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    25 March 2021, Volume 2021 Issue 2 Previous Issue    Next Issue
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    Estuary and Coastal Research
    The distribution of peak wind speeds induced by typhoons along the coasts of the Changjiang Estuary and Hangzhou Bay
    Lu LI, Xiaotao DU
    2021, 2021 (2):  1-11.  doi: 10.3969/j.issn.1000-5641.2021.02.001
    Abstract ( 386 )   HTML ( 697 )   PDF (1647KB) ( 122 )   Save

    In this study, four typical typhoons that significantly affected Shanghai were selected based on their respective intensity and the water level along the Shanghai Coast. The RMW (Radius of Maximum Winds) formula, moreover, was determined using in-situ data from recent typhoons. The typhoon model was built and validated using in-situ wind speeds from the four typhoons selected. The peak wind speed and the forward peak wind speed along the Shanghai Coast were calculated, case by case, during all typhoons over the period from 1949 to 2014 as well as the four typical typhoons selected. Finally, the range and distribution of the peak (forward peak) wind speed were quantitatively studied.

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    Spatial and temporal variations in the residual water level of the Changjiang Estuary and its cause
    Zhengdong YANG, Jianrong ZHU, Yunping SONG, Jinghua GU
    2021, 2021 (2):  12-20.  doi: 10.3969/j.issn.1000-5641.2021.02.002
    Abstract ( 395 )   HTML ( 439 )   PDF (1171KB) ( 156 )   Save

    In this study, we analyzed the spatial and temporal variations in the residual water level of the Changjiang Estuary and evaluated the respective causes. To achieve this objective, we used data from the hourly water level at the Chongxi, Nanmen, and Baozhen hydrological stations in the Changjiang Estuary; daily river discharge levels at the Datong hydrological station; and wind speed and direction at the Chongming eastern shoal weather station in 2016 and 2017. The results showed that the residual water level was the highest at Chongxi station and the lowest at Baozhen station among the three hydrological stations in each month. The drops in residual water level among the hydrological stations became smaller during low river discharge and tended to become larger during high river discharge. Higher levels of river discharge were associated with a larger drop in the residual water level. In 2016, the residual water levels at the Chongxi, Nanmen, and Baozhen hydrological stations were lowest in February with values of 2.09, 1.96, and 1.93 m, respectively; similarly, the residual water levels were the highest in July with values of 2.91, 2.62, and 2.50 m, respectively. The residual water level was mainly affected by river discharge, while the wind was also an important influencing factor in the variations observed. Southerly wind made the residual water level decrease, and northerly wind made it increase. In 2017, the minimum monthly mean residual water level occurred in December with values of 2.04, 1.91, and 1.87 m at the Chongxi, Nanmen, and Baozhen hydrological stations, respectively; this coincided with the lowest annual river discharge observed during the same period. The maximum monthly mean residual water level occurred in October with values of 2.79, 2.58, and 2.49 m at the Chongxi, Nanmen, and Baozhen hydrological stations, respectively. Although the river discharge was lower in October than the one in July by 24214 m3/s, the residual water level was higher in October than that in July. The explanation for this phenomenon is the persistent strong northerly wind observed in middle to late October, which produced strong landward Ekman water transport, and resulted in the water level rise. The spatial and temporal variation in the residual water level of the Changjiang Estuary is remarkable, and should be considered in engineering design and theoretical research.

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    Analysis of the characteristics of the Qingcaosha Reservoir direct saltwater intrusion from the open sea in the Changjiang Estuary
    Yiping ZHU
    2021, 2021 (2):  21-29.  doi: 10.3969/j.issn.1000-5641.2021.02.003
    Abstract ( 435 )   HTML ( 343 )   PDF (1463KB) ( 161 )   Save

    Qingcaosha Reservoir is the main water source for Shanghai, providing approximately 55% of its high-quality raw water needs, and effectively guarantees the safety of water supply for Shanghai. The waters near the Qingcaosha Reservoir experience saltwater spillover from the North Branch into the South Branch; the nearby waters, moreover, suffer from direct saltwater intrusion from the open sea. In this study, a large number of measured salinity data in the upstream and downstream sluice was used to statistically analyze the characteristics of direct saltwater intrusion near the Qingcaosha Reservoir waters in recent decades. The analysis results show that direct saltwater intrusion neat the Qingcaosha Reservoir waters in recent decades was closely related to the river discharge, tide, and wind. There were a total of 16 instances of direct saltwater intrusion at the upstream sluice that occurred from September to March of the following year; likewise, there were a total of 41 instances of direct saltwater intrusion at the downstream sluice that occurred from September to May of the following year. The direct saltwater intrusions at the upstream and downstream sluices appeared primarily in December, January, and February of each year. We found that saltwater intrusions occurred most commonly when the river discharge was less than 18 000 m3/s during neap tide and middle tide (after neap tide) accompanied by persistent northerly or northwesterly winds. We found that the strength and duration of the northerly or northwesterly winds in the days preceding saltwater intrusion had an important role on direct saltwater intrusion.

