Gei Wai Research Articles

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.

Spatial ecology of little egret (Egretta garzetta) in Hong Kong uncovers preference for commercial fishponds.

Many natural wetlands have been converted to human-influenced wetlands. In some instances, human-influenced wetlands could provide complementary habitats for waterbirds, compensating for the loss of natural wetlands. Inner Deep Bay in Hong Kong is composed of both natural and human-influenced wetlands and is under immense development pressure. From an ecology perspective, we need to understand if different wetland types play the same ecological role. To achieve this, we tracked nine little egrets (Egretta garzetta) using GPS loggers for 14 months to study their spatial ecology, home range, movement and habitat use. We found that over 88% of the home range of all individuals comprised of wetlands (commercial fishponds, mangrove, gei wai, channel, and intertidal mudflat). Among these wetland types, nearly all (seven of nine) individuals preferred commercial fishponds over other habitats in all seasons. Little egrets exhibited seasonal movement and habitat use among seasons, with largest home range, greatest movement, and most frequent visits to commercial fishponds in winter compared to spring and autumn. Our results highlight the significant role of commercial fishponds, providing a feeding ground for little egrets. However, other wetland types cannot be ignored, as they were also used considerably. These findings underscore the importance of maintaining a diversity of wetland types as alternative foraging and breeding habitats.

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

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

Impact of habitat management on waterbirds in a degraded coastal wetland

The loss of coastal wetlands in Hong Kong Mai Po Nature Reserve adversely affected wetland-depended species. To mitigate this impact, gei wai ponds were reconstructed according to a set of biodiversity management zones (BMZs). This study, based on Canonical Correspondence Analysis (CCA), investigated if waterbird distribution was related to BMZ characteristics. Based on habitat characteristics, ponds in the same BMZ generally clumped in the same quadrant or within a short distance on CCA scatter plots, indicating that a BMZ zone produced common habitat traits. Ponds in a close distance on the plot had similar bird abundance or community structure. Significant correlations were noted between the abundance of cormorants and tall tree, and between waders and bare ground areas within study ponds. This study indicated that the control of key habitat factors was important for the success of reconstruction of gei wais and management of waterbirds in Mai Po.

Effects of mangrove forest on the biodiversity of macrobenthos under the condition of severe water pollution

AbstractAlthough it is clear that mangrove (MG) forests have a positive effect on macrobenthos diversity in wetland ecosystems, these effects are not very clear under the condition of severe water pollution. The objective of this study is to investigate the effects of MG forests on macrobenthos diversity under severe water pollution in Shenzhen Bay, where water quality is strongly affected by industry and urbanization. For this purpose, we carried out a field study from December 2009 to July 2011 in the MG wetland in Shenzhen Bay, the only MG wetland located near a metropolis in mainland China. Samples were taken monthly from four habitats, namely, a reed fish pond, Gei wai ponds, mudflats and an MG forest. The results show that the seawater in all four habitats is severely polluted, and the total N, NO3‐N, total phosphate, Cd, Pb and chemical oxygen demand are well over the Chinese national class IV level. The high level of organics (chemical oxygen demand and soil organic matter) and nutrients (nitrate nitrogen) has a significant positive influence (P < 0.05) on the density and biomass of macrobenthos but a negative influence (P < 0.05) on the diversity of the macrobenthos community. Despite the fact that the levels of organics and nutrients were also high in the MG habitat, the species biodiversity was also the most abundant of the four investigated habitats. This suggests that MG habitats have a remarkable positive effect on maintaining biological diversity compared with other habitats. Therefore, we suggest that efforts should be made to strengthen the protection of MG forests to maintain their biological diversity and promote a healthy ecological system. Copyright © 2014 John Wiley & Sons, Ltd.

