Mai Po Research Articles

Biogeochemical controls on methylmercury distribution in a subtropical wetland ecosystem

Wetlands are widely regarded as biogeochemical hotspots of mercury methylation but little is known regarding such roles of mangrove forests. Here, we examined the detailed depth profile of mercury, methylmercury, and organic matter in surface sediments within an estuarine pond at Mai Po Nature Reserve in Hong Kong, China. There is a progressive enrichment of organic matter in sites closer to mangrove forests, and methylmercury showed a significantly positive correlation with organic matter content (p < 0.001). Methylmercury in sediments is significantly (p < 0.05) higher in the summertime when the temperature is elevated but salinity is reduced. Further, sediments at or near the mangrove forest have lower carbon to nitrogen ratio, which may imply more labile organic matter in these organic-rich sediments that can promote microbial mercury methylation. In summary, mangrove forests can enhance net methylmercury production and increase the risk to the migratory birds overwintering in this internationally important wetland.

Mercury contamination is an invisible threat to declining migratory shorebirds along the East Asian-Australasian Flyway

Exposure to pollutants is a potentially crucial but overlooked driver of population declines in shorebirds along the East Asian-Australasian Flyway. We combined knowledge of moult strategy and life history with a standardised sampling protocol to assess mercury (Hg) contamination in 984 individuals across 33 migratory shorebird species on an intercontinental scale. Over one-third of the samples exceeded toxicity benchmarks. Feather Hg was best explained by moulting region, while habitat preference (coastal obligate vs. non-coastal obligate), the proportion of invertebrates in the diet and foraging stratum (foraging mostly on the surface vs. at depth) also contributed, but were less pronounced. Feather Hg was substantially higher in South China (Mai Po and Leizhou), Australia and the Yellow Sea than in temperate and Arctic breeding ranges. Non-coastal obligate species (Tringa genus) frequently encountered in freshwater habitats were at the highest risk. It is important to continue and expand biomonitoring research to assess how other pollutants might impact shorebirds.

Salinity, mineralogy, porosity, and hydrodynamics as drivers of carbon burial in urban mangroves from a megacity

Mangrove ecosystems are an important blue carbon store but exhibit considerable variation in soil carbon stocks globally. Unravelling the conditions controlling carbon stock is critical for assessing current and future carbon budgets. Mangrove soil biogeochemical cycles can strongly influence carbon storage capacities. We thus investigated carbon sequestration and the environmental parameters shaping variability in biogeochemical cycling and carbon storage in sediment samples from four mangrove sites along an estuarine-to-marine gradient in Hong Kong, a megacity. Our results showed that organic matter in Hong Kong mangroves is sourced principally from autochthonous mangrove plants. Total nitrogen was higher in the freshwater-influenced sites and supplied from different sources. Marine-influenced sites had larger sulfur fractionations, reflecting higher marine-sourced sulfate concentrations and indicating a relatively open sulfate system. We estimated an average organic carbon stock of 115 ± 8 Mg C ha−1 in the upper 100 cm soil layer placing Hong Kong mangroves at the lower end of the global spectrum of the soil carbon stock. Carbon accumulation was found to be driven by a combination of higher total organic matter inputs, soil fluxes, and porosity. Notably, despite having the highest mass-specific soil organic carbon contents, Mai Po had the lowest integrated soil organic carbon storage (77 ± 3 Mg C ha−1). This was primarily due to lower sediment density and higher tidal pumping leading to a decrease in carbon retention. Total organic matter input, sediment characteristics, and hydrodynamics were the main factors influencing soil organic carbon storage. Overall, our results suggest that (1) while multiple parameters can enhance soil organic carbon content and increase carbon storage capacities, (2) hydrodynamics and sediment characteristics can increase the potential for leakage of carbon, and (3) high carbon content does not always equal high carbon sequestration and stock.