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    Magnetic properties of particle-sized fractions of sediments in the Changjiang Estuary and neighboring shelf, and its environmental implications
    Can GE, Weiguo ZHANG
    2021, 2021 (2):  30-41.  doi: 10.3969/j.issn.1000-5641.2021.02.004
    Abstract ( 331 )   HTML ( 273 )   PDF (1273KB) ( 117 )   Save

    Twenty-two surface sediments collected from the Changjiang Estuary and neighboring shelf were subjected to particle-size measurements, with the intent of understanding the implications for provenance, transport, and depositional dynamics. The results showed that Changjiang River-derived sediments, relict sands, and Yellow River-derived sediments were the primary sources controlling the magnetic properties of sediments in the study area. The three areas, however, exhibited different spatial distributions. Spatial variations of magnetic parameters, including magnetic susceptibility (χ), saturation isothermal remanent magnetization (SIRM), hard isothermal remanent magnetization (HIRM), and anhysteretic susceptibility (χARM), suggest that sediments from the Changjiang River are transported towards the south and southeast when they move out of the river mouth. According to bi-plots of SIRM versus χ and S-ratio (S–100) versus SIRM, the > 63 μm fraction is roughly bounded by the 30 m isobaths that separates the Changjiang River sediment from the relict sands on the shelf. The < 16 μm fraction is derived mainly from the modern fluvial sources of the Changjiang and Yellow Rivers; in particular, the Changjiang River-derived sediment dominates the inner estuary and the Yellow River-derived sediment dominates the northern coast of the shelf. The other areas of the shelf are characterized by mixed sources of the < 16 μm fraction, with a majority being Changjiang River-derived sediment. Spatial variations of particle size compositions and magnetic properties reflect the role of hydrodynamic sorting on particle size as well as mineral density; this results in differences in magnetic properties among the sedimentary units as well as the contribution of different sized fractions to the bulk SIRM values. Particle size separation could reduce the effect of particle size on bulk magnetic properties and lead to more precise provenance discrimination. Our results have great potential in the study of geomorphological changes and quantitative source identification in delta environments.

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    Flux footprint analysis of a salt marsh ecosystem in the Jiuduansha Shoals of the Changjiang Estuary
    Zihan CHEN, Ying HUANG, Jianwu TANG, Bo TIAN, Fang SHEN, Pengfei WU, Qing YUAN, Cheng ZHOU, Jiangtao WANG
    2021, 2021 (2):  42-53.  doi: 10.3969/j.issn.1000-5641.2021.02.005
    Abstract ( 406 )   HTML ( 62 )   PDF (1268KB) ( 150 )   Save

    Flux footprint analysis is an important step in studying the carbon, water vapor, and heat flux exchange of land-atmosphere interactions based on the eddy covariance (EC) method. In this research, we used the flux source area model (FSAM) to investigate seasonal flux footprints with different wind directions and atmospheric conditions on the basis of half-hourly EC measurements throughout 2018. The results showed that: ① The flux footprint area changes with the seasons. The largest flux footprint area, ordered highest to lowest, was found in autumn, summer, spring, and winter under stable stratification; meanwhile, under unstable stratification, the flux footprint area did not change significantly between seasons. The daily variation in the footprint, moreover, was obvious and the footprint was found to be larger comparatively at nighttime than that observed during the daytime. ② The flux source area under non-prevailing wind conditions was larger than that under the prevailing wind condition. ③ The flux source area was much larger under stable stratification. The distance between the location of the maximum value of the flux footprint and the station was also found to be much larger under stable stratification.

