Tropical Hainan Island Research Articles

Heavy metal migration and lithium isotope fractionation under extreme weathering of basalt on tropical Hainan Island, China

Basalt weathering can cause heavy metal enrichment in soils, and lithium isotopes serve as an effective tracer for this weathering process. However, the relations among weathering intensity, heavy metal migration, and Li isotope fractionation remain unclear. We conducted systematic examinations of a basalt weathering profile on tropical Hainan Island in China. The characteristics of mineralogy, elemental and Li isotopic geochemistry indicate that the profile has undergone changes from initial to advanced and ultimately extreme weathering stages. The corresponding dominant minerals are primary minerals, clay minerals such as kaolin-group, and the Al–Fe–Ti (hydro)oxides. The variations of Fe-group heavy metals within the profile are very similarly to that of Fe, exhibiting a pattern of loss-gain-loss. Newly formed secondary minerals preferentially incorporate lighter 6Li, leading to a gradual increase in Li content and a decrease in δ7Li. Due to the high δ7Li value of rainwater input, the ongoing impact of secondary mineral adsorption is partially counteracted. This results in the δ7Li of laterite and topsoil being maintained within a narrow range (−3.2‰ ∼ −1.9‰), despite the broader variation observed across the entire profile (−3.2‰ ∼ +2.8‰). Comparing basalt weathering profiles in different climatic zones reveals a very complex Li isotope behavior and its controlling factors. Therefore, it is essential to carefully evaluate the influence of atmospheric input, secondary mineral adsorption, dissolution, and redeposition processes on Li isotopes. Throughout the entire profile, Cr, Ni, and Cu exhibit enrichment relative to soil background values, indicating that the weathering of tropical basalt may pose potential environmental risks for these elements.

Second-home Tourism in Tropical China: residents’ perception of socio-economic impacts

ABSTRACT Despite the significant growth of second-home tourism research, its geographical focus remains limited to a few countries. China has become a global economic powerhouse, with a rapidly growing middle class with disposable income. A combination of the latter with a range of favourable socialist housing policies and unique cultural forces have encouraged, and in some cases demanded, multiple-home ownership among Chinese families. At the forefront of this phenomenon are vast numbers of senior snowbirds who have chosen the tropical island of Hainan as the location of their second home. While there has been some investigation around this topic in select locations in China, the academic understanding of this phenomenon remains in its infancy. This paper investigates residents’ perceptions of Haikou, the capital of Hainan Province, regarding the socio-economic impact of second-home ownership on their lives, communities and the city. The results of this study will inform policy recommendations for local government while shedding new light on global narratives on second-home tourism phenomena.

Spatiotemporal pattern of coastal water pollution and its driving factors: implications for improving water environment along Hainan Island, China.

In the context of human activities and climate change, the gradual degradation of coastal water quality seriously threatens the balance of coastal and marine ecosystems. However, the spatiotemporal patterns of coastal water quality and its driving factors were still not well understood. Based on 31 water quality parameters from 2015 to 2020, a new approach of optimizing water quality index (WQI) model was proposed to quantitatively assess the spatial and temporal water quality along tropical Hainan Island, China. In addition, pollution sources were further identified by factor analysis and the effects of pollution source on water quality was finally quantitatively in our study. The results showed that the average water quality was moderate. Water quality at 86.36% of the monitoring stations was good while 13.53% of the monitoring stations has bad or very bad water quality. Besides, the coastal water quality had spatial and seasonal variation, along Hainan Island, China. The water quality at "bad" level was mainly appeared in the coastal waters along large cities (Haikou and Sanya) and some aquaculture regions. Seasonally, the average water quality in March, October and November was worse than in other months. Factor analysis revealed that water quality in this region was mostly affected by urbanization, planting and breeding factor, industrial factor, and they played the different role in different coastal zones. Waters at 10.23% of monitoring stations were at the greatest risk of deterioration due to severe pressure from environmental factors. Our study has significant important references for improving water quality and managing coastal water environment.