Analysis of a 131-year longitudinal dataset of the Eurasian otter Lutra lutra in Hong Kong: implications for conservation

AbstractHong Kong is one of the busiest metropolises, and the Eurasian otter Lutra lutra is one of its most threatened species. We collected published data for 1890–2020 to document changes in local otter abundance and distribution over time. The 108 records revealed new distribution data and showed that decline began as early as the 1930s. The local Eurasian otter is strongly associated with coastal and alluvial wetlands, and its last refugium, the Yuen Long floodplain draining the Mai Po Inner Deep Bay Ramsar Site, has always been a critical habitat. Our analysis suggests that hunting is unlikely to be a major cause of the otter's decline. Rather, dependence on lowland wetlands makes it particularly susceptible to habitat loss caused by increasing urbanization. Auxiliary infrastructures and water pollution have also exacerbated wetland degradation to the detriment of otters and their prey. There is a need for greater cooperation amongst government agencies and landowners to guarantee otter survival: priority steps include the establishment of additional and interconnected wetland reserves, better stakeholder engagement and enforcement efficiency to tackle entrenched pollution problems, and flood prevention schemes that preserve or restore functional riverine ecosystems within critical otter habitats. The current otter distribution range has been earmarked for development in a government-led mega urbanization plan; the plight of the local Eurasian otter needs to be widely publicized to garner stakeholders' support and galvanize immediate conservation actions across society.

Multiple drivers for carbon stocks and fluxes in different types of mangroves

Mangroves are highly efficient in sequestering carbon from the atmosphere and can accumulate carbon in sediments for millennials. However, The fate of mangrove carbon has not been well constrained due to the lack of data on different pools of sediment carbon sinks and sources. This study examined the variation of carbon stocks and fluxes at the water-sediment-air interface in both estuarine mangroves (natural: Mai Po, restored: Gei Wai) and oceanic mangroves (Ting Kok). There are divergent patterns in biogeochemical variables at the sediment-water-air interface, likely due to significant variation within sites. Total sediment carbon stocks (TCs) ranked in the order of restored estuarine mangroves (392.5 ± 8.8 Mg ha−1), natural estuarine mangroves affected by aquaculture (315.2 ± 21.4 Mg ha−1) and oceanic mangroves (229.1 ± 32.3 Mg ha−1). Sediment organic carbon stocks (SOC) and inorganic carbon stocks (SIC) accounted for 84.1–90.2 % and 9.8–15.9 % of TC, respectively. The highest sediment-air CO2 and CH4 fluxes occurred in restored and natural estuarine mangroves affected by aquaculture, respectively. The isotope of CO2 fluxes (δ13C-CO2) indicates higher contributions from the degradation of mangrove-derived organic carbon in restored (−25.94 ‰ ± 3.37 ‰) and natural estuarine mangroves affected by aquaculture (−25.54 ‰ ± 0.96 ‰) than in oceanic mangroves (−21.55 ‰ ± 1.36 ‰). The isotope of CH4 fluxes (δ13C-CH4) indicates CH4 production dominated by acetate fermentation in restored estuarine mangroves but dominated by the reduction of CO2 for other sites. Future studies should better constrain the fate of mangrove carbon by considering local drivers.

Combining multi-temporal airborne LiDAR and Sentinel-2 multispectral data for assessment of disturbances and recovery of mangrove forests

Disturbances such as tropical cyclones and insect pests in mangroves can cause defoliation, tree mortality, and other changes in ecosystem processes. Understanding the resistance and resilience of mangroves to disturbance is critical to developing strategies for conservation. However, most studies apply multi-temporal optical data which have limited power to detect structural changes, especially for forests with complex architectures. We combined multispectral Sentinel-2 (S2) images and airborne LiDAR Scanning (ALS) datasets to assemble a comprehensive view of the effects of two disturbance events (a moth pest and a super-typhoon) on mangroves in Mai Po, Hong Kong. A series of normalized difference vegetation index (NDVI) estimates derived from S2 data indicated changes in greenness before and after the moth pest and typhoon events. An object-based stratification method was applied with ALS data to separate the overstory and understory to distinguish stratum changes. The results showed that moth larvae were more likely to encroach leafy mangroves of Avicennia marina. Double-layered and single-layered short mangroves have better resistance to typhoons than younger tall mangroves without understory beneath. NDVI recovered rapidly after three to six months post-disturbance but significant changes in canopy structures were found from the ALS data. Canopy gaps increased both in size and quantity in mature overstory areas, likely benefitting the growth of the understories beneath. Finally, the understory area grew resulting in a transition from single-layered to double-layered structures. The combination of multi-temporal LiDAR and multispectral data used here highlights the power of complementary remote sensing products in documenting mangrove ecosystem processes.