深圳湾不同生境湿地大型底栖动物次级生产力的比较研究

Secondary productivity is an important indicator of the variation of the structure,function and stability of an ecosystem.The goal of this study was to test the hypothesis mangrove habitat promotes the production of macrobenthos and increases ecosystem stability under the influence of urbanization.We collected samples monthly in four basic habitats,Phragmites communis reed beds with frequently inundated soil(reed beds),gei wai ponds,mudflats,and mangrove habitat,and analyzed the secondary productivity of macrobenthos,the production/biomass(P/B) ratio,and the dominance and the diversity of macrobenthos from January to December of 2010.The results show secondary productivity in these four habitats varied widely.The secondary productivity in reed beds,gei wai ponds,mudflats,and mangrove habitat was 6.81,147.50,74.70,and 105.78 g · m-2 × a-1,respectively;and the P/B ratios were 1.10,1.53,1.41,and 3.58 a-1,respectively.Secondary productivity in the mangrove habitat was only lower than in the gei wai ponds,while mangroves had the highest P/B ratio,meaning the turnover rate was fastest.The seasonal variation of secondary productivity among the four habitats also varied;gei wai ponds had the highest secondary productivity and it remained relatively stable all year.The other three habitats had the same trend with secondary productivity high in spring and autumn,and lowest in summer.The seasonal variation of the P/B ratio in geiwai ponds and reed beds was relatively stable,while the mangrove and mudflat habitats had the same trend with higher P/B in spring and autumn,and lowest in summer.The species composition and dominance in the four habitats were significantly different seasonally.Reed beds were dominated by two gastropods,Cerithidea cingulata in spring and summer,and Melanoides tuberculata in winter.The gastropod Sermyla riqueti dominated gei wei ponds all year.The dominant species of mudflats were Nereis glandicincta in summer,S.riqueti in autumn,S.riqueti and Cipangopaludina chinensis in winter.Mangroves were dominated by Ellobium aurismidae in summer and autumn and Uca urvillei in winter.The macrobenthic diversity also varied seasonally in the four habitats.The level of biodiversity in the four habitats was mangrove mudflats gei wai ponds reed beds,with mangroves having the highest diversity in all four seasons.The seasonal variation of macrobenthic diversity in gei wai ponds and reed beds was relatively stable,while the mangrove and mudflat habitats had the same trend with lowest biodiversity in summer and higher in autumn,that may be resulted by tropical storm.The increase of macrobenthic productivity,the P/B ratios and biodiversity in the autum than in the summer is bigest in mangrove habitat.Based on the analysis of the macrobenthic productivity,the P/B ratios,and the seasonal variation of the macrobenthic dominance and diversity,we concluded the mangrove habitat had the highest biodiversity,ecosystem resistance to change and resilience,and conclude the mangrove ecosystem was the most stable ecosystem.Above all,the mangrove habitats played a significant role in promoting species diversity for macrobenthos,improving the turnover rate,and in increasing both ecosystem nutrient retention and stability which reduced urbanization threats to the health of the ecosystem.

Wetland changes and mangrove restoration planning in Shenzhen Bay, Southern China

Mangrove forests and associated gei wai (excavated ponds used for shrimp and fish farming) provide important ecosystem services in Shenzhen Bay. Much of the mangrove and gei wai wetlands, however, have been lost because of intensified human activities in the past 30 years. Using five-phase remote-sensing images, we describe the recent history of the spatial–temporal dynamics for the wetlands in the bay. From 1986 to 2007, mangrove area increased from 1.8 to 4.8 km2, while the area of gei wai decreased from 36.6 to 17.2 km2. Reclamation of gei wai mainly occurred in western and northern Shenzhen Bay, and changed the tidal water environment. The bay has five typical mangrove communities: Avicennia marina + Kandelia candel + Aegiceras corniculatum, Kandelia candel + Aegiceras corniculatum + Acanthus ilicifolius, Bruguiera gymnorrhiza + Excoecaria agallocha, Aegiceras corniculatum, and Sonneratia apetala + Sonneratia caseolaris. The distribution of these communities and their dominant species in the bay exhibit a spatial pattern and temporal (successional) sequence. We describe a mangrove restoration program based on the mangrove successional sequence and the interaction of mangrove and gei wai in the bay. We have planned six mangrove protection and restoration projects in closed areas, semiclosed areas, and open areas to reconstruct the ecological integrity of the entire Shenzhen Bay.