First Report of 16SrII Group-Related Phytoplasma Associated with Witches’ Broom Disease on Cowpea (Vigna unguiculata) in Hainan Province, China

Cowpea (Vigna unguiculata L.), a significant vegetable crop in China, holds particular prominence in the tropical island of Hainan. This region serves as the primary production area for the winter cultivation of cowpea. Phytoplasmas are an idiopathic parasitic pathogen and cannot be cultured in vitro. It is mainly transmitted by the insect vectors with the piercing and sucking mouthparts, such as leafhoppers, plant hoppers, and psyllids. (Kumari et al. 2019). On September 11, 2023, typical characteristics of phytoplasma diseases on cowpeas were observed in the experimental base of Hainan Academy of Agricultural Sciences (20°0′38.6964″N, 110°21′35.4024″E, Haikou City, Hainan Province, China), including reduced leaf size, chlorosis, and the development of broom-like branch deformities reminiscent, as depicted in Figure 1. At the same time, we found a large number of leafhoppers near the diseased plants, and we speculated that leafhoppers are the insect carriers that spread the disease. Following an on-site investigation, it was determined that the disease incidence ranges from 10% to 15%, leading to a consequential decrease of about 10% in yield, which is a potential disease that seriously threatens the cowpea industry in Hainan. Ten disease and healthy samples were meticulously collected and subsequently preserved at -80°C within the laboratory refrigerator. Three disease samples denoted as HNNKY-1, HNNKY-2, and HNNKY-3, were randomly chosen, and total DNA extraction was carried out employing the NuClean Plant Genomic DNA Kit (CWBIO, Taizhou, China), while three healthy samples were randomly selected as control. The 16S rRNA gene was amplified by PCR using the primer pairs P1/P7 (Schneider et al. 1995) and R16F2n / R16R2 (Lee et al. 1993) and the secA gene was amplified by PCR using the primer pairs secAfor1/secArev3 (Hodgetts et al. 2008). After agarose gel electrophoresis analysis, no DNA fragments were observed in the healthy leaf samples, whereas all three disease samples yielded amplification products. The PCR products were subsequently sequenced by Hainan Nanshan Biotech Co., Ltd., Haikou, China. After sequence analysis, it was found that the 16S rRNA gene and secA gene sequences HNNKY-1, HNNKY-2, and HNNKY-3 were identical to each other. We selected two gene sequences of strain HNNKY-3 to submission to the GenBank database, The length of the 16S rRNA gene sequence is 1193 base pairs, identified by the accession number OR666421, while the secA gene sequence is 825 base pairs in length, associated with the accession number OR661282. The phytoplasma strain HNNKY-3 was named 'Vigna unguiculata' witches'-broom phytoplasma. A BLAST analysis of the 16S rRNA gene revealed that strain HNNKY-3 displayed a 100% sequence match with 'Emilia sonchifolia' witches'-broom phytoplasma (MT420682), Peanut witches'-broom phytoplasma (OR239773), and 'Raphanus sativus' witches'-broom phytoplasma (OK491387). All of these phytoplasmas were classified within the 16SrII group. Based on the BLAST analysis of partial secA gene sequences, it was discerned that sequence homogeneity ranged from 99.27% to 99.74% among the studied sequences. These sequences were collectively classified as members of the 16SrII group. In addition, a phylogenetic tree was constructed by MEGA 11 (version 11.0.13) based on the 16Sr RNA gene and secA gene by the neighbor-joining method (Tamura et al. 2004). The results demonstrated the clustering of HNNKY-3 phytoplasma strains within the 16SrII group, as illustrated in Figures 2 and 3. A virtual RFLP analysis based on the 16S rRNA gene fragment of HNNKY-3 was conducted using the interactive online phytoplasma classification tool, iPhyClassifier (Zhao et al. 2009). The results indicated that the phytoplasma strain was the same as the reference pattern of the onion yellows phytoplasma of 16SrII-A (GenBank accession: L33765), and the similarity coefficient was 1.00. To best of our knowledge, this is the inaugural documentation of 16SrII Group-related phytoplasma infecting cowpea in Hainan, China, and lays the groundwork for further research on the dissemination of cowpea phytoplasma disease within China.

