of illegal dumping behavior and joins the global research community in exploring the value of big data, particularly for combating urban crime. It also presents a three-step big data-enabled urban crime identification methodology comprising ‘Behavior characterization’, ‘Big data analytical model development’, and ‘Model training, calibration, and evaluation’.
Article
Summary. Recent work by Reiss and Ogden provides a theoretical basis for sometimes preferring restricted maximum likelihood (REML) to generalized cross-validation (GCV) for smoothing parameter selection in semiparametric regression. However, existing REML or marginal likelihood (ML) based methods for semiparametric generalized linear models (GLMs) use iterative REML or ML estimation of the smoothing parameters of working linear approximations to the GLM. Such indirect schemes need not converge and fail to do so in a non-negligible proportion of practical analyses. By contrast, very reliable prediction error criteria smoothing parameter selection methods are available, based on direct optimization of GCV, or related criteria, for the GLM itself. Since such methods directly optimize properly defined functions of the smoothing parameters, they have much more reliable convergence properties. The paper develops the first such method for REML or ML estimation of smoothing parameters. A Laplace approximation is used to obtain an approximate REML or ML for any GLM, which is suitable for efficient direct optimization. This REML or ML criterion requires that Newton–Raphson iteration, rather than Fisher scoring, be used for GLM fitting, and a computationally stable approach to this is proposed. The REML or ML criterion itself is optimized by a Newton method, with the derivatives required obtained by a mixture of implicit differentiation and direct methods. The method will cope with numerical rank deficiency in the fitted model and in fact provides a slight improvement in numerical robustness on the earlier method of Wood for prediction error criteria based smoothness selection. Simulation results suggest that the new REML and ML methods offer some improvement in mean-square error performance relative to GCV or Akaike's information criterion in most cases, without the small number of severe undersmoothing failures to which Akaike's information criterion and GCV are prone. This is achieved at the same computational cost as GCV or Akaike's information criterion. The new approach also eliminates the convergence failures of previous REML- or ML-based approaches for penalized GLMs and usually has lower computational cost than these alternatives. Example applications are presented in adaptive smoothing, scalar on function regression and generalized additive model selection.
Article
The ecologies of Hong Kong’s mangroves are described in relation to transects undertaken through stands at Mai Po and Lai Chi Wo in the northwestern and northeastern quadrants of this Special Administrative Region, respectively. Also described is the less well-formed mangrove at Hoi Ha Wan also in the northeast. These three stands are important because they are: (i), all situated in protected coastal areas; (ii), representative of, as is described, ecologically dissimilar communities and (iii), all endangered to some extent by various anthropogenic pollutants and land developments, which are also examined. The most recent threat to the mangroves within Hong Kong’s country and marine parks, however, is not, as one might expect, from over-enthusiastic tourism but from small house developments in the village enclaves (tithings) where the mangroves are situated. It is concluded that if Hong Kong’s Small House Policy is not abandoned, mangrove remnants may survive for a while but, one by one, they will disappear as development takes advantage of our collective amnesia and conservation is concerned not with protecting what was but with a degraded what is. It is shown that of all the estimated 107 mangrove stands in Hong Kong (of varying proportions), Lai Chi Wo in the Plover Cove Country Park, because of its remoteness, exhibits a virtually intact transition from landward subtropical forest to seaward seagrasses. It is likely that this is the most intact mangrove in all of China and is herein recommended for World Heritage Site designation.
Article
Floating and stranded marine debris is widespread. Increasing sea-levels and altered rainfall, solar-radiation, wind-speed, waves and oceanic currents associated with climatic change, are likely to transfer more debris from coastal cities into marine and coastal habitats. Marine debris causes economic and ecological impacts, but understanding the scope of these requires quantitative information on spatial patterns and trends in amounts and types of debris at a global scale. There are very few large-scale programmes to measure debris, but many peer-reviewed and published scientific studies of marine debris describe local patterns. Unfortunately, methods of defining debris, sampling and interpreting patterns in space or time vary considerably among studies, yet, if data could be synthesized across studies, a global picture of the problem may be avaliable. We analyzed 104 published scientific papers on marine debris in order to determine how to evaluate this. Although many studies were well designed to answer specific questions, definitions of what constitutes marine debris, the methods used to measure and the scale of scope of the studies means that no general picture can emerge from this wealth of data. These problems are detailed to guide future studies and guidelines provided to enable the collection of more comparable data to better manage this growing problem.
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Plastic debris in the marine environment is widely documented, but the quantity of plastic entering the ocean from waste generated on land is unknown. By linking worldwide data on solid waste, population density, and economic status, we estimated the mass of land-based plastic waste entering the ocean. We calculate that 275 million metric tons (MT) of plastic waste was generated in 192 coastal countries in 2010, with 4.8 to 12.7 million MT entering the ocean. Population size and the quality of waste management systems largely determine which countries contribute the greatest mass of uncaptured waste available to become plastic marine debris. Without waste management infrastructure improvements, the cumulative quantity of plastic waste available to enter the ocean from land is predicted to increase by an order of magnitude by 2025. Copyright © 2015, American Association for the Advancement of Science.
Article
AimTo reassess the capacity of mangroves for ecosystem services in the light of recent data. LocationGlobal mangrove ecosystems. Methods We review four long-standing roles of mangroves: (1) carbon dynamics – export or sink; (2) nursery role; (3) shoreline protection; (4) land-building capacity. The origins of pertinent hypotheses, current understanding and gaps in our knowledge are highlighted with reference to biogeographic, geographic and socio-economic influences. ResultsThe role of mangroves as C sinks needs to be evaluated for a wide range of biogeographic regions and forest conditions. Mangrove C assimilation may be under-estimated because of flawed methodology and scanty data on key components of C dynamics. Peri-urban mangroves may be manipulated to provide local offsets for C emission. The nursery function of mangroves is not ubiquitous but varies with spatio-temporal accessibility. Connectivity and complementarity of mangroves and adjacent habitats enhance their nursery function through trophic relay and ontogenetic migrations. The effectiveness of mangroves for coastal protection depends on factors at landscape/geomorphic to community scales and local/species scales. Shifts in species due to climate change, forest degradation and loss of habitat connectivity may reduce the protective capacity of mangroves. Early views of mangroves as land builders (especially lateral expansion) were questionable. Evidence now indicates that mangroves, once established, directly influence vertical land development by enhancing sedimentation and/or by direct organic contributions to soil volume (peat formation) in some settings. Main conclusionsKnowledge of thresholds, spatio-temporal scaling and variability due to geographic, biogeographic and socio-economic settings will improve the management of mangrove ecosystem services. Many drivers respond to global trends in climate change and local changes such as urbanization. While mangroves have traditionally been managed for subsistence, future governance models must involve partnerships between local custodians of mangroves and offsite beneficiaries of the services.
Article
Surveys of stranded marine debris around Motupore Island, a small island in Bootless Bay, Papua New Guinea, revealed exceptionally high loads (up to 78.3 items m(-2)), with major concentrations in mangrove-dominated, depositional areas. The worst affected, 50-m stretch of shore was estimated to contain >37.000 items with a combined weight of 889 kg. Consistent with studies elsewhere, plastics comprised by far the majority of debris across all sites (89.7%). The lack of centralised waste collection and limited village-based resources, coupled with an increasing population, suggests that this issue is a long way from solution. High debris loads thwart attempts to rehabilitate depleted mangrove forests through smothering of seedlings, perpetuating run-off and water quality issues in the bay. Addressing marine debris is thus of fundamental importance for the sustainability of Bootless Bay and its resources, and a critical step in promoting ecosystem resilience.