Intra- and inter-habitat variation in sediment heavy metals, antibiotics and ecological risks in Mai Po RAMSAR, China

Distribution of heavy metals (HMs) and antibiotics (ABs) in surface sediments of three habitats: mudflat, mangrove and gei wai (inter-tidal shrimp ponds), at Mai Po RAMSAR were determined with inductively coupled plasma and liquid chromatograph tandem - mass spectrometry, respectively. Eight HMs (Cr, As, Pb, Cd, Mn, Ni, Cu and Zn), and ten ABs (tetracyclines, quinolones, macrolides and sulphonamides) were detected in all habitats, with relatively lower concentration in gei wai. Ecological risk assessment based on PNEC revealed that HMs posed a higher ecological risk to microorganisms than ABs. All metals except Mn were above their respective threshold effect levels according to sediment quality guidelines, indicating their potential toxicity to benthos. The enrichment factor and geo-accumulation index on background values suggested sediments were moderately polluted by Zn, Cu and Cd, possibly from anthropogenic inputs. This study implies that HMs pollution must be prevented through proper regulation of agricultural and industrial discharge.

Assessment of Active LiDAR Data and Passive Optical Imagery for Double-Layered Mangrove Leaf Area Index Estimation: A Case Study in Mai Po, Hong Kong

Remote sensing technology is a timely and cost-efficient method for leaf area index (LAI) estimation, especially for less accessible areas such as mangrove forests. Confounded by the poor penetrability of optical images, most previous studies focused on estimating the LAI of the main canopy, ignoring the understory. This study investigated the capability of multispectral Sentinel-2 (S2) imagery, airborne hyperspectral imagery (HSI), and airborne LiDAR data for overstory (OLe) and understory (ULe) LAI estimation of a multi-layered mangrove stand in Mai Po, Hong Kong, China. LiDAR data were employed to stratify the overstory and understory. Vegetation indices (VIs) and LiDAR metrics were generated as predictors to build regression models against the OLe and ULe with multiple parametric and non-parametric methods. The OLe model fitting results were typically better than ULe because of the dominant contribution of the overstory to the remotely sensed signal. A single red-edge VI derived from HSI data delivered the lowest RMSE of 0.12 and the highest R2adj of 0.79 for OLe model fitting. The synergetic use of LiDAR metrics and S2 VIs performed best for ULe model fitting with RMSE = 0.33, R2adj = 0.84. OLe estimation benefited from the high spatial and spectral resolution HSI that was found less confounded by the understory. In addition to their penetration attributes, LiDAR data could separately describe the upper and lower canopy, which reduced the noise from other components, thereby improving the ULe estimation.

Characterization and Expression Analysis of Four Cadmium-Tolerance-Associated Genes of Avicennia marina (Forsk.).

Mangroves colonize the intertidal area of estuaries (e.g., Pichavaram, Payardia, and Mai Po) with remarkable cadmium (Cd) pollution. A study on the mechanism of mangrove plant response to Cd pollution can help to understand the adaptive characteristics of plants under Cd stress. This study explored the roles of peroxidase (PRX), pectate lyase (PL), and phytosulfokine (PSK) genes in cadmium tolerance of mangrove Avicennia marina. Full-length sequences of four genes (i.e., AmPRX1, AmPRX2, AmPL, and AmPSK) associated with metal tolerance were identified with suppression subtractive hybridization and rapid amplification of cDNA ends. These genes showed the characteristic features of the respective protein family, indicating functions similar to other plant proteins. Real-time quantitative PCR analysis demonstrated that cadmium exposure resulted in differences in expression patterns among the tissues. Our findings emphasize the complex regulatory mechanism of these four genes in response to trace metal pollution and reveal their functions in metabolic signaling during the stress response.