Streamflow Response to Climate and Land-Use Changes in a Tropical Island Basin

The effects of climate change and of land use/cover change (LUCC) on streamflow as demonstrated by hydrological models are pressing issues on the frontiers of global environmental change research. The Nandu River Basin (NRB) as the largest of three river basins on the tropical Hainan Island, China, is subjected to an analysis of streamflow response to climate and to land-use change. It is based on the Soil and Water Assessment Tool (SWAT) coupled with climate change signals extracted from the global climate model data in the Coupled Model Intercomparison Project Phase 6 (CMIP6) and with land-use change scenarios modeled by Cellular Automata (CA)—Markov. The results are summarized as follows: (1) Climate change contributed more to streamflow change than land-use change in the NRB, with contributions of 97.57% and 2.43%, respectively. Precipitation and temperature were the most important climate variables, contributing 92.66% and 4.91% to streamflow change. (2) In the tropical island basin from 1990 to 2015, LUCC regulated the hydrological processes in the NRB and affected hydrological processes by increasing evapotranspiration and decreasing surface runoff and subsurface flow, which resulted in decreasing streamflow. (3) Under the climate change and land-use change scenarios of the near-term period (2021–2040), the annual streamflow decreased as during the reference period (1995–2014); particularly, it decreased most (−6.16%) on the SSP126 path. These results present a case study for understanding the hydrological cycle of tropical island basins and to provide a theoretical basis for water resources management and regional sustainable development of tropical islands.

Diversity analysis of the endosymbiotic bacterial community in field-collected Haemaphysalis ticks on the tropical Hainan Island, China.

Ticks are important vectors of various pathogens that cause infectious diseases in humans. Endosymbiotic bacteria have been explored as targets for tick and tick-borne disease control. However, the tick bacterial community on Hainan Island, which is the largest tropical island in China and has an environment favourable to ticks, has not yet been studied. In this study, we surveyed the bacterial community of ticks collected from grass in one village in Haikou. A total of 20 ticks were morphologically and molecularly identified as Haemaphysalis spp. The tick bacterial 16S rRNA hypervariable region amplicon libraries were sequenced on an Illumina MiSeq platform. A total of 10 possible bacterial genera were detected, indicating a low-diversity bacterial community profile. The dominant bacterial genus, Massilia, accounted for 97.85% of the population. Some other bacterial genera, including Arsenophonus and Pseudomonas, have been reported to play a role in tick development and tick-borne pathogen transmission in other tick species. Overall, the study highlights the first descriptive understanding of the tick bacterial community on Hainan Island and provides a basis for deciphering the interactions between the tick microbiome and tick-borne pathogens.

Rapid determination and health risk assessment of neonicotinoids in source water and tap water of the tropical Hainan Island, China.

Neonicotinoids (NEOs) pesticides are widely used around the world, especially in the tropics with greater frequency and intensity. However, little is known about NEOs residue in drinking water of tropics. In this study, a highly efficient method using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was established for determining eight NEOs in source water and tap water of Hainan Island, China. The method adopted a high-throughput direct aqueous injection without sample concentration steps, with a rapid analyzing period of 5.0min, method detection limits (MDLs) in the range of 0.84-1.82ng/L and the average recoveries ranged from 83% to 116%. NEOs were detected in all source water samples and at an upper level as compared with other parts of China. The most frequently detected NEO was imidacloprid with a detection frequency of 94%, followed by clothianidin (88%) and thiamethoxam (78%), with maximum concentrations of 86.4, 164, and 188ng/L, respectively. Moreover, seasonal and spatial variations had remarkable impacts on NEO contamination in source water. Drinking water treatment processes removed approximately 20% of NEOs from surface water. However, 90% of tap water samples contained at least one NEO, With 3 samples' concentration of single NEO exceeding the acceptable value recommended by the European Union (100ng/L). Therefore, the risk of human exposure through drinking water was evaluated for 4 age group and 2 genders. Young children aged 9months to 3years old were found to have the highest risk, with the median exposure up to 4 times greater than teenagers and adults. Next, water intake is likely only a small part of the daily intake of these individuals, thus the potential health problems caused by NEOs present in the tap water of Hainan should not be ignored.

