湛江湾红树林湿地沉积柱粒度特征及沉积动力分析

粒度是反映沉积动力特征的重要参数,红树林湿地沉积物在输送和沉积过程中记录了丰富的沉积环境信息。为探讨湛江湾红树林湿地沉积物粒度垂向特征及沉积动力过程,加强对湿地生态保护,通过运用图解法、对比研究法分析湛江湾南海堤(NHD)、东头山岛(DTSD)、湖光镇(HGZ)和观海长廊(GHCL)4个站位红树林湿地沉积柱粒度参数特征、频率分布曲线以及沉积速率,揭示近百年来湛江湾的沉积动力演变。结果表明:(1)NHD和DTSD沉积柱的²¹⁰Pb_ex比活度都呈现较好的指数衰变趋势,且沉积速率逐年增加。近百年来,NHD和DTSD平均沉积速率分别为1.277 cm/a和1.034 cm/a,但在2011年之后DTSD的速率远超过NHD。(2)各沉积柱粒度特征存在明显差异。NHD沉积柱粒径均值为3.42?,以砂为主(67.23%),为粉砂质砂;DTSD粒径均值为5.71?,分选系数2.21,组分以粉砂为主(55.13%),为砂质粉砂;HGZ沉积柱粒径均值为5.49?,沉积物类型为砂质粉砂;GHCL粒径均值为4.18?,砂为主要组分(55.85%)。(3)各沉积柱4个层位的粒度频率分布曲线呈现多峰态特征,沉积过程掺杂了多种沉积介质的作用。NHD和GHCL粒级集中在砂质颗粒端,指示较强的沉积动力;DTSD和HGZ粉砂粒级突出,沉积动力较弱。(4)沉积物粒度特征与所在陆源或岛屿、径流来沙有关;沉积过程深受潮流动力、红树林的分布及人类活动的影响。近年来湛江湾沉积速率的加快可能会对航道产生影响,应加强对湾内湿地生态环境的重视。

Grain Size Characteristics and Sedimentary Dynamics of Sedimentary Column of Mangrove Wetland in Zhanjiang Bay

Granularity is an important parameter for understanding the sedimentary dynamics characteristics. Mangrove wetland sediments host much sedimentary environment information during the transport and deposition processes. To unravel the vertical grain size characteristics and sedimentary dynamics of mangrove wetland in the Zhanjiang Bay and enhance wetland ecological protection, the grain size parameter characteristics, frequency distribution curve, and sedimentation rate of mangrove wetland sedimentary columns at the Nanhaidi (NHD), Dongtoushan Island (DTSD), Huguang Town (HGZ)and Guanhaichanglang (GHCL)stations were analyzed. Our work reveals the sedimentary evolution of the Zhanjiang Bay in the past century, and our results suggest that: (1)The ²¹⁰Pb_ex specific activity of NHD and DTSD columns both show a good exponential decay trend, with the deposition rate increasing with time. The average deposition rates of NHD and DTSD were 1.277 cm/a and 1.034 cm/a, respectively, but that of DTSD far exceeded that of NHD after 2011. (2)Grain-size characteristics of individual sedimentary column is markedly different, and the average grain size of NHD sedimentary column is 3.42?, mainly composed of sand (67.23%)and is classified as silty sand. The mean diameter of DTSD is 5.71? with sorting coefficient of 2.21. It is mainly composed of silty-sand (55.13%)and is classified as sandy-silt. HGZ is sandy-silt with mean particle size of 5.49?. The GHCL is mainly composed of sand (55.85%)with average particle size of 4.18?. (3)The grain size frequency distribution curves display multimodal features, implying that the deposition process was doped with the process of various sedimentary media. The NHD and GHCL particle sizes are clustered toward the sandy particle end-member, indicating strong sedimentary dynamics, whereas the sedimentary dynamics of DTSD and HGZ is considerably weaker. (4)The grain-size characteristics are influenced by the local terrestrial source, island and runoff, whilst the sedimentation process is significantly influenced by the tidal current dynamics, mangrove distribution, and human activities. In recent years, the rising sedimentation rate in the Zhanjiang Bay may have an impact on the navigation channel, and more attention should be paid to the wetland ecological environment in the bay.