Spraints demonstrate small population size and reliance on fishponds for Eurasian otter (Lutra lutra) in Hong Kong

AbstractLack of data on population sizes and resource requirements are major impediments to the effective conservation of rare species globally. The conservation of the Eurasian otter (Lutra lutra) in Hong Kong reflects many of these key challenges for elusive and difficult‐to‐study mammals. It is a rare carnivore that has narrowly escaped extirpation, now surviving within a human‐dominated environment. Using sign surveys and spraint analysis, we recorded only 40 fresh spraints from 246 otter signs locations, over 4 months of intensive sampling across 2 years. Records were restricted to the Mai Po wetlands, confirming this as the core area for Hong Kong's otter population. Molecular analysis and microsatellite genotyping identified a minimum of seven individuals, two pairs of which were likely related. The genetic and sign data together strongly indicate a small population. Fish dominated the otter diet, highlighting the importance of fishpond habitats as a premium foraging resource. Given the rapid changes surrounding the Mai Po area (especially the new Northern Metropolis Development Strategy), maintaining quality and connected habitats, in addition to sustaining commercial fishponds will be key to otter recovery and long‐term population viability in Hong Kong.

Sediment carbon sequestration and sources in peri-urban tidal flats and adjacent wetlands in a megacity

We investigated the sediment carbon (C) stocks, sequestration and sources in tidal flats and their adjacent mangroves in two coastal wetlands in Hong Kong (the Mai Po Nature Reserve (MPNR) and Ting Kok (TK)), part of a megacity of ∼20 million. At both locations, the C stock of tidal flats was lower than that of mangroves. In MPNR, tidal flats indicated a higher C burial rate (75.2 g C m−2 yr−1) compared to mangroves (64.3 g C m−2 yr−1). The C of tidal flats mainly originated from mangroves and riverine sources, while those in deeper sediments (below 60 cm) in the mangroves originated from the tidal flats. In TK, the C of tidal flats was dominated by oceanic sources. Our study indicates that tidal flats are also important in coastal C sequestration. On highly urbanized coasts, tidal flats and their connected mangroves can play a critical role for C mitigation.

Seasonal variations of n-damo bacterial community in the subtropical Mai Po mangrove wetland of Hong Kong

Mangrove wetland is one of the most important ecosystems along the coast and often suffers from global climate change as well as the anthropogenic activities. Nitrite-dependent anaerobic methane oxidization (n-damo) bacteria play an important role in linking the microbial geochemical cycles of carbon and nitrogen in the wetlands, but the pattern of their diversity and abundance to a changing mangrove wetland is poorly understood. In the present work, we investigated the seasonal variations of n-damo bacteria in vegetated and non-vegetated sediments of a subtropical mangrove wetland by amplifying 16 S rDNA and pmoA gene sequences. Results indicated that n-damo bacterial communities in the surface sediments maintained freshwater lineage characteristics as the majority after the long rainy season, while the abundance of marine lineages dominated in all the subsurface sediments. Shannon-Wiener and Chao1 indices based on 16 S rDNA gene sequences decreased largely in reed sediments by the end of rainy season, but increased in both surface and subsurface sediments of mangrove and mudflat zones, especially in the non-vegetated surface sediments. The majority of n-damo bacterial pmoA gene sequences shifted from Cluster SCS-2 to Cluster SCS-1 by the end of the dry season. Results suggested that Clusters SCS-1 and SCS-3 would be more likely detected in relatively pristine marine sediments, while Cluster SCS-2 tended to be abundant in coastal habitats with a strong terrestrial/anthropogenic influence. Vegetation had either direct or indirect influence on the decrease of alpha diversity of n-damo pmoA gene when the abundance showed an increase by the end of the wet season. The abundances of n-damo bacteria increased by two orders of magnitude to 5.1–9.4 × 107 copies/g dry sediment after the rainy season. Results suggested that NH4+ and NH4+/NO2− were significant factors governing the diversity of n-damo community in mangrove wetland sediments. The findings of this present work provided an in-depth understanding on the variations of n-damo bacterial community to seasonal changes in the subtropical mangrove wetland.