Nesting success and potential nest predators of the red Junglefowl (Gallus gallus jabouillei) based on camera traps and artificial nest experiments

Breeding success is an important factor determining fecundity with nest predation being the main factor limiting avian breeding success. Understanding of nest predation and its influencing factors are highly significant to explore the dynamics of bird populations and developing appropriate conservation strategies. In two breeding seasons of the year 2020 and 2021, natural nests of the red junglefowl (Gallus gallus jabouillei) were systematically searched and monitored using infrared camera, in two nature reserves (Datian and Bangxi) of tropical Hainan island, China. Results showed that breeding season of the red junglefowl is mainly from March to July, with April being the breeding peak. The clutch size was 5.15 ± 1.28 (n = 13), and nesting success of natural nests was 31.2%, with nest predation accounting for 45.4% of nest failure. Artificial nest experiments showed that predation rates of artificial nests were 25% (Datian, 2020), 6.67% (Datian, 2021), and 0% (Bangxi, 2020). Rodents, reptiles, and coucals are the main nest predators of red junglefowls, while activities of Hainan Eld’s deers (Panolia siamensis) may interfere with the reproduction of red junglefowls. We suggest that the conservation management policies should consider the impacts on junglefowls’ breeding success when reconstructing the suitable habitat of the Hainan Eld’s deer.

Heavy metal(loid)s in fruit-growing soils of tropical Hainan Island in China: Pollution, ecological-health risks, spatial assessment, and source analyses

Heavy metal(loid)s in fruit-growing soils of tropical Hainan Island in China: Pollution, ecological-health risks, spatial assessment, and source analyses

A knowledge exchange framework to connect research, policy, and practice, developed through the example of the Chinese island of Hainan

Tropical coastal ecosystems face increasingly severe environmental challenges. Promoting evidence-based management is one way to address these. In this paper, we propose a knowledge exchange framework to promote the uptake of scientific evidence by policy and practice and discuss its effectiveness through on-the-ground implementation on the Chinese tropical island of Hainan. The framework comprises four main components: context analysis, framework building, implementation of knowledge brokering strategies, and monitoring and evaluation. This simple and process-centric framework can serve as a tool to facilitate the transition from "traditional" science to "societally-engaged" science. Notable barriers to the successful application of the framework are discussed, specifically the nature of knowledge, the institutional and cultural context, and resource factors. It is also observed that relevant, legitimate, and accessible research evidence and the involvement of a suitable intermediary play essential roles. We conclude that society has to be empowered as a whole, through institutional reforms of research and funding organizations towards providing a broader basis for improved knowledge exchange between science and society. Such a knowledge exchange framework and case study can provide other scientists and stakeholders with a clear, standardized way to connect science, policy, and practice in two-way interactions, which could increase clarity and understanding in the field of knowledge exchange.

Validation of relative pollen productivities for major tropical plant taxa: An empirical test using the REVEALS model in Hainan, China

The reliability of estimates of tropical lowland vegetation cover based on lacustrine pollen records has long been debated. Here, we assess the reliability of relative pollen productivity estimates (RPPs) obtained in tropical Hainan island using surface pollen assemblages from six reservoirs and the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model. The resulting REVEALS estimates are compared to observations of vegetation coverin the studied region and pollen percentages. The REVEALS estimates for most tropical taxa including Poaceae, Moraceae, Euphorbiaceae, Mallotus/Macaranga, Castanopsis/Lithocarpus, were more similar to the observed vegetation cover than estimates based on simple pollen percentages, suggesting that the previously reported RPPs are reliable. The REVEALS estimates for some taxa (i.e. Rubiaceae and Anacardiaceae) are comparable to those based on pollen percentages, but RPPs for these taxa are difficult to evaluate. However, the pollen percentages for some taxa including Asteraceae and Papilionaceae agree better with the observed vegetation cover than the REVEALS corrections, implying either that there are problems with the corresponding RPPs or that there is bias in the observed vegetation data used for validation. We suggest that the reliability of the RPPs for plant taxa in tropical areas depends strongly on their abundance in the pollen and vegetation data: high abundance implies high reliability and vice versa. REVEALS cover estimates for groups of taxa consistently agreed well with observed vegetation cover, suggesting that the REVEALS model can be applied even in tropical regions if individual species are grouped, which may be useful when reconstructing historical landscape changes in tropical Asia.