Ecotoxicological study on sediments of Mai Po marshes, Hong Kong using organisms and biomarkers

Sediments from Mai Po Ramsar site, Hong Kong were in general shown to be highly toxic based on the results of four toxicity tests (Microtox ® solid-phase test, Daphnia mortality test, algal [ Microcystis aeruginosa] growth inhibition test and ryegrass [ Lolium perenne] seed germination/root elongation test). Sediment of the mudflat (which is open to Deep Bay, i.e., the pollution source) was the most toxic while sediment of gei wai 24g (an enclosed freshwater pond) was the least toxic. Results of biomarker studies (tilapia hepatic metallothionein; glutathione (GSH) and EROD activity using H4IIE rat hepatoma cell) were also concordant with those in the toxicity tests. Significant liner relationships ( p<0.01) were found between GSH contents in the rat hepatoma cells and PAHs, OCPs contents in the sediment extracts. It is recommended that the present suite of bioassays is useful and is biologically relevant for future ecotoxicological studies focusing on similar wetlands.

Distribution patterns of polycyclic aromatic hydrocarbons (PAHs) in the sediments and fish at Mai Po Marshes Nature Reserve, Hong Kong

Sediment samples were collected monthly from eight shrimp shallow ponds (local name gei wais) from July 2003 to January 2004, and from mangrove swamps and inter-tidal mudflats in July and November 2003, respectively. Fish samples (tilapia) were also collected. Polycyclic aromatic hydrocarbons (PAHs) were analyzed by gas chromatography and mass spectrometry (GC/MS). The results indicated that under wet season wet deposition and suspended particulates brought in by nearby rivers, such as the Peal River, served as an important source of PAHs entering Mai Po Marshes. Total organic matter in the sediments showed significant correlations ( p<0.01) with PAHs in the sediments, mainly due to the mechanism that organic matter such as humic substances increased PAH persistence by binding and occluding PAHs. Except for naphthalene, biota-sediment accumulation factors (BSAF) of the PAHs in tilapia were below 1.7, which may be caused by biotransformation and the lower uptake in fish. In addition, aqueous route dominated accumulation of non-biodegradable PAHs in tilapia because higher levels were detected in larger fish than in smaller ones. A general trend was observed that BSAFs declined with the increase of K ow values, which suggested that bioavailability of low K ow isomers was high due to higher gill transfer efficiencies (aqueous uptake) in fish but enhanced biotransformation and decreased gut assimilation (dietary uptake) resulted in decreased accumulation of more hydrophobic PAHs (high K ow). Lastly, viscera appeared to be a promising tissue for biomonitoring, as it contained much higher concentrations than the muscle (3.5 magnitudes), and the levels in the muscle were significantly correlated with those in the viscera ( r 2=0.938, p<0.0001).

Risk assessment of heavy metal contamination in shrimp farming in Mai Po Nature Reserve, Hong Kong

An ecological survey was carried out to determine the sediment concentrations of nutrients and heavy metals and bioaccumulation of heavy metals in fish and shrimp including tilapia (Oreochromis mossambicus x O. nilotica), grey mullet (Mugil cephalus), gei wai shrimp (Metapenaeus ensis) and caridean shrimp (Macrobrachium nipponensis) in the traditional tidal shrimp ponds (gei wais) of Mai Po Nature Reserve, Hong Kong. The sediments collected from the landward sites contained higher nutrient contents, as well as zinc (Zn), chromium (Cr), copper (Cu), nickel (Ni) and cadmium (Cd) than those collected from the seaward sites, but vice versa for lead (Pb) and mercury (Hg). However, the concentrations of all metals were exceptionally high in the two sites located outside the reserve, suggesting that waters from Deep Bay might be the possible source of metal contamination affecting the reserve. All metals studied seemed to accumulate in the viscera of fish. Body size was the determining factor for the accumulation of heavy metals in caridean shrimp and gei wai shrimp but not fish. Concentrations of the metals studied in tissues of grey mullet and gei wai shrimp were found to be safe for human consumption. Concentrations of Cr in tilapia whole body (0.68-1.10 mg kg(-1) wet weight) were close to or over the guideline value of 1 mg kg(-1) set by the Food Adulteration (Metallic Contamination) Regulations of Hong Kong. Tilapia flesh and small caridean shrimp collected from gei wais were contaminated by Cr and Pb but still fit for human consumption. Caution is required if large caridean shrimp is to be consumed in large amounts continuously because the concentration of Pb exceeded the maximum permitted concentration (6 mg kg(-1)). The rather high Cr concentrations in tilapia whole body should not be overlooked as the fish will serve as a food source for migratory birds visiting the site.

