Study On The Grain Size And Heavy Metal Characteristics Of Baimaohai Tidal Flat Sediments

In recent years,“rural tourism” has emerged under the guidance of domestic and foreign market demand and rural revitalization and development strategies.A large number of high-quality rural coastal resources have been developed and valued.In particular,the rise of coastal tourism has brought about great changes in coastal villages and coastal zones.To explore the sedimentary environment and heavy metal distribution characteristics of sandy coastal tidal flats under the background of rural coastal tourism.This paper took the Baimaohai rural coastal zone of Zhanjiang City as the research object,collected samples of tidal flat sediments in winter and summer,through particle size analysis and 8 heavy metal elements(Cu,Pb,Zn,Cr,Cd,As,Fe,Mn)testing and analyzing,explored the temporal and spatial distribution characteristics of grain size and heavy metals of Baimaohai tidal flat sediments,the following main conclusions and understandings were obtained:The main composition of the Baimaohai tidal flat surface sediment was sand,with less silt content and no clay components.The average particle size was 2.53?(1.77?-3.70?),and the sorting coefficient was 0.51(0.37-1.74).The degree value was 0.02(-0.60-2.08),and the kurtosis value was 2.69(2.30-6.97).The main composition of the sediments in the tidal flat 50 cm deep was sand,without clay and silt components,with an average particle size of 2.52?(1.91?-3.02?),a sorting coefficient of 0.47(0.37-0.80),and a skewness of-0.01(-0.70-0.04),kurtosis of2.59(2.36-3.60).The grain size parameter of the Baimaohai tidal flat surface sediment was slightly larger than that of the 50cm sediment.The surface sediment was relatively poorly sorted,the grains tended to be more positive,and the kurtosis was narrower.From the point of view of the size composition,the main components of the surface sediments of the tidal flats in winter and summer were all sand components.There was a significant seasonal diversity in the composition of very fine sand and medium sand.The content of very fine sand in summer was 41.7% and the content of medium sand was 3.11.%;The content of very fine sand in winter was 8.55%,and the content of medium sand was 25.28%.In addition,the content of fine sand and coarse sand was high in winter,and the content of clay and silt sand was high in summer.From the perspective of grain size parameters,the average grain size,sorting coefficient,skewness and kurtosis of summer tidal flat sediments were larger than those in winter.The grain size parameters of the surface sediments of the tidal flat have significant diversity in winter and summer in the vertical direction.The grain size of sediments in the low tide area was fine;the average grain size in the middle tide area was higher than that in the high tide area and lower than that in the low tide area,and the sortability was poor.From the graph of grain size frequency distribution,the surface sediments of the Baimaohai tidal flat were dominated by single peaks in winter and summer,and the frequency distribution of surface sediments in summer had little difference,and the frequency distribution of surface sediments in winter were significantly different.The content of heavy metals in the surface sediments of the Baimaohai tidal flats had little difference between winter and summer,and they were all below the permissible values of the class-I marine sediments(China Marine Sediment Quality Standards).The contents of Fe,Mn,Zn,Cr,Pb,As,Cu,and Cd in the surface sediments of tidal flats in summer were 7049.56?g/g,175.77?g/g,17.37?g/g,11.42?g/g,8.68?g/ g,4.42?g/g,1.76?g/g,0.11?g/g,the contents of Fe,Mn,Zn,Cr,Pb,As,Cu,Cd in the surface sediments of the tidal flat in winter were 6241.73?g/g,121.58?g/g,13.14?g/g,11.98?g/g,7.81?g/g,2.84?g/g,2.66?g/g,0.12?g/g.In the coastal direction,the heavy metal content in the coastal section near the road junction was higher than the average expected value.In the vertical direction,the high tide area and low tide area were prone to enrichment of heavy metal elements in summer,and the concentration of metal elements was more likely to occur in the mid-low tide area to the low tide area in winter.At different depths,the Cd content in the surface and 50cm deep sediments of the tidal flat in winter and summer was higher than that in the soil environmental background value of latosol,and the content of Mn in the surface of the Baimaohai tidal flat and 50cm deep in the summer was higher than that in the soil environmental background value of latosol.The contents of Pb,Zn,Cu,Cr,As,and Cd in the sediments of different depth layers were all lower than the national first-class quality standards for marine sediments.The content of the three metal elements of Cr,Fe,and Mn varied widely in different media.Zn,Cr,Cd,As,Pb elements were strongly related groups,and the metal elements had the same or similar sources.Iron-manganese redox metals were the main factors affecting the content of heavy metals in the sediments.The deposits with a particle size of 0.063 to 1mm in this area did not have a high degree of enrichment of Zn,Cr,Cd,As,Pb,and Cu.The correlation between chromaticity,TOC and metal element content was not significant.The potential ecological risk index of heavy metals in the surface sediments of Baimaohai tidal flat was Cd>>As>Cu>Pb>Cr>Zn in descending order.The potential ecological risk of the other heavy metal elements except Cd were slight,the potential ecological risk degree of the Cd was intensity,and it should be listed as the heavy metal element for priority control in the Baimaohai.