Lithium isotope behavior under extreme tropical weathering: A case study of basalts from the Hainan Island, South China

Chemical weathering of silicate rocks (especially basalt) is an important sink of atmospheric carbon dioxide, and has an important impact on long-term carbon cycle and storage. Lithium (Li) isotopes have been regarded as a good tracer of chemical weathering, however, the behavior of Li isotopes in tropical settings is poorly understood. In this study, we studied the Li elemental and isotopic variation in the solid weathering products (soil and saprolite) from a highly-weathered (CIA ∼100%) basalt weathering profile (>15 m thick, including soil, saprolite, semi-weathered rock and fresh basalt) on the tropical Hainan Island in South China. The weathering products have 1.99–58.1 ppm Li, mostly below the average fresh basalt value (4.6 ppm, n = 5). The δ7Li values (−14.3 to 8.9‰) of the solid weathering products exhibit complex stratigraphic variation across the weathering profile. The Li and Mn enrichments coincide spatially, with the Mn-rich samples having the highest Li content and lowest δ7Li value. Lithium is enriched in the semi-weathered basalt sample, but its δ7Li value (−2.7‰) is close to that of fresh basalts (0.7–5.3‰, avg. 3.0‰, n = 5). Strontium isotope data show that the weathering profile is affected by marine aerosol input, and the marine strontium may have been leached to the profile bottom or out of it under extreme weathering. Sequential extraction results indicate that Li in the soil, saprolites (lower part), and semi-weathered basalt occurs mainly in the residual phase, while Li in the saprolites (middle part) occurs largely in Fe–Mn oxides. We suggest that Li isotope fractionation in the upper, middle and lower parts of the profile was controlled by, respectively, marine aerosol input and secondary mineral leaching, dissolution/re-precipitation of Fe–Mn oxides, and neoformation of secondary minerals from heavy pore water. Our results show that the preferential light Li isotope uptake by Fe–Mn oxides may have been the main cause for the major Li isotope fractionation in the Wenchang weathering profile.

Closed-Canopy Tropical Forests of Hainan, (China) Are Resilient against Invasive Herbs and Shrubs

The successful establishment of many plants in tropical forests often depends on species-specific adaptations related to light availability and forest successional stage. Species that are present in early successional stages generally do not occur in later successional stages. In this study, we documented the diversity, distribution, and abundance of terrestrial invasive plants across the (sub)tropical island of Hainan, China, and tested the germination of specific invasive plants in forested environments. In 97 transects positioned randomly across the island, we found nine invasive herb and shrub species were present in all human-modified habitats but not in intact forest interiors. In separate forest-specific transects, we documented a sharp drop in the abundance of invasive plants >5 m into the forest. High numbers of invasive plant seeds germinated from the soil seed bank sampled at the forest edge, but very few seeds germinated from soil sampled any distance into the forest. Finally, in experiments with four focal invasive plant species, overall germination rates were low; and much lower in shaded sites compared to full gap sites. In conclusion, our findings demonstrated that invasive herbs and shrubs do not yet form a serious threat to native species in the closed-canopy forests of Hainan.

The Breeding Ecology of the Crested Myna Acridotheres cristatellus on Tropical Hainan Island

Abstract Research into the breeding ecology of birds is key to understanding the evolution of life-history traits and developing effective species conservation measures. We studied the breeding ecology of the Crested Myna Acridotheres cristatellus on tropical Hainan Island, China, throughout the breeding season from March to August in 2018 and 2019. Parents Crested Myna build disk-shaped nests together and take turns to incubate their eggs and feed their nestlings, with a nestling period of 18–22 days. Eggs were pure blue-green, and the clutch sizes were 3–6 eggs (averaging 4). Egg mass, egg size, and egg volume were 6.78±0.50 g, 28.74±1.20 mm×21.13±0.53 mm, and 6.56±0.50 cm3, respectively (N=274). Egg-laying mainly occurred between 0700 to 1000, and the average time for laying one egg was 172.36±28.29 s (N=11). Feeding frequency during the mid-nestling period was significantly higher than in the early periods (N=55). The Crested Myna population on tropical Hainan nested earlier, laid eggs earlier and had a longer breeding period than populations in the temperate zone.