Distribution pattern of N-damo bacteria along an anthropogenic nitrogen input gradient from the coastal mangrove wetland to the South China sea sediments

Microbial nitrite-dependent anaerobic methane oxidation (n-damo) process is important for mitigating methane emission and anthropogenic nitrogen inputs in the marine environment. However, the distribution pattern of n-damo bacteria along an anthropogenic N-input gradient from the coastal wetland to the pristine South China Sea is poorly understood. This study investigated the diversity and abundance of n-damo bacteria in samples collected along a N-input gradient from Mai Po (MP) mangrove wetland sediments of the Pearl River Estuary (PRE) to the deep ocean sediments of the South China Sea (SCS). Retrieved 16S rDNA sequences showed a shift of n-damo community composition of complex structures with both freshwater and marine n-damo lineages in MP intertidal sediments to marine dominated characteristic in SCS sediments. The observed variation of Shannon and Chao1 indexes of n-damo bacteria shared a similar trend of a decrease at first followed by an increase along the targeting gradient with previously investigated methanogens, anaerobic methanotrophic archaea, ammonia-oxidizing archaea and ammonia-oxidizing bacteria, but had a reverse pattern with anammox bacteria. The community structure of pmoA gene sequences contained freshwater lineages only in SCS continental shelf sediments closer to the PRE, and turned to group with other marine samples in deeper and pristine sediments. Results suggested that n-damo bacteria might be a major contributor to anaerobic denitrification in the SCS sediments because their abundances were much higher than previously studied anammox bacteria in the same sample set. The distribution pattern of n-damo bacterial diversity, richness and abundance along the anthropogenic N-input gradient implies that they could be used as a bio-indicator for monitoring the anthropogenic/terrestrial inputs in marine environments.

The effectiveness of bird hides in mitigating recreational disturbances of birdwatchers

Bird hides are often built to ameliorate the disturbance of birdwatchers at birdwatching sites. However, the effectiveness of such shelters is rarely evaluated. This study investigated the recreational disturbances induced by birdwatchers at Mai Po Nature Reserve in Hong Kong and examined the effectiveness of bird hides in mitigating birdwatcher impacts. A bird disturbance survey was conducted to record the disturbances caused by birdwatchers and responses shown by birds at three sampling sites in Mai Po Nature Reserve. A total of 469 observations were recorded in 25 field days from Oct 2019 to April 2020. The results indicated that bird hides significantly mitigated the frequency of disturbance and level of response of birds. With a bird hide, the frequency of disturbance was lower than the unsheltered site given that both sites have a similar level of visitation, yet, disturbance frequency was not significantly lower if the bird hide was highly utilized by birdwatchers. Birds had shown less vigorous and slower responses to disturbances at sites with bird hides than that without. On the other hand, at those sites with bird hides, birds responded at a farther distance than birds at the unsheltered site, which a longer distance may represent a greater level of disturbance. Upon disturbances, birds at the unsheltered site tended to stay in the original area, while birds around bird hides tend to settle further from the original habitat. Visual disturbances were well avoided at bird hides when compared to an unsheltered environment, however, disturbance from noise was found to be more prevalent at bird hides. Implications of these findings were discussed, and recommendations regarding the use, setting, and design of bird hides, and visitor management were given.

Shifts in phenology of autumn migration and wing length among reedbed passerines along the East Asian–Australasian Flyway

Climate change impacts bird migration phenology, causing changes in departure and arrival dates, leading to potential mismatches between migration and other key seasonal constraints. While the impacts of climate change on arrival at breeding grounds have been relatively well documented, little is known about the impacts of climate change on post-breeding migration, especially at stopover sites. Here we use long-term (11 years) banding data (11,118 captures) from 7 species at Mai Po Marshes Nature Reserve in Hong Kong, a key stopover site for migratory birds along the East Asian–Australasian Flyway, to describe long-term changes in migration phenology and to compare observed changes to annual weather variation. We also examine changes in wing length over a longer time period (1985–2020) as wing length often correlates positively with migration distance. We found that observed changes in migratory phenology vary by species; three species had later estimated arrival (by 1.8 days per year), peak (by 2.6 days per year) or departure (by 2.5 days per year), one showed an earlier peak date (by 1.8 days per year) and two showed longer duration of passage (2.7 days longer and 3.2 days longer per year). Three species exhibited no long-term change in migration phenology. For two of the four species with shifting phenology, temperature was an important predictor of changing peak date, departure dates and duration of passage. Wing length was shorter in three species and longer in two species, but these changes did not correlate with observed phenological changes. The complex changes observed here are indicative of the challenges concerning the detection of climate change in migratory stopover sites. Continued monitoring and a better understanding of the dynamics of all sites in the migratory pathway will aid conservation of these species under global change.