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    Content and ecological risk assessment of heavy metals in the surface sediments of Qingcaosha Reservoir in Shanghai
    Yiping ZHU, Xiaofei LI, Xia LIANG
    2021, 2021 (2):  54-62.  doi: 10.3969/j.issn.1000-5641.2021.02.006
    Abstract ( 385 )   HTML ( 54 )   PDF (1723KB) ( 66 )   Save

    Surface sediments were collected from five representative areas—the floodgate entrance, the north and south sides of the reclamation area, and the central and downstream sections—of Qingcaosha Reservoir; the pollution characteristics and potential ecological risk of seven heavy metals (Cu, Zn, Pb, Cr, Cd, As and Hg) in these sediments were subsequently investigated. Results showed that the heavy metal content in the surface sediments showed spatial variations: the content was relatively higher in the center of the reservoir and was low in the north and south sides of the reclamation area. Heavy metals in the surface sediments, in addition, were mainly in the residual fraction; the content of heavy metals in the exchangeable fraction was extremely low. A potential ecological risk assessment indicated that the comprehensive potential ecological risk index (ERI) of the investigated heavy metals ranged from 55 to 113. The maximum ERI value was observed around the floodgate of the reservoir entrance, and low ERI values were observed at the north and south sides of the reclamation area. The ERI was lower than the threshold for low ecological risk, indicating that heavy metals in the surface sediments of the Qingcaosha Reservoir have low potential ecological risk.

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    Changes in chlorophyll and nutrients in reservoirs of the Changjiang River basin: The “biological filter” effect
    Meng TONG, Maotian LI, Shujie NIU, Xiaoqiang LIU, Mudong LIN, Huiting GUO, Lijun HOU
    2021, 2021 (2):  63-72.  doi: 10.3969/j.issn.1000-5641.2021.02.007
    Abstract ( 414 )   HTML ( 47 )   PDF (950KB) ( 81 )   Save

    The biological filtering effect of reservoirs has become an area of focus for environmental science. We conducted an in situ survey, with different upstream retention times, of chlorophyll-a (Chl.a) and nutrients at the Zhexi, Zhelin, Hualiangting, and Yahekou reservoirs. We found that: ① In the vertical direction, Chl.a in each reservoir had the largest subsurface layer and generally decreased downward, resulting in upper nutrients assimilated by algae and an average vertical retention rate of DIN, DIP, and DSi of the reservoirs at 6.29%, 14.92%, and 8.60%, respectively. ② The concentration of Chl.a and the biomass of phytoplankton generally decreased from upstream to downstream, resulting in lots of nutrients assimilated by algae upstream, and the average horizontal retention rate of DIN, DIP, and DSi of the reservoirs at 26.53%, 39.89%, and 31.70%, respectively. ③ The total average retention rate of DIN, DIP, and DSi of the four reservoirs were 32.82%, 54.80%, and 40.30%, respectively. ④ The concentration of DIP decreased gradually with increases in the reservoir’s retention time; in fact, the concentration of DIP even decreased to 0.1 μmol/L, i.e. the growth of phytoplankton was fully limited by DIP.

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    Comparison of different extraction methods for alkaline earth metals and its implications: A case study of the surficial sediments from Ningbo Plain
    Jing HUANG, Tongtong ZHENG, Aihua WANG, Wenjing LI, Zhanghua WANG
    2021, 2021 (2):  73-84.  doi: 10.3969/j.issn.1000-5641.2021.02.008
    Abstract ( 347 )   HTML ( 47 )   PDF (1216KB) ( 107 )   Save

    The concentrations and relative ratios of alkaline earth metals, such as Sr, Ba, and Ca, in sediments are widely used to discriminate marine and terrestrial environments in paleoenvironmental research. However, geochemical elements occur mostly in mineral crystal lattices (namely, the residual phase after acid extraction), which is not linked to the physical, biological, or chemical environments of the deposition processes. Hence, only selective extraction of phases can be used to interpret changes in the sedimentary environment. In this study, we collected surficial sediments from the present-day saltmarsh-tidal flat, alluvial plain, and tidal river (Yaojiang River) in Ningbo Plain and used a plasma spectrometer to measure the concentrations of Sr, Ba, and Ca in: the leachates extracted by diluted acetic acid (HAc) and diluted hydrochloric acid (HCl), the residues after acid extraction, and the bulk samples. The results showed that alkaline earth metals in the HAc-leachates were most sensitive to changes in the sedimentary environment, followed by the HCl-leachates. No variation in Sr/Ba (molar ratio) could be distinguished in the bulk samples of surficial sediments collected from different sedimentary settings. Furthermore, consistent results were obtained by using different sample amounts and measuring instruments when applying the HAc method. Significant variations in alkaline earth metals in the HAc-leachates were observed for the surficial sediments in this study. Ca and Sr showed the highest concentrations in the saltmarsh-tidal flat sediments and the lowest concentrations in the alluvial sediments; Ba concentration showed the opposite trend. We thus suggest that end-member analyses of the alkaline earth metals in HAc leachates can be used to effectively identify transgression/regression recorded in sedimentary stratigraphy in the coastal zone.