The influence of temperature and precipitation on the vegetation dynamics of the tropical island of Hainan

Understanding how terrestrial ecosystems respond to climate change can help achieve regional sustainability. The normalized difference vegetation Index (NDVI), which is an important vegetation parameter and ecological index, can directly reflect changes in the ecological environment. Based on meteorological observation data and NDVI monitoring data from 2000 to 2018, we explore the impact of climate change on vegetation on Hainan Island. Firstly, by using Mann–Kendall trend detection together with correlation and partial correlation analysis, we analyze the spatial patterns and trends of the NDVI, annual average temperature, and annual precipitation at grid level and also investigate the spatial relationship between the climatic factors and vegetation. The results show that (1) the ecological conditions on Hainan Island are good and the vegetation trends are positive; (2) the air temperature of Hainan Island has a strong positive effect on the NDVI; and (3) precipitation prevents vegetation growth in the rainy season especially in the central parts of the island. This study focuses on the spatiotemporal characteristics and evolution of vegetation and the influence of climate change on vegetation. Our study provides a scientific basis for achieving regional ecologically sustainable development and valuable evidence related to the impact of climate change on vegetation in tropical island regions.

The mediatory roles of species diversity and tree height diversity: Linking the impact of land‐use intensity to soil erosion

AbstractLand‐use intensification has increased soil erosion through biodiversity loss, which affects ecosystem properties and services owing to changes in species compositional and structural diversity. However, information is limited on how land‐use intensity (LUI) affects soil erosion through species compositional diversity, structural diversity and ecosystem properties. In this study we monitored soil erosion in 15 plots over 12 consecutive months on tropical Hainan Island, where land‐use changes and biodiversity loss have been severe. We quantified the direct and indirect effects of LUI, species compositional diversity (plant species diversity and evenness) and structural diversity (tree diameter and height diversity), and ecosystem properties on soil erosion using Bayesian structural equation models (BSEM). The optimal BSEM accounted for 69% of the variation in soil erosion. The LUI did not affect soil erosion directly but showed indirect impacts via species diversity, tree height diversity, and ecosystem properties. Both high species diversity and tree height diversity reduced soil erosion directly and indirectly by promoting root length density (an ecosystem property), but tree height diversity mediated the more important indirect effect of LUI on soil erosion than species diversity and ecosystem properties. We provide evidence for loss of species diversity and tree height diversity as a result of LUI leading to aggravated soil erosion, but the impact of the latter was more serious. Therefore, we emphasize that maintenance of tree height diversity through management practices may be an effective approach to control soil erosion in the context of drastic land‐use changes in tropical areas.

Plant functional diversity mediates indirect effects of land-use intensity on soil water conservation in the dry season of tropical areas

Land-use intensification has led to biodiversity loss, which affects ecosystem properties and services by altering plant functional traits. However, the mechanistic pathways through which land-use intensity (LUI) affects ecosystem services across functional traits and ecosystem properties remain unclear. We studied the relationships among LUI, plant functional traits, ecosystem properties, and soil water conservation in tropical Hainan Island, China, where land-use changes, biodiversity loss, and seasonal drought have had severe impacts. Soil water conservation was represented by two complementary processes, namely soil water retention (SWR) and soil water capture (SWC). SWR and SWC were observed along a LUI gradient after 27 rainfall events (14 light, 10 moderate, and 3 heavy). We quantified the direct and indirect effects of LUI, the community-weighted mean (CWM) and functional divergence (FDvar) of water-related plant functional traits (tree height, leaf thickness, specific leaf area, and leaf dry matter content), and ecosystem properties on SWC and SWR using Bayesian structural equation models. The results showed that LUI did not affect SWC and SWR directly but presented indirect impacts via functional traits and ecosystem properties. Importantly, tree height FDvar mediated the most important indirect effect of LUI on both SWC and SWR. Tree height FDvar indirectly affected SWC through ecosystem properties, while the direction of the effect changed from negative to positive with increasing rainfall intensity, and promoted SWR directly and indirectly by increasing litter fall and soil organic matter. Our results further provide evidence of an indirect effect of LUI on soil water conservation primarily through tree height FDvar. Loss of functional diversity of plant height caused by LUI resulted in a decrease in SWR and SWC, indicating that seasonal drought causes increased impacts. The results emphasize that maintaining functional diversity of tree height in tropical land use is conducive for soil water conservation to mitigate increased intensity of seasonal drought predicted under climate change.