Detecting the non-breeding region and migration route of Whimbrels (Numenius phaeopus rogachevae) in the East Asian–Australasian Flyway

Determining the migration routes and connections of migratory birds at the population level helps clarify intraspecific differences in migration. Five subspecies have been recognized in the Whimbrel (Numenius phaeopus) in Eurasia. Ssp. rogachevae is the most recently described subspecies. It breeds in Central Siberia, while its non-breeding region and migration routes are still unclear. We tracked the migration of Eurasian Whimbrels captured at three non-breeding sites (Moreton Bay in east coast of Australia, Roebuck Bay in Northwest Australia and Sungei Buloh Wetland in Singapore) and two migration stopover sites (Chongming Dongtan and Mai Po Wetland in China). We determined the breeding sites and inferred the subspecies of the tagged birds in the East Asian – Australasian Flyway (EAAF) based on the known breeding distribution of each subspecies. Of the 30 tagged birds, 6 and 21 birds bred in the breeding range of ssp. rogachevae and variegatus, respectively; one bred in the presumed transition area between the breeding range of ssp. phaeopus and rogachevae, and two bred in the region between the breeding range of ssp. rogachevae and variegatus. The birds that bred in the ssp. rogachevae breeding range spent their non-breeding season in the northern Sumatra, Singapore, East Java and Northwest Australia and mainly stopped over along China's coasts during migration. None of our birds bred in the exclusive breeding range of the phaeopus subspecies. Previous studies have predicted that rogachevae whimbrels migrate along the Central Asian Flyway and spend the non-breeding season in West India and East Africa. We found that at least some rogachevae whimbrels migrate along the EAAF and spend the non-breeding season in Southeast Asia and Australia. The ssp. phaeopus is at best sparsely distributed in the EAAF in the west region, or possibly does not occur at all.

Protecting water birds of wetlands: Using toxicological tests and ecological risk assessment, based on metal/loid (s) of water, sediment and biota samples.

Water, sediment and biota (two fish and one shrimp species) samples were collected from rivers, ponds, mudflat and estuaries within the Mai Po Ramsar site in Hong Kong, China, to determine the concentrations of heavy metals/loid (HMs): cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb), zinc (Zn), and arsenic (As). The mutagenicity and toxicity of water and sediment samples were evaluated using Ames test and Microtox® bioassay, respectively. Ecological risk assessments on water birds were also conducted based on HM concentrations in biota, sediment and water samples. In general, results showed that downstream of Shan Pui River and Ng Tung River had relatively higher HM concentrations (e.g. Cu: 0.992-9.49μg/L; As: 0.342-5.83μg/L) when compared with estuaries (Cu: 0.400-3.69μg/L; As: 0.220-0.931μg/L) and ponds (Cu: 0.0402-2.41μg/L; As: 0.0501-2.10μg/L), except Hg and Cd. On the other hand, sediment samples collected from Ng Tung River showed mutagenicity on Salmonella typhimurium tester strain TA100, while the mudflat samples had mutagenicity on tester strain TA98 used in the Ames tests. Microtox® bioassay indicated that only sediment of Ng Tung River showed acute toxicity with a 15min half maximal effective concentration (EC50) value of 30.5%. Results of ecological risk assessments showed that grey heron (Ardea cinerea), which feeds on fish and shrimps at Shan Pui River and ponds were not at risk. However, common sandpiper (Actitis hypoleucos), which feeds at ponds were subjected to a potential health risk due to its behavior of seeking food from the sediments, especially this bird species has a small body size. This indicates juvenile birds of other species may also be affected. Remediation should be implemented to relief the potential risk of Cu and Pb, to these water birds in the Mai Po Ramsar site.