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    Oxygen depletion and the response of organic matter in Laoyehai, a lagoon with strong aquaculture activities
    Wenchao MA, Yan WANG, Zhuoyi ZHU
    2021, 2021 (2):  85-99.  doi: 10.3969/j.issn.1000-5641.2021.02.009
    Abstract ( 376 )   HTML ( 49 )   PDF (1550KB) ( 39 )   Save

    Laoyehai is a lagoon located on the east coast of Hainan and is impacted heavily by human activities (especially those related to aquaculture). Laoyehai is characterized by its eutrophic and hypoxic waters. During previous dry and flood seasons (specifically, April 2010 and August 2011), when hypoxia occurred, field work was conducted to observe the dissolved oxygen (DO) and to collect organic matter. Hypoxia was significant in the spring season with surface DO as low as 50%, while the bottom hypoxic water prevailed in both seasons. In the spring season, the C/N ratio of particulate organic matter was higher than that observed in the summer season (C/N in the spring: 9.7, C/N in the summer: 7.7). Organic matter composition indicated by amino acids showed that there was strong in situ production in the spring relative to that in the summer. Lower C/N values and higher carbon and nitrogen yields of amino acids (AA C yield, AA N yield) in the summer showed active in situ production, suggesting that organic matter was mainly derived from phytoplankton. This also explains the sufficient surface DO in the summer. The degradation of particulate organic matter increased with the decrease of dissolved oxygen, indicating that the particulate organic matter and its degradation were the key driving factors for oxygen consumption in the lagoon. Meanwhile, we found that the relationship between dissolved organic matter components and DO was not significant.

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    Ecological and Environmental Sciences
    Evolution and change of an urban greenspace: A case study on the outer ring of Shanghai
    Qiong WANG, Bin WU, Shenjun YAO, Jianping WU, Ying ZHOU, Jing ZHANG
    2021, 2021 (2):  100-109.  doi: 10.3969/j.issn.1000-5641.2021.02.010
    Abstract ( 468 )   HTML ( 55 )   PDF (18452KB) ( 163 )   Save

    Urban greenspace is an important part of the urban green system and urban landscape, with important ecological, social, psychological, and economic functions. The evolutionary trajectories and change patterns of urban greenspaces are of great significance to the sustainable development of urban green space systems and the optimization of the urban ecological network. There is ongoing emphasis on urban greenspace research; most previous research studies on greenspace changes have used landscape indices and spatial analysis methods, which struggle to accurately reflect the change process, change types, and spatial distribution patterns of greenspace. In our paper, seven types of greenspace evolution were defined, including continuous, expansion, contraction, dissipation, creation, merging, and splitting. Then, an evolution graph was constructed by defining greenspace patches as nodes and greenspace evolution relations as edges. Based on the greenspace evolution graph, the greenspace evolution process and its corresponding evolutionary trajectory were further extracted and visualized. Taking the Shanghai city center as a case study area, the spatial distribution pattern and change process of the urban greenspace for 2008, 2012, and 2016 were extracted. Results indicated that the most dominant greenspace evolution types were creation and dissipation. The newly added urban greenspace patches were more evenly distributed compared with those patches involved with an evolution type of dissipation. Small patches were more likely to be located in the urban center, while large patches tended to be concentrated in rural areas. The location of greenspace patches that disappeared were mostly concentrated in non-central areas, particularly in the Pudong New Area. Compared with the urban greenspace changes between 2008 and 2012, locations where new greenspace appeared between 2012 and 2016 were more evenly distributed, while locations where greenspace disappeared were more concentrated.

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    Analysis of land use dynamics and driving forces of water source protection areas in the upper reaches of the Huangpu River
    Jian WU, Li CHEN, Sijing QIU, Zhongchun YAN, Jinghua SU, Liting HU, Min WANG
    2021, 2021 (2):  110-119.  doi: 10.3969/j.issn.1000-5641.2021.02.011
    Abstract ( 329 )   HTML ( 60 )   PDF (1100KB) ( 85 )   Save