Responses of five submerged macrophytes to NaCl salinity in a tropical mesocosm study

Submerged macrophytes are important primary producers in freshwater ecosystems in tropical zones. Extreme climate events such as strong typhoons in tropical coastal areas are expected to increase in frequency in the near future, which could induce salinity changes and significantly influence aquatic macrophytes. However, few studies have focused on the effects of salinity on submerged macrophytes in tropical zones. Here, we conducted a three-month, tropical-zone mesocosm study to investigate the effects of salinity stress on the growth of five submerged macrophytes (two widely distributed species Stuckenia pectinata and Myriophyllum spicatum and three narrowly distributed species Vallisneria denseserrulata, Ottelia alismoides, and Cabomba caroliniana). Four salinity-level treatments were established, including P0 (control, no addition of NaCl), P2 (salinity of 2 ‰), P5 (salinity of 5 ‰), and PD (dynamic salinity, initial 2 ‰ with monthly salinity increases of 0.5 ‰). We hypothesized that species with broad distribution would better tolerate higher salinity stress compared to species distributed in narrow ranges. Consistently, both S. pectinata and M. spicatum tolerated P5 treatment, and M. spicatum exhibited smaller leaves and a reduced aerenchyma area in the leaf midrib following exposure. Both V. denseserrulata and O. alismoides survived the moderate salinity levels but showed distinct responses to the increase in salinity in regard to growth and reproduction. In conclusion, in tropical Hainan Island, China, we found distinct species-specific responses of the five submerged macrophytes to salinity stress. Those species with broader ecological niches will likely demonstrate better survival under extreme salinity changes in the future.

Emerging contaminants in municipal wastewaters and their relevance for the surface water contamination in the tropical coastal city Haikou, China

Wastewater treatment plants in large urban agglomerations are worldwide among the main sources of emerging contaminants in aquatic systems. The present study is a first comprehensive characterization of potentially harmful emerging contaminants in sewage of a Chinese urban area. The study area Haikou City is located at the coast of tropical Hainan Island. A GC/MS based non-target screening approach for the identification of a wider range of lipophilic to semi-polar organic sewage constituents was applied. Pollution originating from sewage was tracked in the urban coastal waters by using selected source-specific indicators.A set of sewage constituents with a high structural diversity was identified comprising both, industrial and household chemicals. Ingredients of personal care products, pesticides and pharmaceuticals were found, that were rarely reported from other regions of the world. This observation might be attributed to different environmental legislation and consumption habits in China. Exceptionally high concentrations of the illegal drug ketamine with up to 1100 ng L−1 were detected, suggesting its high popularity and consumption rate. Noteworthy, sewage constituents reported here for the first time were the pharmaceuticals marmesin, oxolamine and ansimar also with high concentrations of up to 1200 ng L−1.Elevated concentrations of sewage indicators in the main city area suggest the overflow of the sewage system, in particular in the period of a typhoon event. Tracing the sewage contamination in the surface water system of the coastal urban area of Haikou revealed a lower level of pollution. The concentration ranges point to no acute risks for the coastal ecosystem due to sewage inputs from the city area.Generally, the detected spectrum of municipal emerging contaminants has to be considered for the testing and technical improvement of wastewater treatment techniques, for regular monitoring of the surface water quality and for environmental impact assessment in China. Furthermore, the compound spectrum reported here is a good reference point for the composition of municipal sewage in other emerging economies.

Egg recognition and chick discrimination in colonial breeding birds

Theory predicts that parents will not raise unrelated offsprings. For colonial breeding birds, evolving an ability to recognize their own eggs and chicks can prevent misdirecting parental behaviour. To verify this hypothesis, egg recognition experiments were performed on colonial breeding Chinese pond herons (Ardeola bacchus) and cattle egrets (Bubulcus ibis) in Chengmai and Lingao, tropical Hainan Island, China. Furthermore, a chick discrimination experiment was conducted on Chinese pond herons. In our study area, we did not record conspecific or interspecific brood parasitism in the two heron species. The results showed that Chinese pond herons had similar recognition rates for the four types of experimental eggs and lacked recognition ability. Cattle egrets had variable abilities to recognize different types of foreign eggs and have low egg recognition ability. Chinese pond herons cannot discriminate foreign chicks. Therefore, we suggest that the two species of colonial breeding herons may lack or have low egg recognition ability, and Chinese pond herons show no nestling recognition ability.