Nutrient and faecal contamination and retention in wetland enclosures (gei wais) in the Mai Po Marshes, Hong Kong

Nutrient and faecal contamination is an increasing problem to the shrimp productivity and wildlife conservation at the internationally important wetland ecosystems of the Mai Po Marshes (Hong Kong, P.R. China). The present study examined the nutrient status and faecal bacteria loading and potential retention capacity of contaminants of two wetland enclosures. Water in the wetland enclosures was eutrophicated with high concentrations of dissolved inorganic nitrogen (inorg–Ndiss= 15.0 mg l−1) and orthophosphate phosphorus (o-P = 1.89 mg l−1) and was loaded with high levels of faecal coliforms (172 ×103 cfu in 100 ml) and faecal streptococci (1.94 ×103 cfu in 100 ml). The pattern of nutrient enrichment of two wetland enclosures is related to a north-to-south pollution gradient from the Shenzhen River to the wetlands. By retaining tidal water in the wetland for an 8-day period, water quality was greatly improved; NH4–N was removed by 83%, o-P by 45% and faecal bacteria by 100%. This implies a self-purification capability of the wetland enclosures and a potentiality of using them as an alternative sewage treatment.

Ecological risk assessment of polychlorinated biphenyl contamination in the Mai Po Marshes Nature Reserve, Hong Kong

The main objective of the present study was to investigate polychlorinated biphenyl (PCB) contamination in Mai Po Marshes Natural Reserve, Hong Kong. During June–December 1997, samples of sediments and aquatic organisms including fish ( Oreochromis mossambica× O. nilotica, Mugil cephalus) and shrimps ( Metapenaeus ensis, Macrobrachium nipponense), were collected from gei wais and total PCB levels were measured. The concentrations of PCBs in sediments reduced gradually from coastal sites (8.13 ng g −1 dry wt) to landward sites (1.47 ng g −1 dry wt), which suggested that PCBs in Deep Bay waters were the main input source entering the reserve. The calculated PCB concentrations in water were generally safe for aquaculture according to the U.S. EPA guidelines, but PCBs in muscle tissues of grey mullet ( Mugil cephalus) exceeded the guidelines. PCB concentrations (ng g −1 lipid) in tilapia increased with increases in fish body size, which was possibly due to active uptake of PCBs by tilapia. Within the same shrimp species, different sized organisms showed similar PCB contents in lipid, indicating that lipid content rather than body size determined body concentrations. The PCB concentrations in the aquatic organisms in the reserve posed no hazards to birds according to predicted egg toxicity effects. The estimated BSAFs (biota-sediment accumulation factors) obtained in the present study ranged from 1.10 to 2.37, which were similar to the reported value of 2.10 derived from various aquatic biota species.

Contaminant release from sediments in a coastal wetland

The Mai Po Marshes Nature Reserve (Hong Kong) which is one of the most important regional wetland habitats, is under increasing pollution pressure, such that the existence and survival of the natural biota, including many endangered species, is threatened. Water quality in the tidal shrimp ponds (locally called gei wais) of the marshes was so poor, that biological impacts arising from the release of contaminants from the underlying sediments were suggested. A study was conducted to (i) investigate the level of contamination of underlying sediments in Gei wai 13, (ii) examine the effects of environmental factors on the behavior of contaminants in the sediments and (iii) study the toxicity of the sediments. Sediment in Gei wai 13 was contaminated with nutrients and heavy metals, of which nitrogen and phosphorus tend to bind to coarser particles, while copper, nickel and zinc to finer ones (silts and clays). Mobility of nitrogen and phosphorus from the sediment increased with increasing levels of salinity and temperature of the overlying water. In respect of the drying effect, the solubility of nitrogen and phosphorus of air-dried sediments was lower than that of wet sediments. Sediment extract toxicity tests indicate, that the highly contaminated sediment resulted in a low toxic level and toxic responses were detected only by bioassays of amphipods and algae, but not by the Microtox® test. The low toxicity is consistent with the low soluble content of contaminants of pore water and the low bioavailability of contaminants in sediments.