    Using a combination of 0.25 m resolution aerial remote sensing data and topographic maps, the land use data for the Shanghai Huangpu River Water Source Protection Area in 2000, 2005, 2010, and 2015 were evaluated by means of manual visual interpretation. With the growth of industrial land from 2000 to 2015, there has been a relative decline in the proportion of agricultural land and water areas and a relative increase in the proportion of urban land areas. In the past 15 years, the areas used for farming and cultivating livestock and poultry have decreased by 44.17% and 71.65%, respectively. The area of water reduction has decreased by 6.44%. The area of green land forests, in contrast, has increased by 645.94%. The area of urban land has increased by 53.53%. All types of urban land use have increased, with the area used for industrial storage increasing the most at 21.77%. From the perspective of land transfer, the area of cultivated land transferred outward was the largest in the past 15 years, accounting for 22,839.96 hectares, and the transfer-outward rate of livestock and poultry farming land was the highest at 91.23%. The area of green land forests transferred inward was the largest at 16190.32 hectares; the transfer of industrial storage land inward was the second largest at 7979.12 hectares. Based on an analysis of development in the region, population changes, policy impacts, and other factors, our results indicate that urbanization and industrialization drove the increases in urban land areas; moreover, environmental policies affected green land areas as well as livestock and poultry farming land areas, market regulations affected aquaculture land areas, and environmental policies and urbanization affected water source protection areas.

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    Distribution and causes of ruderal communities in different urban habitats of Hangzhou
    Mingli ZHANG, Yichong CUI, Liangjun DA
    2021, 2021 (2):  120-131.  doi: 10.3969/j.issn.1000-5641.2021.02.012
    Abstract ( 397 )   HTML ( 49 )   PDF (1017KB) ( 124 )   Save

    With the ongoing urbanization process in Hangzhou, we investigated the species composition and structure of ruderal communities across eight urban habitat types. Habitat factors such as light intensity, soil pH, soil electrical conductivity, soil compaction, soil total nitrogen, soil total phosphorus, soil organic matter, and interference types were measured; we subsequently analyzed the relationship between species composition and habitat factors of the ruderal communities. The results indicated that forest gap and lawn were the most common habitat types, and these community types covered 20.1% and 16.3%, respectively, of the total 1665 sampling plots surveyed. In all seven habitats except tree pool, moreover, dwarf-growth annual ruderals were the dominant species within the community. There were 30 ruderal species distributed across eight habitats. Environmental factors varied across the different habitats. The light intensity was the lowest in the forest gap, the soil conductivity value was the highest in the shrub-grassland gap, and the light intensity and soil compactness were the highest in soil abandoned land.

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    Variation characteristics of plant communities at abandoned farmlands of different ages in the Chongqing suburban area
    Mingming ZHENG, Xiaohan LI, Li HUANG, Shenghe YANG, Siwei HU, Yongchuan YANG
    2021, 2021 (2):  132-141.  doi: 10.3969/j.issn.1000-5641.2021.02.013
    Abstract ( 289 )   HTML ( 47 )   PDF (794KB) ( 101 )   Save

    In this study, we investigated the plant species composition of three types of abandoned farmland and compared with cultivated farmland in the Chongqing suburban area. We analyzed dynamic changes in species composition and community type as well as trends in plant diversity. The results showed that a total of 99 species, 90 genera, and 39 families were recorded in the spring and autumn. At the second level of the TWINSPAN classification, the cultivated farmland, early abandoned farmland, and late abandoned farmland could all be distinguished. As the number of years since abandonment of the farmland increased, the dominant life form of the plant community gradually transitioned from annual to perennial, and woody plants began to become the dominant species. Plant diversity gradually increased from the early to middle stage of abandonment, but declined during the later stage.

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    Vessel characteristics and the density-size relationship of woody plantsat the Shanghai Chenshan Botanical Garden
    Yuanyuan LI, Kankan SHANG, Xijin ZHANG, Kun SONG
    2021, 2021 (2):  142-150.  doi: 10.3969/j.issn.1000-5641.2021.02.014
    Abstract ( 307 )   HTML ( 49 )   PDF (1018KB) ( 72 )   Save