A Thirty-Year Record of PTE Pollution in Mangrove Sediments: Implications for Human Activities in Two Major Chinese Metropolises, Shenzhen and Hong Kong

Sediment cores from four mangroves in two Chinese metropolises, Shenzhen and Hong Kong, were studied to determine historic trends in regional pollution with potentially toxic elements (PTEs). Physicochemical properties, Cr, Ni, Cu, Zn and Pb contents, and their enrichment factors were determined. Correlation analyses and principle component analyses were conducted to investigate natural influences on PTE distribution, while comparisons between PTE trends and industrial activities in the individual regions were conducted to understand anthropogenic influences over the last thirty years in Shenzhen and Hong Kong. Results indicate that grain size composition and organic matter are the main natural factors affecting PTE distribution laterally and vertically. The relationship between PTE pollution and economic development supports the environmental Kuznets curve (EKC) hypothesis. For example, higher PTE levels in developed regions such as the mangroves of Fu Tian and Mai Po are consistent with an early stage of the EKC, where the environment deteriorates due to increased industrial activity. However, sites where PTE levels have decreased in recent years reflect later stages of the EKC, where environmental quality has improved despite continued economic growth. These insights should allow the development of better policies and regulations for environmental protection and sustainable development of coastal cities.

Mini Review on Managing Fishponds to Climate-Proof the Mai Po Inner Deep Bay Ramsar Site, and Implications for the East Asian-Australasian Flyway

Coastal wetlands are important stepping stones and wintering sites for migratory birds along the East Asian-Australasian Flyway (EAAF). But wetlands are being extensively converted throughout Southeast and East Asia, and continued loss can disrupt the long-distance migrations, and result in species population declines and extirpations. Wetlands are also under threat from global climate change; sea level rise can inundate coastal wetlands, and the two forces of coastal development and climate change can subject the remaining wetlands to coastal squeeze. Therefore important wetlands along the flyway should be assessed for the impacts of climate change to implement proactive climate adaptation strategies. The Mai Po Inner Deep Bay Ramsar site in Hong Kong is an important staging and wintering site along the EAAF. A climate model for this wetland showed that by 2100 some of the wetlands and mudflats used by migratory birds could become inundated. In the future, under climate change scenarios, fishponds further inland, now within the ‘wise-use’ compartment of the Ramsar site, could represent supratidal wetlands for migratory birds. Therefore, these fishponds should be maintained and managed without the threat of conversion by providing economic incentives for fishpond operators. This analysis represents a case study for climate proofing the EAAF by engaging fishpond owners and operators for sustained management of coastal fishponds as an integrated approach for wetland management that includes aquaculture, sustainable livelihoods, bird habitat conservation, and climate-proofing coastal areas.

How mangrove plants affect microplastic distribution in sediments of coastal wetlands: Case study in Shenzhen Bay, South China

Microplastic pollution is common in marine and coastal ecosystems, especially in mangrove wetlands. However, factors affecting the distribution of microplastics, such as plants, have not been sufficiently studied. We investigated the effect of different plant species on the distribution of sediment microplastics in two Nature Reserves in South China, viz. Futian Mangrove and Mai Po Mangrove. In Futian Mangrove, the abundance of total microplastics among three monospecific mangrove stands dominated by Sonneratia caseolaris, Kandelia obovata, and Sonneratia apetala was similar. The abundance of microplastics in the mudflat was similar to that in the forest interior, except for the fact that more fiber was found in the mudflat than in the interior of Sonneratia apetala. This suggested that the dense pneumatophores at the fringe prevented fibers from entering the mangrove forest. The significant positive dependence (p < 0.05) between the density of Sonneratia pneumatophores and the abundance of fibers highlighted the importance of pneumatophores. The abundance of total microplastics, predominantly in the form of fibers, in sediments at the forest fringe (2835 ± 713 items/kg d.w. and 2070 ± 224 items/kg d.w. in Futian and Mai Po, respectively) was higher than that in the forest interior and mudflat. There was no difference between the two latter locations in both mangroves, which demonstrated the significance of the fringe effect. This paper reports for the first time that the spatial distribution of microplastics in mangrove sediments was affected by plant species, which provides useful information for environmental processes of microplastics in coastal wetlands.