Water quality degradation at the Mai Po Marshes Nature Reserve (Hong Kong) with reference to nutrient enrichment

There are increasing threats from environmental degradation to wetland habitats all over the world and the internationally important wetland ecosystem of the Mai Po Marshes Nature Reserve in the north-west quadrant of Hong Kong (P.R. China) is no exception. Polluted tidal water is channelled from the Deep Bay to the traditional shallow shrimp ponds (gei wais), giving rise to growing concerns of potential pollution impacts on the biodiversity and productivity of the valuable wetlands. The present study assessed the pollution status by nutrient contents and faecal bacterial counts of the waterways which drain the gei wais and evaluated the spatial and temporal variations. Biochemical oxygen demand, total nitrogen, ammoniacal nitrogen, total phosphorus, orthophosphate phosphorus and faecal bacteria counts were generally lower in the channel waters from the middle part of the Marshes than those of the southern and/or northern ends, indicating a distinctive spatial pollution pattern across the Marshes.

Heavy metals in Metapenaeus ensis, Eriocheir sinensis and sediment from the Mai Po marshes, Hong Kong

The Mai Po Marshes Nature Reserve in north-west Hong Kong is a Ramsar site visited by some 60 000 migratory birds each year. Due to increasing industrialization around the Deep Bay area, the environment at Mai Po may be threatened by heavy metal contamination. In this study, concentrations of four heavy metals (chromium, lead, iron and zinc) were determined in sediment samples and in tissues of the commercial shrimp Metapenaeus ensis and the Chinese mitten crab Eriocheir sinensis. Samples were obtained from four gei wais (8, 11, 16/17 and 19) running along a north–south transect within the nature reserve. Measured concentrations (μg metal g −1 dry wt.) in sediment, M. ensis and E. sinensis tissues were: for Cr, 49.6–559.1, 1.5–3.5 and 6.0–6.2; for Fe, 3168.1–15 478.7, 91.8–180.3, 845.2–2304.0, for Pb, 100.5–154.8, 8.4–11.7, 15.9–19.2 and for Zn, 226.4–421.1, 75.5–96.8 and 163.7–187.1, respectively. Concentrations of the heavy metals in M. ensis were all below the legislation limit but those in E. sinensis were slightly in excess. Analysis of variance showed no significant differences between sites in the trace metal concentrations in M. ensis tissues. Significant differences between sites were, however, obtained for Fe concentration in E. sinensis and for concentrations of Fe, Cr and Zn in sediments. Discriminant function analysis on the metal concentrations in M. ensis and E. sinensis tissues separated gei wai 16/17 from the other gei wais, mostly on account of the lead concentration in M. ensis and the Zn concentration in E. sinensis. For the sediment samples, gei wais 8 and 11 were well separated from gei wais 16/17 and 19 with both Cr and Fe concentrations contributing significantly to the discrimination of gei wais.

The population dynamics of Metapenueus ensis (Crustacea: Decapoda: Penaeidae) in a traditional tidal shrimp pond at the Mai Po Marshes Nature Reserve, Hong Kong

The population dynamics of Metapenaeus ensis in a traditional tidal shrimp pond (locally known as gei wai) at the Mai Po Marshes Nature Reserve, Hang Kong, were studied over a 29‐month period. The population of M. ensis was dominated by either one or two age groups throughout the year. Life span was &lt; 16 months. M. ensis is sexually dimorphic in terms of size, with females growing faster and attaining a larger maximum size than males. The sex ratio did not differ significantly from 1:1. The prawns do not mature and reproduce in the gei wai so that the population is sustained by postlarval immigration which begins in June and ends in December, with peaks in August and November. The gei wai population of M. ensis is characterized by slower growth, lower maximum attainable size, shorter life span, reproductive sterility and an incomplete life cycle, as compared with ‘natural’ population in the coastal waters of Hong Kong.