    In this study, we measured the branch xylem structure of 85 woody plant species at the Shanghai Chenshan Botanical Garden to compare vessel characteristics among different life forms and check their phylogenetic signals. The trade-off between vessel density and vessel size was subsequently compared among different life forms. The results showed that: ① The vessel diameter ((28.55 ± 8.84) μm) and vessel ratio (8.7% ± 2.89%) of evergreen woody plants were significantly smaller than the vessel diameter ((35.81 ± 13.92) μm) and vessel ratio (12.7% ± 4.82%) of deciduous woody plants; meanwhile, there was no significant difference observed in the vessel density between evergreen plants ((149.3 ± 75.62) N/mm2) and deciduous plants ((164.5 ± 154.28) N/mm2). The vessel diameter of trees ((35.86 ± 13.5) μm) was significantly larger than that of shrubs ((26.24 ± 8.84) μm), but there was no significant difference observed in the vessel ratio and vessel density between trees (12.09% ± 5.01%; (151.9 ± 142.73) N/mm2) and shrubs (10.59% ± 2.99%; (208.7 ± 126.37) N/mm2). ② There were significant phylogenetic signals observed in vessel diameter and vessel density, and the signal of vessel density was larger than that of vessel diameter. There was, however, no obvious phylogenetic signal in the vessel ratio. ③ The standardized major axis test indicated that the trade-off between vessel density and vessel size existed in all life forms, with a common slope coefficient of –0.89 and a 95% confidence interval (–0.98 ~ –0.79). However, the intercept of evergreen trees was significantly smaller than that of deciduous trees, suggesting that deciduous trees have a larger vessel diameter than evergreen trees for a given vessel density.

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    Variation patterns and influencing factors of air anionsindifferent plant communities of an urban park
    Wen SUN, Yujie HAN, Shan YIN
    2021, 2021 (2):  151-159.  doi: 10.3969/j.issn.1000-5641.2021.02.015
    Abstract ( 351 )   HTML ( 54 )   PDF (1340KB) ( 95 )   Save

    In this study, we evaluated the variation patterns of air anions in nine plant communities with different structures in Zhongshan Park of the central city of Shanghai; the air anion concentration was monitored continuously over the course of a year. In addition, we analyzed the influence of different factors—community structure, canopy density, and the level of surrounding water—on air anion concentration. The results showed that the air anion concentration within different community types was mostly between 200 cm3 and 700 cm3, and the daily variation showed a single peak. Air anion concentration remained at a high level but fluctuated significantly from July to October. The relationship between community structure and air anion concentration was roughly as follows: herbage > arbor with shrubs ≈ arbor with herbage > arbor with shrubs and herbage; in general, the more complex the community structure, the less the air anion variability. There was a negative correlation between the mean variation of the air anion concentration and the canopy density, implying that higher canopy density values were associated with lower mean variation of the air anion concentration throughout the community. This negative correlation became more significant in the daytime, between 7:00 to 19:00, when photosynthesis was ongoing. In addition, the impact of static water on the anion concentration was not found to be significant. The conclusion of this paper can provide basic data and a scientific basis for the construction of healthy plant communities in urban parks.

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    Distribution characteristics and influencing factors of crabs and crab burrows in the Fengxian coastal wetland
    Xiang LI, Huimin TIAN, Jingying WU, Siyu CHEN, Mingming ZHAO, Ping XU, Xuechu CHEN, Wenhui YOU
    2021, 2021 (2):  160-170.  doi: 10.3969/j.issn.1000-5641.2021.02.016
    Abstract ( 351 )   HTML ( 50 )   PDF (1038KB) ( 77 )   Save

    This study investigated the distribution characteristics and influencing factors of crabs and crab burrows in Fengxian coastal wetland to reveal the main influencing factors in crabs’ and crab burrows’ distribution and deepen the understanding of crabs’ living habits. The results showed that: ① The abundance of Helice tientsinesis in the high-marsh Phragmites australis habitat is higher than that in the middle-marsh Phragmites australis -Spartina alterniflora mixed habitat and low-marsh Spartina alterniflora habitat (p < 0.01). However, there is no significant difference in the abundance of Sesarma plicate between habitats (p > 0.05). ② The density of crab burrows in the high-marsh Phragmites habitat is significantly higher than that in the middle-marsh Phragmites-Spartina mixed habitat and the low-marsh Spartina habitat (p < 0.05), while the average opening diameter of crab burrows is significantly lower than that in the middle-marsh Phragmites -Spartina mixed habitat and the low-marsh Spartina habitat (p < 0.05). ③ There is no significant linear relationship between crab abundance and the density of crab burrows( p > 0.05), while there is a significant positive correlation between the density of crab burrows and the abundance of Helice tientsinesis ( p < 0.01). ④ Crab abundance is negatively correlated with plant underground biomass ( p < 0.01). ⑤ There is a negative correlation between the density of crab burrows and vegetation coverage and plant density. The relative elevation, water content, conductivity, total organic carbon content, and total nitrogen content are positively correlated with the density of crab burrows. Among these factors, the relative elevation is the habitat factor with the highest correlation with the density of crab burrows.

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